built91Z28

I took my car to the track for the first time Friday night. The car had massive traction problems and the times were absolutely terrible so the exact times it ran dont matter. The motor didnt feel as strong in the upper rpms as I thought it should. I pulled the valve covers today to check the valve lash (solid roller cam). My lash was fairly loose. It wount up being .025 cold when it should be .020 hot. From what I've read, that would mean it should be about .015 cold. I also noticed that I had two flat lines across the tip of the valve that were about 30 or 40 degrees difference from each other. I also noticed a complete circles going around the tip of the valve. I'm running Canfield heads which do not have the valves in the factory locations. I also noticed that the side of the roller on the tip of the rocker is whats touching the tip of the valve.

Would the circles on the valve indicated valve float? Could this have been because of the lash getting way too loose? I revved it to about 63 to 6400 rpm.

AlkyIROC

Valve float is from weak valve springs. The cam pushed open the valves but the valve springs close the valves. At high rpms, the valve can close so fast that it will bounce on the seats. When the valve bounces, it allows compression to escape and power is reduced. Having valve springs with proper seat pressures for the cam will control valve float. Valve springs don't last forever. They will lose their tension over time.

Setting the valve lash on aluminum heads should be .006" tighter than the recommendation when set cold. As the heads heat up, the lash will tighten up.

Valves do not normally rotate. OEM exhaust valves have a rotater to make them rotate to reduce the chance of hot spots. At least the BBC engines have them.

Have your valve spring pressures checked and compare them to the recommended springs for your cam. Replace if required. Reset your lash and try again.

built91Z28

I reset the lash today. I have brand new springs. When I did the cam swap (it was 2 years ago but only 200 miles or so) I bought everything brand new that comp recommends for my cam and had a machine shop install them at the recommended installed height. Dont know if they check the spring pressure though.

The fact that the valve lash was roughly .010 too loose couldnt have let the valve bounch when closing and spin?

Also, if it comes down to it, which is more important? Installed height or spring pressure when closed?

built91Z28

Heres what the tips look like. The valve that has two straight lines on it, I'm not really worried about. I forgot that it could have been due to when I had these new springs put on and the valve not staying in the exact same spot while they were doing it. On the other valve though, I dont even see a line. You can just see a circle around the outside of the tip.





Should I get some very fine sandpaper and see if I can polish the tip, the run the car again and check the pattern?