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Old 04-17-2012, 02:15 PM   #1
The Twin
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M20b25 compression test result prior to boost install

cross-posted from the F/I sections...figured get more exposure here.
if Mods feel it's clutter, please nuke the appropriate one.


My 1990 325ic will be undergoing some updgrades shortly.

in preperation for it to accomodate the boost setup that will be installed, I went ahead and performed another compression test...with results that kind of surprised me.

Please note, I overheated my engine last summer during the heatwave while stuck on Decaré in MTL...I suspect HG damage, which will be replaced prior to boost.

regardless, I wanted to get a feel for the health of the block.

COLD TEST RESULTS:

145, 150, 120, 125, 150, 150

JUNK.


WARM ENGINE RESULTS...WITH oil added to cylinder, AND open throttle.

160, 180, 180, 180, 200, 180

...ya.

I'm being told a few things, such as "complete rebuild" to a new ring job+hone+HG.

Would it be wiser to scrap this engine, and just get a new(used) one or even with the "better" results of a warm compression test, still reveals it has issues?

I'll be running 8psi with a .60AR turbo...

thoughts?
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Old 04-17-2012, 04:08 PM   #2
Ceeker
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you may run into the same problem changing the motor.
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I think I've had 14 bmw's in 4 years.
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4 318is all white - sold and parts
1 87 325is red - parts
1 89 325i vert grey - parts
1 90 325is white - keepin
1 87 325i vert -red - keepin
latest addition 1 88-325is red - parts
latest addition 1 89-325i vert - white -fixin/sold
latest addition 1 92-318i vert - blue - parts
latest addition 1 87 325is blk - parts.

latest addition as of 2013-Gold 87-325is auto! it's a keeper!
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Old 04-17-2012, 04:14 PM   #3
The Twin
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yeah...after talking to a boatload of folks, I think the concensus is to simply run it as is (of course change the HG+get head done)...

if bottom end goes, I'll have a descent head to play aroud with come next engine.
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Old 04-17-2012, 04:15 PM   #4
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you should have done the test warm but with no oil... and then one with oil... as that will tell you if the issue is with the top or bottom end of the engine
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Old 04-17-2012, 04:16 PM   #5
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can do it again this evening with no oil, and warm engine...
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Old 04-17-2012, 09:04 PM   #6
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Quote:
Originally Posted by NOTORIOUS VR View Post
you should have done the test warm but with no oil... and then one with oil... as that will tell you if the issue is with the top or bottom end of the engine
Did test again this evening on warm engine. Solid 150 across all 6 cylinders. Maybe a +\- 2,3 psi variance but all where basically the same
Started testing hot, and by end was down to 1/4 temp. No oil in cylinder. Dry test.
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Old 04-18-2012, 09:34 AM   #7
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**** it... boost it.

Fix it when it blows up.
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Old 04-18-2012, 12:35 PM   #8
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Quote:
Originally Posted by The Twin View Post
Did test again this evening on warm engine. Solid 150 across all 6 cylinders. Maybe a +\- 2,3 psi variance but all where basically the same
Started testing hot, and by end was down to 1/4 temp. No oil in cylinder. Dry test.
sounds about right... with that little variance I wouldn't worry about the bottom end.
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Old 04-18-2012, 10:51 PM   #9
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Yeh, sounds like the bottom end is fine. Get your head checked for warps/cracks. Lap your valves, etc etc.

I'd recommend Dave at that machine shop at Bronson and Chamberlain. (down that ramp, across from the Drummond's)

He did excellent work on my bike and M50 builds.

Recommended.
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