Valve clearance

Synchro909

Synchro909

Well-known member
My cam grinder says that the new, stainless valves offered by the vendors require a much wider clearance - as much as 0.025" on the exhaust.
It is obvious that these valves are made from different steel from what Ford used and therefore, the clearances should be different yet nothing is said by the suppliers about it. In one of my engines, I have set them at 0.025" and they are very noisy when the engine is cool but quieten right down when it warms up. That suggests to me, that my cam grinder is pretty right but I have never heard anything about it from any other source.
What clearances have you guys used and how have they performed? If you set them at the recommended by Ford gap, do they seal properly when hot? Have any of you done that and had a valve burn out?
 
Its usually good to listen to the cam grinder.
That said, I've not heard of lash that wide. But the grinder must know something we don't.
Ford spec for the Model B cam was changed to .022" for the exhaust due to some burnt valves with the original spec.
Ask your grinder about lifter foot diameter.
 
i have stainless valves and seats. i set mine to the Les Andrews spec in his book.
the car runs nice and you can still hear the valve train noise, i don't think they are too tight.
.025" seams a little loose

edit. forgot to say i have a stock grind cam.

but

we will have to see what others do
 
0.025" seems a lot to me too - that's why this thread.
The background of this is that while talking with the cam grinder, he told me of a customer who had a Model T and he complained that the car didn't go properly after he fitted the new valves. On stripping down the engine, they found that the cam followers were rubbing the heel of the cam hard. A little research on coefficient of thermal expansion and they calculated 0.025" was right. The Model T owner has had no trouble since. I find it deficient of the vendors that they do not mention anything about different clearances in the valve kits because they are obviously different, as I said in the opening post.
 
.025 is an awful lot of expansion for a stainless steel valve. If that T follower was riding on the heel of the cam there was no clearance. Would be curious what lash was set on those T valves.
 
I installed a modern valve kit with Stainless valves in my B motor 6 years ago and set the gap at 12 thau no noise still going.
Cheers, Rosco
 
0.011 to 0.012 on the intake and 0.012 to 0.013 on the exhaust. Unless the cam grinder did a lousy job.
 


The linear thermal growth of Stainless Steel is more than that of High Carbon Steel material, but is it enough to warrant a significant valve clearance change? For the same temperature, stainless steel expands linear about 0.008" more the high carbon steel.
The 0.008" difference may not be the actual case in the Model "A" or "B" engines because the valves may not be operating at the same temperatures. I suspect that things like the mass of the valves, insert valve seats and differences in valve guides affect the heat transfer rate of the valves, and I think that the stainless valves run cooler.
We need to hear from the professional engine builders and the speed guys in this case.
 
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Let's look at your concerns from a technical point of view. One of the physical properties affected by changing the valve material alloys from original to a stainless is the difference in the coefficient of expansion. I have not looked up the exact difference but it can not be major amount to cause a concern for this application. The comparative difference in expansion is a very low percentage which is physically in the micron region or at most .001". (1 micron = .00004") The exhaust valve doesn't heat up uniformly. The top of the valve is the hottest area and the stem is cooler as a result of being outside of the exhaust chamber and lubricated. I would set the new valve clearance to the standard spec.
 
Synchro909 said:
0.025" seems a lot to me too - that's why this thread.
The background of this is that while talking with the cam grinder, he told me of a customer who had a Model T and he complained that the car didn't go properly after he fitted the new valves. On stripping down the engine, they found that the cam followers were rubbing the heel of the cam hard. A little research on coefficient of thermal expansion and they calculated 0.025" was right. The Model T owner has had no trouble since. I find it deficient of the vendors that they do not mention anything about different clearances in the valve kits because they are obviously different, as I said in the opening post.
Click to expand...

re followers. i can see that happening with a regrind cam. i have a regrind here that i really don't want to used because of the under cut in the shaft. its deep. the lifter base would be very important in this case.

but to ad to my above post, i set my valves to .012 and .014
so far so good. but that being said it maybe wrong as i didn't know that they were to be set loose.
 
I ordered a set of oversize valves from Manley and asked about expansion. Tech guy said maybe .001-.002
 
I would think PC/SR is about right. I set my B and C cams at .012" & .014" and have had no problems, and I run my engines harder than most people.

Setting them too lose is harder on the cam and valves as it bypasses some of the clearance ramp.
 
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My new engine with a specialty motors 350 lift cam has them set .010 and .012 , that has been great and reved out a few times and worked hard in 39C , no drama .
Lawrie
 
It's starting to look like I have a job tomorrow resetting the clearances to 0.012 and 0.014, I think.
Thanks to the forum for the input.
 
I just came upstairs from checking valve clearance on my Margarethe, which i acquired beginning of the year. As i had a leak on the intake and exhaust manifold, i thought it is a good idea to check valve clearances too. On all valves, inlet and outlet, the clearance was 0,012" exactly. Cudos to the former owner.


I will leave it as is.
 
Comparing a performance cam like the Stipe cams isn't a good idea, performance grinds have their clearance ramps designed by the designer of the cam. Many Winfield cams are set at .010"/.010", many Isky cams of similar duration are set at .025"-.030".
 
Something basic about valve clearance:


The purpose of this air gap between the end of the valve stem and the drive mechanism is to ensure that a tiny air gap always remains under all temperature conditions.

This is the only way to ensure that the valve always rests unloaded in the valve seat and that no tiny gap remains through which gases can escape.


The individual materials were known when designing the engine.


It's the different of 'today', so the different steels expansion coefficients of the mechanic parts can be different now.


If the valve clearance is too small, the exhaust valve seat will burn a leak. If there is too much play, the valves will rattle and therefore the valve drive (especially the camshaft run-up path) will wear out a lot.


In the 1940s, there were specialists technican in institutions working on aircraft engines, and they checked this clearance while the engine was running: the clearance was checked with the engine cold and very hot, using a hardened steel gauge pulled through. The difference is the actual expansion between a cold engine and a hot one. There was also a safety margin of additionaly 1/5.
 
I have adjusted valves on over 250 currently running engines and set them at .011" I and .013" E and have not had any issues with any of them. Stainless valves as supplied by AER with solid guides. The few two-piece guide kits I have installed were set the same.
Good Day!
 
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