snapping cranks
05-29-2008, 04:13 PM
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snapping cranks
i broke 2 crankshafts on 2 diffrent hpi .25 engins in a week, i have been running the engines alittle rich but i do go WOT alot and do donuts in the dirt. i didn't think these engines would snap so easily, what am i doing so wrong? they where both broken in properly ( 2 gallons each ) and tuned very good
05-29-2008, 04:55 PM
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RE: snapping cranks
hahaha NEVER !
WOT isnt good for any engine of any type, but these r nitro, designed to rev there butts off, with super lightweight pistons and no rings, there made to rev, if a crank is snapping, l would put that down to over revs or poor design of the crank itself.
Never adjust ya servo so the throdle dont open righ up, ya loose half the fun of nitro remotes, unless ya kids drivin it, LOL !
These nitro engines will tune BETTER at WOT, so long as ya tunes not right out, they like high revs over low revs, they have didly squat torque in the bottom end, they need to rev there anus off to get there full potential.
Dont be scarred of WOT, it sounds like theres an issue with them cranks, l WOT ever nitro engine lve ever owned, thrown a few con-rods here n there, never snapped a crank but, oo, 20 odd years...
WOT isnt good for any engine of any type, but these r nitro, designed to rev there butts off, with super lightweight pistons and no rings, there made to rev, if a crank is snapping, l would put that down to over revs or poor design of the crank itself.
Never adjust ya servo so the throdle dont open righ up, ya loose half the fun of nitro remotes, unless ya kids drivin it, LOL !
These nitro engines will tune BETTER at WOT, so long as ya tunes not right out, they like high revs over low revs, they have didly squat torque in the bottom end, they need to rev there anus off to get there full potential.
Dont be scarred of WOT, it sounds like theres an issue with them cranks, l WOT ever nitro engine lve ever owned, thrown a few con-rods here n there, never snapped a crank but, oo, 20 odd years...
05-29-2008, 05:10 PM
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RE: snapping cranks
Crank pins supposedly break once the lower end con-rod bushing becomes worn, and a "hammering" effect occurs. I've only broken one crank, and it wasn't the bushing. The engine was a cheapie....Force 26.....I'd put it through hell and back over more than a two year stint. It was my test engine for all kinds of experiments and it took a lot of abuse. But the crank pin broke....cheap cast crank I think.
By the way, the piston/sleeve wern't worn, and neither were either of the con-rod bushings. Possibility the crank bearings were on there way out, but they seemed ok (If the crank can move up and down, it puts weird loading on the crank-pin). Again, I think it's jsut cheaply made cranks. A steel billet, or better yet, a forged crank, all make more sense than a cast one....in any engine.
Maybe you were going at WOT for too long. 100 yards at a time is enough. Then, a nice cooling idle..............
By the way, the piston/sleeve wern't worn, and neither were either of the con-rod bushings. Possibility the crank bearings were on there way out, but they seemed ok (If the crank can move up and down, it puts weird loading on the crank-pin). Again, I think it's jsut cheaply made cranks. A steel billet, or better yet, a forged crank, all make more sense than a cast one....in any engine.
Maybe you were going at WOT for too long. 100 yards at a time is enough. Then, a nice cooling idle..............
05-29-2008, 05:56 PM
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RE: snapping cranks
ORIGINAL: Argess
Maybe you were going at WOT for too long. 100 yards at a time is enough. Then, a nice cooling idle..............
Maybe you were going at WOT for too long. 100 yards at a time is enough. Then, a nice cooling idle..............
05-30-2008, 06:49 AM
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RE: snapping cranks
I've blown up two engines. The one I mentioned above, that took a lot of abuse over a 2 year period. Crank pin broke. The other was one where the throttle arm (barrel carb) was loose and the carb was actually wide open when I started it.....extreme revs with cold engine.....conrod broke before I could shut it off. In both cases, they made no sound when it went. Just sudden horrible silence......LOL. I just knew it was bad...............
Now...that look on my face?.....oh, I'll bet there was !!!!!!!!!!!!
Now...that look on my face?.....oh, I'll bet there was !!!!!!!!!!!!
05-30-2008, 07:37 AM
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RE: snapping cranks
My son started an 18 with the throttle wide open and the radio off. Instead of killing it or turning the servo back manually, he dropped it on the ground and ran off with his hands over his ears. It did not blow up, but it never had the same power after that. I am not sure what got damaged.... other than that, everything has held together so far. I am sure my STS is going to croak mid wheelie one of these days. Until then though, the party is on.
05-30-2008, 08:07 AM
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RE: snapping cranks
Yes...my turn too, no doubt. I run a lot on grass, and that puts extra load on the engine.....and I do the 100 yard runs too. With the type of driving I do, temp vs peak performance is always a compromise.
The engine that the throttle lever was loose was owned by a friend of my son.....a Nitro Evader. The ball diff had gone and some one at the hobby shop took it apart and gave him a list of parts to buy. I volunteered to put it back together. To this day I don't know if the hobby shop guy loosened the throttle lever to move the linkage, or it just loosened on its own. I started it in my basement to make sure everything was working OK. It was a mad scramble as the Evader tried to race to the end of my bench, but it really was only a few seconds before the con-rod let go.....seemed like a long time though. Then I had to explain to his parents..... In the end, I called Hobby Services, sent them the engine, and they sent me a brand new one. Good thing, as I was expecting to pay for that engine.
Sometimes when you try to help, things turn to...er....crap.
The engine that the throttle lever was loose was owned by a friend of my son.....a Nitro Evader. The ball diff had gone and some one at the hobby shop took it apart and gave him a list of parts to buy. I volunteered to put it back together. To this day I don't know if the hobby shop guy loosened the throttle lever to move the linkage, or it just loosened on its own. I started it in my basement to make sure everything was working OK. It was a mad scramble as the Evader tried to race to the end of my bench, but it really was only a few seconds before the con-rod let go.....seemed like a long time though. Then I had to explain to his parents..... In the end, I called Hobby Services, sent them the engine, and they sent me a brand new one. Good thing, as I was expecting to pay for that engine.
Sometimes when you try to help, things turn to...er....crap.
05-31-2008, 12:08 AM
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RE: snapping cranks
ive never really blown an engine, i did have an air filter fall off at the track and i drove about 15 mins before i noticed. after i shut the motor off, it would never start after that. lost all compression 
piston and sleeve were scratched up like hell. bought a new engine, went to the track again and air filter fell off again, this time i noticed immediately so i shut it off luckily saving this engine.
BTW i got a new air filter neck and havent had a problem since!
piston and sleeve were scratched up like hell. bought a new engine, went to the track again and air filter fell off again, this time i noticed immediately so i shut it off luckily saving this engine.BTW i got a new air filter neck and havent had a problem since!
