Things were just a little too cozy...

[JeepSJ]

Pulled the heads from my old engine this weekend and found a disturbing sight -



This was a low-miles stock engine when I purchased it. I pulled the heads at that time to inspect the cylinders and all looked good. I reinstalled heads with FelPro gaskets and ARP studs. The only other modification to the engine was a DSG gear drive.

This wasn't the only cylinder. Several others showed imprints of the intake valve in the carbon on top of this piston. This one is the worst though as there is an actual indentation in the top of the piston from the exhaust valve.

I think I found the reason this engine always sounded mechanically noisy.

[JeepSJ]

The more I look at things, the more I come to the conclusion that there must be a problem with the cam timing from the gear drive. Has anyone taken the time to degree a cam after installing a gear drive to verify that these things are accurate?

[Robyn]

How far out of the cylinder is the piston protruding ???

You bought this engine used ??

Was it a rebuild ???

If so, by who, and were the decks cut ???

Almost looks like that piston is above the deck some ???

When you had the heads off did you use a standard head gasket ???

Specs say the piston should be even with the deck to NO more than .005 above the deck at TDC
The decks can be machined .010" butttttttttttttt I have taken them to .015" in a pinch to get a good clean surface.
The thicker (.010") gasket must be used when the decks have been cut.

These engines are really really tight inside even from the factory.
I am thinking that the gear drive would need to be waaaaaaaaaaaaaaaaaaaaaay off to cause this type of issue.

The stock timing chains can and do get pretty loose over time (Causing some valve timing changes) and there are no issues with valves smacking the pistons.

The cam profile on these engines is pretty mundane and should not even be an issue.

How many pistons show valve contact??



More info please

[JeepSJ]

How far out of the cylinder is the piston protruding ???

Haven't measured yet but they appear flush. This was just a rough check using a straightedge across the deck.

You bought this engine used ??

Yes

Was it a rebuild ???

No, it was supposed to be a low mileage used engine. When I pulled the heads and main caps the lack of wear supported this assumption.

If so, by who, and were the decks cut ???

N/A

Almost looks like that piston is above the deck some ???

Actually that picture the piston is down in the hole.

When you had the heads off did you use a standard head gasket ???

Yes, Felpro standard thickness.

Specs say the piston should be even with the deck to NO more than .005 above the deck at TDC
The decks can be machined .010" butttttttttttttt I have taken them to .015" in a pinch to get a good clean surface.
The thicker (.010") gasket must be used when the decks have been cut.

These engines are really really tight inside even from the factory.
I am thinking that the gear drive would need to be waaaaaaaaaaaaaaaaaaaaaay off to cause this type of issue.

I'm going to do some measuring before I take it the rest of the way apart. I know what the factory lobe center should be with a stock chain so I can compare to that.

The stock timing chains can and do get pretty loose over time (Causing some valve timing changes) and there are no issues with valves smacking the pistons.

Yes, but that retards the cam. There may be an issue with advanced cam timing.

The cam profile on these engines is pretty mundane and should not even be an issue.

It is mundane but these are an interference engine. There isn't enough room for the valve to be all the way open and the piston to be at the top of the stroke.

How many pistons show valve contact??

I only have the passenger head off so far and it only looks like 1 exhaust had firm contact hard enough to cause an indentation in the piston. 3 of the intakes have left impressions in the carbon but don't look like they actually made metal to metal contact.

More info please

I will share more as I continue to investigate. I wish I could find the notes I made about what holes I pulled the bent pushrods out of when I took the top end apart a couple years ago.

[arveetek]

I wish I could find the notes I made about what holes I pulled the bent pushrods out of when I took the top end apart a couple years ago.

Sounds like this engine has had this problem for a while then. Valves hitting a piston will definitely cause bent pushrods.

Casey

[JeepSJ]

Got the engine pulled and got the other head off. Amazingly none of those pistons showed any signs of valve contact. Next need to finish disassembly so I can send the rods over to the machine shop for resize and the crank so everything can get balanced. While it is apart I'm going to match-port the intake and exhaust. I'm putting in a new set of valves and I'll have the machine shop cut the minimum go get the heads flat.

But before I pull it apart, I'm going to do some measuring to see if I can find that side had the issue.

[JeepSJ]

Sounds like this engine has had this problem for a while then. Valves hitting a piston will definitely cause bent pushrods.

Casey

Yeah, it was noisy when I first installed it. I pulled it apart about 5 years ago to have the injection pump rebuilt and was going to swap out the lifters because I thought I had a bad lifter. It has been sitting ever since.