2.8L M20 build - Now with 2.7L!

[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!

[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]

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?

[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.

[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.

[acolella76]

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.

lol that makes sense! But why else would the bores be worn more on the intake/exhaust side of the engine? that is where I put the gapped part of the rings on the pistons, opposing each other of course, could that possibly be it? I guess the pistons are fine then, huh?

I will be taking all of my pistons/rods/bearings/rings/block to the machine shop this time.

[LJ851]

lol that makes sense! But why else would the bores be worn more on the intake/exhaust side of the engine? that is where I put the gapped part of the rings on the pistons, opposing each other of course, could that possibly be it? I guess the pistons are fine then, huh?

I will be taking all of my pistons/rods/bearings/rings/block to the machine shop this time.

The bores wear on the intake/exhaust sides because the thrust angle of the con rod as the crank rotates puts side load on the piston in those two directions.

Let me know if you want any pistons, etc.

[acolella76]

I will gladly take them off of your hands, but I don't want them to go to waste! If the machine shop tells me mine are too goofy to use then I will let you know!

[5Toes]

Hey man, Im taking a video today of the rod knock I developed.

Basically me wiggling the rods back and forth. My knock started out the same way yours did

[ForcedFirebird]

Crank is done if they are really .020" out of round, should be .0005" or less. Oil needs about .0003" on a diameter (.00015" per side). Plastigage would tell this if they were applied 90* apart and 2 measurements taken, but you really need a mic to know when it's close to true.

[20gmr]

im In for this thing staying a 2.8 I still have all my short rods and an m52 crank trade me something cool for it lol.

[acolella76]

Hey man, Im taking a video today of the rod knock I developed.

Basically me wiggling the rods back and forth. My knock started out the same way yours did

I would definitely check it out!! Lol

im In for this thing staying a 2.8 I still have all my short rods and an m52 crank trade me something cool for it lol.

Is it already cut down to fit the M20 pistons? What do you want for trade

[TurboJake]

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...

Yes I am. Usually not by their own choice though. It's always the cheapass customer that says "Whatever is the cheapest"

No reason, usually. Unless again, cheapass customer says so. The customer is always right, so they get what they want even if it's doomed to fail. If they want it, and the shop owner/machinist is enough of an asshole or cheapass to do it, that is exactly what will happen.

It's not just the dealer, and not just the small variances. It ranges across a wide amount of engines, especially when the engine shop had to use those small variance bearings from one kit, and mix them with another kit, leaving them with some sitting around. Along with that you can purchase the single bearing pairs in multiple sizes. It's offered, so it happens.

All I'm trying to say is that it's possible, has happened, and will continue to happen because of cheap ass people. Nothing more

[20gmr]

honestly i paid 100 bux for the crank. I tried to sell it twice now and its still taking up space. Im never gonne use it,if you had something cool I would trade you,r3vlimited stickers, yellow fog bulbs just about anything really. im just worried how expensive it would be to ship? and no unfortunately the crank is stock, untouched. did you need the rods too?

[acolella76]

honestly i paid 100 bux for the crank. I tried to sell it twice now and its still taking up space. Im never gonne use it,if you had something cool I would trade you,r3vlimited stickers, yellow fog bulbs just about anything really. im just worried how expensive it would be to ship? and no unfortunately the crank is stock, untouched. did you need the rods too?

I appreciate the offer but since I'm trying to get this finished as soon as possible so my car is drivable, I think I will have to pass for now.