Ok here is the deal, this story is gonna be a little long winded but ill try to cut to the chase ASAP.

Just built a fresh motor, a iron block 6.0L with factory 243 LS6 heads and PRC dual springs. Had the block hot tanked, new cam bearings put in, all the basics. My prior cam had one lobe that was starting to gall, so instead of chancing it i ordered a new cam from Speed inc, a turbo grind they had on the shelf .581/.581 232/232 113lsa, Comp part # 54-000-11.

I also installed NEW GM LS7 lifters during the assembly, using my comp 7.400" PR's which proved to be just fine for preload on the other 7 cylinders. let them soak for 24hrs prior in 10w30 Using stock 1.7 rockers and pedistals.

Basically here is the deal, i got the thing running, it runs half way decent but had some issues right off the bat w/ how it ran and noticed the afr tanking into the 11's while idling so i took it out for a spin around the block and it vibrates like bitch! like running on 7 cyl and slow as ****. So i come back glanced at the header tubes which i just polished, 7 of them were turning color nicely already except for #6, there is the smoking gun... pull the plug and it has never fired ONCE since i had it back together. So i throw the inline sprak tester on, plenty of spark not one miss, the plug was soaked with fuel too. Well one last thing to check, pull the fuel pump fuse and thread the compression guage in and wing it over... Big 0!!! WTF!!??? so i put the leakdown tester on it now and pull the rocker cover and make sure to get it at TDC compression stroke. Open up the LD tester and its all blowing back into the intake and i can change the tone by opening the TB. So i wiggle the rockers and th ex valve has allowable side to side movement like the rest of the valves on that bank that are closed,so i move to the intake rocker and its tight, so i loosen the bolt a couple turns and it lets the intake valve close and the motor rolls over from the compressed air. Tighten it back up again and it opens the valve about a 1/8th inch again.

So my next action was to roll the motor over to get it up in the middle of the intake stroke at max lift. Let it sit over night expecting it to bleed down, no change-same bullshit. after bringing it back to TDC. So my thoughts are one of the new lifters i got is stuck and thats not allowing for any preload into the lifter body. So being the logical thing to pinpoint, i removed the head and pulled the lifters out for #6, they look ok, pull them both apart and cant see any defect.... So i go back and bitch that one must have some kinda issue with it and got a new set warrantied, toss 2 new ones in #6 and lightly bolt the head back together and test it, seems to work ok, intake is still hanging just slightly but atrributed it to jsut needing to bleed off?, it was like a 1/2th turn on the rocker bolt at 0 lash to tighten it, but still wasnt "free" side to side like the rest.

So i get it all back together today and try it again, sure as ****, #6 still dead. same issue, same valve!

Not trying to be a conspiracy theorist here, but IS it possible COMP didnt grind the base circle right on ONE intake lobe?? I dont understand how the rest of the 15 valves and rockers and lifters in the engine can function correctly but this ONE is a repeat with 2 new lifters.

I couldnt accurately measure the lifter body height diff between the in and ex in the block and in the car...

Thoughts? suggestions? is that even possible that one lobe would have an issue like that?

This car makes me want to slit my wrists sometimes.

Thanks in advance.

 

anyone?

 

Either the base circle of the cam is different or that one valve is recessed further into the head. Pull all the rockers off and place a straight edge across the valve tips. If all the valves are the same height you'll need to pull the cam and measure the base circles. Both are very unlikely scenarios, but I can't see anything else that would cause the problem.

 

^^What he said. You might also want to verify your pushrod length (long shot). Also verify the rocker and pedistal condition. You might try swapping the rocker to another valve just to verify that there's no damage or inconsistency. This stuff sounds very unlikely but at this point you have to just verify as much as you can.

 

it souldnt be the BS.. it sounds to me like the valve is bent lightly or sticking tn the guide, did you fill the ports with thinner/ pull vacuum (red neck vs. correct method) to check for valve seal... it could be that once its pushed open the spring cant close it completely ....

bent valve
pushrod/head interference
dead rocker fulcrum
misalligned rocker/guideplate....

 

IDK how this happened, but i put a machined chunk of metal square on top of the intake valve stem and it stands a GOOD .100" higher than the ex valve stem. This must have been this way for a while... The spring looks fine except the coils are spaced ever so slightly further now that i looked at it close, i am so pissed i didnt look at this closer when i had the head off, i figured since it had nearly perfect Leakdown with the rocker loosened the valves were ok and never thought once hey maybe the intake valve deformed or the seat sunk.

How the hell does that happen? and i wonder how long its been like that prior!?!?

 

bent valve.... could be that yout PTV clearance is alittle too tight and the piston kissed the valve

 

To check for a bent valve, just take the rockers off the dead cylinder and pull the spark plug and hook a air compressor to it and see if you have air coming out of the intake or the exhaust port, If there no air coming from there pull the oil cap and see if you here air coming from there ( broke ring landing) Ive seen this happen because the ring gap was not wide enough.

 

Could it be that the intake valve stem is 0.100" too long? Pull two intake valves and measure them.

 

The valve is not bent though. With no rockers it has 10% leakdown. I looked at the valve face inteh combo chamber and the piston crown eyebrows when i had the head off, no signs of ever touching.

These are bone stock 243 heads w/o the longer valve stems and factory valves yet.

Its like the valve did an inside out umbrella routine to grow in height at the end of the stem and the dual spring has enough nuts to make it seal good enough for the LD test.

Or the seat came loose and or moved upward in the head somehow.

What a wreck... ughhhhhhh

 

Looks like the valve head deformed and the seat moved, its "dished: alot more than the others. Time for a set of TFS heads and YT rockers i guess.

Plate is rest square on the intake valve stem, the ex sits lower. Its perfectly level on every other cyl.


Affected Combo chamber, not valve head height.


#4 cyl ahead of it, note much higher valve height and less dished valve.

 

the valve in question looks smaller than the other intake valve. did you get the heads used? looks like maybe someone put the wrong size valve in that cylinder

 

These were bone stock low mile LS6 heads that i took off a car. That valve is tulip shaped now is why it looks smaller, its hard to tell from the pic.

 

Tom,
Maybe it's just the angle of the pic... but the one where you're holding the steel on the valve tip, it sort of looks like the lower one has more 'stem' sticking out above the retainer. Almost like the groove cut in the stem where the locks go are more toward the end of the stem than it is on the other valve.

Again, it could just be the picture.

It just seems like the valve doesnt match with the rest of them.

If you think about how the valve itself could have gotten deformed (compared to the other ones that are normal) the only logical explainations are the piston kissing it (which you said there were no marks on the piston), or the spring would have to be strong enough to PULL it to a deformed shape.... which doesn't seem right, does it?

So maybe the valve is different. Maybe it was something a dealer did before the owner of the car owned it... Who knows?

As long as the head is off, can you take the springs off and compare the valves themselves side by side? Take measurements?

Brian

 

Its the pic that kinda decieving, you cant get a good feel for the way the valve is now shaped by the pic. Either way, to the scrap pile and the TFS heads and yella terra's are gonna be on order in the next few days.