67 L89 Valve Lifter Clearance
What did the factory use for a cold setting for the 1967 L89 that yielded a hot setting of .024 hot intake and .028 hot exhaust? It seems like the difference in the thermal expansion of the aluminum heads would require a different cold setting. I have seen two different TV programs that said you need to adjust the cold settings .006 tighter for an aluminum head cast iron block to yield the correct hot setting. They set the valve clearance .006 tighter started the engine and warmed it up and then rechecked the valve clearance which yielded the correct valve lash. The factory set the valve lash cold, what cold setting did they use?
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Re: 67 L89 Valve Lifter Clearance
Consider that L-78 valve clearance recommendation was .020/.024". Then it was increased to .024/.028" for L-72. Exact same camshaft. Later big blocks used a different part number SHP mechanical lifter cam, but the only difference was elimination of the rear journal groove that was required on the '65 and '66 blocks. Lobe and lobe indexing is identical. BTW this lobe was also used, on a smaller base circle, on the inlet side of the LT-1 cam.
The Chevrolet Power Manuals from the seventies say to cold lash all aluminum big blocks .010" tighter than cast iron. Based on calculations of rocker ratio times clearance ramp height I recommend .020/.022" for iron heads. Since you have an iron block with aluminum heads the difference will be less than ten thou, so maybe the six thou you've read is correct, but I recommend you use all the relevant dimensions and thermal expansion coefficients and compute a number
I know the valve clearance on my Cosworth Vega engine expands two thou when hot - both calculated and measured, but it's a DOHC settup, so you just calculate the difference in expansion the length of the valve. With a pushrod engine you have to consider both the valve and pushrod compared to the aluminum head.
Suggest you do a web search: Williams Hinckley valve adjustment procedure 9/08 revision. It just lists SB mechanical lifter cam clearance recommendations, but use the indexing procedure described therein to be sure that the lifter is on the base circle for each valve. Also it discusses why small block rocker ratio is not 1.5:1. A similar argument holds for big blocks, but I've never gotten enough data to calculate the range.
Duke -
Re: 67 L89 Valve Lifter Clearance
I have a Mark IV LS7 with Aluminum Heads. When I put the car away for the winter every year I check the valve lash using the subtract .006 recommendation for Cast block & Aluminum heads. The engine has sounded great for the last 12 years. Follow the cold adjustment procedure Duke mentions and you will be a happy Big Block owner.Comment
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Re: 67 L89 Valve Lifter Clearance
What is wrong with adjusting the solid lifter valve clearance per the factory manual like I have done on the past? Why is the Williams Hinckley a better approach?Comment
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Re: 67 L89 Valve Lifter Clearance
Is that the hot and running method? Pretty messy! The Hickley-Williams method allows you to do it cold. And the indexing method guarantees that the lifter is on the cam's base circle when you adjust it.
Read the paper... simple web search... 9/08 revision.
DukeComment
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Re: 67 L89 Valve Lifter Clearance
IMO, this procedure is the new gold standard when adjusting lash on these engines. I think you'll find many people will give the same opinion as well.
Here is the link.......
Hope it helps,
TimComment
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