Head carnage

[CoolAirVw]

Anyone remember that sick feeling you got as a kid when you got caught doing something you knew you shouldn't? When my engine that I rebuilt about 1000 miles ago started knocking I got that same feeling. My stomach actually hurt.

I've never invested so much of myself in any vehicle I owned before as some of you have seen by my constant posting here.(floorpan, rust, brakes, engine ect.) I've never enjoyed the work as much on any car I've owned whether it be a project car or my daily driver.

Well the "Saga" starts like this. 1000 miles after I rebuilt the engine it started knocking. I checked this and did that and long story this and long story that....

but eventually I found the Precumbustion chamber (PC chamber) broken....



The piston had some damage (note the "pock" near the numbers.)



But the cylinder wall doesn't seem to be damaged



Lets look closer at the carnage.





With the PC chamber out I could see the damage to the head. Note the "peice" protruding out that cause the "pock" in the piston picture noted above.



See how the PC chamber "erroded" the gasket where it touched the PC chamber



Here's a shot of the gasket comparing good with bad.



I have my theories but I want your opinions on what caused this damage. Note: Head was resurfaced with valve job including new guides and exaust valves.

[libbybapa]

The good news is it doesn't look like there's a crack between the valves...

Seriously, sorry about the damage. What do you suppose actually caused the pre-chamber to break? How's the glowplug in that cylinder look?

Andrew

[surfcam]

I'm also sorry to see this after all your work. My theory of what caused it is the small blank that sits over the prechamber slipped towards the valves during installation. That's my best guess. I notice loose blanks on a head I installed quite a while back. I was thinking maybe I should peen them in a bit. After these scary pictures I think I will next time around.

[CoolAirVw]

The good news is it doesn't look like there's a crack between the valves...

Seriously, sorry about the damage. What do you suppose actually caused the pre-chamber to break? How's the glowplug in that cylinder look?

Andrew

Actually there are cracks between the valves. They were ignored during head work. Glow plug didn't get damaged at all.

[tylernt]

First let me offer my condolences. That really sucks, after all the effort. It was so pretty.

Well there has been a long-running debate about milling VW diesel heads. How much was it milled, and were the PCs milled in-place or separately? Not saying milling is the problem, but just thinking of possible problems.

surfcam, what do you mean by "blank"? Are you referring to the PC inserts?

[82vdub]

Yea, sorry on the issue's your having. My initial thought looked like the prechamber blew out into the cylinder, but that wouldn't explain why it ended up back in the location it should be. Was part of the prechamber loose, or did it just get wrapped back up into itself?

[Dsldub]

edited for content

[Fatmobile]

Sorry to see this happen to you and your project/driver.
I don't see any peen marks around the prechambers.
The machinist at Arnolds always puts 5 peen marks around each PC.
Other shops in town don't do that, I take all my head work to him now.
Looks like it got loose and kept getting looser.

[Vincent Waldon]

The machinist at Arnolds always puts 5 peen marks around each PC.

Sounds like a good precaution.... perchance any pictures ?

[Fatmobile]

No pictures right now but I think I have a head they surfaced, that hasn't been put on yet.

[nicknack2]

Sorry to see what happen to your baby, I have the same feeling about the rebuild I’m doing, I’m putting so much work, time an soul in to it that scares me to fail, my fear comes from something that happened o me 6 years ago...Back then I had a mighty ECOdiesel(my dream car), I bought it for six hundred bucks with engine damaged, it had a broken timing belt, needless to say I sent the head to get it re built, seals, valves and more were replaced, but the machinist resurfaced the head... (a no-no IAW the Bentley manual) I did not know much about the mighty VW diesel engine back then and taught nothing a bout the resurface the head, the head was so nice, clean and shinny some much beauty had me blinded...I did notice that the pre-chambers did not look normal after they cut the head, but did not think nothing of it then after $1800 worth of work on the car(not counting the $600 I paid or the car) in about 1200 miles it did the exact thing that yours did, my theory is that my pre chamber felled from their seat on the head... blame that on the resurfacing of the head 100%.... and I think you ad the same issue.

[tylernt]

in about 1200 miles it did the exact thing that yours did, my theory is that my pre chamber felled from their seat on the head... blame that on the resurfacing of the head 100%.... and I think you ad the same issue.

That would explain the little metal half-moon in the head gasket being eroded, with the PC insert rattling around with every power stroke... heck I'm starting to think that peening the PC inserts is a good idea whether the head has been shaved or not!

[libbybapa]

Shaving the diesel heads is entirely customary at this point. Every head I have rebuilt gets shaved and the machinist I use peens every pre-chamber. He also replaces the galley plugs with allen head plugs, etc.

Andrew

[surfcam]

what do you mean by "blank"? Are you referring to the PC inserts?

Yes I didn't know what those little coins were called. I still think the PC insert might have slipped to the inside during installation. Then the piston could have pushed the other removable part of the PC up. This would give it room to flap and eventually get driven in sideway to the head. I though there was another removable part to the PC. If not the piston still has the power to move things up. I just can't see how the PC insert would come out over that shoulder when it held by the head pinching the gasket. Unless there was alot of vertical room to begin with which you probably would have noticed.

[riddleyo]

What is meant by "peening" around the PC chamber? How does this help the PC insert stay in better?