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Wed Apr 06, 2016 1:28 pm

What are the dimensions of a Wrist pin? More importantly, are they all the same or piston size dependent? Most important, where can I get just the pins for a set of 88mm's? I tried Aircooled.net and they couldn't help me ](*,) #-o :(

Wed Apr 06, 2016 1:53 pm

Brand of piston?

Wed Apr 06, 2016 1:56 pm

Not a clue... they are the same type of slip in base machine in top that Aircooled net recommends for their 1800cc build, but I have no idea what brand they are. They came gently loved in a box with a bunch of other stuff.

Wed Apr 06, 2016 9:37 pm

The rod bearings are 22mm so I'd take an educated guess at 22mm. Measure the distance between the wrist pin lock grooves for length.

Wed Apr 06, 2016 11:12 pm

CB sells aftermarket lightened gudgeon pins, I know they have them for 90.5s, so you could get those, and see how much shortening they would need to fit.

Thu Apr 07, 2016 8:12 pm

Found them, you are now my hero!

Thu Apr 07, 2016 8:53 pm

anyone make an oversized pin?
or has anyone ever bushed a piston?

I've got a set of notched mahles with a "loose" fitting pin. hate to trash them..

Thu Apr 07, 2016 9:24 pm

yes, yes.
It was more common in the past
I think you can get .001" oversize pin, probably, other sizes not sure.

vw tdi have bronze bushes in the pistons so it isn't necessarily an obsolete idea :wink:

Fri Apr 08, 2016 9:28 am

I've found that A&A wrist pin fit is way different than Mahle,consistently looser..the idea is to capture the pin in the piston so it floats in the rod,so I guess the question is how loose is your loose? I wonder if teflon buttons would be enough to secure the pin in the piston..

Fri Apr 08, 2016 4:54 pm

Hyper eutectic alloy pistons don't need to be so tight, as they expand less.

Fri Apr 08, 2016 4:56 pm

Piston pins are 22mm diameter. To find length, use a ruler or dial caliper.

Sorry I could not measure this for you, my psychic powers not strong today

Fri Apr 08, 2016 7:20 pm

no you do not capture the pin in the piston so it floats in the rod. it floats in both. yes you cant get over size pins.as for bushing the pistons....I dont see why not if done properly...... .I have +.001&=.002 pins, but there short nascar stuff ,and casidium coated,(only about 1.780" long and there expensive.) Im sure je, manley or somebody else has them much cheeper.THE CB PINS i GOT LAST TIME WERE ON THE SMALL SIDE... funny thing, the motor in my car needed small pins...but they were on the big side and kinda tight..it seems you never get what you need when you need them. and the aa pistons use a shorter pin than the oe&mahle. so...shorten the cb pins to fit and there lighter too!!! a snug pin in the piston will usualy be ok as the piston hole grows. but a tight pin isant ok. and the rod needs to be right not snug ir tight as it will expand the same as the pin does so clearance will remain about the same pin may grow a tenth or 2 more due to piston heat radiation.

Fri Apr 08, 2016 10:14 pm

The wrist pin does not floats in the piston ,that's why the rod is bushed.As the piston expands with heat the wrist pin actually gets tighter in the piston. A steel wrist pin oscillating in aluminum piston bore would tear up the piston in a few minutes.Thats basic engine 101...

Fri Apr 08, 2016 10:32 pm

No, whoever told you that was a dumbass, or, was messing with ya!

Were they into chevys? :lol:

Fri Apr 08, 2016 10:39 pm

Mark is absolutely correct, the pin floats in both the piston and the rod. :wink:

Fri Apr 08, 2016 11:50 pm

It's actually called a "full-floating" piston (gudgeon) pin. Check the inside surface of the pin clips, you'll see where the pin rubs from going side-to-side.

Sat Apr 09, 2016 7:50 am

You'd end up with a bucket full of aluminum,its why the rod is bushed...but hey,believe what you want,Im not gonna argue with ya..Ever assemble a mahle piston and pin to a rod? ever wonder why the pin is a tight slip fit? ever wonder why there is no annulars or holes on the piston bore to lube the pin? the pin is a slip fit to allow for piston expansion,but not for oscillation caused by converting linear to rotational movement.. that constant movement and load transfer to the rod from the piston is handled by the wrist pin and the bushed rod bore.The wrist pin to piston assembly is designed to be fixed..not during assembly or when cold,but when the engine is running and the piston is at operating temperature..this holds true for most every engine design out there,not just sport model lawm mower engines..

Sat Apr 09, 2016 12:49 pm

johnnypan wrote: You'd end up with a bucket full of aluminum,its why the rod is bushed...but hey,believe what you want,Im not gonna argue with ya..Ever assemble a mahle piston and pin to a rod? ever wonder why the pin is a tight slip fit? ever wonder why there is no annulars or holes on the piston bore to lube the pin? the pin is a slip fit to allow for piston expansion,but not for oscillation caused by converting linear to rotational movement.. that constant movement and load transfer to the rod from the piston is handled by the wrist pin and the bushed rod bore.The wrist pin to piston assembly is designed to be fixed..not during assembly or when cold,but when the engine is running and the piston is at operating temperature..this holds true for most every engine design out there,not just sport model lawm mower engines.. You really, REALLY should read a bit more about the subject before speculating about it.
And perhaps think a little about the millions of vehicles that run pressed in the rod wrist pins.
And maybe top it all off with what will happen to the wrist pin hole in the piston when it heats up.

Sat Apr 09, 2016 2:23 pm

possiably because a steel pin in a steel rod will eat up both.......just another exzample of internet experts at thier best.no thinking no exp.no reliable car. but there the ones we all need as they keep the new parts coming and into the swap meets on a regular basis after they trash them. Ive seen many full floating assys that were done the cheep way and no bush( most v8's & american engines do not have a bush as they are pressed in to the rod with a interfearance fit, some Ive seen upwards of .004"inter fearance. cheepasses just hone the rod till they have some clearance and they have a full floating pin. well it works. but it does eat at both rod&pin. Im sure modock has seen some pistons with bush in them.

Sat Apr 09, 2016 2:33 pm

Sure did, dealt with both piston bushings and steel on steel full floating this week. It can work, does work.
Great example of steel-on-steel would be stock VW rocker arms.
It DOES work, but there is much greater chance of galling if dirt gets in.
Same way with piston pins.

If Johnny keeps this up, can we vote to ex-communicate him for blasphemy?