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-   -   Can I have a bad ring but not burn oil? (http://www.m3forum.net/m3forum/showthread.php?t=334991)

graphite9 Sun, Sep-19-2010 05:51:04 PM

Can I have a bad ring but not burn oil?
 
So, Hello all im new to this forum. I recently picked up a 98 m3 with 157k, super clean for $4500. Problem is, it has one cylinder with 90psi. All others were 175-180. Thats why I got it so cheap. The prev owner said he was driving it, and it started running rough. He pulled over and it sounded fine at idle. Got back in the car thinking maybe it was too cold. Continued driving, to notice it felt like it was missing. Immediately went back home and parked it. Pulled the plugs, all looked clean. Towed it down to the shop and ran a compression test. Cyl 2 was abnormally low... 90. But the car doesnt smoke at all. No coolant in the oil, or vise versa. Is it possible you could drop that much in compression and not burn oil? I have budgeted for a valve job, but if its a piston im screwed!

THanks for any input.

Maginnovision Sun, Sep-19-2010 10:13:41 PM

There are many reasons a cylinder could be low. If you're doing a valve job you'll be able to check every possibility. Valve job should include pressure testing the head and decking it. You'll be able to see if the gasket decided to blow as well, which will have to be replaced anyway. Just because coolant and oil aren't mixing doesn't rule anything out. The mixing of the two is an indication something is wrong, not mixing doesn't mean there isn't a problem. If it is a bottom end problem you should be able to see that as well. I'd say go ahead with the valve job, and you should be able to figure out what's wrong. If nothing else, the shop SHOULD have done a leakdown test after the compression test. If they didn't, or didn't suggest it, don't go back there.

M3F1RST Sun, Sep-19-2010 10:17:26 PM

I was going to indicate the same thing, there could be valve issues or headgasket issues that aren't apparent, it doesn't have to be a bad ring to lose compression. If you do a leakdown test you can usually tell where the air is coming from to determine the issue.

graphite9 Sun, Sep-19-2010 11:03:46 PM

thanks for the input guys. Yeah I'm suprised they didn't do a leakdown test. Im just praying its not bottom end. The car has higher mileage, but I do know it was dealer maintained for its life, and it 100% stock. Is it very common to have a head gasket go, and not have fluids mix? And I was under the assumption that overheating was the cause to blow a gasket. (on a n/a engine). My mechanic is coming over to do a leakdown on it today(I hope). I have done major engine work on hondas, subies, and vr6's, but I'm new to BMW's. I really hope its just a head issue. If the leakdown indicated the bottom end, Im going to look for a good used engine, rather than having it rebuilt. If its a valve, I'm going to do a valvejob/HG, and all assc parts. How long do the chains normally go? My mechanic is super anal and wants to do it all. But in my opinion, if they are in spec, Id like to leave em...Thanks again for your input, Im just praying to the bmw gods its a HG, or burnt valve.

salty Mon, Sep-20-2010 12:44:42 AM

Squirt oil in the cylinder to isolate wether it is the valves or rings. (if the pressure goes up it is the rings) If it needs some rings, it might need a rebore as well. Bottom end refers to the crank and bearings, which is not related to compression issues. Good luck. I'd be going with a used engine if anything is terminal.

graphite9 Mon, Sep-20-2010 01:36:31 AM

well, I just did the oil trick. I dumped an oil bottle cap into the problematic cyl. Think It might have been too much because it jumped to 275...EEK. Im gonna wait till my mechanic brings his leak down tester over. I did notice a tad bit of oily looking substance on the plug when I first pulled it before the tests. But, It could be all the unburned fuel the in the cylinder. Does anyone know where the best source for used motors is? Seems like they run about $3500 with 80-150k. If the head needs a valve job, I can have it machined, and all associated parts+labor for under $1,700. If its the bottom, I'll part out the engine and grab a good donor.

egebhardt Mon, Sep-20-2010 02:33:48 AM

Nice. A big jump with oil in the cylinder. That's good news. Maybe a valve issue after all.

I put in a call to a www.bmrparts.com (Sacramento, CA) a month ago because my engine burns a quart of oil every 1,000 miles, which is not as bad as a lot of them I know of.

They wanted $2,500 for a used engine with 210psi, guaranteed. $100 shipped to anywhere in the Bay Area of CA. I did not purchase it and scrapped the whole idea.

salty Mon, Sep-20-2010 02:52:29 AM

A big jump in the pressure with oil implies rings not valves.

egebhardt Mon, Sep-20-2010 03:37:26 AM

Quote:

Originally Posted by salty (Post 4946572)
A big jump in the pressure with oil implies rings not valves.

Oh. Duh. My mistake.

Braymond141 Mon, Sep-20-2010 03:47:17 AM

Quote:

Originally Posted by graphite9 (Post 4946488)
well, I just did the oil trick. I dumped an oil bottle cap into the problematic cyl. Think It might have been too much because it jumped to 275...EEK. Im gonna wait till my mechanic brings his leak down tester over. I did notice a tad bit of oily looking substance on the plug when I first pulled it before the tests. But, It could be all the unburned fuel the in the cylinder. Does anyone know where the best source for used motors is? Seems like they run about $3500 with 80-150k. If the head needs a valve job, I can have it machined, and all associated parts+labor for under $1,700. If its the bottom, I'll part out the engine and grab a good donor.

An oil cap is certainly not that much. 275psi? That would lead me to believe you have a faulty tester.

Redo that test with your mechanic around. Make sure the engine is warmed up when you do this test.

Braymond141 Mon, Sep-20-2010 03:49:36 AM

Quote:

Originally Posted by salty (Post 4946436)
Squirt oil in the cylinder to isolate wether it is the valves or rings. (if the pressure goes up it is the rings) If it needs some rings, it might need a rebore as well. Bottom end refers to the crank and bearings, which is not related to compression issues. Good luck. I'd be going with a used engine if anything is terminal.

It's not uncommon to hear someone reference the short block as the bottom end. Even the pistons are directly attached to the leg work of the engine.

Magic M3 Mon, Sep-20-2010 04:21:07 AM

Quote:

Originally Posted by graphite9 (Post 4946488)
well, I just did the oil trick. I dumped an oil bottle cap into the problematic cyl. Think It might have been too much because it jumped to 275...EEK. Im gonna wait till my mechanic brings his leak down tester over. I did notice a tad bit of oily looking substance on the plug when I first pulled it before the tests. But, It could be all the unburned fuel the in the cylinder. Does anyone know where the best source for used motors is? Seems like they run about $3500 with 80-150k. If the head needs a valve job, I can have it machined, and all associated parts+labor for under $1,700. If its the bottom, I'll part out the engine and grab a good donor.

Sounds like a ring issue to me! If you end up needing or wanting to do head work, let me know before you do anything. I have a 50K S50 head fresh from the machine shop that I would be willing to negotiate on. Good luck either way.

Pete

graphite9 Mon, Sep-20-2010 04:25:15 AM

well, i think it was a bad reading...somehow. I tested another cyl and it was 180. On the shops test sheet, all of them were 170-180, besides cyl 2. Hopefully my mechanic can look at it soon. Its killing me having a clean m3 sitting in my garage that I haven't gotten to get comfy with!!! It's just wrong!

graphite9 Mon, Sep-20-2010 04:27:45 AM

Quote:

Originally Posted by Magic M3 (Post 4946734)
Sounds like a ring issue to me! If you end up needing or wanting to do head work, let me know before you do anything. I have a 50K S50 head fresh from the machine shop that I would be willing to negotiate on. Good luck either way.

Pete

Excuse me for my noobance. Can you put an s50 head on an s52? I was quoted $500 to do the headwork.


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