Broken Motor - Almost Certainly

[rstclark]

If the piston is beat up  I think we go back to rays original comment   ...."Er  Off with the head"  

Re the plug, Never seen that before. If the electrode is still in place and no other pieces of the plug are missing It doesn't seem to connect whatever is beating up the piston.  Cracked pistons have there own  clacking/slapping sound, so from what you describe it's not likely a bad piston  This is good news 

I think you will have to pull the head to see what has happened  Again hopefully it's something relatively minor  

[Mike G]

Detonation can crack spark plugs and mess up threads. I’ve also seen a spark plug ejected from an engine due to detonation, but it was turbo charged and had the incorrect wastegate spring installed. 

[irdave]

Uh, if it was me, and I hadn't really taken anything else apart yet...  I might be inclined to stick a plug in it and see if it runs like it should...

[jimk]

10 hours ago, rstclark said:

If the piston is beat up  I think we go back to rays original comment   ...."Er  Off with the head"  

If you are not the guy running this engine since it was built, then the PO could have run something thru and beat up the piston top.

[FunkyLaneO]

My experience is if the piston was cracked or a ring land busted then it would likely be smoking like crazy.  Was it blowing smoke when it started running rough?  Like was said before, that damage to the piston could be old and not really a problem, I have taken apart an engine where a spark plug electrode had broken off and bounced around inside and left little dings all over the top of the piston and the head but it didn't happen while I owned the car and I had been running it for tens of thousands of miles with no issue.

 

Do a compression or leakdown check, if it looks decent you can and put a new plug in and see how it runs.

Edited October 22, 2020 by FunkyLaneO

[Dick R]

What great insight and advice. 

 

No smoke after the problem started. 

Compression test next.  If compression is OK (it was 140-145 on all 4 the last time I checked).

Then I'll try replacing the plug and starting it up.  Hard to imagine that everything will be back to normal, but I'll give it a shot. 

Good point about the top of piston damage - this car has had an unknown past and that could have been there for twenty years. 

[BarrettN]

Might be worth swizzling a magnet around inside the cylinder, pick up any leftover ferrous bits of whatever was clanging around if they're still there.

[Dick R]

I tried that already.  While I picked up a trace of grain-of-sand size material, I couldn't manipulate my magnet on a stick to cover much of the area on top of the piston.  Not enough evidence for much of any conclusion. 

[Dick R]

Quote from #3 cylinder:  "Compression?  - I don't need no stinkin compression."

 

Obviously no chance of a miraculous cure.  Off with it's head...

 

The compression gauge moved a bit while cranking - maybe 5 or so psi momentarily - then would immediately go to zero. Not enough compression to hold the reading on the gauge.  And I checked the gauge on another cylinder to make sure it was functioning properly.

 

Probably be a few days before I pull the head owing to my complaining back. 

[Dick R]

This must be my lucky day.  Just pulled the head and found the problem - and it turned out to be probably the least possible thing wrong. 

 

A portion of the he head gasket between #3 and #4 was missing.  Picture below.  That's what I heard rattling around - kind of surprising that something as small and light as that would make that much noise.  Not nearly as loud as a thrown rod bearing, but still loud enough.  Since it opened a passage between #3 and #4, both of those cylinders were not working.  When I was first diagnosing the problem and pulled the plug wire on #3, I stopped there.  Would have found the same thing on #4.  Also, the zero compression on #3 would have also been the same on #4.  I just stopped at #3.  I should have also considered how down on power it was - it hard time maintaining a low speed up pretty gentle hills.  It was running on 2, not 3 cylinders. 

 

Everything looks quite usable to me.  Pistons and valves look OK.  Not pristine, but it was working just fine with good compression across the board.   I think I'll just clean it up and get new gaskets and be on my way.  It looks like the gasket between #2 and #3 was on it's way also.   It's a Victor Reinz gasket.  I'm thinking I should get a gasket from the BMW dealer.  Any opinions welcome. 

 

 

 

A side note: even though I left both manifolds on which made the head quite heavy, I removed it all by myself.  I used a hand-dandy block and tackle that I just got from Harbor Freight for $16.  It's rated for 400 pounds and is sold to be used by hunters to pull up a deer carcass to field dress it - or I guess in your backyard.  It worked like a charm. Picture below. 

 

 

[Preyupy]

Very carefully measure the head and make sure it is FLAT!!! If there is a low spot where the gasket blew then if you just put a new gasket on you will be doing it again in the near future.  The horrible noise was the sound of the burning gas coming through that gap in the gasket when the intake valve on the other piston was OPEN.  You lucked out,  depending on the condition of the head it might be a good idea to have a valve job done, new guide seals and even a light cut on the surface to make sure it is flat and will seal correctly when you put it back together.

 

There is enough carbon on top of all the pistons to make me think it was using some oil even before the gasket went.   

Edited October 29, 2020 by Preyupy

[Dick R]

Obviously good advice all.  Thank you for that.

 

I've checked the flatness of the head and block by laying a straight edge over the areas of concern and shining a light behind it.  To my eye, they look quite flat and without low spots.  This is not as good as doing a proper measurement, but I'm thinking that it is in the acceptable range.  Worst case, it happens again sometime in the future and then I'll repeat what I've just done plus take it to a machine shop for the full monty.  I think it's possible that a valve job was done sometime in the not too distant past.  The valves look to be in decent shape (to my untrained eye) and the compression was 140-145 across the board when I last checked about a year ago.  Also did not seem to be burning oil - no apparent smoke on long decelerations that would normally show up in my experience.

 

Another factor may be something I didn't do - check the torque of the head bolts before removing the head.  I just slowly loosened them with a breaker bar.  It's possible that the bolts were not as torqued as they should have been. 

 

One thing that is a bit of a mystery to me - all the head bolts were very oily when removed and the threaded head bolt holes were all full of oil after I got the head off.  Up to the brim.  Does this seem normal? 

 

 

[Preyupy]

The oil around the head bolts is completely normal.  The head bolts run past the rocker arm shafts and there is oil around the shafts.  The actual oil feed to the head comes up past the front head bolt on the intake side. 

 

Make sure you get the oil out of the bolt holes in the block BEFORE you put the head back on and do not use a air gun to install the bolts (even on a low setting). If there is oil in the holes you can hydraulic it bad enough to crack the block around the bolt holes (had a factory Turbo engine with 8 of the 10 bolt holes cracked a few years ago).  You want the head and block as clean and dry as you can get them before you install the gasket.    

[tech71]

I have always been partial to Fel-Pro gaskets, have installed head gaskets on many engines including M10 with good results.

A few more bucks more but a good choice it in my opinion.

 

Fel-Pro 21212 B

 

Edited November 1, 2020 by tech71