Okay, I have decided to get the opinion of the great engine minds on this board. Let's say that you adjust the valves at room temperature in your garage. Let's use 75 degrees and the car has set for a few days and is at the same temperature. So we set the valves at 18 thousandths. What happens to the clearances when the engine gets up to operating temperature? Do they get tighter or looser? I have heard both ways and I was wondering what the true scoop is. Thanks for your input.....
Do they tighten - or loosen?
- Thread starter Oldschool
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Tighter. Metal expands with heat and closes the gap. Solid lifters usually rattle a bit when cold. They tighten up and get quiet when warmed up.
65wgn440
Well-Known Member
Clearance decreases, thermal expansion.
69_340_GTS
Well-Known Member
I have found that the valve lash changes very little with heat. It almost makes sense... if every part expanded at the same rate, clearances wouldn't change much.
The correct answer is "it depends" on what everything is made of. ALuminum heads for instance expand and contract at different rates than cast iron. Also, I disagree that "it changes very little" and here's why I disagree. I've had a LOT of engines through the years with solid lifters. They always and I mean ALWAYS get quieter when they warm up. That is.......with cast iron heads. I have very little experience with aluminum heads as I've never had the coin for such.
Cast iron:.002-.003 from what I have seen.
That's a fair guess. It's enough to make a difference in sound.......probably not much else, which is why I adjust cold. Who wants to get burned?
Agreed. I have never tried it "wet" either. (running) Idle it down real slow. I don't like cleaning the engine and inner fenders off. LOL
Exactly. I don't know "what's got into" the cats that insist that adjusting running and hot is the only way. They're crazy. I don't give a DAMN what "the book" says. lol
That reminds me, I need to run the valves on my 273. It has been a couple years. Probably only 5,000 miles though.
DodgeLad
Skipped the Light Fandango
All my motorcycles and other adjustable vehicles get done cold. But I adjust my slant wet and I hate it. I adjust to specs and then tweak each valve just a tad by ear. You end up with the valvetrain quiet and smooth as possible.
jos51700
Green Bearing thread connoisseur
"It depends" is the standard engineering answer. The valves get the hottest, and they expand the most, which reduces lash. The pushrods get hot and this also reduces lash, but not as much. Remember, the growth is a certain amount per inch so longer parts grow more, assuming uniform temperature.
The block and heads get hot and that increases lash because it pushes the rocker arm further from the 'center' of the motor. Aluminum heads will expand more. So the net is some 'cancellation' of the decreased lash from valve growth.
For example, if it's an Evolution or later Harley, the expansion of the aluminum cylinder and head increases more than the pushrods and steel cylinder studs, so if you don't warm up your Harley, you'll pop head gaskets and base gaskets when you beat on it cold. This also means that on the aforementioned Harleys (which are all pushrod), the lash increases as it warms up since the pushrods are steel. This is mitigated somewhat by the tension of the cylinder studs, but lash does increase and setting the cold lash on HD's is just adjusting so that it has no lash but still free-spins, and it loosens slightly from there.
Overhead cam engines mitigate most of this and then it's just down to head material, valves, and whatever's between the cam and valve. Most jap bikes just have a bucket and shim, and the clearance hot becomes very small. As long as it's not negative lash, you're fine.
And I love it when guys go "Motor's quiet, no need to adjust the valves!"
That makes no account for the valves being held open and burning since they cool through the seats! Be careful trying to make it quiet!
BigBlockMopar
BigBlockMember
I'm running mechanical lifters on a hydraulic cam, means you have to use a tight lash of at least 0.006"-0.007".
Iron block and heads.
Any tighter and the engine starts to run rough at idle when warm, meaning some valves aren't positively closing.
At 0.010" lash the engine/valves gets noisy.
Iron block and heads.
Any tighter and the engine starts to run rough at idle when warm, meaning some valves aren't positively closing.
At 0.010" lash the engine/valves gets noisy.
I've had both opinions as well. When Dad n I put new top end in the 273, I called a certain tech line and they said clearances get bigger(in our situation). I set them cold.
mderoy340
Well-Known Member
Best way is set one cylinder to spec hot motor. Let it sit until cold and check lash.
DodgeLad
Skipped the Light Fandango
Thanks never knew it. I go to spec and then increase the lash until I hear clacking, then back off a little. When I first got the truck, the valves were so out that I had to use a stethoscope with a rubber hose pickup to single out a valve since there was so much clacking everywhere.
I just did this on my slant earlier in the year. I set hot running clearance to specs (.010/.020). I checked them cold a few days later (I was waiting on a valve cover gasket), and they were .011/.025! The exhaust valve expands a lot hot, which makes sense, but the intake valve barely changed at all.
famous bob
mopar misfit
Mostly correct.^^^^^^^^^^^^^^^^^^^^^^^^^
I set mine cold at .010-.011 , alum. heads expand increasing the clearance about .006 . A friend that has been a mech all his life put me onto this, he said a lot of the alum. headed foriegn cars factories even recommend it . ALUM. .006 TIGHTER, CAST IRON .003 TIGHTER.
Have had no problems w/ it. Checked them a couple times , all good .
Solid roller------
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