'70 L46 with LT1cam and solid lifters

[Barney Joe Flick]

Hello again,After reading through the archives,I can see that there are some people here who should be able to help me with this one.Allthough this motor runs strong,it leaks oil from just about everywhere.I am trying to correct this problem with new gaskets and seals,but before I put the valve covers back on I wanted to adjust the valve lash.I'm sure there should be some kind of gap now that it has solid lifters,just not as much as there is on some of them.Does anyone know what I can set these at cold? The only book I have shows hydra.lift engines.I bought the car this way,but can't get ahold of the guy who did the work.All I have is a peice of paper showing the work done.It claims cam and solid lifters to LT1 specs.Thats about all the info. I can give y'all,Besides the fact that the car wants to go.Thanks for your help. Barney Joe Flick

[Joe L.]

Re: '70 L46 with LT1cam and solid lifters

Barney-----

You'll see various lash specs on the 70-72 LT-1 cam. However, GM Performance Parts and the Chevrolet Power manual list the specs as .024"--intake and .030"--exhaust. Both are HOT specs; I've never seen any COLD specs published.

[Clem Z.]

Re: '70 L46 with LT1cam and solid lifters

the cold VS hot setting is a wash set them cold to .024/.030. rotate the engine in the normal rotation,when the exhaust just starts to open set the intake valve on that cylinder. after the intake valve opens all the way and then almost closes set the exhaust on that cylinder.

[Duke W.]

Re: '70 L46 with LT1cam and solid lifters

I recommend you set them at .021"/.026" cold and I will e-mail you a special procedure to use when adjusting them. The LT-1 cam has very long ramps and properly indexing the engine to adjust pairs of valves is important. You cannot adjust the valves of each cylinder at TDC because one valve is still on the ramp and the other is very close.

Duke

[bruce11495]

Re: '70 L46 with LT1cam and solid lifters

I hate to argue with Duke, but the stock specs are the ones that are the best. Absolutely.....The hot/cold specs will be so close, you won't notice the difference. Been there with an LT1 for 20 years, the difference is not worth the aggravation.

[Duke W.]

Re: '70 L46 with LT1cam and solid lifters

Based on my measured and very accuate, including the ramps, lift crank angle diagram of the LT-1 cam, the top of the inlet ramps are .016" inlet and .020" exhaust off the top of the base circle. Multiply these by 1.5 and you get .024"/.030". Trouble is, the rocker ratio is NOT 1.5:1, and it's not even constant. It's about 1.37:1 at the top of the ramp and 1.44:1 at max lift. It's actually pretty easy to measure the rocker ratio with a couple of dial indicators.

Now multiply 1.37 times the height of the ramps off the base circle and round down and you get .021"/026". The reason to round down is to be sure the valves are closed before the end of the ramp, so they are set at ramp velocity.

If they are loose the valves will be set down at higher than ramp velocity, and this will increase the rate of valve seat recession, and at high revs they can bounce off the seats.

Also, with the LT-1 cam you cannot set the valves with the engine at TDC because the exhaust is on the ramp and the inlet is barely off the ramp. With the 30-30 cam, BOTH inlet and exhaust are on the ramp at TDC (Thanks to Bill Clupper for providing me with an accurate 30-30 cam lift-crank angle plot of analysis.)

If you don't have the Word document put together by John Hinckley based on my research on how to set the valves, email me and I will sent it to you. After using this procedure on his '69 Z-28 John became a convert and so has everyone else who has tried it.

Not to many guys have reverse engineered any Chevy cams or the rocker geometry, but I did, and I try to spread the gospel as far as possible.

Duke

[Clem Z.]

Re: '70 L46 with LT1cam and solid lifters

just make sure you are on the heel of the cam lobe and you will be OK. here is another way to make sure you are on the heel. with #1 cylinder intake at full lift adjust #6 intake, # 8 adjust #5, #4 adjust #7, #3 adjust #2, #6 adjust #1, #5 adjust #8, #7 adjust #4, #2 adjust #3 and the same for the exhaust. this takes time but you will always be on the heel of the cam lobe. this works because of the 90 degree firing order.