Wrist pin discoloration

How much is considered "acceptable"?

Obviously, if it's really blue, dabo dee dabo da, then you have issues

But, say this guy for instance...

Mild, I know. But it was only run for about 2 miles before I pulled the top end to inspect. I was surprised that there was discoloration that quick.

This is on a stock E50 crank with brass bushing, which is not sloppy, and whose oiling hole is still aligned.

Would you be more worried about the crank bushing, or just attribute this to a cheapo quality wrist pin?

Re: Wrist pin discoloration

tolerances might be wrong between the brass bushing and the new pin. hone it out with some sandpaper wrapped around a pencil in a drill until the pin moves freely. Chrome+heat=blue so if you've got friction, thats where the blue is coming from. cheap chrome does blue easier, but i think you've probably got friction somewhere you should try to get rid of.

Re: Wrist pin discoloration

On the engine this one came out of, the bushing falls out if you turn the engine sideways and tap on the con rod with a screwdriver.

The lubrication hole was lined up when the parts were installed, but probably a combination of not quite perfect fit, and high RPMs. Yuck...

<a href="http://s36.photobucket.com/albums/e20/novakarl/Pinto_old/?action=view&current=wristpin.jpg"; target="_blank"><img src="http://i36.photobucket.com/albums/e20/novakarl/Pinto_old/wristpin.jpg"; border="0" alt="Yuck"></a>

Re: Wrist pin discoloration

Your piston pin should pretty much float in both your piston and your con-rod. Not enough clearance to fall out but not too little to be hard to turn.

Too loose and you get piston rattle and could damage the skirt of the piston if there is excessive slop.

Too tight and you will get discoloration and binding, if that binding causes the brass bushing to rotate in the rod it's quickly downhill from there. The chance of the brass bushing rotating is less if the brass bushing is really pressed into the rod but can still happen. I had the oiling hold on my ZA motor rotate and the 80 metra piston pin did not last long, purple city.

Yours looks ok... granted it was only run for a very short period of time. It's interesting that there looks to be transfer of brass from the bushing on the edges. Could be the bushing is not perfectly smooth and the edges are dealing with a lot more pressure compared to the rest of the bushing. I would take some 320-600 grit sand paper and try to chamfer the edges of the bushing just a tiny amount. Run it for a but and inspect again.

Re: Wrist pin discoloration

i've had the same thing happen when i had to really ream on a pin to get it out, and jacked up the edges of the bushings.

Re: Wrist pin discoloration

Thanks for the great replies guys. I'll hit both the pin and the edges of the bushing with just a tiny bit of fine sanding action.

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