Compression results

[Bmr]

I was having a weird hissing noise coming from the head, seemed to be by the exhaust port. So i decided to do a compression test yesterday. My results were.

1 - 185
2 - 183
3 - 189
4 - 75

So some feedback from you fellow r3ver's what it might be. 245k miles, car gets about 20-24 mpg. Starts within 3 cranks every time in the morning. No smoke when starting. I go through about 1/4 quart of oil about every 2 months. If i WOT the car runs rich with a little black smoke at 6k up. Also the coolant looks good, goes up to 3/8 then back down to 1/4 when cooling down. So im thinking the rings but it doesn't seem like it. I have a spare engine i've been working on but i've been taking my time cause of my previous m20 failure i had 2 years back. So i really dont want to replace just yet.

TDLR

1. Rings
2. Valves
3. Head gasket

-brandin

[Dj Buttchug]

a leakdown test will tell you more. Do one on cyl 4 and report back

[Bmr]

a leak down test will tell you more. Do one on cyl 4 and report back

Great idea, was considering after the compression test. If i can this weekend i'll definitely report back my findings with a update.

[bmwman91]

Weird. With those compression numbers it sounds like your car runs way too well for there to be anything major going on. Is the hissing noise that you hear constant, or does it sound like it is pulsing (such as a HG leak between #4 and the atmosphere that miraculously has not affected coolant passages)?

The M42 does seem to run a bit rich and black smoke when at WOT isn't uncommon.

[Bmr]

Weird. With those compression numbers it sounds like your car runs way too well for there to be anything major going on. Is the hissing noise that you hear constant, or does it sound like it is pulsing (such as a HG leak between #4 and the atmosphere that miraculously has not affected coolant passages)?

The M42 does seem to run a bit rich and black smoke when at WOT isn't uncommon.

Ill try to explain best in words, wap chu wap chu.....i would say pusling could be it, does not get louder or quieter. At fist i thought it was a exhaust leak, being that the header is common to do that at high mileage. I guess i could test by putting some liquid by #4 to see if air comes out?

[Bmr]

Burnt valve. It has a nice size hole.
Pistons look like crap also.
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[Dj Buttchug]

if op needs valves for cheap pm me.

[oldmann]

Looks like damage from detonation, Bad gas? You run 91 or higher, always?

[bmwman91]

Bummer, but that's better than a cracked head for sure.

[decay]

good opportunity to upgrade to the e36 valves and some VW lifters, on the bright side...

[Bmr]

Engine has about 270k. I havr no idea if the PO put 91 in. I have another block/head just need to get main bearings/rod bearings and new rings.

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