Why people should not mod a crank!
11-05-2008, 06:05 PM
#1
Member
Thread Starter
Join Date: Nov 2008
Location: southern,
ME
Posts: 96
Likes: 0
Received 0 Likes
on
0 Posts
Why people should not mod a crank!
This is a heads up for the whole RC comunity.If you do not have a equipment to properly mod+ BALANCE a crankshaft,Dont waste your time you will servely damage your engine in a little as a quart of fule.When you take off weight by cutting or grinding and do NOT counter balance the crank before reinstalling,What happens is you can and will have premature bearing failure,wich is the start to totaling your whole engine.The failure comes from unwanted vibrations,wich is a big no no in a any engine.Also beware of people who claim they mod engines,make sure they have the right equipment to properly mod your engine and try to use PAYPAL WHEN PAYING FOR A MOD.This way you are covered in may ways.Sincerly Rich[8D]
11-05-2008, 06:41 PM
#2
Senior Member
Join Date: Jan 2007
Location: Tampa,
FL
Posts: 1,812
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
i've modded many motors and they lasted at least 2 quarts
good points. my modding days are long over, wish you had posted this a year ago.
good points. my modding days are long over, wish you had posted this a year ago.
11-05-2008, 07:00 PM
#3
Senior Member
RE: Why people should not mod a crank!
I myself don't beleive it is truly possible to balance these motors.....you can somewhat limit vibration at certain RPM's but there is no true way to balance these cranks..beware of anyone claiming they can actually balance these motors !!!!! The only equipment that will truly test the vibration is a vibrex machine...but in order for the testing to be valid the motor must be running and using the plug/fuel and mixture that you are aiming to " balance" ...even so much as changing nitro percentage will alter the harmonics of the engine and require a new " Balance " to hit the same target vibration at the goal RPM..... As much as we like to think we are balancing these engines the fact remains the topside of the piston is exposed to combustion pressure, which will definitely affect the pistons " Weight" in the the scheme of balancing.... the combustion pressure can be altered by so many factors that it makes truly balancing these engines nearly impossible....different glowplug,fuel%, needle setting etc will alter the pressure on the topside of the piston.......... Anyways regardless I have lightened hundreds of cranks and to date never had a motor failure due to bearing damage, but of course I am not merely hacking material off at will !!!!...... the only moddr I know of who has an actual Vibrex machine is EB mods, however I truly dont know what other modders have for equipment.... but I do know unless the engine is being run and tested the results are invalid. the harmonics and balance of an actual running engine are far different then a engine that is being spun by outside mechanical means.... Any form of static balancing done will be invalid once the motor is running and the piston is faced with combustion pressure !!!
11-05-2008, 07:27 PM
#4
Senior Member
Join Date: Apr 2005
Location: Charlottesville,
VA
Posts: 5,253
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
Single cylinder engines can not be fully balanced period, BUT they can be balanced to a certain extent to minimize the inherent vibrations.
He is right, cutting out a random amount of material as shown on several occations on this site is not a great idea.
If you do you should check the balance and adjust as good as it can get.
This is an excerpt from Prestwich Models: ([link=http://www.prestwich.ndirect.co.uk/technical_balancing.htm]Link to article![/link])
Firstly, any material that you can remove to reduce the reciprocating mass( piston/wristpin/ring/top half of rod) will make an improvement in engine performance, maybe not noticeable at lower rpm's but certainly at high rpm's plus it reduces stress on the engine parts. This will affect the balance of the engine but not greatly. However , it is a fact is that it is IMPOSSIBLE to balance a single-cylinder engine. The best that can be done is a compromise. The crankshaft counterweights will partly balance the reciprocating mass (piston/ring/wristpin/top half of rod). but this will introduce an out of balance at 90 degrees to the line of the cylinder but we have to put up with that. Simply put, to balance a single cylinder engine to the best compromise, do this if you have LOTS of time.
Use a good quality scales, digital if possible. Take apart the crank assembly, weigh the bottom half of the rod and then the top half of the rod. Then weigh the piston/ring/clips/wristpin as one assembly. Add the weight of the top half of the rod to the weight of piston/ring/clips/wristpin. Now you need to take a percentage of this weight of between 50 to 60%. Lets say we use 55%.
Add this 55% to the weight of the bottom of the rod and machine a piece of brass or steel of this weight to fit over the crankpin. Reassemble the crank with this weight in place and balance the crank on the ballrace surfaces on 2 knife edges. If the crank rotates because its heavier one side than the other( which it will do) you must grind metal off the heavy part of the crank-webs around the crankpin area or wherever until it does balance. At this point you will have balanced the engine to a balance factor of 55%. This balance factor will vary from engine to engine and is rpm dependent to a certain extent but at 15,000 rpm a factor of 55% is not too far off.
He is right, cutting out a random amount of material as shown on several occations on this site is not a great idea.
If you do you should check the balance and adjust as good as it can get.
This is an excerpt from Prestwich Models: ([link=http://www.prestwich.ndirect.co.uk/technical_balancing.htm]Link to article![/link])
Firstly, any material that you can remove to reduce the reciprocating mass( piston/wristpin/ring/top half of rod) will make an improvement in engine performance, maybe not noticeable at lower rpm's but certainly at high rpm's plus it reduces stress on the engine parts. This will affect the balance of the engine but not greatly. However , it is a fact is that it is IMPOSSIBLE to balance a single-cylinder engine. The best that can be done is a compromise. The crankshaft counterweights will partly balance the reciprocating mass (piston/ring/wristpin/top half of rod). but this will introduce an out of balance at 90 degrees to the line of the cylinder but we have to put up with that. Simply put, to balance a single cylinder engine to the best compromise, do this if you have LOTS of time.
Use a good quality scales, digital if possible. Take apart the crank assembly, weigh the bottom half of the rod and then the top half of the rod. Then weigh the piston/ring/clips/wristpin as one assembly. Add the weight of the top half of the rod to the weight of piston/ring/clips/wristpin. Now you need to take a percentage of this weight of between 50 to 60%. Lets say we use 55%.
Add this 55% to the weight of the bottom of the rod and machine a piece of brass or steel of this weight to fit over the crankpin. Reassemble the crank with this weight in place and balance the crank on the ballrace surfaces on 2 knife edges. If the crank rotates because its heavier one side than the other( which it will do) you must grind metal off the heavy part of the crank-webs around the crankpin area or wherever until it does balance. At this point you will have balanced the engine to a balance factor of 55%. This balance factor will vary from engine to engine and is rpm dependent to a certain extent but at 15,000 rpm a factor of 55% is not too far off.
11-05-2008, 09:24 PM
#5
Senior Member
Join Date: May 2008
Location: Longueuil, QC, CANADA
Posts: 430
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
Ive also done a good quantity of crank and ive blown no engines or bearing or the one of my friends, and we run them at unreal rpms for extended periods.
Thats mostly what modders with balancer will say, "get them balanced or it will blow the bearing!" ...its more like "buy my stuff or you will regret it!"
no offense
I would be more worried in the case of a bent shaft.
Thats mostly what modders with balancer will say, "get them balanced or it will blow the bearing!" ...its more like "buy my stuff or you will regret it!"
no offense
I would be more worried in the case of a bent shaft.
11-05-2008, 09:42 PM
#6
Senior Member
Join Date: Jul 2005
Location: Torchy the Fiery Fast RC Turtl
Posts: 10,544
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
ORIGINAL: Over_revO
Thats mostly what modders with balancer will say, "get them balanced or it will blow the bearing!" ...its more like "buy my stuff or you will regret it!"
no offense
Thats mostly what modders with balancer will say, "get them balanced or it will blow the bearing!" ...its more like "buy my stuff or you will regret it!"
no offense
Balancing these engines is SNAKE OIL! Supertib and SManMTB gave the best descriptions in how to make compromises to possible combat the imbalances, and I agree with them 100%, it is impossible to eliminate all imbalances in our single cylinder engines.
11-05-2008, 10:00 PM
#7
Senior Member
Join Date: Jul 2005
Location: Torchy the Fiery Fast RC Turtl
Posts: 10,544
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
ORIGINAL: RR Mods
This is a heads up for the whole RC comunity.If you do not have a equipment to properly mod+ BALANCE a crankshaft,Dont waste your time you will servely damage your engine in a little as a quart of fule.When you take off weight by cutting or grinding and do NOT counter balance the crank before reinstalling,What happens is you can and will have premature bearing failure,wich is the start to totaling your whole engine.The failure comes from unwanted vibrations,wich is a big no no in a any engine.Also beware of people who claim they mod engines,make sure they have the right equipment to properly mod your engine and try to use PAYPAL WHEN PAYING FOR A MOD.This way you are covered in may ways.Sincerly Rich[8D]
This is a heads up for the whole RC comunity.If you do not have a equipment to properly mod+ BALANCE a crankshaft,Dont waste your time you will servely damage your engine in a little as a quart of fule.When you take off weight by cutting or grinding and do NOT counter balance the crank before reinstalling,What happens is you can and will have premature bearing failure,wich is the start to totaling your whole engine.The failure comes from unwanted vibrations,wich is a big no no in a any engine.Also beware of people who claim they mod engines,make sure they have the right equipment to properly mod your engine and try to use PAYPAL WHEN PAYING FOR A MOD.This way you are covered in may ways.Sincerly Rich[8D]
Balancing? Unless you do the calculations based on some of the key factors that Supertib brought up, no, it is impossible to eliminate all imbalances. So, as a modder who wishes to shoot to reduce the imbalance to its absolute min, you would have to shoot for certain factors: A given BMEP and a given RPM, and also calculating the linear and moments of inertias of the crank, conrod, and piston at their various geometies. This is something mechanical engineers love to chew on, so if you are engineer trained, you can calculate weights of the pieces to remove or add and where to remove/add to reduce the imbalances to tehir absolute minimum. Now, this is only CALCULATED weights to add/remove.
As Supertib said, you would have to validate it by actual running. The reason? Nitro fuel and ambient factors rarely behave in their ideal calculated predictions. With nitro fuel, you will have to control the factors rather preciesly to ensure you achieve the desired BMEP in the cylinder at the desired RPM. Otherwise, the forces will not act in teh manner you calculated fo teh linear and moments of inertias for the geometries of the parts, thus, your desided reduced imbalance will not be achieved.
My bottom line is these engiens have to put up with a fair degree of imbalance for all sorts of conditions. They most likely are a whole lot more robust than you are claiming them to be, even if modded impropperly (unless the mod work was really done very badly).
11-05-2008, 11:56 PM
#8
RE: Why people should not mod a crank!
Read and reread carefully everything that SManMTB posted. This is the only way a single cylinder engine can be close to balanced other than extreme complications like using counter-rotating balance shafts etc. This is totally impractical in our engines however. Most engines don't even come close to that 50-60% mentioned by SManMTB and it takes some serious engineering using tungsten carbide inserts to get there. Engine revs make no difference to the actual balance other than the unavoidable vibration could set up a harmonic in the chassis/fuselage. Likewise, combustion pressures make no difference either because the pressure down on the piston is felt equally upwards on the cylinder head. Action and reaction, Newton's third law and all that stuff 
.
Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
.Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
11-06-2008, 02:30 AM
#9
Senior Member
Join Date: Apr 2005
Location: New Albany,
IN
Posts: 685
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
Listen to what tib, SavageJim, SmanMTB and Over Revo have said. I will not write an essay but I have been telling a few of these guys this for years now... And have talked about this through and through.... There is definatly as limit as to where and how much to cut a crankshaft... The less you can cut to get the job done the better. Some crankshafts dont even need any cutting on the counter balance.... 
Alot of things some modifiers say is just a ploy for you to buy there mills. I run a proffesional legit and unfortunatly taxed modifying business. I have a dyno etc and do alot of R&D. Everyone can believe what they want but you cant truely and fully balance these single cylinder engines. You can modify them correctly and not creat more vibration that will affect the engine. And you can also cut too much off and cause excess vibration that will shorten the life of the engine. But knowing where and when to draw the line is where experience comes into play
Alot of things some modifiers say is just a ploy for you to buy there mills. I run a proffesional legit and unfortunatly taxed modifying business. I have a dyno etc and do alot of R&D. Everyone can believe what they want but you cant truely and fully balance these single cylinder engines. You can modify them correctly and not creat more vibration that will affect the engine. And you can also cut too much off and cause excess vibration that will shorten the life of the engine. But knowing where and when to draw the line is where experience comes into play
11-06-2008, 07:31 AM
#10
Senior Member
Join Date: Jul 2005
Location: Torchy the Fiery Fast RC Turtl
Posts: 10,544
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
ORIGINAL: downunder
Read and reread carefully everything that SManMTB posted. This is the only way a single cylinder engine can be close to balanced other than extreme complications like using counter-rotating balance shafts etc. This is totally impractical in our engines however. Most engines don't even come close to that 50-60% mentioned by SManMTB and it takes some serious engineering using tungsten carbide inserts to get there. Engine revs make no difference to the actual balance other than the unavoidable vibration could set up a harmonic in the chassis/fuselage. Likewise, combustion pressures make no difference either because the pressure down on the piston is felt equally upwards on the cylinder head. Action and reaction, Newton's third law and all that stuff.
Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
Read and reread carefully everything that SManMTB posted. This is the only way a single cylinder engine can be close to balanced other than extreme complications like using counter-rotating balance shafts etc. This is totally impractical in our engines however. Most engines don't even come close to that 50-60% mentioned by SManMTB and it takes some serious engineering using tungsten carbide inserts to get there. Engine revs make no difference to the actual balance other than the unavoidable vibration could set up a harmonic in the chassis/fuselage. Likewise, combustion pressures make no difference either because the pressure down on the piston is felt equally upwards on the cylinder head. Action and reaction, Newton's third law and all that stuff
.Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
The reason why I bing up RPM and BMEP, but more improtantly, the pressure curve as the crank turns from the point of combustion to the point when the exhaust port opens is for the acceleration component. And that accelerationg, just like 3rd law, also acceleratets the cylinder head and everting else attached to it: i.e the block, the head, and the entire RC. Or to look at it in a different manner, you can look at it in the impulse-momentum theorem, or even work-energy theorem. Just as a gun is kicked back as the bullet is pushed forward when you pull the tigger, so does the the engine block get pushed up as the piston is pushed down.
11-06-2008, 08:05 AM
#11
RE: Why people should not mod a crank!
Here is the problem of balancing our engines in non-engineering terms.
Consider the piston, rod and wrist-pin moving upward several degrees before reaching top dead center. At this moment this assembly does not want to change direction and would prefer to continue out the top of the engine. To counter this mass and its momentum as it changes direction, we create a counterweight on the crank that, as the piston is changing direction at the top of the engine, the counterweight is changing direction at the bottom of the engine. If that were all there was to it, we could (nearly) perfectly balance our engines.
The problem comes when the engine has rotated 90 degrees from top/bottom dead center. Now the piston/rod/pin are moving at a static velocity (for and instant) but the crank counterweight is trying to move out the side of the engine. So while the crank counterweight is effective at offsetting the mass of the piston "up and down"n in the engine, it is counterproductive "side to side".
As model engine are produced today (i.e. single cylinder, no-balance shaft), we are forced to make the mass of the crank weight under the ideal for longitudinal balance so that lateral balance isn't excessive.
In short, the crankshaft counter balance is an OK fix for the mass of the piston being tossed up and down but, without the mass of the piston to offset it, becomes a detriment when its mass is tossed side to side.
Bill
Consider the piston, rod and wrist-pin moving upward several degrees before reaching top dead center. At this moment this assembly does not want to change direction and would prefer to continue out the top of the engine. To counter this mass and its momentum as it changes direction, we create a counterweight on the crank that, as the piston is changing direction at the top of the engine, the counterweight is changing direction at the bottom of the engine. If that were all there was to it, we could (nearly) perfectly balance our engines.
The problem comes when the engine has rotated 90 degrees from top/bottom dead center. Now the piston/rod/pin are moving at a static velocity (for and instant) but the crank counterweight is trying to move out the side of the engine. So while the crank counterweight is effective at offsetting the mass of the piston "up and down"n in the engine, it is counterproductive "side to side".
As model engine are produced today (i.e. single cylinder, no-balance shaft), we are forced to make the mass of the crank weight under the ideal for longitudinal balance so that lateral balance isn't excessive.
In short, the crankshaft counter balance is an OK fix for the mass of the piston being tossed up and down but, without the mass of the piston to offset it, becomes a detriment when its mass is tossed side to side.
Bill
11-06-2008, 09:05 AM
#12
Member
Thread Starter
Join Date: Nov 2008
Location: southern,
ME
Posts: 96
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
Not trying to sell anything here,Im booked up till Feb.Just trying to let people know there are alot of people out there moding engines that shouldent be.A properly balanced crank is a must for a REAL racer,This is more so in your highend .21s were upper RPMs are slightly affected by a unbalanced crankshaft.In todays race world Pros are looking more and more for that extra edge.The 1/8th scale class buggy is so competitve these days,Leaving no margin of error.Rich from RR Mods!
Just trying to let people know there are alot of people out there moding engines that shouldent be.A properly balanced crank is a must for a REAL racer,This is more so in your highend .21s were upper RPMs are slightly affected by a unbalanced crankshaft.In todays race world Pros are looking more and more for that extra edge.The 1/8th scale class buggy is so competitve these days,Leaving no margin of error.Rich from RR Mods!
11-06-2008, 09:13 AM
#13
Senior Member
RE: Why people should not mod a crank!
ORIGINAL: RR Mods
Not trying to sell anything here,Im booked up till Feb.Just trying to let people know there are alot of people out there moding engines that shouldent be.A properly balanced crank is a must for a REAL racer,This is more so in your highend .21s were upper RPMs are slightly affected by a unbalanced crankshaft.In todays race world Pros are looking more and more for that extra edge.The 1/8th scale class buggy is so competitve these days,Leaving no margin of error.Rich from RR Mods!
Not trying to sell anything here,Im booked up till Feb.
Just trying to let people know there are alot of people out there moding engines that shouldent be.A properly balanced crank is a must for a REAL racer,This is more so in your highend .21s were upper RPMs are slightly affected by a unbalanced crankshaft.In todays race world Pros are looking more and more for that extra edge.The 1/8th scale class buggy is so competitve these days,Leaving no margin of error.Rich from RR Mods!
Rich Reid ?
11-06-2008, 09:23 AM
#15
Senior Member
RE: Why people should not mod a crank!
ORIGINAL: RR Mods
I would like to keep my name anonmus if thats allright
I would like to keep my name anonmus if thats allright
WOW..i was just curious who you were.....nothing meant by it or anything like that.. you make some bold claims so I was curious to see your balancing setup.....
11-06-2008, 10:07 AM
#17
Senior Member
Join Date: Apr 2005
Location: Charlottesville,
VA
Posts: 5,253
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
ORIGINAL: SAVAGEJIM
No disagreements here, and yes, SmanMTB's conditions are also for ideal conditions.
The reason why I bing up RPM and BMEP, but more improtantly, the pressure curve as the crank turns from the point of combustion to the point when the exhaust port opens is for the acceleration component. And that accelerationg, just like 3rd law, also acceleratets the cylinder head and everting else attached to it: i.e the block, the head, and the entire RC. Or to look at it in a different manner, you can look at it in the impulse-momentum theorem, or even work-energy theorem. Just as a gun is kicked back as the bullet is pushed forward when you pull the tigger, so does the the engine block get pushed up as the piston is pushed down.
ORIGINAL: downunder
Read and reread carefully everything that SManMTB posted. This is the only way a single cylinder engine can be close to balanced other than extreme complications like using counter-rotating balance shafts etc. This is totally impractical in our engines however. Most engines don't even come close to that 50-60% mentioned by SManMTB and it takes some serious engineering using tungsten carbide inserts to get there. Engine revs make no difference to the actual balance other than the unavoidable vibration could set up a harmonic in the chassis/fuselage. Likewise, combustion pressures make no difference either because the pressure down on the piston is felt equally upwards on the cylinder head. Action and reaction, Newton's third law and all that stuff.
Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
Read and reread carefully everything that SManMTB posted. This is the only way a single cylinder engine can be close to balanced other than extreme complications like using counter-rotating balance shafts etc. This is totally impractical in our engines however. Most engines don't even come close to that 50-60% mentioned by SManMTB and it takes some serious engineering using tungsten carbide inserts to get there. Engine revs make no difference to the actual balance other than the unavoidable vibration could set up a harmonic in the chassis/fuselage. Likewise, combustion pressures make no difference either because the pressure down on the piston is felt equally upwards on the cylinder head. Action and reaction, Newton's third law and all that stuff
.Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
The reason why I bing up RPM and BMEP, but more improtantly, the pressure curve as the crank turns from the point of combustion to the point when the exhaust port opens is for the acceleration component. And that accelerationg, just like 3rd law, also acceleratets the cylinder head and everting else attached to it: i.e the block, the head, and the entire RC. Or to look at it in a different manner, you can look at it in the impulse-momentum theorem, or even work-energy theorem. Just as a gun is kicked back as the bullet is pushed forward when you pull the tigger, so does the the engine block get pushed up as the piston is pushed down.
SAVAGEJIM, seriously. What are you talking about? There's a lot of fancy terms and words in there......
11-06-2008, 01:42 PM
#19
Senior Member
RE: Why people should not mod a crank!
ORIGINAL: RR Mods
Thats alright manI dident take offence at all I just dont want to be PMed to death.
Thats alright man
I dident take offence at all I just dont want to be PMed to death.
seriously lets see your balancing jig.....or explain to us how you balance them........if you can make a post criticizing other engine modders you should at least have some proof to backup what your saying........ no offense but i think your fooling yourself into thinking your actually balancing these motors............Many old schol guys claim you cant cut the sleeve chrome as well to alter port height, another false claim, which IMO is the same as balancing an engine, all hogwash !!!
11-06-2008, 02:02 PM
#20
Senior Member
Join Date: Dec 2007
Location: nicosia, CYPRUS
Posts: 1,060
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
ORIGINAL: supertib
seriously lets see your balancing jig.....or explain to us how you balance them........if you can make a post criticizing other engine modders you should at least have some proof to backup what your saying........ no offense but i think your fooling yourself into thinking your actually balancing these motors............Many old schol guys claim you cant cut the sleeve chrome as well to alter port height, another false claim, which IMO is the same as balancing an engine, all hogwash !!!
ORIGINAL: RR Mods
Thats alright manI dident take offence at all I just dont want to be PMed to death.
Thats alright man
I dident take offence at all I just dont want to be PMed to death.
seriously lets see your balancing jig.....or explain to us how you balance them........if you can make a post criticizing other engine modders you should at least have some proof to backup what your saying........ no offense but i think your fooling yourself into thinking your actually balancing these motors............Many old schol guys claim you cant cut the sleeve chrome as well to alter port height, another false claim, which IMO is the same as balancing an engine, all hogwash !!!
rr mods???? website please???
hey supertib, did you get my pm???
11-06-2008, 02:09 PM
#21
Senior Member
RE: Why people should not mod a crank!
ORIGINAL: rc rock
i'd like to see it too
rr mods???? website please???
hey supertib, did you get my pm???
ORIGINAL: supertib
seriously lets see your balancing jig.....or explain to us how you balance them........if you can make a post criticizing other engine modders you should at least have some proof to backup what your saying........ no offense but i think your fooling yourself into thinking your actually balancing these motors............Many old schol guys claim you cant cut the sleeve chrome as well to alter port height, another false claim, which IMO is the same as balancing an engine, all hogwash !!!
ORIGINAL: RR Mods
Thats alright manI dident take offence at all I just dont want to be PMed to death.
Thats alright man
I dident take offence at all I just dont want to be PMed to death.
seriously lets see your balancing jig.....or explain to us how you balance them........if you can make a post criticizing other engine modders you should at least have some proof to backup what your saying........ no offense but i think your fooling yourself into thinking your actually balancing these motors............Many old schol guys claim you cant cut the sleeve chrome as well to alter port height, another false claim, which IMO is the same as balancing an engine, all hogwash !!!
rr mods???? website please???
hey supertib, did you get my pm???
I am not sure if I got your PM....
11-06-2008, 05:25 PM
#22
Senior Member
Join Date: May 2008
Location: Longueuil, QC, CANADA
Posts: 430
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
A modder do not want to get PMd by giving his real name but enter RRmods as a username....
Do you have any of your stuff on the internet? like videos of engines in action... just curious
Do you have any of your stuff on the internet? like videos of engines in action... just curious
11-06-2008, 08:19 PM
#23
Senior Member
Join Date: Jul 2005
Location: Torchy the Fiery Fast RC Turtl
Posts: 10,544
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
ORIGINAL: SManMTB
SAVAGEJIM, seriously. What are you talking about? There's a lot of fancy terms and words in there......
ORIGINAL: SAVAGEJIM
No disagreements here, and yes, SmanMTB's conditions are also for ideal conditions.
The reason why I bing up RPM and BMEP, but more improtantly, the pressure curve as the crank turns from the point of combustion to the point when the exhaust port opens is for the acceleration component. And that accelerationg, just like 3rd law, also acceleratets the cylinder head and everting else attached to it: i.e the block, the head, and the entire RC. Or to look at it in a different manner, you can look at it in the impulse-momentum theorem, or even work-energy theorem. Just as a gun is kicked back as the bullet is pushed forward when you pull the tigger, so does the the engine block get pushed up as the piston is pushed down.
ORIGINAL: downunder
Read and reread carefully everything that SManMTB posted. This is the only way a single cylinder engine can be close to balanced other than extreme complications like using counter-rotating balance shafts etc. This is totally impractical in our engines however. Most engines don't even come close to that 50-60% mentioned by SManMTB and it takes some serious engineering using tungsten carbide inserts to get there. Engine revs make no difference to the actual balance other than the unavoidable vibration could set up a harmonic in the chassis/fuselage. Likewise, combustion pressures make no difference either because the pressure down on the piston is felt equally upwards on the cylinder head. Action and reaction, Newton's third law and all that stuff.
Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
Read and reread carefully everything that SManMTB posted. This is the only way a single cylinder engine can be close to balanced other than extreme complications like using counter-rotating balance shafts etc. This is totally impractical in our engines however. Most engines don't even come close to that 50-60% mentioned by SManMTB and it takes some serious engineering using tungsten carbide inserts to get there. Engine revs make no difference to the actual balance other than the unavoidable vibration could set up a harmonic in the chassis/fuselage. Likewise, combustion pressures make no difference either because the pressure down on the piston is felt equally upwards on the cylinder head. Action and reaction, Newton's third law and all that stuff
.Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
The reason why I bing up RPM and BMEP, but more improtantly, the pressure curve as the crank turns from the point of combustion to the point when the exhaust port opens is for the acceleration component. And that accelerationg, just like 3rd law, also acceleratets the cylinder head and everting else attached to it: i.e the block, the head, and the entire RC. Or to look at it in a different manner, you can look at it in the impulse-momentum theorem, or even work-energy theorem. Just as a gun is kicked back as the bullet is pushed forward when you pull the tigger, so does the the engine block get pushed up as the piston is pushed down.
SAVAGEJIM, seriously. What are you talking about? There's a lot of fancy terms and words in there......
Impulse-momenta, work-energy, these two only reinforces the action-reaction of Newton's 3rd law. I only brought those up for those who understand these principles, but for those who do not, Newton's 3rd law will suffice.
Linear inertia can simply be though of inertia along a straight line.
And of course, moment of inertia is rotational or angular inertia.
Consider another one of Newtons laws: A mass at rest will stay at rest. At least until a force pushes it, then it will move. A mass in motion will stay in motion, at least until a force acts on it such that it slows down, or speeds up, or changes its direction of its movemnt. What I'm trying to say is mass wants to either stay moving or if not moving to begin with, it wants to stay put.
How does this apply to our engines in our discusion? Our engines will have both rotaing and linear motions, and as such will hve momenta and kinetic energies. Linearly, the parts are constantly changing, especially the piston (whose movemnt is purely linear).
Mass in a rotaing motion will produce a harmonic just as wjvail described. At a given RPM, the harmonics are what causes the most vibrations. Worse, as the engine accelereates or decelerates to differnt RPMs, the harmonics change.
Now, combustion does a couple of things. It of course pushes teh piston down and that downward movement of teh piston is converted into rotation by way of teh conrod and crankshaft, but that combustion is also pushing up at teh same time against teh heatsink & head with equal force. That action does impart some up ward movement on the entire engine, definitely a very small movement in compared to te piston since the rest of the engine, and teh entire RC posses way more mass.
What I am trying to say is the combustion itself does contribute to the vibrations, even if there were no rotating parts. For eplaining this, lets assume the piston is simply not attached to anything at all, no conrod, not crank, it is just in the cylinder. At combustion, the piston is shot downward and moves at a very high velocity. The rest of the engine, which of course is very much heavier than the piston is also shot upwards too, but at a significantly slower energy. Applying Newton's third law here, the force on the engine head is exactly equal to the force pushing teh piston down. Since forces cause accerelation, the whole engine will of course move up. And that too adds to vibrations.
11-06-2008, 08:27 PM
#24
RE: Why people should not mod a crank!
I have a feeling Rich won't be posting again[sm=confused.gif]. Wow guys, great job scaring away a pro modder ye meanies!
lol, that was funny to read though. I don't know what makes me more skeptical of his modding ability, the 6th grade level writing and presentation, or his expertise on the subject?
Seriously, if a person is trying to promote their business, they should essentially try to come off as professional, trustworthy, experienced in their craft, and skilled in basic English. I must say, failure in each category so far is not looking good[&:],
Tom.
lol, that was funny to read though. I don't know what makes me more skeptical of his modding ability, the 6th grade level writing and presentation, or his expertise on the subject?
Seriously, if a person is trying to promote their business, they should essentially try to come off as professional, trustworthy, experienced in their craft, and skilled in basic English. I must say, failure in each category so far is not looking good[&:],
Tom.
11-06-2008, 08:35 PM
#25
Senior Member
Join Date: Apr 2005
Location: Charlottesville,
VA
Posts: 5,253
Likes: 0
Received 0 Likes
on
0 Posts
RE: Why people should not mod a crank!
ORIGINAL: SAVAGEJIM
LOL, I guess all I am simply trying to say is that the forces do play a part in the balance of vibrations a running engine produces.
Impulse-momenta, work-energy, these two only reinforces the action-reaction of Newton's 3rd law. I only brought those up for those who understand these principles, but for those who do not, Newton's 3rd law will suffice.
Linear inertia can simply be though of inertia along a straight line.
And of course, moment of inertia is rotational or angular inertia.
Consider another one of Newtons laws: A mass at rest will stay at rest. At least until a force pushes it, then it will move. A mass in motion will stay in motion, at least until a force acts on it such that it slows down, or speeds up, or changes its direction of its movemnt. What I'm trying to say is mass wants to either stay moving or if not moving to begin with, it wants to stay put.
How does this apply to our engines in our discusion? Our engines will have both rotaing and linear motions, and as such will hve momenta and kinetic energies. Linearly, the parts are constantly changing, especially the piston (whose movemnt is purely linear).
Mass in a rotaing motion will produce a harmonic just as wjvail described. At a given RPM, the harmonics are what causes the most vibrations. Worse, as the engine accelereates or decelerates to differnt RPMs, the harmonics change.
Now, combustion does a couple of things. It of course pushes teh piston down and that downward movement of teh piston is converted into rotation by way of teh conrod and crankshaft, but that combustion is also pushing up at teh same time against teh heatsink & head with equal force. That action does impart some up ward movement on the entire engine, definitely a very small movement in compared to te piston since the rest of the engine, and teh entire RC posses way more mass.
What I am trying to say is the combustion itself does contribute to the vibrations, even if there were no rotating parts. For eplaining this, lets assume the piston is simply not attached to anything at all, no conrod, not crank, it is just in the cylinder. At combustion, the piston is shot downward and moves at a very high velocity. The rest of the engine, which of course is very much heavier than the piston is also shot upwards too, but at a significantly slower energy. Applying Newton's third law here, the force on the engine head is exactly equal to the force pushing teh piston down. Since forces cause accerelation, the whole engine will of course move up. And that too adds to vibrations.
ORIGINAL: SManMTB
SAVAGEJIM, seriously. What are you talking about? There's a lot of fancy terms and words in there......
ORIGINAL: SAVAGEJIM
No disagreements here, and yes, SmanMTB's conditions are also for ideal conditions.
The reason why I bing up RPM and BMEP, but more improtantly, the pressure curve as the crank turns from the point of combustion to the point when the exhaust port opens is for the acceleration component. And that accelerationg, just like 3rd law, also acceleratets the cylinder head and everting else attached to it: i.e the block, the head, and the entire RC. Or to look at it in a different manner, you can look at it in the impulse-momentum theorem, or even work-energy theorem. Just as a gun is kicked back as the bullet is pushed forward when you pull the tigger, so does the the engine block get pushed up as the piston is pushed down.
ORIGINAL: downunder
Read and reread carefully everything that SManMTB posted. This is the only way a single cylinder engine can be close to balanced other than extreme complications like using counter-rotating balance shafts etc. This is totally impractical in our engines however. Most engines don't even come close to that 50-60% mentioned by SManMTB and it takes some serious engineering using tungsten carbide inserts to get there. Engine revs make no difference to the actual balance other than the unavoidable vibration could set up a harmonic in the chassis/fuselage. Likewise, combustion pressures make no difference either because the pressure down on the piston is felt equally upwards on the cylinder head. Action and reaction, Newton's third law and all that stuff.
Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
Read and reread carefully everything that SManMTB posted. This is the only way a single cylinder engine can be close to balanced other than extreme complications like using counter-rotating balance shafts etc. This is totally impractical in our engines however. Most engines don't even come close to that 50-60% mentioned by SManMTB and it takes some serious engineering using tungsten carbide inserts to get there. Engine revs make no difference to the actual balance other than the unavoidable vibration could set up a harmonic in the chassis/fuselage. Likewise, combustion pressures make no difference either because the pressure down on the piston is felt equally upwards on the cylinder head. Action and reaction, Newton's third law and all that stuff
.Minor modding of the crankweb will increase the amount of imbalance but because they're generally so far from the ideal compromise you may not notice any extra vibrations.
The reason why I bing up RPM and BMEP, but more improtantly, the pressure curve as the crank turns from the point of combustion to the point when the exhaust port opens is for the acceleration component. And that accelerationg, just like 3rd law, also acceleratets the cylinder head and everting else attached to it: i.e the block, the head, and the entire RC. Or to look at it in a different manner, you can look at it in the impulse-momentum theorem, or even work-energy theorem. Just as a gun is kicked back as the bullet is pushed forward when you pull the tigger, so does the the engine block get pushed up as the piston is pushed down.
SAVAGEJIM, seriously. What are you talking about? There's a lot of fancy terms and words in there......
Impulse-momenta, work-energy, these two only reinforces the action-reaction of Newton's 3rd law. I only brought those up for those who understand these principles, but for those who do not, Newton's 3rd law will suffice.
Linear inertia can simply be though of inertia along a straight line.
And of course, moment of inertia is rotational or angular inertia.
Consider another one of Newtons laws: A mass at rest will stay at rest. At least until a force pushes it, then it will move. A mass in motion will stay in motion, at least until a force acts on it such that it slows down, or speeds up, or changes its direction of its movemnt. What I'm trying to say is mass wants to either stay moving or if not moving to begin with, it wants to stay put.
How does this apply to our engines in our discusion? Our engines will have both rotaing and linear motions, and as such will hve momenta and kinetic energies. Linearly, the parts are constantly changing, especially the piston (whose movemnt is purely linear).
Mass in a rotaing motion will produce a harmonic just as wjvail described. At a given RPM, the harmonics are what causes the most vibrations. Worse, as the engine accelereates or decelerates to differnt RPMs, the harmonics change.
Now, combustion does a couple of things. It of course pushes teh piston down and that downward movement of teh piston is converted into rotation by way of teh conrod and crankshaft, but that combustion is also pushing up at teh same time against teh heatsink & head with equal force. That action does impart some up ward movement on the entire engine, definitely a very small movement in compared to te piston since the rest of the engine, and teh entire RC posses way more mass.
What I am trying to say is the combustion itself does contribute to the vibrations, even if there were no rotating parts. For eplaining this, lets assume the piston is simply not attached to anything at all, no conrod, not crank, it is just in the cylinder. At combustion, the piston is shot downward and moves at a very high velocity. The rest of the engine, which of course is very much heavier than the piston is also shot upwards too, but at a significantly slower energy. Applying Newton's third law here, the force on the engine head is exactly equal to the force pushing teh piston down. Since forces cause accerelation, the whole engine will of course move up. And that too adds to vibrations.
What I meant was.... Do you KNOW what all these copy and paste paragraphs actually mean?