[RHD ZL1]

Sorry to hear about your engine. Never good to see a fellow enthusiasts having engine issues.

It does look like there are witness marks in the squish band where the marks seem to line up with the marks on the piston. Year ago i seen the same thing happen (same issue different type of engine) and it ended up being a small part of the valve guide braking away and getting caught between the valve and valve seat which was enough to bend the valve slightly and then the broken piece of guide made its way into the chamber and damaged the piston/squish band on the head very similar to your pics. The only way you could tell if it is the valve guide is to remove the valves and inspect the guides. I’m not saying this is definitely the case with yours, just that it looks very similar to what i had seen happen on another engine.

[cmitchell17]

Originally Posted by RHD ZL1

Sorry to hear about your engine. Never good to see a fellow enthusiasts having engine issues.

It does look like there are witness marks in the squish band where the marks seem to line up with the marks on the piston. Year ago i seen the same thing happen (same issue different type of engine) and it ended up being a small part of the valve guide braking away and getting caught between the valve and valve seat which was enough to bend the valve slightly and then the broken piece of guide made its way into the chamber and damaged the piston/squish band on the head very similar to your pics. The only way you could tell if it is the valve guide is to remove the valves and inspect the guides. I’m not saying this is definitely the case with yours, just that it looks very similar to what i had seen happen on another engine.

Thanks for the info, I guess you tore the engine down and replaced the piston?

From trying to look into the intake port with a flashlight behind the valve on the combustion chamber side, it looks like a piece is missing from the valve seat, so yes it looks like that came off and got chewed up in the cylinder.

I don't even know if TSP puts their own valve seats or they use the stock ones or what? I have the PRC heads, I know TSP doesn't give their customers much info besides some fancy sales pitch description, it was hard enough to get them to tell me how much they milled from the head (.030). I am wondering about the quality of the seats they were using, I just can't find any failures, well besides the one you just mentioned, like this. I mean everything is bent rod or broken ringland.

[95 imp]

try a small block of wood (plywood) under the valve head and smacking it again. There might be too much give on the spring to shock it loose.

It might be from detonation.

It can cause those pock marks and bend valves (as well as other things).



This link shows pock marks in the squish area like yours
http://pcwww.liv.ac.uk/~goodhew/stud...e%20Repair.htm

After blowing up the pics of CC side of the intake valve I see pock parks in the CC and by the seat

My vote is with s346k... Pull the piston...

[RHD ZL1]

Originally Posted by cmitchell17

Thanks for the info, I guess you tore the engine down and replaced the piston?

Yes, the customer decided to rebuild with rods/pistons. Slightly off topic, the engine at the time was an RB26 from an R32 GTR. At the time (15 years ago) i had just finished calibrating the ecu. We took the car off the dyno after finishing the cal, parked it for a few hours till the customer arrived and then went for a street test drive with him. We literally got 3 miles of driving into the test drive, stopped at a red light and then out of no where could hear a ticking noise that i assumed was coming from a diesel truck next to us. Once the light went green we then realised it was coming from us as the noise was in sync with engine rpm. Just proves that when a faulty part decides to fail, it can happen at any time, spent 3 hours on the dyno with nil issues and then while idling at a set of lights part of the stock valve guide lets go!

Personally i doubt it is due to det (I could be wrong), that said, how far have the knock sensor settings been desensitized in your calibration? Is there a decent safety buffer between your high and low octane tables? How far have the knock learn thresholds been adjusted? Are the “Burst Knock” tables in your cal been totally disabled? Surly if you experienced such heavy knocking that the OEM sensors would register the knock and act accordingly if the calibration isn’t overly desensitized. I could be wrong but the indicated marks on the piston in your pics does seem like some foreign material has been caught in the squish band more so then heavy det. It might be a good idea to number each fuel injector as per cyl and have the injectors flow tested. If you find that the inj that has the damaged piston is in fact flowing less, then it could have been due to det in that cyl due to running too lean.

[95 imp]

Originally Posted by RHD ZL1

Personally i doubt it is due to det (I could be wrong)...

You could be right!

I'm just trying to figure out how the marks got there in the absence of anything foreign in the cylinder. I guess if it blew in from the intake it could blow out the exhaust too.

Conversely, it doesn't explain the bent valve since there are no marks in the valve pocket.

We'll have to wait for the intake valve to come out....

[L78toLT1]

Try taking a small punch, or better still a brass drift rod and give the edge of each keeper a light rap to dislodge any residue that may be preventing the kerpers from falling off. Sqiirting a little carb cleaner between the gaps in the keepers couldn't hurt either

[Choda]

get a real spring compressor. I fought my 660 dual springs for hours with hammers and sockets. One retainer shot out somewhere in the garage. Then drove 20 min to borrow my buddies and it literally took 10 seconds a piece after that. So then I had to spend 17 bucks on one retainer, wasted hours of hammer..... Go get the right tool man.

[vtirocz]

Originally Posted by Choda

get a real spring compressor. I fought my 660 dual springs for hours with hammers and sockets. One retainer shot out somewhere in the garage. Then drove 20 min to borrow my buddies and it literally took 10 seconds a piece after that. So then I had to spend 17 bucks on one retainer, wasted hours of hammer..... Go get the right tool man.

I agree 100%.

[L78toLT1]

Originally Posted by vtirocz

I agree 100%.

I concur. You're going to need a proper compressor eventually.

[cmitchell17]

This one seems way overpriced, but is there a specific one that is better:
https://www.ebay.com/itm/Valve-Sprin...AAAOSwzTFcDtzh

Also I got it off:

[95 imp]

Obviously the seat is toast and that's where the piston/head damage came from...

Did you have valve float?

What does the exhaust seat look like?

[laynlo15]

Man that sucks. At my age my johnson has failed a few times half way thru the event.

[cmitchell17]

Originally Posted by laynlo15

Man that sucks. At my age my johnson has failed a few times half way thru the event.

Haha, lets hope it wasn't that.

The exhaust side looks fine:




I know the exhaust valve retainer and lock were a lot easier to get off. I don't know how I would know if I had float? I guess given how hard it was to get this lock off the valve maybe that the tale tell sign, i'll have to try to pull the rest of them and see if they are as easy.

Does anyone know what TSP does to the valve seats on PRC heads? Do they replace the stock ones or use their own, or just port whatever you have if it looks good? Does anyone see the seat being an issue here or the porting?

Maybe it initially had a sealing issue at took a year and 15-20k miles to finally burn out?

If I am going to pull the piston, I would rather just get aftermarket ones I guess and if I am going to fix that I might as well fix the heads and they are already milled .030, so I might as well just buy aftermarket ones. And if I am going to do that I might as well do a stroker crank, just seems there is a lot of different info on what you can and can't do or what you could do and you probably shouldn't.

[laynlo15]

Originally Posted by cmitchell17

Haha, lets hope it wasn't that.

The exhaust side looks fine:
Attachment 1059690

Attachment 1059691

I know the exhaust valve retainer and lock were a lot easier to get off. I don't know how I would know if I had float? I guess given how hard it was to get this lock off the valve maybe that the tale tell sign, i'll have to try to pull the rest of them and see if they are as easy.

Does anyone know what TSP does to the valve seats on PRC heads? Do they replace the stock ones or use their own, or just port whatever you have if it looks good? Does anyone see the seat being an issue here or the porting?

Maybe it initially had a sealing issue at took a year and 15-20k miles to finally burn out?

If I am going to pull the piston, I would rather just get aftermarket ones I guess and if I am going to fix that I might as well fix the heads and they are already milled .030, so I might as well just buy aftermarket ones. And if I am going to do that I might as well do a stroker crank, just seems there is a lot of different info on what you can and can't do or what you could do and you probably shouldn't.

Sorry, couldn't resist, I've had several failures during my Camaro years, broken ring lands on the original Lt1. Bent valve on my Manley forged motor and then after I fixed that the same motor broke the snout on the crank. Man
the shit that does break hurts the wallet and down time.