Broken crankshaft

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Bignscale

Bignscale

Active Member
Messages
37
Please have a look at the photo. This is a crankshaft for a 36cc motor, but the engine suddenly stopped while driving, and when I looked at it, I found that the side that fixes the flywheel had broken off at the base. Have you ever had something similar?
IMG_7512.jpeg
 
A little hard to tell from the picture but it almost looks like it might have been cracked before it decided let go. Doesn’t look like a clean break across the entire thing. Funny looking little pocket in the center as well.
Rather new to 1/5 scale but to answer the question I myself haven’t seen this.
 
I would bet that over 90 % of crankshafts used in model cars are made in the same factory, could be a casting flaw , never seen one fail like that , were the bearings free ? was it running , or were you trying to start it ?
Replacement is not expensive assuming the rest of the engine is ok.
 
Zenaoh cast parts are made in Japan, rovan is 100% Chinese. With out having the metal tested there's no way for definitive quality, however annicdotal evidence of the countless rovan engines I've messed with says they have sloppy tolerances, poor casting techniques and quality control issues.
That crank, was broken long before look at the dark spot on it. That indicates a flaw in the casting process/long term defect/crack. The shiny bits is all that was holding it together, just finally gave up the ghost. Grab another crank and move on. It's certainly not a normal failure, even for a rovan engine. They can be built to be good runners if taken apart and gone over.
 
Bignscale said:
Please have a look at the photo. This is a crankshaft for a 36cc motor, but the engine suddenly stopped while driving, and when I looked at it, I found that the side that fixes the flywheel had broken off at the base. Have you ever had something similar?
View attachment 92254
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thank you everyone. I didn't write down the cause when I posted this. While driving at high speed, the clutch suddenly broke and the engine locked up. Can this be considered as a cause?
This engine was ported and used at full power for several months.
 
Bignscale said:
thank you everyone. I didn't write down the cause when I posted this. While driving at high speed, the clutch suddenly broke and the engine locked up. Can this be considered as a cause?
This engine was ported and used at full power for several months.
Click to expand...

If it locked up and came to a sudden stop and the crankshaft most likely was partially fractured to begin with, I would guess that answer is " yes" since the flywheel tried to twist itself off when the rest of the engine stopped. Or should I say did twist itself off.
 
smokinwheel said:
If it locked up and came to a sudden stop and the crankshaft most likely was partially fractured to begin with, I would guess that answer is " yes" since the flywheel tried to twist itself off when the rest of the engine stopped. Or should I say did twist itself off.
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Luckily I was able to rebuild this engine, so I'll check the problem next time.
 
Seandonato73 said:
Everyone spits out a bad egg every now and then. I agree though, it nit a normal failure.
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Yeah, I'm sure Rovan isn't bad at all. I've been using it for two years and haven't had any major problems. This time I think the shaft snapped due to the clutch disengaging.
 
smokinwheel said:
Considering the crank is around $50 at two years = $25 a year.
Thats peanuts compared to the fun you had.
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You won the comments for the day IMO.

OG or Copy, for me it is all about the fun per $$. If you have the coin, spend it on the best thing you can afford. More $$ does not 100% of the time mean the Best Quality.

I had a King Motor 5B that i converted to 8S brushless. Liked it so much i turned into into a SC truck. Other than the terrible shocks it took a beating and as all 5B/T/SC do it raised it arms, sat on it's arse and begged for more.
 
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