Valves hanging open at high RPM?

[shackwrrr]

This has been driving me nuts ever since I put my van together. I have this problem where if I go over 4000rpm under boost the engine just flat out looses power and quits pulling. When I let off to shift it will either die or chug along on 1 or 2 cylinders and sound like a subaru. If I get on it again it continues to missfire and run like crap, its only until I let it idle that it slowly "clears up". Today it did it and it died completely, probably because it was stone cold after start up, when I tried to start it the engine just free spun with no compression at all, slowly one by one the cylinders started to fire and away I went and it ran like nothing happened. It seems to me the valves are sticking open or something with the valvetrain is holding the valves open when the engine gets spun too high.

I thought for a while that I was blowing the valve springs open, I have 3.3 conicals and I have no idea if the previous owner shimmed them or not. Other than the valve springs the cam and lifters are stock.

Anyone ever experience this?

[shackwrrr]

Was doing some reading on this and I might have myself a combination of issues. I could be blowing the weak valve springs open at 18psi and when they float the lifters pump up to compensate for the increased lash, now when the valve tries to close the lifter is too far out for the valve to close all the way creating a miss.

Any input on this theory?

[GLHS60]

100% good theory.

Thanks
Randy

[zin]

Seems plausible, any idea what the seat pressure might be? I'm guesstimating close to 40 lbs of force acting on the valve at 18PSI, might be enough to let the lash adjusters "pump up".

Mike

[Vigo]

I agree with Randy, your idea sounds plausible and even likely. I cant think of any other way that you could have 'no compression' and then slowly get it back. In fact, it's an impressive bit of diagnostic thinking on your part!

[iTurbo]

How about switching back to stock stuff for a test? All these threads of people running PT lifters, springs from xx application, shims from Bob Marley himself....etc makes me wonder. I'd switch back to stock stuff to rule stuff out all I'm saying.

[bgbmxer]

There is a still a valve lash spec for the stock stuff and I remember when I was shimming my pt lifters I had to make custom thickness shims to get the correct lash so the valves wouldn't hang open

[shackwrrr]

How about switching back to stock stuff for a test? All these threads of people running PT lifters, springs from xx application, shims from Bob Marley himself....etc makes me wonder. I'd switch back to stock stuff to rule stuff out all I'm saying.

I wish I still had some stock stuff to throw on there. I had a whole head that was cracked that I scrapped a while back but I was in that mode of convincing myself that I wouldn't need any of it (or I had just watched an episode of hoarders lol). I may ask my buddy if he's got a set.

[bgbmxer]

I wish I still had some stock stuff to throw on there. I had a whole head that was cracked that I scrapped a while back but I was in that mode of convincing myself that I wouldn't need any of it (or I had just watched an episode of hoarders lol). I may ask my buddy if he's got a set.

What thickness shims did you use

[shackwrrr]

The previous owner put the valve springs in, I dont know what the shims are that are in there.

[bgbmxer]

The previous owner put the valve springs in, I dont know what the shims are that are in there.


Could pull a lifter out and see what they shimmed them to.

[turismolover22]

If you have the stock lifters, you can have a set of stock springs and seats i pulled from a 2.2 turbo 782 head.

[4 l-bodies]

Did the exhaust guides get changed at some point? Any backfires? I bought a GLHT a long time ago from someone supposedly very knowledgeable on our TM's and they were running conicals. This was like 15+ years ago. Car would just not rev past 4000K at any boost level. Took valve springs out and had them checked. 60 PSI closed seat pressure! No amount of shims were gonna fix these (hehe). Fix was to install low tech correct valve springs with around 120 PSI on seat. I think you're on to your problem.
Todd

[shackwrrr]

Did the exhaust guides get changed at some point? Any backfires? I bought a GLHT a long time ago from someone supposedly very knowledgeable on our TM's and they were running conicals. This was like 15+ years ago. Car would just not rev past 4000K at any boost level. Took valve springs out and had them checked. 60 PSI closed seat pressure! No amount of shims were gonna fix these (hehe). Fix was to install low tech correct valve springs with around 120 PSI on seat. I think you're on to your problem.
Todd

I'm not sure on the guides, no backfires though. I do believe that the 3.3 springs are close to 60ish.


If you have the stock lifters, you can have a set of stock springs and seats i pulled from a 2.2 turbo 782 head.

Thank you, I'll let you know if I don't find any locally.

[shackwrrr]

Just an update to this thread, just got done putting in a set of 26995 comp springs. All my problems have gone away, even the noise I always thought was piston slap got quieter. Nice to be able to take it to recline now.

[GLHS60]

Appreciate the up date. There is a fine balance between the hydraulic lifters ability to absorb valve spring pressure and your 3.3 springs were obviously under that limit.

Thanks
Randy