Bottom's up M20B27 e2i Build

[cek]

and the housing doesn't show any scoring at all- which is even more impressive... if the bottom
plate's smooth, that's a new pump.

I doubt the pump is new. It was extremely encrusted. Also, see the plate:


It's got some wear on it. Doesn't seem like much, but what do I know?

[TobyB]

Gears show no wear

and the housing doesn't show any scoring at all- which is even more impressive... if the bottom
plate's smooth, that's a new pump.

As to ring end gap, yes, it's good to check. I only do on race motors, or where I
am not familiar with the ring vendor.

Side clearance should be minimal- this is why I usually buy new pistons. When it gets
much over the maximum allowed, the ring starts to twist back and forth in the gap,
wear escalates, and then the ring breaks in pretty quick order. I've had it happen with 2
M10's- the first was an unknown shortblock, but the second was only at the max clearance
when I re- ringed it, and it lasted exactly 2 lapping seasons before it ventilated a
piston.

hth

t

[cek]

Two 325i M20 throttle bodies. One has a broken spring holder. They have different vacuum attachment thingies. I'm wondering which one will be the right one to use.


Oil pump cleaned (mostly). Gears show no wear.


Cleaned up a bunch of other parts today too.

Hopefully I'll be able to pick up the 'new' block and crankshaft this week.

[cek]

Mostly done measuring things...



There's almost no conicity (taper) on this block.

The bores are also almost round; well within spec.

It wore very uniformly. At ~0.0028" cylinder to piston clearance I could slap this back together and still be way within max (0.0047").

Kinda mind-blowing for a 360k block. The pistons account for much of the wear.

Crank bearings are worn. Connecting rod bearing diameter is 1.7705-1.7709" with minimum spec being 1.7707".

Main bearing diameters are 2.3609-2.3613" with minimum spec being 2.3614".

Of course, it could be ground down to next size. But I have another crank incoming anyway.

I did not use plastiguage to measure the radial clearances. Out of time for today. But I plan on doing it for the main bearings and caps sometime soon just to get the experience. Never used platsigauge before...

[cek]

Question about piston ring side clearance:

The main ring side clearance spec is 0.0028". I can get a 0.0030" feeler in there. What's worn, the rings or the piston? Or is this close enough?

I've searched and found no (!) discussions on piston ring side clearance...

[cek]

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".

Yeah, I just saw that in Bentley. On page 5-17 (E28) it reads "On 528e models, double classification replacement bearings are no longer available from BMW. The triple classification bearings (yellow, green, and white) can be used in engines with double classification bearings. Replace red bearings with yellow bearings and blue bearings with green bearings."

I've updated the sheet to include yellow, green, and white for Standard size. I'll do the undersize one's later.

[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".

[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.

[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:

[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]

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.

[cek]

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

[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.

[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.

[TobyB]

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

t