New head gaskets, new timing belt; misfiring at idle

Hello everyone. 99 Subaru EJ25D DOHC.

The timing belt idler sprocket was smoked, and the timing belt was severely over it's service life. Ended up having 3 bent valves, and both sides were done at the head shop. Resurfaced heads, new gaskets, new timing belt.

Getting misfire codes on 1 and 3, shakes at idle, but smooths out when driving.
I did a compression test, and got well above spec on the right side (1/3), around 200-210.
When I did the left side, it was around 160, which is very normal.

I pulled the front apart and verified I got the timing belt on correctly, which it was. 

I don't understand how I got excessively high compression on 1/3, which is also registering idle misfires.
What should I be looking at to resolve this?

An advanced intake cam will result in higher compression.

I am not familiar with this engine and I don't know the exact specs for this engine, but intake valves, usually, close around 30°- 60° After Bottom Dead Center. That means that the intake valve is, still, open as the piston begins its compression stroke. Compression does not begin until the valve closes (30°-60° ABDC). If the the intake valve closes early, there is more air volume in the cylinder when the valve closes, and compression begins sooner. The result is, significantly, higher compression.

I appreciate the response, and the explanation.

I've checked the timing on the crank and cams several times at this point, even counted teeth on the belt.

I just checked valve clearance, and it's tight all around (both sides). I would have thought that would cause less compression though; if they are tight, they should open early and close late, yes?

Tolerance on the valves is +- 0.02mm. Only 1 valve was measured at -0.02, the rest are tighter than that.

Too tight is not right, adjust and re test.

I can only think of a few different causes for abnormally high compression. One would be advanced intake timing like Chad mentioned. Another would be excessive carbon buildup on the pistons. But it'd have to be a LOT of carbon.

The other is that the bank one cylinder head got too much milled off at the machine shop, reducing the volume of the combustion chamber and increasing compression. That'd account for the higher compression on one bank despite correct valve timing. It'd also be tough to prove without disassembly.

As you know, this engine uses bucket shims for valve lash adjustment. So, if most of the valves have insufficient lash, then you're going to end up disassembling most of the upper end to adjust them. Plus buying a shim set, if you don't already own one. At that point, I might consider installing a set of remanufactured or new heads instead.

Tyler wrote:

The other is that the bank one cylinder head got too much milled off at the machine shop, reducing the volume of the combustion chamber and increasing compression. That'd account for the higher compression on one bank despite correct valve timing. It'd also be tough to prove without disassembly.

 

With such a significant difference in compression, I'll bet a pulse sensor in the intake would see something.

Chad wrote:

With such a significant difference in compression, I'll bet a pulse sensor in the intake would see something.

Oh it would definitely see something, I agree. I'm just not sure it'd tell us anything we don't already know from the compression numbers. Might show a valve timing issue, if the intake cam on bank one is still advanced.

The only test I could think of that'd help would be in-cylinder on both banks. That'd allow a direct comparison of valve events.

Tyler wrote:

The only test I could think of that'd help would be in-cylinder on both banks. That'd allow a direct comparison of valve events.

 

There are other ways, you may want to read the attachment and the linked document which is too big to be attached.


drive.google.com/file/d/17YA39LvA5etWpJZ...ho/view?usp=drivesdk

Somehow I messed with the quote function and made Tyler write things he didn't.....

juergen.scholl wrote:

Somehow I messed with the quote function and made Tyler write things he didn't.....

No worries, I fixed it. The new quote system kinda sucks.

Tyler wrote:

I can only think of a few different causes for abnormally high compression. One would be advanced intake timing like Chad mentioned. Another would be excessive carbon buildup on the pistons. But it'd have to be a LOT of carbon.

The other is that the bank one cylinder head got too much milled off at the machine shop, reducing the volume of the combustion chamber and increasing compression. That'd account for the higher compression on one bank despite correct valve timing. It'd also be tough to prove without disassembly.

As you know, this engine uses bucket shims for valve lash adjustment. So, if most of the valves have insufficient lash, then you're going to end up disassembling most of the upper end to adjust them. Plus buying a shim set, if you don't already own one. At that point, I might consider installing a set of remanufactured or new heads instead.

 

I've been talking to the shop that did the heads, specifically about the valve lash. They offered to correct it, but they want me to take the heads off and bring them in. The person I was talking too didn't seem to understand quite how the shim over bucket works, as she mentioned taking the valves out to adjust them. But either way, they have offered to fix that. If I take them up on this, I suppose the head can then be inspected for being milled too much. They did offer to cover the head gaskets as well.

They sent a guy over to adjust the valve lash at my house. But when he got here, he looked at it and said he couldn't do it, because it was the shim over bucket style... Yeah, if it was the screw type, I would have just adjusted it. I pulled the engine and heads off, I think I'm capable of turning a screw with a feeler gauge. 

As for the carbon buildup: there was some, but it's wasn't excessive. I could clearly see the tops of the pistons and the indentations that the tops have.

Before I take the heads off, and to the shop that worked on them, someone on another forum requested a dry/wet compression test. So I thought I'd post that over here too.

Dry Wet
1 210 220
3 210 220
2 155 170
4 165 175

Well I may have found my problem. Took the engine out to take the heads off, and while loosening the cam sprocket bolts, the right intake was spinning without loosening when I was loosening it. Got it to break loose, and found this: 

Camshaft

Don't know if it was damaged before, or if I did this. But it seems that this could explain the higher than normal compression readings, with it being a few teeth off on cam timing as a result.

I didn't see the pic, but I'm glad you found the issue