Misfire #8

[516SC]

Look intake manifold gaskets. My gues is there is leak and you have hole in piston.

Do leakdown test.

[Laust]

Kouks, sad to hear. What a bummer.

To everyone: how does an exhaust valve just go bad like that?

Carbon and other combustion products build up in the combustion chambers and flake off on a regular basis. If unlucky, a chunk can get caught between the valve head and valve seat and get stuck there. This allows a very high temperature flame to exit through the small opening during combustion, essentially acting as a torch. Since the valve head has lost full contact with the seat, it cannot adequately get rid of the heat. As a result it locally heats up above its melting point.

My former 205k mile E32 750iL (cylinder #9) suffered that fate. It got increasingly worse and it took maybe 20k miles before it became impossible to smog. A quarter of the valve head had disappeared.

Based on a leak-down test, which included listening to crankcase, intake and exhaust, I had guessed correctly before taking it apart.

Laust

[shenofjo]

Sad to hear! Hope it's still salvageable.

[racer2086]

Carbon and other combustion products build up in the combustion chambers and flake off on a regular basis. If unlucky, a chunk can get caught between the valve head and valve seat and get stuck there. This allows a very high temperature flame to exit through the small opening during combustion, essentially acting as a torch. Since the valve head has lost full contact with the seat, it cannot adequately get rid of the heat. As a result it locally heats up above its melting point.

My former 205k mile E32 750iL (cylinder #9) suffered that fate. It got increasingly worse and it took maybe 20k miles before it became impossible to smog. A quarter of the valve head had disappeared.

Based on a leak-down test, which included listening to crankcase, intake and exhaust, I had guessed correctly before taking it apart.

Laust

Wow great explanation. Thank you

[kouks]

Traveling and have not taken the head off yet. When I did the heads on both side about 30k miles ago, the machine shop told me one of the valves on the 8 cylinder had a slight bend, but it was sealing fine and they did not recommend I do anything. I’m guessing after 30k miles it was off enough to create hot spots and burn the valve. I’ll see when I pull it off. Prolly take a look this weekend.

[kouks]

Some good news, if there is good in this

while shopping to surprise my wife this Christmas with a slightly used X5, I talked with the service manager at Santa Monica BMW about this. He mentioned on occasion, a fuel injector can fail and saturate the cylinder wall with fuel, destroying the thin layer of oil and causing the cylinder to lose complete compression pressure. He suggested I squirt a teaspoon of oil in the cylinder and do another compression check before I commit to more invasive work. So I did. Still 0 psi. Although it did not work for me, never knew this was possible, so thought I’d mention it for education.

I then rented a digital camera borescope from Autozone, never knew they had those. From what I could see, there was no damage to the piston, no signs of valve impact, and I could only see about 3/4 of the cylinder wall, but what I could see was smooth with no noticeable scrapes.

Then drained oil, no evidence of coolant in the oil, a big relief.

Then in hand turned engine to seal the valves on cylinder 8 and hooked up a compressor for a leak down check. At about 60 psi air pressure there was no noise in the crankcase (piston rings ok), no noise in the radiator (head gasket ok and no head crack), no noise from the intake valves ( intake valves seal), but I could feel a slight breeze out the tailpipe, the exhaust valve or valves were either failed or not sealing. The lifters were free and could easily rotate so they are fine, it’s an exhaust valve failure.

Time me to pull the head, take it to a shop and get going again. I’m crossing my fingers that what I saw with the scope was correct and no damage to the cylinder and piston. Could be back on the road before Christmas with less than a $500 bill.

[oldroller]

Good news indeed, Kouks... well performed diagnostics!

[shenofjo]

awesome! hope it all works out!

[kouks]

Coming apart.

Has anyone removed the head without removing the entire exhaust? Just trying to avoid some extra work. It may work on the passenger side, but since I'm doing the driver side the steering box is in the way.

[oldroller]

Yes, when I did the left head I removed the collector pipe bolts, left motor mount bolt, and raised the engine about 2 inches to access the manifold bolts.
Much better clearance, still a couple that were easier from below. Once loose it just moved aside.

[kouks]

Head is out and at the machine shop.

Exhaust valve on #8 had about a 3/8" triangular section missing. That valve will be replaced, and four valve guides will also be replaced since they found some play in a few other valves. The head is straight and no cracks. Should have it back by Friday, just in time for me to go on another trip and delay the rebuild longer. Slow and steady...should be done before Christmas though.

[racer2086]

Wow that's good news I guess. Better than other things it could have been...

[cyclops2]

Good group diagnostics and best case outcome considering all possibilities.

I am confused as to why the first machine shop you had do the heads (only 30k earlier) noted a bent valve and didn't replace. Nor did they identify the vavle guides you are getting replaced now. I am assuming that you didn't ask them for a head job, but perhaps an inspection.

For those not familiar with a leak check; it is the perfect companion test to a failed compression test. Also note that a compression test should be done dry and then done wet (oil).

Here are 2 useful videos by "Eric the Car Guy":

Compression Testing



Vacuum Testing

[kouks]

Started putting it together and got ahead of myself. Related thread: https://www.bimmerforums.com/forum/s...-(Head-install)

On the road again, back at it next week.

[kouks]

Head came off fine, installed the dang OSV, head back on, timing complete, exhaust manifold on, valve covers on, engine mounts connected, went to connect the coolant manifold and could not find the gasket I know was in the box when it came. My son and I went through the garage for over an hour and finally gave up. Ordered new gasket and at a standstill until they get in after Christmas. Bet you I'll find the gasket after I'm done the project.

By the way, do not ever buy Erling VCGs, complete junk. Would not fit the valve covers and constantly came off every time I tried to fit the covers on the car. Usually get Victor Reinz but the Erling were a little cheaper and I just thought rubber is rubber, all vcgs are the same, apparently not. Finally gave up just got some FelPro from Autozone which worked great.

Merry Christmas everyone!!

[kouks]

Got it all together over the holidays and got it running. Engine sounds great and is smooth, but I have a big issue...

On the initial startup there was a tapping sound that was mostly from the back or underside of the engine. Went for a short test drive and the tapping continued rhythmically, once per revolution, thought it could have been a valve, not as sharp as a lifter tap. and not as dull as a head tapping like when there is knocking. Took out the stethoscope and tried to locate the tap but it slowly went away, so I considered that an oil passage was blocked and now was free to allow lubrication.

Then tried to bleed the cooling system and couldn't. It boiled over and steamed like there was a blown head gasket. I'm no expert but this was my third time I did a head gasket and I followed the TIS, torqued to 30Nm + 80 deg + 80 deg. Engine ran smoothly the entire time.

I'll be doing another leak down test soon, this is disappointing.

The shop checked all the valves and I thought they checked for cracks and squareness, but I'll call and ask to make sure.

[shenofjo]

Good luck!

[Old525i]

Bill: Did you lift the front end slightly and turned the heater on when bleeding the cooling system? Removed the radiator bleed screw and filled it very slowly? I usually end up with a perfectly bled cooling system when I follow these steps. Good luck.

[740iSport303]

Sounds more like an exhaust leak to me. If you remember when Michael had that leak on the E39 540 that sounded exactly as you describe your's sounds.

[kouks]

Bill: Did you lift the front end slightly and turned the heater on when bleeding the cooling system? Removed the radiator bleed screw and filled it very slowly? I usually end up with a perfectly bled cooling system when I follow these steps. Good luck.

Yes, but in this case the coolant is acting like its boiling rapidly, which is a classic blown head gasket behavior. Also, when I open the bleed screw it vents steam for a long time, not just for 10-20 seconds like a normal bleed.

- - - Updated - - -

Sounds more like an exhaust leak to me. If you remember when Michael had that leak on the E39 540 that sounded exactly as you describe your's sounds.

It was more mechanical than an exhaust leak, louder actually. Then when it went away, the coolant started boiling over and I had to replenish with almost an entire container of coolant. Again, a classic blown head gasket or head/block crack behavior.

Its coming apart today again to find the real culprit.

[AquilaBMW]

Just catching up on this thread. My White Wagon seems to have some to a similar end. About to get rid of it. I check back with you on this project. Hope it works out, you've put a ton of work into this.

[kouks]

Well, no coolant in the oil, and no oil in the coolant as far as I can tell. That usually means no block/head cracks. Could the new head gasket have failed already? Did I not clean the surface enough during the install?

Drove it for a few miles and the temp stayed steady, but after about 10 minutes running in the driveway it boiled over again.

Packing up for a trip to Paris...the one with the tower, not Texas...so won't be at it for a while.

[racer2086]

Just make sure there isn't something else that just so happens to coincidentally have gone bad, like a fan clutch or something, which may be why it is ok driving and overheats in the driveway?

[acspecialists]

You should hear the fan when you start the engine then is clutches out. The secondary electric fan should also kick on when the car is sitting. When I did my valley pan I had a heck of a time getting the air out!

[kouks]

Well,

After two months in the driveway on jacks, finally got back to it, replaced the head gasket again, putting it back together. Either will get good used cats from another member or new ones from Autozone. Just need to install the exhaust manifolds and the intake system and she'll be ready to try again.

The aux fan is dead, getting a new one of those. Although no aux fan will cause an overheat, it will not cause hot air or steam in the coolant, that is purely exhaust gasses.