Motors apart, help me do some preliminary diagnosis before the machine shop trip?

Hello GRM,
Long story short, I've got a blown up motor. I'm trying to get this rebuild done in less than 3 months, including back in the car and everything.

Background info: I have/had a ton of blow by, so much that oil was leaking out of the air cleaner like a faucet with low pressure. My Vacuum gauge test was inconclusive in my honest opinion. Luckily a few days later my compression tester came in and gave me a result. Cylinder two is dead with only 10PSI compared to one, three and four all having ~100PSI.

A couple weekends later and the motor was out, this weekend I'm tearing the thing down. I'm wondering whether or not there is anything I can do to help determine if there are bad rings or a burnt valve. If I don't have to do extra work I'd rather not but if its necessary and required I will. So far the only things on this motor that are still together are the valve train, bottom end and flywheel/clutch. Tomorrow I plan on finishing the tear down and if possible, drop the necessary parts off at the machine shop.

As always, Thanks in advance!

Head Gasket:

Head:

Bottom End Overview:

Cylinder 1 (i think):

Cylinder 2 (i think):

Cylinder 3 (i think):

Cylinder 4 (i think):

Head gasket and combustion chambers look questionable between #2 and #3. Looks like an oil burner.

What kind of ring ridge can you catch with your finger?

Can you still see the original crosshatch honing pattern?

Has the engine been overheated?

"If you can't afford to fix it - don't measure it."

Have you put gasoline in the head chamber's?

When gas leaks through it's a bad valve (or seat). If it stays that's a good sign the valves are sealing well.

To my knowledge it has only overheated twice for less than 45 seconds total. Both times the temperature spiked and returned to normal.

I'll try the gas thing tomorrow. That should be an easy test.

Ring ridge is to see if there is a lip at the top of the cylinder bore right? I'll check tomorrow as well.

Didn't check the cross hatch pattern.

So I lied, about to go to bed and I checked the cross hatch and ridge.

For the ridge I didn't feel an actual lip. Most I could say was a rough, almost sandpaper like texture at the top of the bore.

I saw no cross hatch whatsoever, it looked like a shiny glad finish to me. These pictures capture more detail than I saw with my naked eye.

.

Just guessing by the compression numbers....

At 100 PSI, could be weak or worn rings, but little hard to say, without know what normal numbers are for this particular engine. But I would assume a little more than 100 PSI would be normal.

At 10 PSI there is a small hole somewhere, leaking valve or a head gasket leak. Depending on the goal of the project, you could remove and inspect those 2 valves. Then either lap those or replace a bad valve and lap in a new one... Or since you have the entire engine out, do a total rebuild. If the cylinders are not very worn, might be able to hone and re-use the pistons with new rings. Or again depending on the desired end result, bore and use over bore pistons. A rebuild without a bore increase could be considered a repair, while boring and new pistons would be a true rebuild, making it like new.

It is possible the valve adjustment or valve lash was keeping the valve from fully closing, if it ran very long like that, that could damage the valve.

Compression test numbers should be similar for all the cylinders on the engine, if they are all a little low but similar, then the engine should still work OK, but it could be worn, if one is a lot lower, something is really wrong.

TED_fiestaHP wrote: Just guessing by the compression numbers.... At 100 PSI, could be weak or worn rings, but little hard to say, without know what normal numbers are for this particular engine. But I would assume a little more than 100 PSI would be normal. At 10 PSI there is a small hole somewhere, leaking valve or a head gasket leak. Depending on the goal of the project, you could remove and inspect those 2 valves. Then either lap those or replace a bad valve and lap in a new one... Or since you have the entire engine out, do a total rebuild. If the cylinders are not very worn, might be able to hone and re-use the pistons with new rings. Or again depending on the desired end result, bore and use over bore pistons. A rebuild without a bore increase could be considered a repair, while boring and new pistons would be a true rebuild, making it like new. It is possible the valve adjustment or valve lash was keeping the valve from fully closing, if it ran very long like that, that could damage the valve. Compression test numbers should be similar for all the cylinders on the engine, if they are all a little low but similar, then the engine should still work OK, but it could be worn, if one is a lot lower, something is really wrong.

I didn't do the test with the carb at WOT, after I made the video I realized that I should have done it at WOT. oops...

Could the small hole you mention be a bad ring? that was my guess.

I'm about to do the gasoline check on the head, it should tell me about the health of the valves/valve seats.

lol well 3 of the cylinders are 10X's the compression of the cylinder w/ no compression.

I provide you all with an answer. Or part of one... I'll share the gas head test results in a a moment or two

https://www.youtube.com/embed/0oZIGRnT50E

Looking at that head gasket, that's a "newer" style, iirc, so the motor had been apart at some point pretty recently (someone correct me if I'm wrong...). Or maybe it's a mfg I was never familiar with when I rebuilt motors as a kid...

To the mention of the issues between cylinders 2 and 3, the following: I don't know if the iron heads warp as much as aluminum is capable of, but be sure to have the machine shop check the head for straightness (they say decks don't really ever warp...), even if the valves check out.

I'd have thought as part of a head rebuild they'd have done that on mine.... But I had exhaust gas going through to the water jacket on the 320i - since it was several years between picking up the motor and head and firing it, I didn't have a lot of recourse.

Looks like a cheap re-ring, check the head for straight, and you're good! Good show!

A great experience, no doubt - is this your first motor??

First motor I'm taking lead on, so basically yea.

Do we all conclude that the rings were bad? Head gas thing didn't have dramatic results when I did the test.

I guess I'll take it down to the machine shop anyways and have them check. It's the only thing I didn't look at

OldGray320i wrote: Looking at that head gasket, that's a "newer" style, iirc, so the motor had been apart at some point pretty recently (someone correct me if I'm wrong...). Or maybe it's a mfg I was never familiar with when I rebuilt motors as a kid... To the mention of the issues between cylinders 2 and 3, the following: I don't know if the iron heads warp as much as aluminum is capable of, but be sure to have the machine shop check the head for straightness (they say decks don't really ever warp...), even if the valves check out. I'd have thought as part of a head rebuild they'd have done that on mine.... But I had exhaust gas going through to the water jacket on the 320i - since it was several years between picking up the motor and head and firing it, I didn't have a lot of recourse.

I'll have him check both, I don't know about it being apart or anything like that. I will say that the bottom end bearings all say GM on them.

Lapping the valves still might be a good idea and i think it'd be worth it for peace of mind. It's something you can definitely do yourself.

All you'd need is the plunger, the lapping compound, a valve spring compressor, and a bit of spare time. All in, you probably wouldn't even break $50 in tooling.

Interesting how 3 of them showed fairly good compression and 3 were equal.

 I would still look close at the head for the weak one, or maybe a head gasket leak.

Wonder why so many broken rings, worn piston ring grooves? Or maybe the bore is worn to large for the piston size. Something is off.

Measure the bore, before assuming you can just hone and reuse the pistons with new rings.

Hungary Bill wrote: Lapping the valves still might be a good idea and i think it'd be worth it for peace of mind. It's something you can definitely do yourself. All you'd need is the plunger, the lapping compound, a valve spring compressor, and a bit of spare time. All in, you probably wouldn't even break $50 in tooling.

I'm sure I could eBay.de the lapping compound and valve spring compressor no problem but as far as the plunger I'm lost. All I'm think of is toilets...

TED_fiestaHP wrote: Interesting how 3 of them showed fairly good compression and 3 were equal. I would still look close at the head for the weak one, or maybe a head gasket leak. Wonder why so many broken rings, worn piston ring grooves? Or maybe the bore is worn to large for the piston size. Something is off. Measure the bore, before assuming you can just hone and reuse the pistons with new rings.

I dropped it off at the machine shop today for a hone, straighten/flatten the block and head mating surfaces and measure the crank.

I was quoted 300€ for the whole thing. Seemed reasonable for the price so I said ok go ahead.

They seemed ok with helping me pick the correct size rings and bearings.

Just search valve lapping tool and you should be able to find it. Looks like a hardwood suction cup dart.

Here ya go: https://m.summitracing.com/parts/oes-25040

Awesome, i'll more than likely be doing that as well. If i dont do it and its an issue pulling the head off this thing is ridiculously easy. i freakin love it