Bottom's up M20B27 e2i Build

[cek]

I obtained an M20B27 from an 88 528e with 340K miles on the clock and a broken timing belt.

I'm considering re-building the head with a 325i camshaft, slapping it on the bottom end, doing an "e2i" conversion (I already have all the e2i parts).

Pics:







[url=https://flic.kr/p/r2QPP4][/url

Obviously the pistons need to be cleaned up where the valves hit and I'll re-build the oil pump. However, I'm reticent to pull the bottom end apart any further. It turns smoothly and the PO of the car says it was running very well before the belt broke.

If I pull the bottom end apart, I know I'm going to find things that are marginal. It's got 340k on it. Knowing me, I'll want to fix those things.

How crazy am I to NOT pull the bottom-end apart and inspect?

Should I just abandon this motor and start with something that has far less miles on it?

[catech11]

its not super expensive to rebuild the bottom while your at it, especially with that many miles. Even if you just get it cleaned, rehoned, get some new bearings you would be a lot better off in my opinion. would only run you around 400-600 total.

[jayuuey]

88 528e was a super eta, right? looks like you are set for e2i done correctly already.

[mr2peak]

You will always regret not doing it when it was easy

[cek]

I found my head! I've had a search going on CL for a while for a good 885 head and I finally hit the jackpot.

Just a few thousand on it (supposedly) since rebuild.









For a little extra $ he threw these in:




I'm going to pull the bottom end apart and measure the cylinders. If they are w/in spec I'll stick with this block. Otherwise, I'll go source one with less miles.

[Stapes]

That's a nice engine project you got going on. I remember reading that craigs post. I thought about getting it after reading kamotors ITB built. Btw I'm in Bellevue too, maybe one day I'll get to see your engine.

[TobyB]

Do it all- 340k is just too much for a set of pistons. They'll be worn out.

t

[jlevie]

I am going to be real surprised if the cylinders are still in spec. I typically see (for race motors) more than acceptable wear at half that mileage. They'd be okay on a street engine with a new set of rings and honing. In a like manner, the crank journals and bearings can be expected to need attention.

If the cylinders are worn an overbore and new pistons will be needed and is going to be expensive. Probably much more than much a lower mileage bottom end.

[rcsoundn1]

Thats a lot of miles. And your plan is to make more power with it i assume. Rebuild or get one with lower miles. If you were just going to slap a head on it and DD thats a different story. GL with the build.

[cek]

After honing, what is the correct diameter for the cylinders to be w/in spec?

[cek]

What's the best resource/reference for M20 measurements, tolerances, and specs?

Anyone have a good spreadsheet for blueprinting? I've searched the forum but only found dead links.

[TobyB]

Doesn't Bentley have the numbers?

As to the honing, I am usually looking to be sure that the cylinders are still cylindrical within
about a thou- that's 0.001".
Then you measure the piston skirts of the pistons you're wanting to use, and hope
that they're about 0.0015" smaller, or so. If they're within 0.003", you're probably ok.

One way,
t

[cek]

I found the BMW tech reference for "Specifications and Tightening Torques" and am coalating it into a single spreadsheet.

I also found another source of specs, for the 528e here.

This page is from the 528e reference. It says the "Max. permissible total wear clearance on piston and cylinder" is 0.1 .. 0.12 mm.

The broader tech reference (318i - 750i U.S.) has this page, which conflcts. It says "Max. permissible total wear clearance between pistons and cylinder (engine run)" is 0.01 .. 0.12mm.

The former seems to be incorrect. Right?

FWIW, here's what how my spreadsheet is shaping up:

[cek]

I still need to cross-reference with Bentley but I have just about every measurement now documented in my M20 Blueprint spreadsheet.

I really like having all this in one place. I'll continue to update it as I learn more.

M20 Blueprint

If anyone notices any errors, or measurements that should/could be tighter/looser based on real experience I'd appreciate it. I'll add them.

I'm now going to add the ability to enter measurements while I take them, letting Excel do the math and report results.

[jlevie]

That is pretty neat and represents a lot of work. When you get this finished I'd like to add a reference to it in the "Diagnostics, tips, & tricks by Jim Levie (E30 Jedi Master)" in the FAQ & DIY section. A PDF would probably be ideal and if you will email me a copy I'll add a notice that members could PM you or myself for an email delivered copy.

FYI: The Bentley and ETK shows five main bearing "colors" and slightly different numbers for the journal sizes for each "color".