What the **** is happening to this engine?!

[Eric D.]

I have a 1970 1600cc VW motor that I just got done rebuilding. It was running strong up until today when it started making a bad clunking noise. I pulled the heads off and this is what I found

http://i.imgur.com/gF7PQ.jpg

http://i.imgur.com/6tQZc.jpg

So what the **** is happening? Detonation? Cavitation? This is only happening on one cylinder.

[MAUSER202]

I have seen two things do damage like this; detonation ( usually damages the plugs to) or foreign material in the cylinder like broken pieces of rings ect.

[ICANHITHIMMAN]

It really looks like something was bounching around in there

[PdxMotoxer]

It really looks like something was bounching around in there

Same thing i was thinking.
But it's tough to see from just the pic's.. would you call those like bubbles, pits, or gouges?

Good reminder to take an air hose after you pull the boot off the plug
and make sure to blow around the plug before removing it! even if it's a newer plug and your just checking how it's burning.

But most i've seen with foreign matter hit ALL over and the valves.
yours seems to be isolated to just those two outer edges.

Sorry, I don't know much about VW parts but if no one here can help you.. you might TRy a VW forum.

[Kokopelli]

Detonation. Whats the compression ratio and what grade fuel are you running. Probably a good ides to know the cam as well.. Ron

[MistWolf]

Not an expert on Volkswagen engines, but I did some deep research into stroking an AMC 4.0 for my Cherokee. Those flat spots outside the dished area look like what they call a "squish area"
http://i.imgur.com/gF7PQ.jpg
If so, what they are supposed to do is squirt the air/fuel mixture out of there on compression to create a swirl effect to improve burning. The squish area is supposed to be so short, that it will not be a part of the combustion chamber. If there is too much distance between the piston and the head, the squish area will cause detonation. I believe your problem is detonation from too much height at the squish area. Is the head gasket extra thick?

[Eric D.]

These motors actually don't have head gaskets, the top of the cylinder seats against that flat area on the outer edge inside the head.

I also noticed what I thought was a loose rod, turns out the #3 rod bearing was shredded somehow, allowing the rod to flop around on the crank journal. I lubed everything during assembly and followed all factory torque specs so I'm not sure how it happened. It was a cheap aluminum bearing set I used :mad: There is also a crack in one of the heads near the valve guide.

My goal was really just to get this old thing back in the fight so to speak, I knew it wasn't going to last. It sat in a barn for 10 years and it was obvious that someone else attempted to rebuild it before (valve springs upside down, etc) It only has about $400 into it and I think its time to cut my losses. It did make one last victory lap around my block though :D