MT70CC TWIN
08-13-2012, 05:02 AM
#1351
RE: MT70CC TWIN
ORIGINAL: captinjohn
This is the only twin engine under $500 and can swing 24-8 prop up to 7K with stock muffler and engine weight only 3.26lb with plug !!!. People know the advantage of twin engine compare with single. Smooth without vibration and we made it still light weight just like single cylinder engine is what was posted. Now a 24X8 prop turning 7000 RPM sure should hover something!!!!
ORIGINAL: 3DDino
in that case single is not that bad after all
how do you determine to use twin or single of the same size for 3d flying
thx
in that case single is not that bad after all
how do you determine to use twin or single of the same size for 3d flying
thx
08-29-2012, 07:52 PM
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RE: MT70CC TWIN
Today i re assembled a broken 70 cc twin,,i could clearly see why and how it failed as well. for one contributing factor would be the questionable metalurgy of the case which appeared pressed or stamped from soft ,,,,maybe recycled beer cans for all i know,,then machined with a dull bit from a possible poorly serviced cnc machine,or a overworked unskilled machinist.To add to the failure which was
noticed when a cylinder made its way from the rest of the engine,, by its unfortunate previous owner,,, the,,fact the case halves did not meet or were in the same plane at the cylinders nor the intake ,,,, caused the cylinder to rock and ,,im quite surprised the resulting air leak didnt shut it down first.or even obtain a seal in the first place,,..either way it had the previous issues along with a broken piston and stripped threads,,,,,,,I first washed out and inspected cleaned up and lightly honed and chamfered the cylinder shank decked the case and aligned the case halves and tapped for 8/32 ,,also had to use a diamond ball to clear where the cylinder bolts might touch the case upon exit,after tightening, if i had the toolig i would have also cleaned up the rear of the crank where it meets the case,,i got super fast reasonable parts from valleyview ,,thanks Tom ,,,the piston skirt at the inner bottom needed to be ground at a 45 deg to prevent hitting the crank a bdc,, i think many engines had this problem,,,installed the new piston roller bearing pin and ring ,,made sure the arrow on the piston pointed down,,and made a final rinse and light oil,,reassembled all the engine making sure all the bolts had loctite and a dab of silicone because it can leak through the threads to the case ,also the same for the reed block and timing sensor ,,and because of no confidence with machine work used a dab of nickle counpound in the plugs ,,reset the timing and in the process of mounting it in my test bed yak,,,i think i have figured that clanking sound many mt owners have and that is caused by the poorly fitting piston sides slapping the cylinder walls when you wiggle the prop it would seem a few thousands more would have been a cleaner fit but with expansion shouldnt be a big issue ,,i will report how this orphan engine runs in a few days ,,this is all for shi%ts and giggles for us plane guys ,maybe one day some industrious machinist will take this design and do it correctly .
08-30-2012, 03:22 AM
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RE: MT70CC TWIN
so VV still has a few parts for the 70?
there is a guy over on the FG that has three of these engines,one new in the box and two that he is running now,all three are for sale.the NIB engine he wanted 300.00 for it, and all engines came fro VV,so you would think that they have been inspected.
there is a guy over on the FG that has three of these engines,one new in the box and two that he is running now,all three are for sale.the NIB engine he wanted 300.00 for it, and all engines came fro VV,so you would think that they have been inspected.
08-30-2012, 06:20 AM
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RE: MT70CC TWIN
The one new MT 70s has been sold and the two running are not for sale. They are presently doing fine in my big TigerCat. So far they have not leaked from any seal, start easily and turn the XOAR 22X10 props at around 6100 rpm. These two were the latter 4 bolt hub(DA 50) with CM6 plugs. I will probably rering them this winter just to get a little more performance out of them. They were put together by Jody at VVRC and have run fine ever since I have had them. When I received the two for the Cat I inspected them and was pleased at what Jody did with them. I will report on the new ring job when it is completed and let everyone know if there is any improvement.
08-30-2012, 06:43 AM
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RE: MT70CC TWIN
it's amazing the demand for a good 60-70cc twin,even when they are out of production and parts are not around,guy's still will buy them.
good to hear you sold your engine it was a good deal,for someone.
good to hear you sold your engine it was a good deal,for someone.
08-30-2012, 12:49 PM
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RE: MT70CC TWIN
For what i paid,, to put this thing back together,,and to buy the carcass from someone who pretty much got burnt,,its probably not a great value only due to the brand,,,,but i am greatful to the seller,, this is why i ,elected to just tap out the stripped threads instead of investing time and money for helicoils,,or even using the prototype case i still have,because of work i havent attempted to start it up and still need to finish setting it up to test,,,heck it may blow the other cylinder off,,,im actually thinking it will be fine,,i also think the ones doing low rpms may be one of those with dragging parts,or a combination of all the faults found on mt engines my 70 standard plug engine does over 7k with a 23x8 also running coleman pure white gas with none of that ethanol or octane thats designed for 4 stroke automobiles wil;l boost output and smell nice doing it.
08-30-2012, 05:49 PM
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RE: MT70CC TWIN
I also would speculate that its possible the grade of fuel and altitude and not looking for peak rpms on the ground,,even restrictive fuel lines could be causing the lower than expected rpms,, usually modellers flying twins,,will richen to match the best setting on the weaker or slower engine ,,especially with glow engines ,,but if i had one doing several hundred more than the other ,,i think ,i might have the weak one checked ,,,and back to fuel ,,ive read a few say,,use good clean premium fuel,,,,,i suggest regular non additive especially ethanol,, or coleman fuel ,,,,,good sized tight fuel connections and a oversize filter if using one,,also many gassers get junk in the inner carb screen when breaking in,,and that alone can count for a few hundred rpms loss as well as plug type,, gap,,timing even an inferior ignition battery will cause losses in rpms
08-31-2012, 06:06 AM
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RE: MT70CC TWIN
Mine has been flawless so-far. I got about 20-gallons through it. What the problem you have is a torquey engine that is not meant to spin the props at the speed of sound! WE have all met the guy with a O.S 160 that will only top-out about 9200rpms, constant complaining and telling everyone how big a piece of crap it is. It is a lot of fun for us he works for some big ass, enginern, company! (He runs a APC 10-6 from his trainer days, and says the math he does with the H.P. rating of the O.S, he should be getting 17000+, no tellin' him otherwise! Last thing on the MT-70, alot of them (50%?) had the reeds installed upside-down with sealing read valve ABOVE the stiffener reed. If your engine has this, correct it and bump timing up a few degrees at a time. you will be amazed at the improvements as this engine gets kinda scary-powerful. By-the-way I run only 23" or 24" props.. Sorry to have carried on so long, Brian
08-31-2012, 09:20 AM
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RE: MT70CC TWIN
I agree with your assesment,,brian,,i cant think or speak for the manufacturer,,and dont know for sure but the engine was targeted twards aerobatic flying,,and top end rpms arent as important to me as accelleration midrange transition starting and realibility,,ill gladly trade a few hundred rpms ,,for performance in the forementioned aereas.
08-31-2012, 09:53 AM
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RE: MT70CC TWIN
Interesting post Brian I did plan to check out the reed blocks when I rering both of them this winter. Frank the ring guy suggested I do this when I do the job for the same reason you stated. The ignition is 28 degrees BTC on both and I have heard of people going as far as 34 degrees to get more steam. Right now I can get about 6300 rpm if I really tweak the mixture, but with a big twin I really need reiability over a rip snorter. As previously stated they have been running good for a year and a half now with no indications of failure.l
08-31-2012, 11:59 AM
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RE: MT70CC TWIN
I checked my static timing today and I am about 33-34 degrees B.T.C. Make sure you listen for detonation, as of all the conditions out there that can affect max timing
08-31-2012, 12:23 PM
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RE: MT70CC TWIN
also try to avoid high octane and ethanol fuels,,ive been educated on using octane,, yes it prevents detonation,,,pre ignition,,,but in our little low compression two strokes, lees agressive timing will prevent detonation.we are all aware of squeezing every last bit of power can damage an allready less than perfect engine and the trade off is bigger displacement with the weight gain .or spending 3 times as much for a mintor high quality engine,, a little attention to things like cleaning up rough casting in the cylinder ports when re ringing may help performance as well
08-31-2012, 01:37 PM
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RE: MT70CC TWIN
There is a big difference between pre-ignition and detonation. Pre-ignition is just that...the spark plug fires way too soon after B.D.C, causing the rapidly expanding fuel charge to reach its maximum P.S.I. before the piston reaches T.D.C. Engine mechanical related detonation can be caused by many things, such as too much compression, port timing issues, hot spots in the cylinder and to much load (Bigger prop then it was rated to turn.) Now this is the part that I spent my 2-cts discussing. High octane does NOT mean more energy content, or power output. In fact in most of engines not designed for it (probably 95%.) I don't care if is 2 or 4 stoke, in a car, boat, motorcycle, big, small, Asian or American. I find it odd that people will spend up to 40 cents more for "premium" gas, when the car they are putting it in will have less power, and lower gas mileage. It's says Premium, so it MUST be better! Back in the early day of getting my degree, One of my profs. had a very interesting way of demonstrating this on a special engine that turned very slowly with a clear plexiglass cylinder. He would run the engine with the room lights on, so we could all HEAR the sound of detonation, then he turned off the lights and all of the questions that we had and did not at the time were answered instantly.You can win any discussion on premium fuel this way: Octane is the rating which the fuel will self ignite (think diesel) So engines with high cylinder pressures, such as turbos and compression ratios of over approx. 10.5-1, high octane fuel is need to control the maximum cylinder pressure that it can take be for lighting up on its own without and ignition source (spark plug.)
So where in I going with all of this? Octane additives can be thought of as candle wax added to slow the burn rate and raise the maximum cylinder pressure before it burns on it's own. Now you can see why in MOST engines you loose power as the don't need, or want octane higher then a true 87! Sorry to get carried away, but I love to hear myself talk!! Brian
So where in I going with all of this? Octane additives can be thought of as candle wax added to slow the burn rate and raise the maximum cylinder pressure before it burns on it's own. Now you can see why in MOST engines you loose power as the don't need, or want octane higher then a true 87! Sorry to get carried away, but I love to hear myself talk!! Brian
08-31-2012, 02:33 PM
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RE: MT70CC TWIN
agreed,, octane is a long chained alkyloid that slows or retards COMBUSTION and is supposed to help prevent detonation
+due to exactly what was mentioned,,i found out by being corrected a while back,,and from my broither who actually designs and operates hydrocracker units
+due to exactly what was mentioned,,i found out by being corrected a while back,,and from my broither who actually designs and operates hydrocracker units
09-01-2012, 04:40 PM
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RE: MT70CC TWIN
Well i have come to the conclusion that either the previous owner got a double whammy ,,because after starting this thing up ,,discovered the engine way out of balance with a bent crank or output shaft,,from what i was told the engine had never been in a plane,,and either it got damaged in shipping,or sold defective,,and i am a personal witness to this condition coming from mt,, the 57 i had was rediculously out of center ,,the box i recieved was in perfect condition,,and would have expected a big old gash or smash mark to justify that this occured when sent to me,,,Now my options would be to use the prototype case ,,which i dont trust,,or to see if valleyview has parts ,,i do not think i can scavenge parts from the proto case because i was told the crank is different.I also cannot say for sure even a real unbalanced engine would have popped the cylinder,,and could have added or hastened the failure but still believe crappy assembly and machine work was the main cause ,If I had have gotten screwed that badly ,,plane crazee,s complaints would have been considered rather mild in comparison to ,what i would have said...
09-01-2012, 05:49 PM
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RE: MT70CC TWIN
Amen! WE should all be ashamed just to save a buck or two. I have hear that if US citizens would pay just 1-2% more, the Chinese could not compete. I for one am sick of buying a product that used to last a lifetime and get handed down, now to last a yr or less just to buy a new one and "Throw-away" the old one. If the parts available at all, they cost more than the unit new. I am sure you all know about the brand name game they play......"Sorry no parts available, no sell anymore. Tractor supply had my exact compressor for sale (different color and name) bragging about it's great warranty. So I took the serial# and model # down .and called the warranty line. I never got thru to any human, but I was told by a strong Indian voice the the model was too new or obsolete, no warranty, no parts! Just like all those cheap dirt-bike, scooter, go carts ect., no parts, BUT, Honda OEM parts fit perfectly. The Chinese, like the Russians, have no problem copying and producing other peoples engineering. Soon China will have to normalize it's currency to the standards of all other nations and then, BOOM, GAME-OVER!
09-01-2012, 06:21 PM
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RE: MT70CC TWIN
i think this is how the dealers got screwed,, they would buy a pallet of engines,,then wind up dissasembling half of them,,for repairs, because they didnt get many spare parts to start off,and all their spare time is spent correcting defects,,,i read in f.g. forum and this was tommys post ,on how he was going to personally reject any defective parts assemble and test every engine before shipping and fully cooperate with and support his dealers,,and all this was said after several pleas to do just that ,,and this was before the 70 was even put on the market,,,as of this current date absolutely nothing has happened ,,even worse mr. shen has seemed to have dissapeared...and has made people associated with him ashamed to speak up...sad commentary here...
09-03-2012, 05:11 PM
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RE: MT70CC TWIN
Today i found time to tinker,, when i discovered the bent crank ,i had to decide whether i wanted to see if a crank was available,,what i decided to do was seperate the front and back case flanges on the prototype case ,,which leaked like a sieve and i had given up on,,coated all mating surfaces with rtv and let set ,,i also filled in this weird spot that tommy had filled with a silicone piece with jb weld and shaped to look like it was made into the engine,,,instead of using the studs and nuts tommy suggested,,i found socket head allen bolts and had to grind the heads to allow clearance against the cylinders,and found lock washers to fit,,i carefully assembled using used gaskets and sealer on the cylinders ,,made a reed block gasket and used blue locktite on all bolts ,,cleaned up the plugs installed and the same with the sensor for timing ,i found this setup nice and smooth and not draggy ,,so i mounted the thing and to my surprise ,it didnt run too bad considering i still need to final set the timing and and carb which may have stiff parts due to additive type fuel and sitting up,,i used my rcexl tach and saw 7.6 k this is with a vess 22a open exhaust setup,,i will be using a 23 to 24 prop once in satisfied ,,,,i think i know how the crank got bent ,,,this is my best guess ,,,the previous owner got so frustrated ,,he unbolted the junk from his test bench and threw it in the corner.......i bet if he reads this post hes grinning and saying thats exactly what happened...so far no case leaks runs reasonably good ,,, not draggy ,,compression seens reasonable ,, rings need to set,,,even the one plug i pulled had a nice tan look,,will be using safety wire over the plug caps ,,one popped off and the engine continued to run on one plug,,we all know what that would have done to my radio,in the air.maybe i will see if anyone else has a 70 they have given up on,,i dont know if my concience would allow me to fix then and sell on ebay ,,but they will be ok for personal use.
09-07-2012, 09:29 AM
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RE: MT70CC TWIN
Let me speak for myself here,,, im definitely not in love with mt engines,,,its more like regret ,,not with the engine,,but in how it never panned out as far as a company ,,,,but there may be a surprise on the horizon,,,we all know whan the engines are good thats just what they are,,,,,,,and when bad and no support and the manufacturer dosent listen to his dealers or customers,,we all are aware of that outcome....yes i could put my remaining mt products in the scrap pile ,,but i currently have 2 great running 70 s that suit my flying style and needs ,,and im going to keep em running ,,more will be revealed in regards to revival of this engine line,, from who assembles how they are assembled who sell s them and how the end user gets treated,,and a certain individual wont have anything to do with this as not to interfere with anything besides the actual design and nothing else. bottom line ,,ive given up one the guy who put them out but not the engined i own,,and as far as the enigines ,,,yes id like to see them introduced correctly and done right..otherwise when my junk gets crashed or worn out ,,that will be the end
09-07-2012, 09:55 AM
#1374
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RE: MT70CC TWIN
ORIGINAL: capitalB
There is a big difference between pre-ignition and detonation. Pre-ignition is just that...the spark plug fires way too soon after B.D.C, causing the rapidly expanding fuel charge to reach its maximum P.S.I. before the piston reaches T.D.C. Engine mechanical related detonation can be caused by many things, such as too much compression, port timing issues, hot spots in the cylinder and to much load (Bigger prop then it was rated to turn.) Now this is the part that I spent my 2-cts discussing. High octane does NOT mean more energy content, or power output. In fact in most of engines not designed for it (probably 95%.) I don't care if is 2 or 4 stoke, in a car, boat, motorcycle, big, small, Asian or American. I find it odd that people will spend up to 40 cents more for ''premium'' gas, when the car they are putting it in will have less power, and lower gas mileage. It's says Premium, so it MUST be better! Back in the early day of getting my degree, One of my profs. had a very interesting way of demonstrating this on a special engine that turned very slowly with a clear plexiglass cylinder. He would run the engine with the room lights on, so we could all HEAR the sound of detonation, then he turned off the lights and all of the questions that we had and did not at the time were answered instantly.You can win any discussion on premium fuel this way: Octane is the rating which the fuel will self ignite (think diesel) So engines with high cylinder pressures, such as turbos and compression ratios of over approx. 10.5-1, high octane fuel is need to control the maximum cylinder pressure that it can take be for lighting up on its own without and ignition source (spark plug.)
So where in I going with all of this? Octane additives can be thought of as candle wax added to slow the burn rate and raise the maximum cylinder pressure before it burns on it's own. Now you can see why in MOST engines you loose power as the don't need, or want octane higher then a true 87! Sorry to get carried away, but I love to hear myself talk!! Brian
There is a big difference between pre-ignition and detonation. Pre-ignition is just that...the spark plug fires way too soon after B.D.C, causing the rapidly expanding fuel charge to reach its maximum P.S.I. before the piston reaches T.D.C. Engine mechanical related detonation can be caused by many things, such as too much compression, port timing issues, hot spots in the cylinder and to much load (Bigger prop then it was rated to turn.) Now this is the part that I spent my 2-cts discussing. High octane does NOT mean more energy content, or power output. In fact in most of engines not designed for it (probably 95%.) I don't care if is 2 or 4 stoke, in a car, boat, motorcycle, big, small, Asian or American. I find it odd that people will spend up to 40 cents more for ''premium'' gas, when the car they are putting it in will have less power, and lower gas mileage. It's says Premium, so it MUST be better! Back in the early day of getting my degree, One of my profs. had a very interesting way of demonstrating this on a special engine that turned very slowly with a clear plexiglass cylinder. He would run the engine with the room lights on, so we could all HEAR the sound of detonation, then he turned off the lights and all of the questions that we had and did not at the time were answered instantly.You can win any discussion on premium fuel this way: Octane is the rating which the fuel will self ignite (think diesel) So engines with high cylinder pressures, such as turbos and compression ratios of over approx. 10.5-1, high octane fuel is need to control the maximum cylinder pressure that it can take be for lighting up on its own without and ignition source (spark plug.)
So where in I going with all of this? Octane additives can be thought of as candle wax added to slow the burn rate and raise the maximum cylinder pressure before it burns on it's own. Now you can see why in MOST engines you loose power as the don't need, or want octane higher then a true 87! Sorry to get carried away, but I love to hear myself talk!! Brian
+1
So many people think if they run 110 race gas that their engine will run better. i think all new car/truck engines have knock sensors to prevent this and some may retard timing some but the power difference is very little from 92-95 pump gas. I think all the car MFG's work for the oil companys lol because they say only run premium fuel. heck even lawn mowers and weed wackers with 7-1 computed ratios.
If you have low compression 11.5-1 or less and running high octane fuel you will lose power in the long run as carbon will build up faster in the exhuast ports or so i have read. In my quad i run 13-1 computed compression ratio. i run 92 pump gas. the piston is over 4" in Dia. since pistons of this cant burn the fuel in the chamber fast enough at high rpm I run three spark plugs per cylinder. i do this to burn all the fuel and reduce the negative torque... making more power. :-)
09-07-2012, 10:34 AM
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RE: MT70CC TWIN
I had to laugh at one review on the hk site ,,where this guy was so happy with how his new hobby king engine ran with 20 to 1 oil to fuel rtatio and using the best premium grade fuel ,,he claimed the high octane really made his engine run well...i can bet if he used the correct oil to correct fuel he may have,,,,,,,,passed out from the thrust ,if what he had impressed him.in the first place.