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Crankshaft counterweight question
Hi Guys,
I'm in process of designing and building a 2 cylinder in line 4 cycle engine. The bore and stroke is going to be 1”. I want to know when building the crankshaft, how much counterweight I need to add. Basically what is the formula to determine the counterweight? Thanks Borna |
RE: Crankshaft counterweight question
I don't know the formula, but it will depend on whether the crank is a 180 degree or 360 degree throw. Power pulses are equally spaced on a 360 crank (one each revolution, or 360 degrees, and the pistons travel together); on a 180, the pulses come irregularly spaced, 180 degrees, or half a rev, then a 540 degree space, the again at 180 degrees. The pistons travel opposite each other. If you flatten out the engine (opposed twin), the 180 crank becomes a classic boxer and the pulses become 360 degrees apart again (the advantage of the flat, or opposed engine is even firing pulses and smoother power delivery with less vibration and the pistons/rods tend to counterbalance each other). On either the flat twin or 360 crank in-line, the counterbalance is essentially the same mass as both pistons and rods. The distribution of the counterbalance mass is basically opposite the pistons on the 360 inline and at 90 degrees to the opposed twin pistons, equally divided. There is a lot more involved, as there are harmonics to consider.
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RE: Crankshaft counterweight question
IMHO the straight twin is the worst layout you could pick. If you use a 360 crank it shakes like a single, if you use a 180 crank you have uneven power pulses from a very buzzy engine.
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RE: Crankshaft counterweight question
ORIGINAL: borna Hi Guys, I'm in process of designing and building a 2 cylinder in line 4 cycle engine. The bore and stroke is going to be 1”. I want to know when building the crankshaft, how much counterweight I need to add. Basically what is the formula to determine the counterweight? Thanks Borna Good luck, Dave Olson |
RE: Crankshaft counterweight question
Right, an inline twin is a shaker, in modern motorcycles a 180 degree crank plus a balance shaft is used to tame the beast. This is how my ninja 250 engine is designed.
Now, a 90 degree V twin on a single crankpin type crankshaft can be balanced very nicely, and makes a smooth running twin. I know that's not what you asked, but something to think about. |
RE: Crankshaft counterweight question
Thanks for the comments. The crank is 360 throw. The reason I want to use 360, is no ignition distributor needed.
I was searching the net and find a formula but not sure how true it is The formula says A - Weight of Piston, with ring and gudgeon-pin B - Small-end of connecting-rod (Not sure what it means by this? Is this the diameter of pin hole on the rod? C - Big-end of connecting-rod (Not sure what it is also) ((A + B) /2) + C = Counterweight Thanks Borna |
RE: Crankshaft counterweight question
ORIGINAL: borna Hi Guys, I'm in process of designing and building a 2 cylinder in line 4 cycle engine. The bore and stroke is going to be 1”. I want to know when building the crankshaft, how much counterweight I need to add. Basically what is the formula to determine the counterweight? Thanks Borna Lower half of the conrod is deemed to be rotating mass, the upper half is reciprocating. |
RE: Crankshaft counterweight question
Still not clear, can you please give me an example?
Thanks Borna |
RE: Crankshaft counterweight question
Pe's example is your formula in words.
You need a very good set of scales, Put one end of the connecting rod on each scale. Find the weight of the small end (piston end) of the rod, find the weight of the big end of the rod (crankshaft end). Weigh the piston. ring and wrist pin, add to the weight of small end of the rod, divide by 2, add the weight of the big end of the rod and that's your counter weight. |
RE: Crankshaft counterweight question
Take a connecting rod by itself and lay it on a table horizontal. Lift the small end of the rod and set it on a scale calibrated in grams. Now lift the big end of the rod until it is horizontal and level again. The scale will show the weight of the small end of the rod. Record this number. Now swap the rod end for end, level it again and the scale will show the weight of the big end. Record this number also. Now place the entire rod on the scale to get the gross weight. The little end and big end added together should equal the gross.
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RE: Crankshaft counterweight question
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For example lets consider the following drawing. Lets assume this is the connecting rod. You can see both crank side hole and piston side hole is .28 diameter. The shape is fairly symmetric. Can I simply assume both crank side and piston side are equal?
Thanks Borna |
RE: Crankshaft counterweight question
OK with that rod shape it should be symmetric. Half the weight is rotary (C) and half is recpt (B).
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RE: Crankshaft counterweight question
Just to stir the pot some.
You know that the British twins, BSA and Triumph used this layout and over-balanced their twins so that rather than just shaking up and down some of the shake was side to side, it made it feel like they shook less. |
RE: Crankshaft counterweight question
Yep, and both of them were great machines for getting you there. Getting back was another story because you had to walk back to pick up all the parts that shook off on the way there.
Been there, done that, with a few of them.......... Norton was a little better but you could never find parts. |
RE: Crankshaft counterweight question
ORIGINAL: Tired Old Man Yep, and both of them were great machines for getting you there. Getting back was another story because you had to walk back to pick up all the parts that shook off on the way there. Been there, done that, with a few of them.......... Norton was a little better but you could never find parts. Dave Olson |
RE: Crankshaft counterweight question
Nortons had featherbed frames and the best front forks made if I remember correctly. My dream bike as a Dunstill 750 Norton Domaracer.
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RE: Crankshaft counterweight question
...
but they lost big time to the slick Japanese bikes. I had a Douglass dragonfly boxer at the time, and even succeeded to eliminate the perpetual oil puddle. The English were dead on their feet without knowing it. I had a Honda as well at the time (remember the sixties), slick as could be, steering properties like a moped. The two were seperate worlds. Guess who survived? I did for sure to tell the tale [8D] |
RE: Crankshaft counterweight question
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I also need to make the valve
I want the valve face to be 45 degree. Question is do I need to set the cross slid to 22.5 degree or set it at 45 degree? Also can I use a boring bar to cut the face? Can someone give me the procedure of how to do it? here is a simple drawing of how I want to set it up in the lathe Thanks Borna |
RE: Crankshaft counterweight question
wow Borna,
If you ask this kind of questions about using a lathe, you have a long way to go. You set the cross sled at 45° and use a pointed chisel with rounded nose (R=0.05mm) for final turning. If set up right, you could use the boring bar, but it is not the best tool for the job. |
RE: Crankshaft counterweight question
Hi Pe,
Thanks for clarification. Well yes I got a long way to go for sure but I'm not that bad at machining Once I know what I need to do. I usually get the job done [8D] Hey have you ever looked at my GMS conversion from glow to GAS http://www.rcuniverse.com/forum/m_61...tm.htm#6165393 |
RE: Crankshaft counterweight question
Borna, I see that you paid your dues, but I was not aware of that. I take back my previous comment.
BTW, I use the piston stopper system to find TDC and set the timing. The spark should fire when I apply some pressure, and then use the strobe light to check it with engine running. It mostly is spot-on. |
RE: Crankshaft counterweight question
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Today I made 4 valve guide, spring retainer and only got chance to make one valve.
The valve hasn't been lapped to the seat yet, but it seals very nicely already. I tested the seal by filling the valve guide with acetone and place the valve in with no leak. Borna |
RE: Crankshaft counterweight question
Nice work.
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RE: Crankshaft counterweight question
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Borna, Very nice work. I got to make some valves for my "Holt' 4 cyclinder engine. I may be asking a few questions as I go. I will post a couple of photos. Best Regards, Capt,n
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RE: Crankshaft counterweight question
Hi Captin,
I'll be happy tp help if I can. That is is nice engine. Did you make it? Borna |
RE: Crankshaft counterweight question
Borna, I got lucky. I do old time engine shows and have 2 engines I show. A lot of people stop and chat about engines of course! I must of gave out my e-mail to the right person. He gave my email to a nice person who emailed out of the blue. She said her husband had passed away and wanted to sell this engine partly done. I drove to her homes a few weeks later and looked at the engine. The hard part of deciding if to buy this engine, was if I thought I could finish it. I bought it and have worked on the rods and pistons. The crankshaft, camshaft, and cylinder bores was done. I got the rest to do. I got to decide if to use one ring per piston or 2. I was thinking of using Boman rings. I got to do the valve guides and valves. I am working on the rocker arms. I got to come up with most easy way to make the valves. I was thinking about using valves for a OS, Magnum, Enya or a YS 4 stroke and making custom guides. The heads have no valve seat ground into it yet also. I got some new glasses coming and plan on getting back to this project! It is fun sometimes...but a pain in the _ _ t other times. I hope someday to hear it run like the first engine I finished. Best Rgards Capt,n
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RE: Crankshaft counterweight question
ORIGINAL: captinjohn Borna, I got lucky. I do old time engine shows and have 2 engines I show. A lot of people stop and chat about engines of course! I must of gave out my e-mail to the right person. He gave my email to a nice person who emailed out of the blue. She said her husband had passed away and wanted to sell this engine partly done. I drove to her homes a few weeks later and looked at the engine. The hard part of deciding if to buy this engine, was if I thought I could finish it. I bought it and have worked on the rods and pistons. The crankshaft, camshaft, and cylinder bores was done. I got the rest to do. I got to decide if to use one ring per piston or 2. I was thinking of using Boman rings. I got to do the valve guides and valves. I am working on the rocker arms. I got to come up with most easy way to make the valves. I was thinking about using valves for a OS, Magnum, Enya or a YS 4 stroke and making custom guides. The heads have no valve seat ground into it yet also. I got some new glasses coming and plan on getting back to this project! It is fun sometimes...but a pain in the _ _ t other times. I hope someday to hear it run like the first engine I finished. Best Rgards Capt,n borna,nice looking parts you made there. captinjohn, please post some close up pictures of the rods, pistons and such, that you actually machined in your shop, like Borna did. I'm also considering doing a kit from castings. Thanks. |
RE: Crankshaft counterweight question
Quote:
“I got to decide if to use one ring per piston or 2. I was thinking of using Boman rings”. captinjohn, Question: Is this a wet sump engine? if so, are you really considering using a single ring piston in this engine. Were you given the engineering drawings with the kit? If so, why do you feel the need to deviate from the designer’s specifications with rings and valves? Woops...Sorry borna for hijacking your thread. ;) |
RE: Crankshaft counterweight question
Nito Joe, Please PM me and if you give mw your phone no....we can talk about the Holt engine. I also have photos in my computer to email direct to you. Makes it a lot more easy. Thanks capt,n |
RE: Crankshaft counterweight question
All 4 valves completed. The cylinder sleves are done too. Over the weekend I'm planing to make the 2 pistons and if I get the chance, the rings.
I'll post more pictuers by the end of the week. Bora |
RE: Crankshaft counterweight question
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Here are some more pictures of Roshi-2 inline.
This engine is my own design, once completed, it is going to be 2 cylinder 4 cycle inline water cooled 1" bore 1" stroke. Next in the list is Crankshaft and Camshaft |
RE: Crankshaft counterweight question
Nice
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RE: Crankshaft counterweight question
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A little more progress. Crankshaft and flywheel calculations and machining completed.
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RE: Crankshaft counterweight question
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More progress
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RE: Crankshaft counterweight question
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Ok, here are some more progress on my engine
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RE: Crankshaft counterweight question
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Last thing I need is the radiator
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RE: Crankshaft counterweight question
I'm a bit slow - I just worked-out what the clear plastic assembly is and why it's fitted where it is [sm=red_smile.gif]
It looks like you should be adding fuel soon! |
RE: Crankshaft counterweight question
the clear plastic assembly is the distributor cap with the rotor inside connected to the camshaft.
I could have used waste spark ignition system, but what the hell, decided to go with distributor. On the other side, the one with the small pulley is the water pump. Borna |
RE: Crankshaft counterweight question
Nice work, Just a few coments to make
1. Your water pump is designed on a oil pump design and not a impeller like most are. Have you checked the output pressure it puts out by chance. A standard water system is between 8-14 PSI Radiators don't like it much more than that. 2. I never did see your rods or camshaft, did you make them yourself, do you have a pic of those items ? 3. Is the crank balanced with the two blocks that go to the rod pin, I don't see any other counter weights on it, or do you plan on using the flywheel to do the balancing, external type of balance. If so you will need something on the front as well. 4. It apears that you pinned the crank together, did you happen to weld it also. 2 strokes have been pressed together forever and they seem to work fine, but a hard prop strike can throw them out of alignment. 5. Did you go with Bowman rings or decide to just make your own, just wondering what material you used for them if you made them yourself, also what material did you go with for the pistons? 5. Since the crankshaft appears to be one piece what type of bearings did you use? Sorry for the 50 questions this is just a few things I noticed about your engine. |
RE: Crankshaft counterweight question
Homelite has the formula. The counterweight should be 66 to 68 % of the receipocating weight. If any one wants to argue about this, please call Homelite. I have used this formula in the past and it workked reasonablly well. This is for a single cylinder engine. Good luck.
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