2.8L M20 build - Now with 2.7L!

[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.

[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?

[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)

[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]

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]

Will do!

So at this point I may have rings that don't seal and might have to get new or resized rods... This sucks a bag of dicks

[LJ851]

I have 5 "i" rods and pistons you can have if you need them.

[whodwho]

You have the head off and the rod caps off, you might as well pull the pistons and inspect them at this point.

[acolella76]

Yeah. Pulled the piston out, nothing weird is really evident.


I have come to the conclusion that I either need a new crank, need to have this crank machined, or I need to use oversized bearings. Or just start over with an entirely new motor. I put good rods with good bearings on two of the worst journals and torqued them down with Plastigage. They were so fucked that they wouldn't even register.. so I am afraid that the crank is worn down pretty badly.

[TurboJake]

I'd just do a new crank.

ETA crank? I haz.

[LJ851]

Measuring the crank with a micrometer will tell you if it is good or bad. A bore gauge will tell you if your rod big ends are ok. Make sure to use one that reads down to .0001 inches or .001 metric.

[acolella76]

I'd just do a new crank.

ETA crank? I haz.

Thanks for the offer, but I have two of them sitting next to me lol. Really don't want to have to go back to 2.7 though... but it looks like I might have to :(

Measuring the crank with a micrometer will tell you if it is good or bad. A bore gauge will tell you if your rod big ends are ok. Make sure to use one that reads down to .0001 inches or .001 metric.

I am pretty certain that the crank is bad. I just don't know how badly.

I think I may take the crank to a machine shop and see if they can turn it down for oversized rod bearings. Thoughts?

[whodwho]

You need to check the journal diameter, it is possible it was already undersize?? For a quick and dirty you could also try the plasigauge trick on a good journal and see if it registers.

[frankenbeemer]

Thanks for the offer, but I have two of them sitting next to me lol. Really don't want to have to go back to 2.7 though... but it looks like I might have to :(



I am pretty certain that the crank is bad. I just don't know how badly.

I think I may take the crank to a machine shop and see if they can turn it down for oversized rod bearings. Thoughts?

That's what I'd do. I want to see this 2.8 running on the dyno, so please make it work. I know, I'm selfish.

[acolella76]

You need to check the journal diameter, it is possible it was already undersize?? For a quick and dirty you could also try the plasigauge trick on a good journal and see if it registers.

3 or 4 out of the 6 journals were perfect. Don't remember which ones exactly though. I was wondering if it was already undersized but it wouldn't make sense for someone to cut down only 2 or 3 of the journals lol

That's what I'd do. I want to see this 2.8 running on the dyno, so please make it work. I know, I'm selfish.

You aren't the only one that wants to see this thing tuned, I promise! :)