4drgl

Well... in my vw experience this has never happened. I always get buy used motors and swap them in (most often times, been sitting in someones garage for a couple years for a swap that never happened).... I always crank them over by hand first, and clean out the fuel rails... especially with the cis motors...

I'm a bit of a cheap skate when it comes to my vw's but the engines are a dime a dozen and the junkyards are full of spare parts... so it's not nearly as expensive/frustrating to repair them (at least everything from 04 and older)!!! I'm not speaking for the mk5/6 audi look alikes they're manufacturing now!

So this is a first for me as well.. I've had several heads redone, and never had any valve problems...

If could do over again... I would've pulled the engine from the getgo, pulled it apart and cleaned everything, replacing all my seals, done my valve job... pulled the fuel tank etc... cleaned lines... you get the idea. I would have spent the money checking things prior to.. instead of after the fact.

However this car was pretty well beat... albeit complete for the most part it was not taken care of... from top to bottom. It was my first 928 on a list of many p-cars I'd like to own... so live n learn.

So just be careful and use your judgement...

1. If the gas is 12 months old even with fuel stabilizer.. i'd get rid of the fuel.

2. Insist that the po not try to start the engine.. (my po was trying like he!! to get it started, and probly stuck the valves at that point).

3. Change the oil before you try and start the engine.

This is probly just a freak thing that happened due to this cars serious state of disrepair and neglect... If it's gonna happen I don't think there's much you can do to prevent it.

Pray to the 928 gods every so often maybe they'll smile upon you!

danglerb

Starting fluid can do some magic things in the wrong hands.

I'm still not getting how this could happen. Non interference means the valve at its lowest point doesn't contact the piston even at its highest point, so a valve "sticking" doesn't put it any lower, it just sticks at some point in the normal travel range and that should be safe. Six bent valves and its kind of ridiculous.

BTW how were the guides and seals?

SQLGuy

I'd say either sticking PLUS signifant carbon buildup on the piston crown or, more likely, over-rev.

4drgl

I didn't see either the guides/seals, didn't ask.

It could have been overrevved, but the pistons have no damage on them at all... Plus it's an automatic... Isn't it pretty difficult to over rev an auto unless you neutral drop it????

I usually only deal with standards.

There was plenty of starting fluid going around at that point.. PO used an entire can trying to start it that night...

If the motor was over revved how would that bring the valves any closer to the pistons that just under normal operating conditions???

I'm fairly new to 928's and even newer to serious valve train problems... so help me understand!! Please.... I'd like to prevent anything like this from happening again in the future!

ptuomov

The standard answer is that valve springs fail to keep the valves on the cam profile and the piston hits the lagging exhaust valves. This is standard answer, I have no idea whether the geometry of your engine is such that this is possible/likely.

SQLGuy

My recent bent valve engine is a motorcycle and it is, I think, an interference engine, so may not be 100% applicable.

In the case of the bike, though, there was no noticable damage to the pistons. All the intake valves, though, were bent to some extent, with #3 (of 4) being much more bent than the others. All four had nicks on the stems corresponding to where they were relative to the top of the valve guides at the time when contact occurred.

I would guess (just a guess) that an overrevved engine could lift the valves further than the top lift of the cam lobe due to inertia (i.e. the valve effectively flying into the cylinder before the spring can stop it). I can say for sure that if you downshift to 2nd in a 928 (at least in the '85 that I had) it WILL shift to 2nd at that point, regardless of whether it's going to go over red line or not.

Other than that, maybe if something bad happened with the lifters? Or, are the cams stock?

4drgl

Stan and I checked the cams, I read the link he posted up here this morning,

174.01 is the stamp # on the cam, and that's a stock US 80-82 cam according to that link...

So it's not the cams...

SQLGuy

Well, the stamp by itself doesn't prove things. There are a number of places that will do custom grinds on your cams. If you grind down the low part of the cam surface, you're effectively increasing the lift, since (up to a point) the hydraulic followers will fill the gap.

Shark Attack

well yeah, if he told you the heads were so-so... you may abondon the job and then they get no moony

4drgl

There's nothing wrong with the heads... just bent valves...

James Bailey

Still wierd. as noted you can cut the timing belt leave a numbser of valve fully extended and NEVER bend a valve. That is what none intererence means ! 944s are ALL interference and many many shops EXPECT 928s to be the same ! But once they have sold the head rebuild that is what the car gets....

Mrmerlin

I would suspect that the engine was over revved by the PO he didnt care a bit about this car, and since he was having problems keeping it running whats the first thing you do to an engine thats not wanting to run?? Rev the wee out of it.
Anyway with a very high RPM the valves floated and tagged the pistons, ( this is my thought of what happened) i couldnt find any marks on the pistons i didnt see the valves

danglerb

Does this model have a rev limiter?

Mrmerlin

it might in the distributor rotor but that begs the next question was it working??

S4ordie

Though there was no evidence of it couldn't water in the cylinders bend valves? I know it can bend rods. Compressed water does not give much and the pressure might have been high enough to keep the valve from being pushed into the cylinder and so therefore bent. Too much starter fluid could have flowed into the cylinders as a liquid, bent the valves and then evaporated or was purged in further starting attempts. Weak sauce I know but I sure can't understand how those valves got bent in a non-interference engine. I'm not aware of excessive carbon bending valves. I've seen it cause a valve to get stuck and then have the piston hit and bend it in interference engines.