2.8L M20 build - Now with 2.7L!

[LJ851]

spray brake cleaner or similar into the intake and exhaust ports onto the back side of the valve. If the valve is sealing none will leak out into the chamber area.

As far as the cylinder goes, you really need to pressurize it to test unless there is visible damage like broken rings or scored bores.

[acolella76]

Leak down test?

Kinda hard to do with the head off :p

Your options are limited

1) intake valve not sealing.
2) exhaust valve not sealing.
3) piston/cylinder damage (this includes rings)
4) head gasket (this includes deck/head damage)

Yeah :( It definitely looks like the valves are sealing pretty well. Any way to check the rings with the head off? Or I guess I could just pull the piston out and replace those rings.

[LJ851]

The bad news is that since the valves are not bent I now have NO idea what is causing the seriously low compression in cylinder 2.

Your options are limited

1) intake valve not sealing.
2) exhaust valve not sealing.
3) piston/cylinder damage (this includes rings)
4) head gasket (this includes deck/head damage)

[Cronopoulos]

I come bearing good news and bad news! Good news is no valves are bent and the head is still perfectly fine. The bad news is that since the valves are not bent I now have NO idea what is causing the seriously low compression in cylinder 2.

Leak down test?

[acolella76]

I come bearing good news and bad news! Good news is no valves are bent and the head is still perfectly fine. The bad news is that since the valves are not bent I now have NO idea what is causing the seriously low compression in cylinder 2.

[Cinnabar325is]

Remove the oil galley plugs on either end of the block and use a rifle cleaning kit.

I did this after I got my block back from the shop and it was amazing what came out after it was "already clean".

[acolella76]

Got a known working oil pump. Going to go over everything today and make sure the intermediate shaft is spinning, etc. How would you guys go about cleaning the oil journals and passages

[Cronopoulos]

Rebuild it and get it going again!

[TurboJake]

I'm going to second oil starvation.

The bearing you show in the second picture was looks like it was much warmer than the others, indicating friction. Symptomatic of oil starvation. When they wore down enough for the rod to start banging around, they got mushroomed out from that.

I'd start at passages, journals, and pump bud. Looks closely at that crank to make sure it didn't wear it down or damage it. Chances are it will be fine, BMW cranks are tough things.

As for using a caliper and not plastiguaging, I know TONS of people that do it that way, and have never had a problem. So I won't say that it is bad that you did it that way. I always plastigauge. It's quick, easy, and pretty difinitive.

[acolella76]

Haha yes I remembered to install that.

[Myster-E]

Seems like oil starvation to me. Did you make sure to put it the oil pump drive shaft piece that turns the pump?

[acolella76]

Alex, was the oil pump drive in place? Oil relief valve? What did you lube the rod bearings with on assembly? Did you clean all the oil passageways in the crank and block well after the machining?

Yes, yes, Lucas Oil assembly lube, and I thought I cleaned them pretty well however I can go check again

[LJ851]

not that it adds anything to the diagnosis but strictly speaking cam timing can affect cylinder pressures and hence can cause knock etc.

Yes, i was being very general on purpose. Not nearly as much pressure change on a single cam engine compared to a twin cam where overlap can be altered, however.


Alex, was the oil pump drive in place? Oil relief valve? What did you lube the rod bearings with on assembly? Did you clean all the oil passageways in the crank and block well after the machining?

[acolella76]

BMW hardens their cranks, as long as there was some bearing shell left between the crank and rod and they never made contact you can usually clean them up and there is minimal scoring and there is still a chance of using it. There will be a lot of metal transfer from the bearings that needs to be cleaned up. You should pull the pump if you haven't and disassemble and inspect. As mentioned you should try to find the cause.

Is there anything that would show that the pump was dead? Right now i THINK the cause is a bad oil pump. Maybe it just wasn't pumping enough oil to the bearings. Earlier in the thread you can see that I took apart the pump and cleaned it, didn't see anything that really stood out. Either the pump was dead or the timing belt was slipping over the intermediate shaft gear...

[whodwho]

BMW hardens their cranks, as long as there was some bearing shell left between the crank and rod and they never made contact you can usually clean them up and there is minimal scoring and there is still a chance of using it. There will be a lot of metal transfer from the bearings that needs to be cleaned up. You should pull the pump if you haven't and disassemble and inspect. As mentioned you should try to find the cause.