Shift_Happens

When setting valve lash on a solid lifter motor, would you set them tighter or looser than the manufactures recommendations when adjusting them cold?

R66

Maybe a couple to thousandths looser (more gap) setting them cold as the length of the valve will grow very slightly as the valve is heated during the combustion process. I don't know what the coefficient of expansion is for each valve material, but all will grow some when heated.

Powershift

Measure it both ways on your engine and you will then know for sure.

For most stock engines it will be close to the same.

Larry

cardo0

Copy and paste from Crane Cams Tech Tips.


MECHANICAL LIFTERS TECH TIPS
Compensating for a Cold Engine when Adjusting Valve Lash
When installing a new cam, the engine will be cold but the lash specifications are for a hot engine. What are you to do? There is a correction
factor that can be used to get close. We mentioned that the alloy of the engine parts can be affected by thermal expansion in different ways,
therefore the amount of correction factor to the lash setting depends on whether the cylinder heads and block is made out of cast iron or aluminum.
You can take the “hot” setting given to you in the catalog or cam specification card and alter it by the following amount to get a “cold” lash setting.
Remember this correction adjustment is approximate and is only meant to get you close for the initial start up of the engine. After the engine is
warmed up to its proper operating temperature range, you must go back and reset all the valves to the proper “hot” valve lash settings.
Setting Valve Lash on Mechanical Cams
All the valves must be set individually and only when the lifter is properly located on the base circle of the lobe. At this position the valve is
closed and there is no lift taking place. How will you know when the valve you are adjusting is in the proper position with the lifter on the base
circle of the cam? This can be accomplished by watching the movement of the valves.
1. When the engine is hot (at operating temperature) remove the valve covers and pick the cylinder you are going to adjust.
2. Hand turn the engine in its normal direction of rotation while watching the exhaust valve on that particular cylinder. When the
exhaust valve begins to open, stop and adjust that cylinder’s intake valve. (Why? Because when the exhaust is just beginning to open,
the intake lifter will be on the base circle of the lobe, so the intake is the one we can now adjust.)
3. Use a feeler gauge, set to the correct valve lash, and place it between the tip of the valve stem and rocker arm. Adjust until you
arrive at the proper setting and lock the adjuster in place.
4. After the intake valve has been adjusted, continue to rotate the engine, watching that same intake valve. The intake valve will go to
full lift and then begin to close. When the intake is almost closed, stop and adjust the exhaust valve on that particular cylinder. (Again,
when we see the intake valve almost closed, we are sure that the exhaust lifter is on the base circle of the lobe.) Use the feeler gauge
and follow the procedure described before in step 3.
5. Both valves on this cylinder are now adjusted, so move to your next cylinder and follow the same procedure again. In the future you
may find shortcuts to this method, but it still remains the best way to do the job correctly.
Using Valve Lash to Help Tune the Engine
The engine only responds to the actual movement of the valves. Since the valve cannot move until all the running clearance (valve lash) has
been taken up, the amount of valve lash you use affects the engine’s performance. For example, if you decrease the amount of (hot) valve lash,
the valve will open slightly sooner, lift higher, and close later. This makes the camshaft look bigger to the engine, because of a slight increase of
actual running duration and lift. If you increase the amount of (hot) lash the opposite occurs. The valve will open later, lift less, and close sooner.
This shows the engine a smaller cam with slightly less actual running duration and lift. You can use this method on a trial basis to see what the
engine responds to and keep the setting that works the best. Just remember, the more lash you run, the noisier the valve train will be. If the
clearance is excessive it can be harsh on the other valve train components. Therefore, for prolonged running of the engine we do not
recommend increasing the amount of hot lash by more than +.004" from the recommended setting. Nor do we recommend decreasing the hot
lash by more than -.008".
Warning: “Tight Lash” camshafts cannot deviate from the recommended hot lash setting by more than +.002" increase, or -.004" decrease.
“Tight Lash” cams are those which have recommended valve settings of only .010", .012", or .014" on the specification card. These lobe
designs have very short clearance ramps and cannot tolerate any increase in the recommended valve lash. The extra clearance can cause
severe damage to valve train components. With “Tight Lash” cams, we recommend using only the prescribed amount of hot valve lash, and that
close inspection of the engine be maintained.
Iron Block Iron Heads Add .002"
Iron Block Aluminum Heads Subtract .006"
Aluminum Block Aluminum Heads Subtract .012"

Hope this helps.

PAmotorman

most specs are hot lash. hot adjust one cylinder hot and let it set over night. check the lash cold and then you have your answer. aluminum heads grow about .004 and all aluminum engine grows about .010 from cold lash to hot lash

jim lockwood

I agree with this number. I discovered, by trial and error, that setting the cold valve lash .010 tight on my aluminum racing engine would get me the correct hot lash.

SDVette

I guess it depends on how precise you want to be on this... but for mine, I simply run the car to warm it up, pull in, remove the valve covers, and set the lash while it's "warm".

Also, you can set all 16 with minimal engine movement.. Here is a helpful article (written by Formum members JohnZ and Duke).

Shift_Happens

Thank you all for your insight. ....all very helpful

SWCDuke

On a cast iron block/head engine there is no measureable difference in cold and "hot" (idling) lash because the steel pushrod and cast iron block/head have virtually the same thermal expansion rate; however, when the engine is run at continuous high load lash will close up a few thou, especially on the exhaust side, and that's why some cams have greater exhaust than inlet lash. There needs to be room for thermal expansion so the lash doesn't completely close up and hang the valve open, and that's why mechanical lifter cams have long constant velocity clearance ramps.

The pdf attached a couple of posts up recommends slightly tighter than OE lash based on valve train loading as explained in the paper. These settings will increase effective overlap and reduce idle vacuum and low end torque, but are easier on the valve train as explained. Some guys prefer the OE settings or even looser to smooth out the idle and make better low end torque, but both will increase valve train shock loading.

If you need to set lash looser than OE recommended to get the idle behavior and low end torque you want, you should go with a lower overlap cam.

Duke

jtranger

Duke,

According to the paper, the Duntov cam should be set at .010 and .016 cold correct?

PAmotorman

the early chevy performance cams were designed to work best with open exhaust and close lash settings. back then you had to run the stock cam that came in the engine to be legal for road racing and drag racing

1snake

That's how I've been setting mine for over 40 years. No problem so far.

MikeM

If the lash is supposed to be set hot, how hot is hot?

Hot after the engine idles for twenty minutes is one temperature and hot after running hard down the road is quite another hot.

Maybe twice as hot as far as head temperature.

PS.

According to the Chevy "paper", the 097 had two different settings, "hot". .008/.018 and .012/.018. Take your pick for your particular usage.

But I still don't know how hot is hot.

PAmotorman

when the coolant is up to operating temp will do. the part that would get hotter after a hard run would be the exhaust manifold but the coolant would keep the rest of the engine at a fixed temp. the reason you don't use a gasket between the head and the cast iron exhaust manifold the head helps cool the manifold. with a gasket you do not get that benefit

Chuck Gongloff

I've always "believed" the "hot" .008/.018 numbers with a Duntov cam.

That being said, I've set mine at .010/.020 cold for decades and my solid lifter car runs just fine.

MikeM

I would agree that the exhaust manifolds would be a lot hotter as would the combustion chamber and valves.

I'm sure there is a sweet spot on engine temperature somewhere to adjust valves but I have no idea what it is. In the meantime, I use the lash the manufacturer of the cam recommends even though they don't say what "hot" is either.

I suspect some are splitting hairs on their valve adjustments, hot vs cold.

Now if you're going for the Racer's Edge........................

SWCDuke

Nothing has changed since the Sept/2008 revision of the paper. Also, with the Duntov cam you can adjust both valves at TDC of the compression stroke of each cylinder.

With the 30-30 and LT-1 cams you MUST do all the inlets at 90 degrees ATC and exhausts at 90 degrees BTC because the lobes are still on the late/early part of the clearance ramps at TDC.

For either method, starting at TDC #1 you need to rotate the engine 90 degree eight times. The only difference is what valves you adjust at each TDC point.

With a helper holding the clipboard that has the sequence and calling them out I can do the job in a few minutes, not including removing/installing the valve covers and any other hardware that needs to be removed to start the actual adjusting job and reinstalling said parts.

Duke

MikeM

Two man job, eh?

GTOguy

"Hot" for valve lash purposes (and doing compression testing) is having had the engine up to full operating temperature and then letting it cool enough so that you can remove things like spark plugs and valve covers without getting badly burnt. I've been using this method in industry on probably 1000's of cars that specified 'hot valve adjustment' with excellent results. I also adjust the valves as specified by the engine or camshaft manufacturer. If specified as a cold adjustment, the car sits overnight. If specified as a hot adjustment, I follow the first procedure I listed. Not rocket science.

MikeM

Has anyone put this is writing. Seems that hot/idling is one temperature and hot during operation is two different things.

I am just trying to be careful and make sure I don't mess up. I have been adjusting solid lifters since 1956 but I am trying to make sure I do it right. No problem so far but you nevere know.