Just a quick question about a needle bearing

Martin Fotak /

Hey guys need some help.

I was riding hard and snapped upper piston ring, destroyed cylinder and ruined piston on my Tomos A3 MS

Im wondering if i did damage to my crankshaft.

After inspecting the upper needle bearing which connects piston and crank there is no up/down play but the bearing has “letf/right” play as can be seen in picture. Im wondering if that is okay. It cant go much left or right but it moves.

If you want pictures of piston ring being welded inside of the piston just say ill upload hehe..

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Re: Just a quick question about a needle bearing

A little rod side play is fine , as it allows for 'centering' or proper alignment .

In/out play of very much , if any , will have you replacing/rebuilding the crankshaft .

Re: Just a quick question about a needle bearing

Martin Fotak /

Maybe ill just put bronze bushing just to be safe since im going to get a35 cylinder and piston which has 12mm connecting pin.

Doubt theres much difference in performance between the bronze bushing and needle bearing since theres not much rolling rotation on that point of the crank.

Re: Just a quick question about a needle bearing

I'd stick with a bearing .

Re: Just a quick question about a needle bearing

Martin Fotak /

If i manage to get bearing that can fit 12mm connecting pin and also not be too big for a hole where it sits ill do that

Thanks!

Re: Just a quick question about a needle bearing

> Martin Fotak Wrote:

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

> Maybe ill just put bronze bushing just to be safe since im going to get

> a35 cylinder and piston which has 12mm connecting pin.

>

> Doubt theres much difference in performance between the bronze bushing

> and needle bearing since theres not much rolling rotation on that point

> of the crank.

Needle bearings are superior, especially if you up the displacement and power.

Re: Just a quick question about a needle bearing

Overpriced Parts /

> live ɘvil Wrote:

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

> > Martin Fotak Wrote:

>

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

>

> > Maybe ill just put bronze bushing just to be safe since im going to

> get

>

> > a35 cylinder and piston which has 12mm connecting pin.

>

> >

>

> > Doubt theres much difference in performance between the bronze bushing

>

> > and needle bearing since theres not much rolling rotation on that

> point

>

> > of the crank.

>

> Needle bearings are superior, especially if you up the displacement and

> power.

Yeah but some bikes, some engines that have a bushing on the small end of the conrod have bushings on the large end of rod also

Re: Just a quick question about a needle bearing

> Martin Fotak Wrote:

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

> If i manage to get bearing that can fit 12mm connecting pin and also not

> be too big for a hole where it sits ill do that

>

> Thanks!

You're likely gonna be pushing it to it's limit .

I doubt you'll find a bearing for that conversion , so just do the bushing and wait for things to seize . ;)

If you weren't prone to pushing , I'd think about honing the small rod end to fit the less than 2mm bigger bearing , but ...

Re: Just a quick question about a needle bearing

Martin Fotak /

Id rather risk with bushing that most likely wont seize, than risk with making small end hole lager and also prone to breaking due to forces of pulling and pushing of the piston that is fighting the compression.

Am i right or am i missing something???

Re: Just a quick question about a needle bearing

If you think about it , most of the force involved is almost all straight through the rod into the crank . Compression is upward against mounting pressure and then the big boom driving things back down . All that action is , for the most part , exerting pressures right though the rod into the crank . A downward pressure . So , 'other' pressures are much less . The rod ends are round to basically keep the pins and rod in alignment and as a byproduct keeps things together .

Anyway , like I said , you'll be pushing , so go with the bushing .

I'd make sure that that bushing gets enough lube while it's doing it's job .

Re: Just a quick question about a needle bearing

well two things.

post a pictures of your cylinder damage to figure out why it was damaged.

was it excessive heat or did it snag or did a...

post a picture of your wrist pin, is it worn? did it get hot?

if u identify the problem, then u can focus on the solution.

Re: Just a quick question about a needle bearing

Martin Fotak /

> pat splat Wrote:

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

> well two things.

>

> post a pictures of your cylinder damage to figure out why it was

> damaged.

>

> was it excessive heat or did it snag or did a...

>

> post a picture of your wrist pin, is it worn? did it get hot?

>

> if u identify the problem, then u can focus on the solution.

I guess the ring snapped because i accidentally sprayed water with pressure washer on left side of the hot cylinder, and after that full throttle to where ever i was riding.

This is not stock tomos just to be clear.

This is modded a3 cylinder (not the bigger a35 cyl) that was pushing 64 kph messured with gps

Which was running extremely hot.

As the water cooled metal on the left side of the cylinder, the top of the piston was hitting the cyl wall and compressed piston ring which made it snap.

Wrist pin is in a perfect condition both from inside and outside. As i said im wondering if play I described in previous posts is okay or not, because im used to having fixed bushing that doesnt move inside of the small end of the rod

Thanks!

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