NOR-CAL General Chat.

[mbonanni]

NOR-CAL General Chat.

Need advice guys

On Friday I was trying to diagnose a rough idle/miss I have on my 325i and swapped out a few injectors to no avail. Saturday, the next day, I do a compression test and come up with 90, 0, 95, 90, 90, 95. I was mainly testing for inconsistencies because my dad said his gauge reads low, but never guessed I would see a 0. Not having access to many other methods to test the cylinder I put stuff away for the day. Sunday suspecting my motor to be toast I got eager and started tearing into the motor to remove the head expecting cyl #2 to be toast. Well, second to last step before lifting off the head I start removing the fuel rail and when doing so injector #2 stayed in the intake, so my guess is it was never fully seated in the rail potentially messing up the compression test results for that cylinder. Not thinking much about it I continue with removing the head and everything looks fine. No bent valves, cylinder walls have cross hatchings, and head gasket looks fine.

So now do I throw the head back on with new gasket and bolts with the risk cylinder #2 and the others have damage. Or pull the motor and swap in a spare 2.7i I've got?

A couple shots of what Im working with

[McGyver]

...Well, second to last step before lifting off the head I start removing the fuel rail and when doing so injector #2 stayed in the intake, so my guess is it was never fully seated in the rail potentially messing up the compression test results for that cylinder...

I can't think of any reason why that would have any effect since it's not direct injection. The gas is sprayed into the manifold, then the intake valve lets the fuel/air into the engine. So having an injector stay behind doesn't indicate anything.

That being said, low (or zero) compression is because either
1) Your tool is broken or you have a bad seal
2) Combustion chamber breach (crack in block or head)
3) Valves not sealing

It would have been a good idea to do another compression test with good equipment. If you still had low compression, then do a leak down test and listen for where the air is escaping (intake, exhaust, cooling system, adjacent cylinder, etc). But it's too late for that now.

Your best bet would be to take the head to a shop to be decked and rebuilt, they can also inspect it to see if you have any cracks in the head. You might be able to get away with just using a new gasket, but the right thing to do would be to rebuild it so you aren't pulling the head again in another couple thousand miles.

[mbonanni]

NOR-CAL General Chat.

You're right, I was expecting there to be a bent or stuck valve in that location but everything seems fine. And true, I wish I had not jumped the gun and got better equipment to test it with, but it is what it is now. Regardless of that I have three head gaskets, a new set of head bolts as well as a rebuilt head just sitting so parts are not really my issue. I assume a crack in the block or head would lead to the oil and coolant mixing which I am getting none of so I ruled that out. I did have my dad helping/listening for leaks and said he did not hear any.

I feel like my best bet, because I've got time and spare parts, would be to put everything back together with a new gasket and bolts then run the series of tests to check the condition of the motor. Just would hate to do that and then find out the bottom end is toast and have to swap the motor. Buutt this thing has only 135k on it, so I have "hopes" of the motor being healthy.

[McGyver]

Yeah, that might be the best option. It just sucks to spend so much time putting it back together with no guarantee that it'll work. Good luck with it!

[mbonanni]

NOR-CAL General Chat.

I don't think I need to put it back together 100% before I run a compression test right? For the most part its just bolting the head down and slippin the timing belt back on. I don't need to bolt on the exhaust or airbox

[mbonanni]

NOR-CAL General Chat.

Took a second look at the head from a different angle and found this, bent exhaust valve on cyl #2



So Ill be throwing on the other good head I've got and then rebuilding this one on the side.

[McGyver]

Took a second look at the head from a different angle and found this, bent exhaust valve on cyl #2



So Ill be throwing on the other good head I've got and then rebuilding this one on the side.

Glad you found your problem! Sucks to have a bent valve, but at least you won't find out after reassembly!

I guess it's a bit of a haul for you, but Shaun at Star Machine in Emeryville is awesome if you want any head work done.

[mbonanni]

It does suck, but I'm just glad I found the issue. Could the valve/piston contact cause any issues with the bottom end, or mostly just results in bent valves?


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[McGyver]

Well I'm not an expert on that. I would assume that it should be fine since the top of the piston isn't deformed from a hard/repeated valve slap, but it would be better to ask someone who actually builds engines.

[BlackbirdM3]

It does suck, but I'm just glad I found the issue. Could the valve/piston contact cause any issues with the bottom end, or mostly just results in bent valves?


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First off, clean the top of the piston to see if there is any evidence of contact. Assuming there is, you could have an issue. If not, I'd have to guess you will be fine. The big question is, what caused the bent valve? You might check the valve springs and see if you have a broken one. Obviously, valves don't bend without a reason.

Will

[mbonanni]

There was definitely contact on the piston, tiny little knick on it, should not be an issue. I read people reusing bottom ends after break timing belts and pistons slapping the valves much worse. However, piston #1 seems a bit worn down not sure what this is from.

[2mAn]

That bottom end looks solid, I wouldnt worry. my

[mbonanni]

Well, I got the head back on and did a compression test and I am getting like 65psi across the board when doing a dry compression test with cold motor. I am waiting on an oil squirter I ordered to do a wet test, should be here today. However, my cam gear was kind of suspect, it had a notch where the pin holds it in place on the cam, so it allowed for the gear to rotate about a tooth and a half after putting in on. Is this normal? I was going to use the cam gear from the head i just removed, but the pin is on the cam side not the gear on that head...weird. I wish I could take pictures, but my buddy just broke my phone. Can the timing being a tooth or so off cause a drop in compression?

[McGyver]

Can the timing being a tooth or so off cause a drop in compression?

Well yeah. The camshaft controls the lift, duration, and timing of when the intake and exhaust valves open. The timing belt synchronizes the camshaft with the crankshaft. The crankshaft controls the stroke of the piston. IIRC, the camshaft gear has 36 teeth, so each tooth is worth 10-degrees. If you were off by 10-20 degrees your compression would be terrible because valves are opening early/late.

Bottom line, the camshaft gear should not have any play in it.

[mbonanni]

I am going to have to take some pictures of it for you guys, It seemed sketchy. Anyways while taking the intake manifold off, because I forgot to install the bitch tube /:, I noticed a wire to the oil pan was a little exposed and corroded. I cut back about two feet of the wire harness and it was still corroded. Because I was blowing a fuse and had a rough idle before I decided to pulled the harness and I will be wiring in a new plug and rewrapping it, so just more work. In the mean time I am going to deep clean the engine bay and figure out whatsup with this camshaft/gear.