Replace con rod bearing?

A hypothetical question! Is it possible or even worthwhile for the average person to disassemble a moped crankshaft and replace the connecting rod and or bearing? And If it is possible, how would you do it? I have several worn cranks in my parts pile that I would like to experiment with. Any suggestions would be appreciated. Thanks. Jack

Re: Replace con rod bearing?

I just did it last year.

if you dont have a hydraulic press, you’ll need one.

I used the new conrod pin to push the old pin half out, placed new conrod on the new pin, used a couple deep sockets to line both cheeks up through the holes (and eye balled it) then pressed the pin all the way in.

Use feeler guages/ caliper before disassembly and write down all the dimensions. how far the cheeks are apart, conrod clearance, stuff like that. Then, try to get as close to that as possible.

You have to true it afterwards. If you did your best at getting it close, that wont be a huge job.

* Disclaimer *

I did replace my conrod, I have not run it yet. Soooo... That’s how a person can do it. Don’t know if it is the best way.

Re: Replace con rod bearing?

Jack Nielsen /


Thanks for the response. Yes I have a press and all type of precision measuring equipment. i do not understand all the details you were discussing but I will figure it out. My first attempt will be to get it apart and see if Treats has replacement parts.


Re: Replace con rod bearing?

♣Slew Foot♣ /

Been there get a farm guy with the jig for a cadet tractor or chainsaw. It will properly space the lobes. I had a machinist friend help me out even then the inner journal was rubbing and tempered the journal and lobes showing extreme friction.

A new race crank is cheaper than fixing an oem. Imo

Re: Replace con rod bearing?

Keep us posted, i wanna learn too. Nothing in mopeds is really worth a snot, Popping in your own crank arm is priceless. I'm thinking the worst is trueing the crank down to that .00000 runout.

Re: Replace con rod bearing?

Yes truing is a tedious thing.

Two Stroke Stuffing has a simple, home mechanic, explaination.

I did my crank for a stock-ish engine going into a bike for my 7 year old daughter.

I trust my work for that.

If you are trying to make a race engine, I agree with just buying a built crank.

I forgot to mention, after I measured the space between the lobes, I found a wrench handle that was a press-fit. It kept the gap perfect. I think there was some beginner luck involved for me.

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