# Loose Wrist Pin In Rod



## 69-er (Feb 8, 2011)

What would cause a wrist pin to come loose in the rod? The engine developed a knock and upon tear down I found that the wrist pin had moved back against the cylinder wall and gouged two grooves in it. It's a factory 68 400 with the exception of 9.5 pistons and a mild cam. The engine has 1,000 miles on it since a complete rebuild.

A little background:

There have been two sets of pistons installed recently. The first set was during the first rebuild, 7,000 miles ago. The second set was after the engine overheated and the engine rebuilt again. The overheating caused piston and cylinder scuffing on two cylinders. The majority of the damage was with the same cylinder as the loose pin. The adjacent cylinder also had a little bit less scuffing.

I'm thinking the overheating had something to do with it. I'm wondering if the machine shop should have detected a little bit less force required to remove the damaged piston. I'm sure if the overheating did in fact cause the loose pin, it should have been noticed then.

At this time, the pin is loose enough to be pushed out with light tapping.

Any ideas? Thanks!


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## geeteeohguy (Feb 2, 2008)

Press fit pins are a hard interference press fit, as you know. The pin needs to be checked, as does the piston and the con rod. Something was too loose. This is not a very common problem, in my experience.


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## 646904GTO (Feb 10, 2008)

Be smart, replace that rod and the sister on that journal along with the pin and the piston. Don't assume or guess, just do it.


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## Rukee (Feb 8, 2007)

I'd throw a whole set of rods at it, if one is that worn out, the others have seen just as much use.


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## 69-er (Feb 8, 2011)

646904GTO said:


> Be smart, replace that rod and the sister on that journal along with the pin and the piston. Don't assume or guess, just do it.


Absolutely, that rod is no bueno. I'm thinking more in line with Rukee, get another set.

Here are some pics...


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## gjones (Oct 8, 2012)

Yikes!  69-r, did you have to sleeve that cylinder, or is it a basket case?


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## 69-er (Feb 8, 2011)

gjones said:


> Yikes!  69-r, did you have to sleeve that cylinder, or is it a basket case?


Yeah, sleeving will be our first choice as it's .060" over already. It's a numbers matching motor. Would hate to trash it.


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## BearGFR (Aug 25, 2008)

69-er said:


> Absolutely, that rod is no bueno. I'm thinking more in line with Rukee, get another set.


And if you're going to do that, please do get a good set of aftermarket forged rods. You can get a set of Eagle H-beams for not much more than it would cost to have a stock set of factory rods cleaned up and reconditioned. Considering that the rods have always been 'the weakest link' in these engines it's a no-brainer, especially if you want that numbers-matching block to live forever.

Bear


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## 646904GTO (Feb 10, 2008)

I would be looking at total timing also. That piston should not have scuff marks on the skirt. That could have contributed to the pin movement.


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## 69-er (Feb 8, 2011)

Too late to check that now but that's a good idea. However, I figured since the piston was only being secured at one end of the pin, that caused the piston to rock excessively which caused binding, therefore extra friction and heat on the skirts.


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