Piston pin galling in a drag race engine

[Belgian1979vette]

What's the verdict?

I still don't get why this engine has an aluminum pin. What is it, a drilled alu pin w/ coated chromemoly sleeve? with all the alu smeared over the coated sleeve it seems to me that the pin was flexing, seizing in the small end resulting in a failure. The pin is too weak.

The pin was made this way to reduce the weight with 60 gr. Go figure. That it's an inherently weaker design and thus flexing is obvious.

That was not the caused the engine failed. But plz wait untill the end of next week. Then I can elaborate on this.

 

[Belgian1979vette]

All right,

In the picture with the wrist pin, you can see that the center of the spot where the smalle end of the rod is, is not affected. Also the outer edges of where the small end is are not affected with aluminum.

In the center of the small end there is a hole, which serves to let oil in. Seen the fact that the center is almost not affected, this would mean there was a shortage of oil.
However, there was also a groove machined right under the hole on the inner diameter and the top halve of the small end.

However I also discovered that the piston pin was machined slightly larger. (+ 0.03 mm) which played a roll also. Still have to figure out what the normal size of the wrist pin hole in the piston is.

What I would like to know is if the wrist pin hole in the piston would enlarge or stay the same size when the piston expands ?

 

[Ozzy]

A hole will enlarge with an increase in heat.

A press fit wrist pin will have the small end of the rod heated so the pin will drop in. Freezing the pin will shrink it a bit also.

 

[Ralphy]

I would think a good look at the other wrist pins, rods and pistons that were not damaged may show indications.