Wrist Pin Bearing
 

Hi guys,
Need answers quick. I'm rebuilding the top end in my bike after it siezed last weekend (ring pin failed, ring rotated and then got caught in the exhaust port....ouch). I forgot to order a new wrist pin bearing to install, so I need to know (1) how much play is acceptable in this bearing and (2) will a Honda CR250 wrist pin bearing fit (which year?)? Let me know ASAP.

Thanks,

Steve

Reuse the bearing.
They really don't wear out.

Seriously? It feels really sloppy in the little end of the rod.

It will if the wrist pin is not inserted as well, as the needles move in the cage slightly.

Figured that out. Once I put the wrist pin in, everything was nice and smooth.

haha. dad tried to tell me that my new wrist pin bearing was worn out as it had movement when it wasnt running on anything... doh, it needs to be between the pin and the rod to measure the play. the one i replaced looked brand new if not a bit blackened. no play at all

When you think about it, whats the point of replacing the bearing if your not going to do the rod kit as well?

The wrist pin bearing hardly sees any action.
In comparison, the crank rod bearing is always spinning, while the wrist pin is rocking back and forth.
In some automotive applications the wrist pin is fixed, with the pin floating in the piston with no bearing.

Consider that the primary load on the bearings is due to the compression and combustion. The bearings are loaded the same when the engine fires. The rod bearing has much more surface area to distribute the load. The wrist pin bearing is proportionally higher stressed with the same load.

4 strokes dont have wrist pin bearings....

I concur.Extensive testing by Husky ,re; oil ratios, revealed that the most severly effected component by using lean oil/fuel ratios was the top end bearing. Since I only run @100-1. I replace the $12.00 bearing every top end service. I realize that this topic is'nt about oil ratios but as Eric pointed out that little bearing does take alot more abuse than people might at first think.

Replacing wrist pin bearing
 

I have been riding for 40 years, replacing the wrist pin bearing, along with the wrist pin, clips, rings and gaskets was always done when the top end was serviced. The possible damage from not doing so is not worth risking the small savings. Racing highly strung 100cc aircooled MX bikes in the early 70's
probably had something to do with it.
Trailrider

The pin is replaced because it comes with the piston. Sometimes I'll replace the bearing, sometimes not. Yes, its cheap, but depends on if I have one or can get one when I want it. I never seem to notice any wear, but I run 36:1. The point is the rod is just as prone to wear as the bearing and pin, and you don't replace that until a total lower end rebuild. If the pin and top end bearing are obviously worn for whatever reason, it seems like you would be kidding yourself to ignore the rod.

Do you replace a hooked countershaft sprocket and keep the trashed chain?

What bike do you have? That's even leaner than I run my trials bike.

i think you mean that 100:1 is richer. rich and lean is refering to the volume of fuel not oil. so 32:1 or 40:1 i leaner than 100:1

at least i think thats what its refering too...:confused:


i get what GMP is trying to say, in that why replace the wrist pin bearing if you dont do the rest of the bearings, in the same way that you dont replace one wheel bearing if its worn out.

but i also get the hassle that you have to go to in order to get to the bottom end bearings.
i think most people just see that its there and its easy to change so they just do. i did

What I'm saying is the wrist pin, bearing, and rod surfaces should all wear together. Its not a big deal either way. Who has had a failure? No one I know, and its cheap even if it makes no difference.

:p 97,99.01 kx 250's and all four of my gasgas two strokes 01x2, 02 200, 03 mc 250. No problems ever and they are all jetted very, very krisp!