Wrist Pin Failure - Why and Now What?

To try and make a long story short, at least 4 wrist pins and associated rod ends are galled (I only took one apart and the galling was severe in the rod end and the pin was also toast).

This is my old detuned race motor that was in my street/strip car. Has old Arias dome pistons that had the dome cut down - the pistons look fine. I had the motor rebuild (and detuned) and it does not have a lot of time on it since the rebuild. The motor has home ported 906 heads on it and 9:1 compression.

Took the motor apart because it had a very annoying noise in it that was driving me nuts and the converter went south so I decided to go back with the original 383.

Was getting ready to reassemble this motor (no plans for it other than a viable spare and was tripping over the parts) when I found the bad wrist pins.

The pins are floating. What would have caused it and now how do I fix it on the cheap?

Two things can lead to galling, lack of oil and lack of adequate clearance for the oil to go into the pistons, wrist pin bores and rod pin bores
Or maybe even bad oil
I would see about honing the pistons, rod pin ends and polishing the pins to see if they are savable I hope so
I like loose wrist pin to rod pin bushing clearances, .0010+ on .990 pins, more for bigger pins

I've seen pins that were bending gall like that.

If the pin and piston bore are not lubercated when installed galling can occur on initial fire up and can get worst after running time.They usually make a knocking sound as the bore galling creates loose wear.

Are they 1.094 or .990 od? Trend and others have oversized wrist pins available. IDK about 1.094 but I know they have them in .991 to .994. Also look and see if the pins have forced pin oilers. On a street car you need it for sure.

I always wondered if the pins were tight on the rod, wouldnt they still act like a pressed pin oem rod setup?

Floating pins have to float. If they seize up in the rod you can likely knock out one of the wrist pin locks - or both. Plus when you seize up a pin in the rod you cause all kinds of issues with skirt to bore - the rod has to float side to side on the crank journal - if it doesn't you can have bearing issues too.

Thanks for all the replies. Since those are stock rods they owe me nothing and they have not had an easy life.

For $400 I will put in a set of Scat rods that are bushed. I wonder if some of the issue was the fact that the rod was not bushed.

Will suck it up and re-balance the assembly.

When we used to run our stock rods like that (unbushed) years ago we would drill a 1/8 hole in the top of the rod and champher it to give the pin some oil. it helped some but not totally.

I know that some SBC and BBC came from the factory with floating pins and without bushings. 69 302 for example.
The drill the top and chamfer was a common mod for those too.

Mark

You have learned a valuable life lesson from this ,huh
Buynig or choosing cheap parts in a non stock Hi Po motor will buy you future problems, usually
Good luck from now on

These rods do have that mod.

You need to understand that when this motor was originally put together cheap aftermarket rods and cranks did not exist. It was a great motor. When we detuned it the crank went THUD when put on the ground so it got replaced. Other than that was a great motor for a very long time.

The replacement motor is a 2001 megablock with Eagle parts. The new build is a new "The Block" with all Molnar internals. This is just a low power spare motor now.

not enough clearance, my If it even matters at this point. Steel on steel is asking for trouble though.

Back in the 80's we all ran the stock rods, heavy TRW pistons and floated the rods the same way - steel on steel with the 1/8th inch oiling hole. just about every engine I ran like that eventually galled the pins at the rod - we just changed the pins honed the rod and kept going. Nothing wrong with that old set-up it just had its limitation back then.

Maybe the clearance changed as the pin got hotter and made it gall?

For some reason I don't remember the pins to be floating when the motor was originally built but I could be wrong on that. Perhaps they got converted at some point.

I do remember that very early on during a rebuild found several pins blued. The machine shop honed the pistons/rod (not sure which) replaced a couple pins and cleaned one or 2 up. Never had a repeat problem until now.

These rods have seen 6800 rpm far too often - it might be a good omen for them to fail like this just so that I replace them with a reasonable rod.

You said the torque converter went bad. How is your thrust bearing looking.
I have seen the wrist pins blue when the converter shoves the crank forward and rear face of the thrust gets it too of course.

Mark

Thrust bearing is not great and needs replacing. Not total toast but not good.