L89 valve lash recommendation

[Patrick B.]

I thought I had seen in a previous post a recommeded valve lash for the stock BB mechanical cam with aluminum heads using the Hinkley/Williams cold adjustment method. However, I can not find it in my search. Can anyone direct me to the information?

[Clem Z.]

Re: L89 valve lash recommendation

I thought I had seen in a previous post a recommeded valve lash for the stock BB mechanical cam with aluminum heads using the Hinkley/Williams cold adjustment method. However, I can not find it in my search. Can anyone direct me to the information?

the lash will grow .004 if set cold on a cast iron block with aluminum heads. if you want to experiment get the engine hot and set the hot lash on 1 cylinder and the next morning check that cylinder cold and you will have your answer as to what to set the lash cold on the rest of the cylinders

[Duke W.]

Re: L89 valve lash recommendation

Google search and use the latest version on the Web site "lbfun."

Use the procedure, but the SHP BB valve settings are a bit "squishy", which is why they are not included in this paper.

The cam's clearance ramp height is .012" on both lobes and using the theoretical 1.7:1 rocker ratio the maximum running clearance should be .020, however the rocker ratio, like the SB is not constant. According to my measurements the SB rocker ratio is about 1.37:1 at the beginning of lift and achieves a maximum of 1.44:1 at max lift with a lobe lift of about 0.3"

Big blocks likely have similar characterisitics, but I don't have enough reliable data to determine for sure how the rocker ratio varies with lift. Perhaps you could run a test.

For '65 the OE SHP BB clearances are specified at .020/.024" even though both lobes are identical. Why did they call for additional clearance on the exhaust side? I don't know, but I don't think exhaust valve expansion would be enough to justify more. That's why mechanical lifter cams have clearance ramps, however, many designs have higher clearance ramps on the exhaust side to allow for greater valve stem expansion.

Complicating the issue is the '66-up recommendation of .024/.028". Why did it change?

Cast iron block/head engines see little, if any change between cold and hot clearance because pushrod expansion is about the same as the block and head.

My Cosworth Vega clearance is .016" hot when I set them at .014" cold, which is due to greater expansion of the aluminum head and cam carrier relative to the steel valve stem.

I would expect aluminum heads on a SB to BB to behave similarly, but Clem is saying it's 004" rather than .002".

Until I can get more accurate data for big blocks I tentatively recommend .020/.022" cold for iron block/head big blocks with the OE SHP cam, and you'll have to decide whether to go .002" or .004" tighter (cold) with aluminum heads.

I would certainly recommend you do your own test. Check them hot immediately after shutdown, or hot and running, then let the engine to room temperature and determine the difference yourself.

Keep in mind that "hot" clearance is, at best, based on idling since there is no practical way to determine actual running clearance when the engine is under load. No doubt at high load the exhaust clearance tightens up more than the inlet clerance, and this is why mechanical lifter cams have clearance ramps - to allow the valve stems to grow without hanging the valve off the seat, and because the exhaust valve runs much hotter than the inlet at high load, exhaust lobe clearance ramps are usually higher.

Duke

[Patrick B.]

Re: L89 valve lash recommendation

Thanks. At this point I am looking for clearances for the assembly of the engine. I think I will uses .020/.022 for that. Later I can experiment with cold/hot comparisons and make a further adjustment.

[Michael H.]

Re: L89 valve lash recommendation

Keep in mind that "hot" clearance is, at best, based on idling since there is no practical way to determine actual running clearance when the engine is under load. No doubt at high load the exhaust clearance tightens up more than the inlet clerance, and this is why mechanical lifter cams have clearance ramps - to allow the valve stems to grow without hanging the valve off the seat, and because the exhaust valve runs much hotter than the inlet at high load, exhaust lobe clearance ramps are usually higher.

Duke

Duke,

High RPM/load that increases chamber temp does cause the exhaust valve stem to expand which will tighten the lash. However, at the same time, the valve head expands from the same increased heat which will cause the lash to loosen.
For short bursts of full throttle/high chamber temp. the valve head expands first which increases the lash but after a slightly extended period, the expansion of the stem will probably decrease the lash about the same amount.

Aluminum heads will change the lash at temp a bit more than cast iron heads but not much. The big change between cold/hot lash was with aluminum block and heads.

.024-.028 still works best for that cam.

[Ray K.]

Re: L89 valve lash recommendation

Patrick

I also would suggest using the .024 int & .028 exh valve lash settings for initial settings for this camshaft. The engine will start and run well and later after a few start cycles you can determine if you need to adjust the setting by .002 /.004. My L89 falls within that range from hot to cold .

Ray