L76 valve lash

[William F.]

Both my current Corvettes have hydraulic cams, but I'm looking at a '65 L76. Just asking, with all the threads and controversy about setting valve lash cold-.023 vs .030, getting cam on base, etc, why not just do it like in the Chassis Service Manual-"running and hot"-can put clips over rocker arm to prevent oil mess? Can use old trick on SB's -get steel valve cover from junk yard and cut out most of top to further prevent mess while setting lash.Again, Just asking.

[Joe C.]

Re: L76 valve lash

Both my current Corvettes have hydraulic cams, but I'm looking at a '65 L76. Just asking, with all the threads and controversy about setting valve lash cold-.023 vs .030, getting cam on base, etc, why not just do it like in the Chassis Service Manual-"running and hot"-can put clips over rocker arm to prevent oil mess? Can use old trick on SB's -get steel valve cover from junk yard and cut out most of top to further prevent mess while setting lash.Again, Just asking.

Try it and tell us if you splash/spill/lose 2 quarts or only 1 quart of oil.

"Cold" v "hot" settings on an iron block engine with iron heads are virtually identical.

Warm the engine, shut it off and let it cool to the point that you don't burn yourself, and then set them.

I like to set them at .025/.025, but you will get VEHEMENT arguments supporting a .030/.030 setting as well. The theory behind the .023/.023 setting makes sense, and the original engineering drawings back them up. Setting at .030/.030 will not do any harm. What it WILL do (if you like that sorta thing), is tame the 30-30 cam by lowering its lift and duration./overlap. This results in a smoother idle with higher vacuum. It also results in noticeably more low/midrange torque, but with a much faster dropoff of torque from the torque peak (loss of horsepower).

[William F.]

Re: L76 valve lash

Like I said, I haven't tried it but do you lose all that oil IF you put clips on the rockers and do it with the old valve cover with top cut out installed while your're doing it hot, or are you just going at it "like you're killing snakes?"

[William C.]

Re: L76 valve lash

Actually the cool-down rate is not so horrendous that with a hot engine you can't set them easily before it cools significantly if you start the process right after shutoff.

[Larry M.]

Re: L76 valve lash

Like I said, I haven't tried it but do you lose all that oil IF you put clips on the rockers and do it with the old valve cover with top cut out installed while your're doing it hot, or are you just going at it "like you're killing snakes?"

There are many ways to "skin this cat". Your recommendation will work well, and should have minimal oil loss.

I have always had trouble doing it "hot and running" due to both the oil loss and the valve stem / rocker arm wanting to grab and hold my feeler gage. My father, who was a professional auto mechanic, always did this job with the engine hot and running, and he never had problems. I prefer to have the engine down and cold......but that is just me. I feel that I can do a better and more accurate job with this way.

Larry

[Joe C.]

Re: L76 valve lash

Like I said, I haven't tried it but do you lose all that oil IF you put clips on the rockers and do it with the old valve cover with top cut out installed while your're doing it hot, or are you just going at it "like you're killing snakes?"

Of course, I'm "embellishing" a bit here. Not 1-2 quarts, but you'll lose a few ounces of oil. The point is, most of it gets on the exhaust manifolds, which then smoke like hell, and the rest drips down the sides of the engine. It's just, plain messy........................clips, special covers and all. Trust me on this one. The more important point is that you lose the accurate "feel" with the motor running, as Larry said. I never had many "solid" cars as a young man and never developed the necessary "feel" for doing them hot and running. There is definitely more than a little technique involved in doing it that way "painlessly". That's a lot of oil spilled and smoky garages to endure during the learning curve.

[Michael H.]

Re: L76 valve lash

William,

As an experiment, try setting the valves to specs on just one cyl when the engine is thoroughly warmed up, then shut it down for the night. In the AM when the engine is cold, measure the lash again on the cyl that was adjusted to see just exactly what the difference is.

The difference between hot/cold setting has more to do with the expansion of the valves than the cast iron of the block and heads. The valve temperature can change the lash more than anything but as soon as the engine is shut down, the extreme heat in the valves quickly transfers into the head.

Once you know what the rate of change is between hot/running and cold, you can then adjust valves cold/statically using the settings you have from the test.

Remember, valve stem expansion tightens lash. Valve head expansion loosens lash.

[Stuart F.]

Re: L76 valve lash

I have a set of clips if you want to try. I haven't used them in about 50 years - since my last attempt in a garage with both doors open in the middle of a Wisconsin winter. I got so sick from the fumes that I thought I was going to die. Effects lasted a whole week. I'll tell you one advantage; if you have a badly worn rocker (more common with forged rockers than stamped steel), it will have a groove worn in it and it will punch holes in your feeler gauge so you will know for certain you have a bad rocker. Save your health and sanity, dry set them.

Stu Fox

[Duke W.]

Re: L76 valve lash

William,

As an experiment, try setting the valves to specs on just one cyl when the engine is thoroughly warmed up, then shut it down for the night. In the AM when the engine is cold, measure the lash again on the cyl that was adjusted to see just exactly what the difference is.

The difference between hot/cold setting has more to do with the expansion of the valves than the cast iron of the block and heads. The valve temperature can change the lash more than anything but as soon as the engine is shut down, the extreme heat in the valves quickly transfers into the head.

Once you know what the rate of change is between hot/running and cold, you can then adjust valves cold/statically using the settings you have from the test.

Remember, valve stem expansion tightens lash. Valve head expansion loosens lash.

If you really want to set them "hot and running", do it on a dyno at WOT with the engine at redline.

The valves aren't that hot at idle and stem expansion is virtually undetectable. Under high load the stems will expand. That's why solid lifter cams have generous clearance ramps.

Of course, if you check the the cold clearance on a 30-30 that was set "hot and idling" at TDC of that cylinder they will be .002-.003" tighter because the lifters are on the clearance ramps, not because the stems have shrunk.

From the beginning of the opening clearance ramp to the end of the closing clearance ramp, the 30-30 cam is about 540 crank degrees, so the base circle covers only about 90 degrees of the cam lobe.

Duke

[Dan D.]

Re: L76 valve lash

50 years ago I used to set the valves hot and running. That was the hot setup back then, and we believed that was the only way to get accurate results.

But I soon found out that the oil got on the manifolds, smoked real bad, and much loss of oil. So I developed a way to do it. You had to be creative back then. I placed a piece of sheet metal (clean of course) on the inside bottom lip of the head. The metal rested on the manifold at an angle and diverted the oil back into the head. With a little practice you could do the whole bank in a matter of just a couple of minutes. Worked great! -Dan-

[William F.]

Re: L76 valve lash

Thanks for all the help from those of you who have the experience. Sounds like cold is the way to go.

[George J.]

Re: L76 valve lash

I think you guys are denying him a "valuable" learning experience. Everyone should try setting them hot and running once. Then there would be no explanation necessary. I tried it once and thought, "how the heck do people do this? There HAS to be a better way."

George

[William F.]

Re: L76 valve lash

I'll take most everyone's word that doing it cold or at least not running is the way to go and skip the "valuable learning experience."
Thanks again

[Clem Z.]

Re: L76 valve lash

if the lash is to be set hot get the engine up to temp and with the engine off set one cylinder. the next day recheck that lash cold and set the rest of the valves at the cold setting you find.

[Michael H.]

Re: L76 valve lash

if the lash is to be set hot get the engine up to temp and with the engine off set one cylinder. the next day recheck that lash cold and set the rest of the valves at the cold setting you find.

That's what I said in post #7.

Once the lash change is known, the valves can then be set cold from then on and eliminate the oil bath.

Hot and running isn't the same as hot and not running.