M20 Compression, and Plugs

[Blobsters]

BMW 325I w/ 220k+ miles (broken odo)

Disconnected Ignition coil, removed all plugs, removed main relay (DME and fuel pump relay). Inserted harbor freight compression tester (lubed with oil) into plug hole. Cranked 6 times with no throttle. No oil was added to the cylinder. Engine was ice cold (wasn't started in 3 days, 55 degree garage)

Dry Test Results (with above conditions):
Cyl 1 - 115
Cyl 2 - 115
Cyl 3 - 117
Cyl 4 - 120
Cyl 5 - 109
Cyl 6 - 116

Plugs were bosch platinums, forgot to check #

They all looked similar in terms of color and wear, however #5 had the most build-up by far:https://drive.google.com/file/d/0Bzh...l5T3ozNTQ/view


What are your thoughts on the compression and the plug condition? I plan on replacing them with NGK ZGR5A plugs, but what does the color and condition indicate?

[digger]

how does it drive? consistency is not bad for 220k. do it hot and numbers will go up a bit, probably not to ~150 though which is what id expect with good gauge. have you done any other tests with that gauge to know it reads ok?

do you use shit fuel or any additives in the fuel or oil? does it burn oil ?

id put new plugs for sure

[Blobsters]

how does it drive? consistency is not bad for 220k. do it hot and numbers will go up a bit, probably not to ~150 though which is what id expect with good gauge. have you done any other tests with that gauge to know it reads ok?

do you use shit fuel or any additives in the fuel or oil? does it burn oil ?

id put new plugs for sure

Odometer is broken at 220k, so could be well beyond that. No other tests to base it on besides another dry test on my other vehicle. Owned the car for only about a week now so unsure if they used additives. Engine is pouring oil everywhere so hard to pinpoint the leaks. For sure leaking around valve cover, but also looks like it might be flowing from the rear main seal aswell. Too cold to see if its smoky exhaust, but if it was seriously burning oil I would be able to smell/see that I would think. Gonna do a ElringKlinger
Cylinder Head Gasket Set install soon so I assume the oil leaks will stop. Mainly wanted an opinion on the compression results and how to interpret the plugs.

[TobyB]

harbor freight compression tester

your compression is better than your tester. your headgasket is sealing the bores.

ditch the platimums and get standard plugs. You are burning some oil,
but since you don't know how long the plugs were in there, it's probably
no more than any other older M20.

don't change the headgasket unless there is milk in your oil, or the oil pouring
out can be definitively traced to the exhaust side of the head, at the gasket.

hth

t

[tim88325is]

"Gonna do a ElringKlinger Cylinder Head Gasket Set install soon so I assume the oil leaks will stop."

May or may not without decking the head as well. i wouldn't bother just drive and enjoy the car at this point...

http://www.r3vlimited.com/board/showthread.php?t=232364

[jlevie]

While low, your compression numbers are reasonably uniform.The low numbers could be from testing on a cold engine. Repeat the test on a hot engine with the fuel pump fuse removed to prevent fuel injection. Or better yet, jumper the starter with the ignition off and all plugs removed. After running a dry test, squirt a bit of oil into each cylinder as the again check compression. The numbers may go up if the rings/cylinders are worn.

While a compression test is a useful tool, a leak down test tells more about the condition of the engine. And it can give an indication of where leakage is occurring. Sounds of air in the intake or exhaust indicate a valve problem and sound from the crankcase indicates worn rings.

At this milage it would be reasonable to expect to see valve problems and at least some ring/cylinder wear. I'd pull the head, have it surfaced just enough to take out any warp, do a valve job, and have the valve guides checked and replaced if worn. Use an OE or BMW head gasket, new head bolts, and VR kit for the rest of the seals/gaskets. Since they aren't in the VR kit you will need new oil return tube seals. I get them from my dealer.

The NGK plugs are the best alternative to the NLA original Bosh plugs.

[RobDog]

Correct me cause I may be wrong, but I thought a compression test should be done with the throttle wide open?

[jlevie]

Correct me cause I may be wrong, but I thought a compression test should be done with the throttle wide open?

That is correct.

[ForcedFirebird]

Correct me cause I may be wrong, but I thought a compression test should be done with the throttle wide open?

"Should" yes, but I have found the numbers don't change when closed, just takes a couple more revolutions - just remember to keep the revolutions the same between cyls.

Those numbers look really low, but also a HF tester has never worked properly for me. The ones you buy at Advance/PepBoys etc are only a couple dollars more and far more accurate. Try the tester on another vehicle to verify. I have found 200k+mi m20's tend to be in the 140-160 range pending maintenance and 180-185 when fresh.