Broke crankshaft in 80cc sd stinger motor..

Misfitchopper1990

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Jun 19, 2019
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Well I took the magneto cover off of the brand new engine... found that the magneto sheared off the threaded end of the crankshaft... fml🤦🏼‍♂️ On the upside I have a spare motor, would it be a good idea to tear em both down and replace the crank shaft with what I have, or order a new crankshaft?
 

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Greg58

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I would use the spare motor as it is and replace the crankshaft on this engine, there are several different piston/rod combinations, I know of two pistons with different pin heights. Take a lot of pictures and post here and someone will tell you what you have.
 

GreasyChris

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Your going to have to take the jugs off both engines to see if they have the same cranks. Some engines have a long rod high hole piston, some have a short rod low hole piston. Some cranks have 38mm stroke some have 40mm stroke. If they are cheap ebay kits they are most likely 38mm stroke short rod low hole pistons. If that's the case then ya you can swap them.
 

inspectorcritic

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Man that's gonna be tuff you need an air hammer I'd toss it or throw in the bone yard get another Motor for a hundred bucks
 

Misfitchopper1990

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Jun 19, 2019
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So I think I’m just gonna have to order a new crankshaft assembly, I took the jugs off of both motors and one crank arm is stamped ZAE50 and one with ZAE80. I can get a new long crank for under 24$ on a few different sites.
One of my clients is a engine tech and specializes in 2 stroke motors; he offered to help me with splitting the case and showing me how to properly rebuild it for no charge. So I think I got lucky here with this.

Im also contemplating throwing a 32 tooth rear sprocket on the bike too, found a gear ratio calculator on a post a while back and input the required info; it told me that I could potentially have a top speed of around 50 mph. So if it can do that I’m totally down with it.
 

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GreasyChris

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I really like that bike. Very very cool. Shame about what happened but im sure after your buddy shows you what to do it will be alot more responsive. I feel your pain I just had one of the circlips holding the wrist pin break on me and destroyed the jug and piston. Im up and running again tho. Once you figure these engines out they are pretty easy to work on.
 

GreasyChris

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Lol did I tell you how much I like that bike. I was thinking it needs a jackshaft and a suicide shifter. Using a jackshaft and a multi speed single gear hub you'd be able to get that bike flying with the right port work and carburation. And you get lots of low end torque with the gearing of the multi speed hub.
 

Misfitchopper1990

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Jun 19, 2019
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Lol did I tell you how much I like that bike. I was thinking it needs a jackshaft and a suicide shifter. Using a jackshaft and a multi speed single gear hub you'd be able to get that bike flying with the right port work and carburation. And you get lots of low end torque with the gearing of the multi speed hub.
I’ve thought about getting the Jackshafts kit, but I don’t own a welder currently so I just decided not to for now. Might change my mind later but idk haha. I’m gonna get a smaller sprocket for the rear wheel and that should help even out speed to acceleration ratio.

But here’s some better pics of the bike
 

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