2.8L M20 build - Now with 2.7L!

[LJ851]

Just whipped out the handy dandy caliper and noticed that the piston from cyl 2 was seriously oval shaped. Vertical diameter was roughly 0.01" bigger than the horizontal diameter on nearly all of the pistons. I guess this is why the cylinder walls look like shit and it has poor compression!

Also just for shits I checked the rod journal with the caliper. Vertically (parallel to counterweights) was 1.74something, horizontally they measured 1.76something. I know a caliper is not the most accurate tool for the job but I don't need expensive tools to tell me that my crank is FUBAR. So 2.7L it shall be! Now... whaaaat pistons?

Lorin, how much do you want for those pistons? And are they all perfectly round and within OEM spec still? And why do you only have 5? lulz is that for some sick Volvo conversion?

Pistons aren't round, silly! Well, not when they are cold anyway.

I have 5 pistons/rods because i gave one to delatlanta1281 to help someone out. You can have them for free because i like you.

Seriously, if you don't have the proper measuring equip to to measure your parts, save yourself much future pain and anguish and pay a machine shop to spec your parts before you assemble your engine again. It is not a lot of work if you have the right tools.

[Delraco]

Just read through, start to finish.
Sorry to hear this happen mate, but it looks like you're bouncing back quickly.

Your observation of the cylinder wall condition seems to be pretty telling.
Scoring + oval shaped pistons = le fucked

At least you know now? It's hard to think of a positive way to spin this; the situation is just shit wall to wall.


Best of luck.

[acolella76]

I remember reading that somewhere as well. Yes it is an M52 crank. If I have to toss the crank then I will just start over at 2.7. I don't feel like paying another $100 for a crank then $250+ to have it machined and balanced.

Just whipped out the handy dandy caliper and noticed that the piston from cyl 2 was seriously oval shaped. Vertical diameter was roughly 0.01" bigger than the horizontal diameter on nearly all of the pistons. I guess this is why the cylinder walls look like shit and it has poor compression!

Also just for shits I checked the rod journal with the caliper. Vertically (parallel to counterweights) was 1.74something, horizontally they measured 1.76something. I know a caliper is not the most accurate tool for the job but I don't need expensive tools to tell me that my crank is FUBAR. So 2.7L it shall be! Now... whaaaat pistons?

Lorin, how much do you want for those pistons? And are they all perfectly round and within OEM spec still? And why do you only have 5? lulz is that for some sick Volvo conversion?

[Cinnabar325is]

When I was going to turn down the crank in my old M20, some members here explicitly told me not to turn down a BMW crank because the hardening process BMW uses is most effective on the outer material of the crank and turning it down will remove that material significantly shortening the life of the crank.

Surprised nobody has mentioned this? I know BMW makes oversize bearings and it would make sense to use them with a crank that was turned down, but I was told not to waste my time and to trash the crank, which I did.

Without looking back... is this an M52 crank?

[acolella76]

Rolled the car out into the light and stuck a flashlight into the bore of cylinder 2 and I could see that the cross hatching had worn away completely on the intake and exhaust sides of that bore, and had replaced the cross hatching with straight up and down lines. So I suppose that this means either the pistons or the cylinder bore were out of round?

I think I am just going to build up the motor into my old block since it still has visible cross hatching and I don't feel like chasing all of the oil channels in the old block. Haven't decided on 2.7 or 2.8 yet though. Going to call a machine shop Monday and see how they feel about turning down a crank!

[deutschman]

Man I am sorry you are having problems with your m20. Hope it all works out for you. It is all a learning proses ha?
Hope mine works out for me.

[whodwho]

So you are saying that you know of a company that will only machine a couple rod journals of a crank undersize?!?

There is no reason they would turn just one down if it is already chucked up to turn any. Just the fact that it would throw the crank out of balance should be enough to see why they wouldn't.

The dealer(possibly others) sells single pairs of rod bearings with different color codes for the same size journals with slight size variances, not because somebody turned down one journal...

[TurboJake]

You have no idea, although, I will say they will generally turn down the mains and rods to different specs, but won't often do rod pins in different sizes since you have to double up on the bearing kits you need to buy, it's not cost effective in the end to do it that way.

I know exactly well. I have my ASE P2 (Which is a Joke of a cert) and was the commercial parts pro for NAPA and Advance auto parts over the span of 5 years. I not only dealt with cheapass retail customers, but cheapass commercial customers being governed by cheapass retail customers. I know of only one shop in the greater wausau area that actually does the whole job correctly and well using good parts, regardless of make or model.

BUT!

That very situation popped up from a company around here who shall remain nameless because they're very aggressive and I don't feel like defending against a slander lawsuit. I had to deal with the aftermath of an angry customer who wasn't angry with me. All I could tell them is it was pretty much their fault for trying to do it as cheap as possible. They didn't take kindly to it but eventually agreed. Hopefully they learned.


I will agree with you. It's a pain in the royal ass to get get bearings of multiple sizes, but it does happen. You can buy single rod bearings for a lot of engines out there instead of kits, and I have watched people do it. So it's never a situation that's out of the realm of possibility.

[ForcedFirebird]

Shut the lights off and put a flashlight in the port. If you don't see anything that way, pour some alcohol, gas or other thin agent in the port with th head sitting so the valve should hold it. Clean paper towel under the valve should show any seepage. Compression that low means a bent/burnt/unseated valve if there's oil in the cyl during comp test.

Think about it, man, that compression is escaping somewhere ;)

[acolella76]

Head is already off and the valves look like they are sealing pretty well :(

[ForcedFirebird]

You need to pull the head if the compression numbers don't change when you squirt oil in the cyls as that generally means you have a bad valve (or two).

[acolella76]

Well I will try to get that crank to a machine shop as soon as possible. If cost is the only reason not to have the crank turned I will probably just have the rod journals turned.

Need to figure out why there is horrible compression in the 2nd cylinder as well. Rings, pistons, and cylinder wall all look normal.

[ForcedFirebird]

have the current one spec'd.

[acolella76]

So what would you say my options are at this point? New crank?

[ForcedFirebird]

It costs more. 99% of people are cheapasses when it comes to maintaining vehicles.

That right there is explanation enough if it happened. It's cheaper to turn down only a couple and it's cheaper to buy only a couple oversize bearings.

The vast majority of people will always seek out the cheapest way to keep something running.

You have no idea, although, I will say they will generally turn down the mains and rods to different specs, but won't often do rod pins in different sizes since you have to double up on the bearing kits you need to buy, it's not cost effective in the end to do it that way.

Alex, don't turn the crank in an inline 6. Turning and polishing is going to run you $40-60 per journal, not so bad on a v8 that has 4 pins, but get's pricey on even fire v6 and inline since they have 6 individual rod journals, a v8 has shared pins, therefore, having 4 rod dowels (usually $250 for a v8).