Idea of flanged wrist pin bushing in piston

I have had a few pistons that got loose pins, and it was super annoying. Rattly and fucked but the piston size and shape was still fine. I’d like to have a way to fix these pistons. These aren’t 15k rippers, usually 9-10k rpm.

What if one were to bore the piston wrist pin holes to press in 2 flanged bronze bushings with the flange on the inside of the piston so it couldn’t come out? A small boring bar could cut a groove in the bushing to keep the pin in.

I find this idea kinda neat.. Piston would be slightly heavier but not too much as the bushing would be very smol. One could convert 10mm pin pistons to 12mm pin.

Re: Idea of flanged wrist pin bushing in piston

Like these.

I wonder how tight their nominal 10mm bushing would be compared to buying an 8mm or standard bushing and then reaming it perfect

https://www.mcmaster.com/flanged-bushings/ (edited)

Re: Idea of flanged wrist pin bushing in piston

I bet it could work. But bushings and reamers cost way too much for most people to want to try it instead of just buying a new piston.

I think it would be tricky to get the right expansion rates as well. With only 2 metals (pin and piston) they are engineered to be just right at op temp. 3 metals, might get loose faster if they fight each other while expanding and contracting. If the bushing was made out of the same alloy as the piston, that would be ideal.

Even with all things as perfect as possible, it would never last as long as the original. Try it. Just bang out the simplest, cheapest version and see if there is any merit in trying fancier stuff.

Oooh, I just thought about this, and I think you said you liked the thread about electroplating. Maybe you could tape off everything but the pin holes and plate on enough material to tighten up the pin? So sexy and sciency. Yeah do that one instead.

Re: Idea of flanged wrist pin bushing in piston

I’m more of a cutter smasher driller than a plater. Oh wait.

What if I brazed the wrist pin holes surface then reamed them back to correct size. Pretty sure the wrist pin area doesn’t get crazy hot, and all my bikes are water cooled so that could help

Re: Idea of flanged wrist pin bushing in piston

Overpriced Parts /

I never did understand why many moped/kit pistons have oiling holes on the piston to the wristpin, they’re not supposed to move Because once the very hard steel of the wrist pin starts moving freely in the piston it will wear away the soft aluminum,

Someone should try to make moped pistons and conrods like car pistons, the wristpins pressed on to the piston and the con rod should have cap, two piece bearings or bushings and bolts to take it apart,

But on the small end not the big end bearing, I mean all has to do is rock back-and-forth So it’s less then the 360° a car engine rod that has the caps and the bearings on the bottom big end of crankshaft,

That being said Maybe you could use high temperature bushing adhesive to help hold your worn piston to the wristpin.

I’ve found that a new wrist pin or one from a different kit sometimes fits a bit tighter on a worn piston than a old one and I have cut them down to fit then polished the end

I wonder if those or something like those McMaster Carr brass spacers could be used so a connecting rod doesn’t move back-and-forth Sideways to reduce Conrod/crank side play wear

Re: Idea of flanged wrist pin bushing in piston

This idea is stupid prove me wrong.

I do know that cutting the groove for the snap ring is really picky, gotta be just right or it pops out.

Re: Idea of flanged wrist pin bushing in piston

> Graham Motzing Wrote:

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

> I do know that cutting the groove for the snap ring is really picky,

> gotta be just right or it pops out.

Better a touch deep than not deep enough . ;)

Re: Idea of flanged wrist pin bushing in piston

Brandon Weiss (Detective brandon to you) /

> Overpriced Parts Wrote:

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

> I never did understand why many moped/kit pistons have oiling holes on the piston to the wristpin, they’re not supposed to move Because once the very hard steel of the wrist pin starts moving freely in the piston

it will wear away the soft aluminum

I've pondered the same thing

Re: Idea of flanged wrist pin bushing in piston

If your bushing was like a cap over the end of the pin then if the pin was cut short it would all hold together with the piston's original snap ring grooves.... Like u-joint bearings.

Pondering in public now ...

Would it be stupid to go from a bearing in the conrod to bearings at the piston?

Re: Idea of flanged wrist pin bushing in piston

> Thomas TPRF Wrote:

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

> Pondering in public now ...

>

> Would it be stupid to go from a bearing in the conrod to bearings at the

> piston?

The rod is much harder then the piston . Wear would be a huge concern .

Re: Idea of flanged wrist pin bushing in piston

classic carl jepsen /

> Papa _ Wrote:

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

> I bet it could work. But bushings and reamers cost way too much for most

> people to want to try it instead of just buying a new piston.

>

I got into wrenching on cars 40 years ago so I have ALOT of SAE tools. I was pissed when I had to buy Metric stuff to allow me to work on all the import stuff popping up in the 70s... I also got interested in British motorcycles (mainly Triumphs) and once I got heavily involved with those I found that I needed British Whitworth tools as well.. Then some jerk invented Torx and as soon as I got all of those they came out with inverted Torx & tamperproof torx, & WTF

Re: Idea of flanged wrist pin bushing in piston

One side would be sealed or stepped and use no snap ring because there’s no need. The other side would have a snap to keep it all together.

I’ll be trying this as I’m sure it would work.

I’ve had moby pistons where the pin is ungodly tight and there’s never been an issue. My goal will be to keep the bushing very very tight yet lubed in a reamed piston hole with the understanding that it will loosen up and can move once the piston heats up. Then try to get the pin very tight on the id too.

I just got a feeling it would be ok on a mid power build.

My moby conversion to a bushing in the small end was a huge success. Never had any issues.

But that’s not piston modding. We shall see!!!

Re: Idea of flanged wrist pin bushing in piston

Hell yeah.

Re: Idea of flanged wrist pin bushing in piston

not to be lazy but destructive, slightly knurl one end of the wrist pin, so the pin can pass small end crank can still slip thru piston wo damage then jamb that sucker in the rest of the way and it shouldn't move.

Re: Idea of flanged wrist pin bushing in piston

Ahaha, think in the right direction x) (edited)

Re: Idea of flanged wrist pin bushing in piston

or.... just flipp you piston over and whack the thinner material by the hole thus makink it slightly oblong.

or... drill and tap underneath if theres eanough meat and put a small set screw to lock the pin in...

Re: Idea of flanged wrist pin bushing in piston

> pat splat Wrote:

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

> or... drill and tap underneath if theres eanough meat and put a small

> set screw to lock the pin in...

If that every unscrewed itself I would cause havoc. A few vintage engines I've worked on had split small ends and pinch bolt arrangements, splits can split or bolt falls out wrecking bores, all of these were changed to carrillo patt rods. Soft gudgeon pins buttons were also used, made out of soft brass, I have heard of people making them out of teflon lately but I think that's mostly water cooled stuff so idk if it'll take the heat of air cooled (edited)

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