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.

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

Paul Archibald /

Treats told me it doesn’t exist!

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

What doesn't exist? He had a 12mm pin rod pressed into his crank, so this is no longer a stock crank.If you have a 10mm pin this doesn't apply...get a 10mm pin Piston for your kit or buy a ready made kit...

Or imma dummy

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

Paul Archibald /

Treats told me just a few days ago that the bush to use a 10mm pin in a 12mm piston does not exist.

My question to Treats followed by their response.

Hi,

I have a 1986 Tomos A3 and a 50 cc Airsal kit for a Puch Maxi of a similar era (1980). I would like to fit the Puch kit to my Tomos can you please tell me what I will need apart from a 12mm internal diameter bearing for the wrist pin? I also have a 15mm Bing carburettor which came with the kit and would like to use this too if possible. Can you supply an inlet manifold which would be suitable for the Bing or perhaps a Dellorto sha15?

Thanks in advance for your help, any advice will be appreciated.

Regards,

Paul

Q

questions@treatland.tv

to me

4 DecDetails

Hi Paul, You would need to change the crankshaft, cut and reweld the pipe to a different angle, and perhaps make a custom intake for this to work, so it will for sure not be worth it. I would probably get https://www.treatland.tv/tomos-A3-airsal-kit-p/tomos-a3-airsal-kit-02210544.htm plus intake and dellorto SHA instead or find a good stock A3 replacement cylinder. We may have a used one around if you want us to look. Thank you!!! Treats

Hope this clears things up, their answer is to change the crankshaft or buy their 44mm Airsal kit with a 10mm pin. The answer re the Bing carburettor was what I suspected but I had thought they would suggest the bush if the roller bearing wasn’t available as a few people have mentioned it before. If it does exist can someone please give me the part number. (edited)

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

Paul Archibald /

Isn’t it amazing, seconds after I posted, I had a message from a UK supplier, YPVSpares, saying that he has the bush in stock!

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

> Paul Archibald Wrote:

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

> Isn’t it amazing, seconds after I posted, I had a message from a UK

> supplier, YPVSpares, saying that he has the bush in stock!

You ordered it , right ?

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

@paul Way to dig up an old thread.. a puch bushing fits in the a3 rod and will accept a 12 pin. There are no bushings to fit a 10 pin in a 12 pin piston. The bushing must be reamed for proper fit or you’re gonna have a bad time.

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

Not your setup, but:

I noticed the crank in my 1980 A3 has a small end conrod bushing, but a large end conrod needle bearing. The small end conrod bushing measures 14mm diameter, and there are 10x14 needle bearings that should work just fine in its place for a 10mm wrist pin (such as with the A3 airsal kit).

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

as others have said, there's a chainsaw bearing you can use from Stihl, or really any needle bearing you can find that's the right specs. That's the route I might go on mine if I hog out the cylinder some more. Otherwise puch rito con rod put in by a machine shop would be the way to go and open up opportunities.

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

Make your own damn bushings.

So easy.

Every hobbiest needs a little lathe for making shit. You can make whatever the fuck you want.

But you can use a drill and sandpaper only just as well and still make it work fine.

One goal I have is to fix piston wrist pin wear problems with a replacement pressed in bronze sleeve. Drill out the fucked holes and make some bitchin bushings and press them in. Only trick is the clip groove but it shouldn’t be too hard to cut in.

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