Cobra4B

Last night I installed my '04 LS6 springs in my '01 Z06 as part of the work I'm doing. I followed the instructions off of www.ls1howto.com under their F-body cam/spring swap.

Everything went fine except for the #6 exhaust valve seems to not fully seat now. Here's what happened:

*Hooked air compressor to spark plug hole
*Increased pressure to 70psi (how-to says 60-80)
*Normal dull hiss from air getting out of cylinder like all others
*Hooked up crane spring tool
*Compressed tool... the valvestems didn't want to come out of the retainers at first. As I was pushing down initially the valves opened a bit like all the others.
*As I backed off the compressor the valves closed, but the exhaust valve is somehow still letting air out of the port.
*I proceeded to swap the springs and play w/ the valve but now it's not making a full seal.
*I took it apart again, removed the valve seal, and ran the valve up and down in the guide a few times... feels fine.
*Put it all back together and still air comming out of the exhaust port.

Conclusions... at first I feared bent valve, but if it was bent I'd have known that driving the car for sure. Second, if it was bent and not sealing properly then when I first hooked up the air it should have been hissing, this was not the case.

I'm clueless? Could a bit of carbon lodged itself in the valve seat? Is this a "normal" thing when swapping springs in this manner that will go away when I fire up the car?

Any help would be appreciated

Cobra4B

any input from the tech heads?

XPC5R

If it was a bent valve, you might not have noticed it driving. It may only manifest as a little extra valvetrain noise. I ran a whole season in an old race car with ALL the exhaust valves bent from an over-rev/valve float event.

Sounds more like a piece of carbon got lodged, either at the seat, or maybe on the stem itself (on the backside of the valve). There is a small chance the exhaust valve or valve seat is burned (has a superheated spot where the seal failed), but that should have leaked air when you initially compressed the cylinder.

One method of seating/loosening the valve spring/reataner/locks is popping the valve tip sharply with a hard plastic mallet. This will cycle the valve a few millimetersand let it settle on the seat under spring pressure. This also works just before valve spring removal to break loose the locks/retainers.

BlackZ06

Only possible (and I think this is extremely unlikely) way you could have damaged the valve was if the piston was at Top Dead Center and you drove the valve into it with enough force to bend the valve. But I can't see how this should happen as you're compressing the spring ... so ..... I'd have to think something got in there and contaminated it. Maybe someone else has experienced this ?

vettenuts

I was thinking the same thing, but, if you used any force (hammer) to loosen the locks that might do it. As for carbon, if you have a compressor blowing by the valve I would think that would dislodge the carbon. Other option would be to lower the valve by hand and blow some WD-40 into the spark plug hole to see if you can dislodge any carbon, assuming that is the issue.

pro1955

I had the same issue, on a diff. car this worked great, you could also do the decarb procedure.

Cobra4B

I doubt it... as soon as I started cranking the springs down air came out, then when I backed it off it kept comming out. So I did it a few more times all while tapping the retainers w/ my wrench trying to loosen them.

Hmmm... I've only overrevved the car one and that was back in '03 when I stuck it in 2nd from 3rd at 65 mph... I caught it before it ever truly overreved.

I have a rubber mallet and I'll ttry tapping the valves with it. Do I have to worry about bending a valve at all?

I agree that if it was bent it should have leaked initially... not after the first compression. The #8 cylinder actually did it too... but then it re-sealed. WHen I first let it back up it was still hissing out the exhaust port, but then stopped. Which leads me to believe carbon... also becuase the intake ports aren't gving any issue.

The car has been dyno-tuned but set for a road-race safe 12.5:1 and plenty of enrichment to keep things cool at the track.

Cobra4B

I only tapped down very lightly on the retainers w/ my wrench. I'll use my rubber mallet from now on.

I made sure not to whack on the valve stems at all. I took it apart again and removed the valve seal... I then ran the valve up and down in the valve guide by hand... it felt fine and felt like it was seating.

0Randy@DRM

Just hit that valve square as you can. Give it a good hit and try putting air in again. If this doesn't work. Then grab your 15 mm socket and start taking your head off so you can install a new valve.

Randy

vettenuts

Did you pull it up against the seat and then rotate it by hand? That might help if its just dirt. If you lower the valve, can you see it through the spark plug hole? You can check it for burnt spots if you can.

Any access to a boroscope, you can check the piston for an eyebrow.

Cobra4B

Not what I want to hear... the thing is I don't see how I could have possible bent the valve. Like I said it didn't leake when I first started adding air to it. Only once I copressed it then let it back out.

The car has a stock cam... so there's no way the piston could hit the valve.

I mean I guess I could have cranked it down to far and hit the piston, but the intake valve is larger than the exhaust valve... so if that was the case the larger diameter intake valve would have made contact first right? (I'm useing the crane dual tool so both go down at the same time) The intake valve is sealing fine.

Cobra4B

No boroscope... I'm going to take it apart again... and then try some wd-40 and rotating it like you've said.

Cobra4B

ttt... anyone else ever run into this?

RonSS

In the end you have two choices. Put it back together and see what happens or pull the head and eyeball the valve. I’d put it back together and see what happens. Yes that’s easy for me to say when it’s not my car but that’s still what I would do. Good luck either way.

Cobra4B

^ That's kind of how I'm leaning... I can't see how the heck I would have bent a valve.

It's not that much work to put it back together... so I figure I'll try cleaning it out tonight and see where I get.

Plus I have the '01 solid valves.

0Randy@DRM

The exhaust valve hits first. Because the piston is chasing the valve back up. Intakes open up when the piston is going down.

Yes you may have a bent valve with a stock cam. It happens all the time. Miss 4th and hit 2nd= bent valve.

Randy

ajg1915

Just for your info, all vettes have interference motors (i.e. if the timing chain breaks, jumps a link, cam walk, etc) your valves will hit the pistons.

Hopefully, that not the case in your situation. Put together and see if it works, elsewise off with the head.

Cobra4B

^ Randy I can see that happening when the valve train is all hooked up and the valve operation is controlled by the cam driven by the crank.

However... right now the piston is stationary, and I'm using the crane spring tool which looks like this:



So... you compress both valves at once in this case. Both springs and valves are moving down at the same time... so I'd think in this scenario the intake valve would hit first because the piston is stationary and they're both going down at the same time.

It shouldn't matter... becuase as I said when I first hooked up the air there was no leaking... then as i marginally comressed the springs and both valves opened some I stopped... tapped on the retainers, then let it back up only to have the exhaust still hissing. I thought it was odd and that the plug fitting had come loose.

I'll probably clean it up as best I can and hope I can figure this out... I'd hate to have to pull the head.

Cobra4B

ttt... this is fun

BlackZ06

Cobra4b

Here's my thinking ....

1) Unlikely you had a bent valve before you started .. as you point out, it wouldn't have sealed when you hit it with compressed air the first time

2) While possible you might have bent it changing the spring (Hit that valve hard enough with a wrench/hammer and if piston at TDC then MAYBE you could do it). But sounds like you had the two valves connected with the spring compressor, so as you say, you'd bend the intake first ... so pretty unlikely you bent it.

3) Since the rocker arms are off, I don't see how, even if you have the cam/crank chain disconnected, spinning the motor is gonna be a problem as none of the valves can depress without the rockers.

4) I like (sorry, didn't note who it was) the advice about nailing it with WD40. Only thing I can add to that is IF you really put a lot of oil past the valve, I'd crank the engine (preferabbly by hand) with the spark plugs OUT so that any excess oil can get out. It is possible to hydrolock the cylinder with the starter motor if you have a liquid in the cylinder and the spark plugs are installed.

Keep us posted, we're ALL pulling for ya !!!