Another wtf...

[Superdave]

I tore down my 3500 today and found a little problem..


Keep in mind, it ran perfect aside from smoking b/c of the valve seals. This is deffenetly a head scratcher. I was running Camaro 3.4 headgaskets which are around .020" thinner than the FWD ones. Exaust lift @ valve is .549 and 293 advertised duration, cam is 4 degrees advanced.

these marks are .034" deep, all 6 pistons have them. All from the exhaust valves. The valves are not bent and show no signs of anything, not even a clean spot.

I spun the engine during assembly and watched for any signs of piston to valve contact, saw nothing. Heard no weird noises on startup, no knocking or anything.. Hell, i might even have a datalog of the first start. Maybe the rods stretched a little too much on the many trips to 7000 RPM.






I had planned on upgrading the pistons, atleast now i know that i'll have to get valve reliefs cut in..

[3100 MPFI]

My 3100 did that when I built it, but it was a TIMING problem. My timing was off, and it DID damage my heads. I had to replace them both.

Keep in mind that when you tested the clearance, most likely, your lifters had deflated. Once the engine pumped the lifters back up, it probably hit.

When my timing was off, I ALMOST made it all the way around the block before the valves bent and the car would not restart.

[IsaacHayes]

Ouch. Lucked out again. Just piston damage.

[PCGUY112887]

Dang, I hope my 3500 is OK inside
I used more stock parts than you though... so hopefully I will be fine. Stock valve seals, stock headgasket, not turning 7k

I feel 6500rpm's is safe for my 3500.

[19Cutlass94]

ouchies! Well atleast you know about it now than when something happened!

So what are these upgraded pistons your getting?!

[Superdave]

Damon (V6bluebird) had a large cam in his 3400 and i guess there is small marks on his pistons as well.. i'll see if he can get some pics.

[El_Diablo]

smashed a piston into atleast my front head and only left marks on the piston and knocked off some of the carbon on the head in a circular ring

[3100 MPFI]

See the little indent in the rim of the piston (one on each side. KNICK on the LEFT, and VALVE RELIEF on the right)? That is what happend when I ruined my heads. Keep in mind it was a 3100 with the high compression pistons.



In my setup, I had the timing SLIGHTLY off, and that is what caused that. Once I replaced the heads, and fixed the timeing, it was fine, and I was CONSTANTLY pulling it up to 7,000 RPM. That 3100 was REALLY rev happy. With everything set CORRECTLY, it didn't give me ANY issues.

But still, when it DID it, it bent valves.

[AaronGTR]

Yeah, it sounds like having that cam advanced could be the culprit and/or the lifters not being pumped up when you checked it. I'd check the clearance with clay on the pistons next time too, just to be sure of exactly how close they are getting.

Amazing that the valves and heads aren't showing any damage from that. I wonder if the contact could have contributed to the valve seals coming off though? Might want to check the valve guides while you're at it.

[merlot566jka]

so before i put mine together i should probably cut some reliefs into at least the exh side? .533 lift on the exhaust with iron head gaskets

[treeZ24]

what was your calculated piston to valve clearance?

[PCGUY112887]

So I'm curious, how did you guys get your timing off so bad to help cause damage?

I am still running a stock 97 3400 timing setup on my 3500. Unless of course you mean mechanical timing... in that case I have mine set to whatever stock is.

[Superdave]

so before i put mine together i should probably cut some reliefs into at least the exh side? .533 lift on the exhaust with iron head gaskets

Check yours with clay to see if anything gets close.. Other people have ran lots of lift on these engines w/o problems.. mine might be the crazy duration plus cam chain stretch and the way the cam was ground..


Either way, my new pistons will have plenty of clearance after a trip to the machine shop... hehe

what was your calculated piston to valve clearance?

-.034"



My cam is installed straight up, it's ground 4 degrees advanced because it's a regrind. I didn't physically advance it at all.

there is also no excessive wear on the dampener.

[merlot566jka]

the guy at crane recomended .060 min, lol -.034 sounds like a prob lol.

ill check it with clay like i did with the iron head motor. how much duration did you run?

[95Grand-Am]

I wonder if you had a little valve float at high Rpms. If it was making contact all the time it should have been clean.