996 GT3 - Equal leakdown out of both exhaust valves?

[cstreit]

Okay I'm stumped....

Getting low compression (obviously) and high leakdown out of my Cup engine. It's coming out of the exhaust.

Whats weird - is that it's coming out of both exhaust valves at the same time. As if the cam wasn't closing them properly. It's only on one cylinder. Why would both valves do this? They don't share a lifter, spring, etc...

Baffled.

[DRACO A5OG]

Carbon build up? Have you removed your headers to see what the ports look like?

[cstreit]

Yes. Valves look nice. Most likely that they are both bent I guess.

Purely a race engine run on 100 Octane- so carbon is minimal.

[DRACO A5OG]

Damn, bent valves, what a nightmare :-( Sorry to read that brother.

[Steve@Rennsport]

What are your leakdown values????

Bent valves not uncommon, especially if you missed a shift.

[Walt Fricke]

A missed shift overrev in the engine's history? Is the fact that it is only one cylinder with this leakage the good news part of this good news/bad news story?

I gather that the reason you know both exhausts on that cylinder are leaking is that you pulled the header? Can't see how you could know it was both otherwise.

[Dan J]

It is extremely rare to bend valves on the GT3 engines. The valves are very lightweight being small and titanium
Is it a solid lifter motor or has it been converted to hydraulic? The mechanical cam followers wear the
cam carrier and can get hung up

[cstreit]

I'm pulling the engine for a refresh because it's got 80 hours on it. I did the leak down with the headers off. Even sprayed soapy water on the valves to watch. It's definitely both valves but only cylinder 2.

Overrev? Definitely. Several in fact so this is the most likely cause. When I wrote it it didn't occur to me that both valves would bend, but of course this makes sense.

[Steve@Rennsport]

Originally Posted by cstreit

I'm pulling the engine for a refresh because it's got 80 hours on it. I did the leak down with the headers off. Even sprayed soapy water on the valves to watch. It's definitely both valves but only cylinder 2.

Overrev? Definitely. Several in fact so this is the most likely cause. When I wrote it it didn't occur to me that both valves would bend, but of course this makes sense.

Solid lifters or stock hydraulics?

[cstreit]

Stock GT3 Cup legal engine.

[Dan J]

in mid 2001 Porsche changed from mechanical cam followers to hydraulic
many other parts were changed Cam carriers, rod length, crankshaft etc
Many of the parts for the early engine are no longer available
Cam carrier lifter bore wear was an issue on the earlier engine
Hope you have the later one