Hello,

I sort of high-jacked a thread earlier (here) and wanted to delve further into my issue, so starting a new thread.

Like many of the threads I've read on here, I was driving and lost power, pulled over and car died. I got home in "limp mode" and haven't been able to figure this out yet, still running on three cylinders. I pulled the replaced the plugs and wires. Plug #2 was damaged... melted for lack of a better word, first time I have seen that.



I did take it to a local shop (Monterey, CA) mostly just to get the code read, and they didn't really help out much. According to the shop there was 0 compression on cylinder 2. Most of my tools are up in Seattle (I'm here for school) so I'm thinking of buying a new compression tester just to check myself. Anyway...

Shop had told me they thought the plug was loose, so originally thinking that I might need to repair the threads. There is some resistence just before the plug bottoms out, busts through and then tightens again and can be tightened to spec torque. However, I cannot guage any air escaping from the plug hole (with plug in) with the engine running. So this doesn't make much sense to me. I think I hear air escaping from the back of the engine, (possibly exhaust valves?) but I can't be certain.

The new plug in #2 has shinny ground electrodes and the white ceramic is covered in carbon. Not sure if this means the plug isn't firing or what.

I guess my questions revolve around what I'm missing or what can I do to troubleshoot this issue. I've been looking at different leak down tests, but have never done this before. I did order a new valve cover gasket and was planning on pulling the valve cover to check the springs in the event something broke. Any thoughts on this are highly appreciated

-David

 

Since you said the first plug was damaged pretty bad, sounds like thete might have been a detonation event...and the newer plug is dirty...like it is dead, with 0psi compression....
Since you hear air escaping, imo next step is remove the head, and have a check of the valves, etc....you may gind it is rebuild time if the piston failed...you might get lucky and find a broken spring or something when you pull the valve cover...guess it might be worth a try. Any old threads come out on the sparkplugs you removed? This might be indicidive that you need a helicoil...but not likely THE CAUSE of your problem....
Was the compression check done both dry and "wet", ie with oil?

 

I believe it was a wet compression test, at least that's what the mechanic said, however I'm not too confident in that shop. I don't recall any shards coming out with the plug. I don't mind doing the work of pulling the head, but I would much rather rule out everything I can before I go there. I'm thinking if I have to pull the head, I may as well take that opportunity to get a new one. For what its worth, the top of the piston looks good from what I can see peering down the spark plug hole.

 

Get a leak down test done as this will give more info then doing just a compression test.

 

It could be worn camshaft lobes/cam roller follower too. Get a good shop to do leak down test to point you in right direction. Before that you could pop the valve cover and inspect valvetrain.

Jeremy

 

I'm afraid that if you had 0 compression in a cylinder, no matter how the test was done, a leak down will just be redundant: you have mechanical failure in cylinder 2. The head's got to come off. If you're lucky it's in the head (I doubt it's the rocker/cam assembly, based upon the burnt plug). If you're unlucky, it's a cracked piston at the ring landing. Good luck.

 

Oh yeah 0 compression is all bad. Too early in AM for me....good luck!

Jeremy

 

Thanks for the input guys.

Yesterday I took the valve cover off, mostly as wishful thinking that it would be a broken spring. But all springs looked good, in fact everything looked clean and fairly normal. So on to the next step.

I put it all back together and am planning on bringing it to a more competent shop to be tested. I don't really buy the "zero compression" statement from the first shop. I regret bringing it there to begin with. I have two choices in shops here in Monterey, a shop called German Motorwerks and the local BMW dealership.

At this point I'm resigned to the likelihood of pulling the head. I will be doing the work myself, which mostly only sucks because I don't have a good place to work on it and I don't really have time to spare. If I pull the head, I plan on replacing it.

 

Just as a heads-up, I finally got around to pulling my head today and I believe I found the problem...










I have a replacement ready to go, but not sure if I should be checking for anything else before I put the new head on. Clearly the exhaust valve was causing issues; but I'm not sure as to why the valve would break like this.

 

Thermal strain can affect both intake and exhaust valves, but tends to cause failure more often in the latter. There are ususally two reasons. First, the exhaust valves do not enjoy the same exposure to air as the intake valves. Second, following ignition of the air-fuel mixture, the EV is exposed to much higher temperatures as the exhaust rushes out of the chamber. It is not uncommon for the EV to be exposed to temperatures that approach 1,400 degrees Fahrenheit.
In some cases, the intense heat can slowly cause the metal of the EV to deteriorate. Cracks and holes can develop, leading to a loss of compression. Other times, the valve may stick in an opened or closed position. A valve that remains open can be damaged by the piston.
So now it is very important for your mechanic to determine what caused it to fail. Are they any other issues for him to fix to avoid future failures again? Thats what he will need to tell you and fix before just slapping another one in.

 

I'm the mechanic...

 

Shade tree mechanic? just curious on why you would ask the causes if you are a mechanic. And I mean nothing by it. Just curious.

 

Nevermind I got my answer. LOL

 

yeah... I suppose I used the term loosely at best. As you figured out, all I meant was that I'm the one doing the work. I've done similar repairs, but never for this reason or on this vehicle. Unfortunately, I just don't have time to really get into this repair; I think I'm just going to have to put the (new to me, though used) head on and get back to driving. Hopefully the head I just pulled off is good other than the valve, then I can use that as a core for a performance head later.

 

Keep us posted and good luck.

 

Thanks again for everyone's input.

As an update...
I got the replacement head installed the other day with new gaskets and torqued to speck, and everything bolted back on. It took a little longer than I was hoping, but I wasn't really pushing and was trying my best to enjoy the work so I was a bit slower than others could be. Also, I did it without the cam tool, which added some time in just figuring out a good work around. I ended up being lucky in that I had a very thin bicycle box end wrench that happened to be the same size as the end of the cam. The wrench fit behind the cam sprocket and allowed me to turn the cam slowly until the sprocket could slide on at just the right spot. Was able to torque cam bolt to 75 lbs with the help of a strong friend holding a screwdriver through the cam sprocket. Not too bad really, but I'll be buying the tool next time around.

Basically the install is complete. It was getting dark and I had to fly out the next morning so I just left it at that until I get back home.

Any further thoughts on completion are highly appreciated. Once I'm back tomorrow afternoon I'm planning:
-compression test
-top off oil
-flush/bleed coolant
-try to make sure the timing chain tension plug re-expands
-take for test drive if all seems well.

If I'm not thinking of something or if there's any advice on accomplishing the above, feel free to let me know.

Thanks again.

 

You missed one important step. Pray!!!
LOL just kidding. Sounds like you got it all figured out so good luck.

 

Too funny; but I'd be lying if I said it didn't cross my mind.

 

All seems well, my mini is running smoothly again.

Thanks for the help, job wasn't too bad with the resources here and the Bently book.

 

Excellent, good luck.