Valve lash.. Hot /cold ? How hot is hot?

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Kent mosby

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After reading many threads about valve lash, I learned that the valve lash on the cam card is for hot lash. I also learned that many opposing opinions are held as to whether the lash increases or decreases with the engine warming up. Most seem to indicate that you need to tighten the lash when cold as it will loosen as the iron block and aluminum head expand with heat. Most would say for a hot lash of .016 inch to set it at .010 inch cold and recheck when hot. My cam card calls for .016 intake and .018 exhaust. So I am going to set it at .010 and .012 cold and warm it up. The question is.... how hot do I have to get the motor before I can check the "hot" lash????? I have an iron block with aluminum heads and solid flat tappet lifters.

The coolant temps are going to be lower than the block temps. What gauge do I use for the warmup? Do I run it for 5 minutes,, 10 minutes?? Or do I run it until coolant temps reach XX temp?? I have to at least be able to touch the motor and Can't have it steaming hot..

Any and all advice welcomed. Thanks
 
Adjust cold and add .002". Why in the world anybody would want to work on a hot engine and risk getting burned, I have no idea, but some folks insist on adjusting hot. There's just no need for it. Good luck and keep us posted!
 
We used to adjust those Stovebolts and Slants with the engine running!!!!
 
We used to adjust those Stovebolts and Slants with the engine running!!!!
Yeah and there's some here who insist on advising adjusting slants running. That is absolutely crazy and askin to get hurt.
 
I as well set lash cold ! When I have set lash hot the engine was at operating temperature ! What ever that would be on your ride ! It never has been a big issue for me hot or cold !
 
Hang on now......Kent, what heads are you runnin? Don't you have aluminum heads? That makes things a little different, I believe.
 
Aluminum trick flow 240 heads .
I do it exactly as you described in your first post. Except I would split the difference and do them both that way so it just makes it easier.. something called and check them when they're hot meaning just full temperature 180 190 whatever your car runs...
 
Aluminum trick flow 240 heads .

Aight den. Lets let one of these other guys advise you. I've worked with aluminum heads very little, but I know they have different requirements. I still recommend adjusting cold, but they expand differently than cast iron, so you need to adjust accordingly....and I don't know exactly HOW that is.
 
The RPM & TF heads on my motors have seen lash open consistently .005"-.006" after running. The safe bet is start .004" tighter cold, then check a few as quickly as possible after shutting down a well-heated engine. If it's still a couple thou shy of your hot goal, then just adjust the difference once it's cooled down again...dead cold, like overnight at the minimum.
 
All engines expand with heat. So cold lash is always tighter. Iron/iron engines need to be .002-.004 tight cold, while iron/aluminum engines need to be .004-.006 tight. Aluminum/aluminum engines need to be .012-.014 tight cold and that may not be enough. You just have to check it.
 
I have only once measured the difference between hot/cold on an engine with iron block/alum heads. It was 0.003". Veeeeery easy to check. In my opinion, too much lash difference is allowed for alum heads. 0.003" for most alum heads, & 0.004" for a tall head [ that has longer valves/taller ports ]. Performance heads usually have s/steel valves; s/s expands at a higher rate, so that needs to be factored in, which means the hot to cold difference will be less.

To check on your engine. Have tools [ & feeler gauges, pen & paper ] ready for quick removal of the valve covers. Drive the car until engine is at normal operating temp. Switch off engine & quickly remove one v/cover. Check for loose rockers, measure the lash & record. Leave overnight to cool down & re-check the lash cold. There is your hot/cold difference.
 
To check on your engine. Have tools [ & feeler gauges, pen & paper ] ready for quick removal of the valve covers. Drive the car until engine is at normal operating temp. Switch off engine & quickly remove one v/cover. Check for loose rockers, measure the lash & record. Leave overnight to cool down & re-check the lash cold. There is your hot/cold difference.

I like that approach. I'm switching to solid cam soon from hydraulic . Let us know how it goes.
 
I set mine .014 intake - Exhaust-.016 cold solid roller Alloy head
 
All engines expand with heat. So cold lash is always tighter. Iron/iron engines need to be .002-.004 tight cold, while iron/aluminum engines need to be .004-.006 tight. Aluminum/aluminum engines need to be .012-.014 tight cold and that may not be enough. You just have to check it.
Remember the pushrods get longer with heat, and so do the valves... most sources I have seen recommend .002 looser than spec lash when cold for iron/iron, but .006 tighter when cold for iron/aluminum...
 
AFAB2240-B96E-4A88-912B-B13F00297834.jpeg
 
Remember the pushrods get longer with heat, and so do the valves... most sources I have seen recommend .002 looser than spec lash when cold for iron/iron, but .006 tighter when cold for iron/


True. The mass of the block and heads is much greater than that of the pushrods. Cast iron and steel expand at different rates. I check the cold/hot lash on everything. No two engines are never the same. One thing that has proven out over the years is that I’ve never found a single instance of valve lash closing up with heat. I know it’s all over the web, it’s been published in magazines since before I was born and it still gets said today, but never have I seen lash close up hot on anything.
 
Hay thanks yall for gettin Kent on the right path with this. I just didn't have enough experience with aluminum heads to know which way to tell him. I knew yall would come through.
 
One thing that has proven out over the years is that I’ve never found a single instance of valve lash closing up with heat. I know it’s all over the web, it’s been published in magazines since before I was born and it still gets said today, but never have I seen lash close up hot on anything.
How does the mass affect the total expansion? I'd think it would only alter the rate at which expansion occurs (since it takes longer to heat up all that iron and reach thermal equilibrium)...

Very interesting point on your own lash measurements. Thanks for contributing your experience!

On the subject of automotive urban legends... I have quit banging my head against the wall with those people who keep repeating that "coolant moving too fast through the radiator means it doesn't have time to give up heat". Forget thermodynamics, it must be so since it's been said before I was born, etc. :realcrazy:
 
I have only once measured the difference between hot/cold on an engine with iron block/alum heads. It was 0.003". Veeeeery easy to check. In my opinion, too much lash difference is allowed for alum heads. 0.003" for most alum heads, & 0.004" for a tall head [ that has longer valves/taller ports ]. Performance heads usually have s/steel valves; s/s expands at a higher rate, so that needs to be factored in, which means the hot to cold difference will be less.

To check on your engine. Have tools [ & feeler gauges, pen & paper ] ready for quick removal of the valve covers. Drive the car until engine is at normal operating temp. Switch off engine & quickly remove one v/cover. Check for loose rockers, measure the lash & record. Leave overnight to cool down & re-check the lash cold. There is your hot/cold difference.

I like the approach. I have silicone/rubber valve cover gaskets for easy removal. You indicate that the "difference" should be less. Are you of the camp that says that it will loosen up .003 as it heats up? Or that it will tighten as it heats up. For a .016 lash, would you cold set at .013?

I will set and measure all my valves and perform the test to heat them up and measure again. I will post all results.

For what it is worth, I set the original flash cold to cam card specs. Meaning that I was actually looser than I should have been. For those who follow/followed my degreeing cam thread, I now know that the cam events were retarded even more than the 8*retarded that the cam/crankshaft orientation said. By how much, I will have to do some studying. I will post if anyone is interested in how much .006 loose lash affects cam timing.
 
I like the approach. I have silicone/rubber valve cover gaskets for easy removal. You indicate that the "difference" should be less. Are you of the camp that says that it will loosen up .003 as it heats up? Or that it will tighten as it heats up. For a .016 lash, would you cold set at .013?

I will set and measure all my valves and perform the test to heat them up and measure again. I will post all results.

For what it is worth, I set the original flash cold to cam card specs. Meaning that I was actually looser than I should have been. For those who follow/followed my degreeing cam thread, I now know that the cam events were retarded even more than the 8*retarded that the cam/crankshaft orientation said. By how much, I will have to do some studying. I will post if anyone is interested in how much .006 loose lash affects cam timing.

The only way to know for sure what your cold lash should be is to test it. No two castings are the same, so they don’t grow at the same rate. Checking one engine and claiming they all do the same thing is not real world.
 
How does the mass affect the total expansion? I'd think it would only alter the rate at which expansion occurs (since it takes longer to heat up all that iron and reach thermal equilibrium)...

Very interesting point on your own lash measurements. Thanks for contributing your experience!

On the subject of automotive urban legends... I have quit banging my head against the wall with those people who keep repeating that "coolant moving too fast through the radiator means it doesn't have time to give up heat". Forget thermodynamics, it must be so since it's been said before I was born, etc. :realcrazy:

The mass of the castings and even the shape of the castings will change how and where a casting grows. The heat in the head and block is much higher than the heat in the pushrods. Localized heat in the heads is much higher than the pushrods. Changes in engine coolant temps will change how much the lash changes from cold to hot.
 
The mass of the castings and even the shape of the castings will change how and where a casting grows. The heat in the head and block is much higher than the heat in the pushrods. Localized heat in the heads is much higher than the pushrods. Changes in engine coolant temps will change how much the lash changes from cold to hot.
So... too many variables to know for sure, measure it yourself :D As you've said.
 
Kent,
Set the lash 0.006" tighter than what the cam card says. This is an initial setting. It will probably be a little too tight by a couple of thousands, but going tighter [ unless an excessive amount ] causes no harm, whereas going too loose can allow the lifter to run off the lash ramp & cause noise/valvetrain wear.
Get the engine running, thoroughly warmed up & broken in, & then use the procedure I posted in post #11. That will tell you the hot/cold difference for your engine.
 
I like the approach. I have silicone/rubber valve cover gaskets for easy removal. You indicate that the "difference" should be less. Are you of the camp that says that it will loosen up .003 as it heats up? Or that it will tighten as it heats up. For a .016 lash, would you cold set at .013?

I will set and measure all my valves and perform the test to heat them up and measure again. I will post all results.

For what it is worth, I set the original flash cold to cam card specs. Meaning that I was actually looser than I should have been. For those who follow/followed my degreeing cam thread, I now know that the cam events were retarded even more than the 8*retarded that the cam/crankshaft orientation said. By how much, I will have to do some studying. I will post if anyone is interested in how much .006 loose lash affects cam timing.

Kent, ur engine and mine are closely built, I run my valves cold at .010 , recommended setting is .016 hot , no problems , and has been at least a yr since I set them.
Doesnt get driven a whole lot , life gets in the way ------------solid street roller --
 
I have had a few different combinations of iron block and aluminum heads. .003-.008 difference. The more the cold lash was the more the difference. Kim
 
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