James Bailey

Very unusual ! I have heard that major carbon buildup on the valve and the piston notch can bend valves when the belt lets go but never seen it.......Being an automatic it is really hard to overev it !!! not easy to miss shift.

4drgl

There was quite a bit of carbon build up... When I pulled the heads my garage smelled like rotten gasoline for at least 2 days.

The car had been serviced at some point in GA... There were receipts from a dealer in the car found in the seat..

I would venture to guess it was never tuned for altitude either... since I bought it here in colorado, and it lived in Evergreen for some time..

docmirror

Yep, concur with the 'weird' comment. I'm thinking that the combination of a broke belt, and carbon the valves and piston faces prolly did this. Inspect the piston tops carefully and see if you can detect any small impact areas from the valve face.

ptuomov

Spring dyno, I think?

Another possibility comes to mind. Is it possible that the timing belt has slipped in a way that the camshafts were advanced dramatically? It would have to be a weird situation. In any case, I think that a big advance might in theory cause the car to idle ok, then burn the exhaust valves, and run out of breath at higher rpm. (All of the above is based on some "theory" acquired from the internet for free, so stick a big caveat sticker on it all.)

Rob Edwards

Yep, spring dyno:

danglerb

Don't the exhaust valves poke into the cylinder even less than the intake valves? 0.394 vs 0.432, seems real odd, especially 6 out of 8.

4drgl

So here's the deal...

I went to the shop to see the bent valves for myself... The valves have a very very very slight ding on them...

the mechanic suggested, that possibly the valves got stuck (because the po was trying to fire it on old gas at least 12 months old if not more, and the valves got stuck from the old fuel), and they were tapped shut ever so slightly by the pistons, causing them to be tweaked just enough that they wouldn't close....

Or the carbon built up around the seat not allowing the valve to seat properly.... Who knows but whatever caused it was slight.

1 Intake
6 exhaust

7 total valves bent just enough... to require replacement...

I asked again about the heads and he said they were in great shape and no evidence of overheating, I talked to the mechanic (had to be at least 70!) he said they're the nicest heads he's seen in a while... He's going to inspect the springs again tomorrow. Too bad they need valves! The bent valves were in both heads... I don't remember which head the bent intake valve came out of...

IcemanG17

this is quite odd.....very rarely seen in 4.5L engines.....it seems excessive carbon build up is typically the culprit.....

piperporsche180944

My offer still stands

Mark Anderson

I have a limited supply of new valves for $15 ea.

Mrmerlin

I took a look at block and the cams the number on the back of one of the cams was 174 01, could this be a Euro cam??
Another, question are the tolerance group numbers supposed to be matched at the top of each piston and then also along the top of the block on early pistons??
On this block the tolerance number on the piston is facing towards the girdle , and the tolerance number on the block is along the top edge in the V
isnt there also supposed to be an arrow that tells what way the piston is installed to the front of the block??

Found some cam specs in this thread
https://rennlist.com/forums/928-foru...hlight=+174+01

docmirror

Ok, the stuck valve theory is actually pretty good. We run into that with piston aircraft engines from time to time, and being that the exhaust suffered more than the intake, that would also fit the idea. I think you may have found it.

4drgl

I was going to grab the camera and forgot it this morning...

I've literally built another vw waiting on the heads for this project!

jwillman

So are there any lessons learned here for recent buyers of older 928's?

I have a 1979 showing 160,000 miles. Car would start by pouring fuel into inlet when I bought it. The car had a busted clutch line so I have not driven it since purchased in April. I have gone through clutch and brake systems before I put those back togather and refill the hydrualic system.

I have also had to drop the fuel tank (drained first) to resolve a spinning threaded insert and failed in-tank pump.

Should I be considering pulling the heads and looking inside the engine before I run it? What else should I check engine wise to avoid causing myself major heartburn?

Tampa 928s

I have rebuilt four non-runners and never had a problem, does not mean it would not happen. I would remove the plugs and turn over by hand and look for binding. Seems like you are looking for problems that a rare, at least that is what I feel, take it for what its worth.