evangood69

So pic is a 2.0t ltg exhaust valve on from a 15 ats. This is the third broken exhaust valve we've had on a third different cylinder head on the same car. so the mods on this car are stage zzp two cams, 82# springs, z 54. the first broken valve went two years, and now the last ones now go about 2 miles before they do it again. It's been a different head every single time. The car had a stock turbo on it before, on the first two failures. And on the third one, a larger turbo to reduce the exhaust back pressure. the failure happened at 4500 revolutions per minute. What's interesting is the break is about a half an inch away from where the retainer holds the valve. You would think it would break like right there where the valve is the smallest, but it's way below that. And going from that stock turbo to a z 54 eliminates a ton of back pressure getting away from heat from the valve. The other thing to know is it's been a different cylinder every time. Three different cylinders, three different heads, two different turbos, off the shelf Springs and retainers. Typical stuff that is used in 100s of builds. new valve springs and retainers. factory cat back. The most recent head was a zero mile GM head off a crate engine. the cam phasing wasn't even wild. There was no overlap, you know, 15 degrees and ten at the failure.



Anyone else got an idea??

The breakage point almost seems like the spring is pulling the valve apart, when pull the valve cover off, the valve spring still sitting in the pocket, the rocker arm still holding it down, you otherwise wouldn't even know that there's a valve that's been dropped in the cylinder. the keeper's still there, the retainer's still there.

Gumby22

Has it been the same cylinder each time, or are the valves breaking on different cylinders? If the same, which cylinder?

Have you had the bottom end apart to inspect the crankshaft, main bearings and connecting rods?

Have you properly measured the head sealing surface on the block to verify it’s not warped beyond specification?

evangood69

Different Cylinder Each time. 3 different cylinder heads each time too, used a a 0 Mile GM reman and still happened. Valve spring still in pocket after failure like its still there. Car runs perfect other than this happening. Not sure if bottom end has been taken apart(I am passing along Info, trying to help diag), but car idles and ran fine up till failure around 4000-4500.

Lasted 2 years before happening, now only lasts couple miles before same failure in different cylinder. .

Gumby22

If it’s that frequent, either there’s something wrong with the bottom end - worn crank bearings, bent connecting rod, loose wrist pins, etc - or the wrong performance kit/parts are being used.

Are there any witness marks to indicate the valves and piston are making contact? It’s usually pretty obvious on top of the piston, if not the valve face.

I don’t know anything about zzp kits/products, but if all the mods were top end, I’d do a thorough inspection of the crankshaft, rods and wrist pins/pistons. If it’s in good condition and nothing is out of spec (which I’d be surprised if that’s the case), I’d verify the performance kit is correct.