Tomos A3 wrist pin bushing, 50cc kitted engine

Aled Williams /

I fitted an Airsal 50cc cylinder to my A3 Tomos, along with a SHA15.15 and an Estoril pipe - the performance is a huge improvement. Unfortunately, the phosphor-bronze wrist pin bushing lasted 50 miles of use, see before/after pic. Is changing to an A35 conrod the only real answer, or are there harder bushings available?

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Re: Tomos A3 wrist pin bushing, 50cc kitted engine

Brad William /

Interested here too.

Did you ream the bushing after installation for good fit on the new wrist pin? Check the alignment of the installed piston skirts against the deck of the motor (just to eliminate gross error or bent con rod)?

I'm not a very experience engine builder by most standards here, but I've always been astonished at how well these little bronze bushings have held up, with almost no wear over manyK in the puchs I've owned.(edited)

Re: Tomos A3 wrist pin bushing, 50cc kitted engine

They can last a long time but the fitment/clearance had to be perfect. If you read the puch manual it gives specs for the clearance.. of course that is 12mm, are you running a piston with a 10 pin or did you ream it out? I'm not sure if you can even do that. Yeah pressing in a new rod is probably the best.

Re: Tomos A3 wrist pin bushing, 50cc kitted engine

spencerrrrr r /

I sent my crankshaft to Mr. Crankshaft and had a 12mm Rito Conrod pressed in, they balanced and cleaned up the crank as well. I think with the rod and shipping it was ~$150.

Re: Tomos A3 wrist pin bushing, 50cc kitted engine

theres a chainsaw needle bearing 10x13

Re: Tomos A3 wrist pin bushing, 50cc kitted engine

^ I've done it, works great. Treats sells that bearing too.

Re: Tomos A3 wrist pin bushing, 50cc kitted engine

Get out....did not know that one. Good to know. I recommend getting a new rod pressed in but there is always someone who does not want to do it. Dude in our club pressed in another bushing in a e50 crank and it has been working surprising well. I told home it would not last....but somehow it has. I just always recommend fixing it correctly while it is apart.

Re: Tomos A3 wrist pin bushing, 50cc kitted engine

Brad William /

**(edited)

Re: Tomos A3 wrist pin bushing, 50cc kitted engine

Aled Williams /

The bushing that failed didn't require reaming, it pushed into the con rod by hand, and the wrist pin also went on by hand - the outside diameter was 13.95mm, and the wrist pin is 11.95mm diameter. I'll probably de-kit this engine and put the 10mm pin/piston back in and have it as a spare engine - I've gone and bought a Tomos MC50 which has a low miles A35 engine, I'll kit and fit this engine to my A3K.

Re: Tomos A3 wrist pin bushing, 50cc kitted engine

> Aled Williams Wrote:

> -------------------------------------------------------

> The bushing that failed didn't require reaming,

yep thats yer problem. the bushing needs to be press fit into the rod and it has to be reamed, because the pressing operation actually shrinks it.

if the bushing spins in the rod it will be junk.

the pin is chromed and ground so it forms a bearing with the bushing, if the bushing spins in the crank it is spinning against a rough steel surface and wont last long at all.

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