48cc/60cc crankshafts the same? (need replacement in Aust)

soup325

soup325

Member
My big end bearing has had enough (after 8 years and 350+ hours of riding).

I cant find any 48cc replacement crankshafts on the net + shipping to Australia.

Are the ones sold as 80cc crankshafts fit a 50cc?

Got the old grubee gt2b engine.
 
I remember a thread that was about changing crankshafts, it had pictures to compare the two. Since the cases are the same basic size and use the same bearings and seals if you find the same length connecting rod and stroke it should work.
 
Thanks, Greg.

I managed to find one that is labelled ZAE50 last night while (and a decent price). Most were a decent price apart from the shipping cost to Australia.

I was thinking of rebuilding the crankshaft, however, there were a few threads that noted the accuracy needed to be spot on when pressing it back together. Which I may not be able to achieve.
 
Some may say otherwise but the gt2b has been good for me, I have built or help friends with six and all are still running. I bought five at once in February 2011, my son in law has one that has had nothing done to it, it still has the cns2 carb and runs fine.
 

Took a short video of the play in the crank. note the play is not as much as the whole unit moves.

It that too much play or worth sticking it back in.
 
If you hold the crank still can you move it up and down? That's what will cause a failure not as much with side to side. If that's all it's got I would give it a try, at this point if you can't get parts to replace it I'd run it till it starts knocking or rattling/vibrating then maybe buy a complete kit and use this one for parts.
 
Thanks, Greg. I have ordered a new big end bearing and will change the bearing over. My good neighbor has a shop press that I can use. So it will be a good learning experience at the same time. It will be a challenge finding something that is 5.15mm in diameter (size of the locator holes) for alignment.
 
I've rebuilt exactly one crankshaft and it was a challenge.

DSCF0541.JPG


Good idea to measure the width across the 2 crankwheels before you start. You'll wanna end up in the same place.

Broaching can be a problem if you don't start the press right. The crankpin can damage the crankwheels on the way in if it's not straight when you start. I stacked some shims between the crankwheels to keep them parallel for a light but straight start with a hammer

Side clearance at the rod is .015 -.019 on this crank and I set that with hard stops on the press. Check your clearance with feeler gauges before you take it apart maybe?

DSCF0540.JPG



And then there's the final alignment. Hopefully the pressure's required are less on a smaller crank than what I had to use!

The crankwheels may not be parallel. Start there. A bench vise can squeeze them together and a wedge will separate.

The crank journals need to be checked in 4 places. In and out on both sides. Under .001" of runout is the norm.

I used a decidedly low tech method for that final alignment and I mean after all this precision work I wound up on the floor slamming the thing into a lead brick to get one wheel or the other to move!!

I hope that helps and I also hope I haven't scared you off the idea. It wasn't easy but I was damn proud of it when it was done. 4500 miles on it to date ...
 
Thanks for the tips. Certainly not a put off - if this fails - I'm going electric.

I suspect mine is in the ballpark of 6500 miles (Distance = time x ave speed) therefore - 10,500km = 350hrs engine running time / 30 - 35kph average speed)

I have a mate who will machine a 5.10mm-ish rods for the locator pins. New big end bearing and crank bearings hopefully arrive today.
 
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