Dear Forum members,
A friend of me asked me to put this on the Forum, he do's not know how to do it.
Valve clearance for Stainless Valves.
In the Ford T Manual the min/max. clearance are advised between 1/64[min] and 1/32 [max]
The [new]Stainless valves are advised by the supplier at a clearance of 0.01 inch.
With an expansion coefficient for Steel being 0.12 and Stainless Steel being 0.16 there is the following situation :
Steel Valve : The clearance of 1/64 is totally absorbed at a temperature of 260 C equals 500 F
St. Steel valve : Clearance of 0.01 inch is totally absorbed at temp. of 150 C equals 300 F
Can one of you give us some light on this dark subject.
Thank you for your help.
I think what you are also not factoring in is block growth. But I do agree that .010" is a little tight. I don't run adjustable lifters, so I can not experiment with the numbers, but I am sure there have been others that did. There is a point where you can go overboard.
I am not sure of the expansion factors of a T block, but on V-8 stuff of the 60's-70's, we /I typically set the cold lash tighter than the recommended cam specs, and upon warm up, readjust if necessary. Typically .006" tighter for cold would be sufficient. But those you have block and cylinder head growth factored in, and it was different if you ran aluminum heads---again, muscle car era V-8 stuff.
With a new or re-ground cam to modern specs, I set all at .015" cold. With an original cam, it may be best to use the piston travel method to set the valves, and then your lash will be varied.
Allan from down under.
I use 15 on the intakes and 17 on the exhaust
Just replaced my valves in my 11 touring with SS valves, all are from .010/.012". No issues at all
You can check with a magnet, I think you'll find that your stainless valves have carbon steel stems. Dave in Bellingham, WA
My thoughts on trying to answer your question, first the numbers of heat would be far from what the valve stem and push rod would run at so the clearance wouldn't close up to zero, if the expansion numbers did then the stems would lock up, s/steel expansion coefficient of 16 and grey cast of the block is 10.8
Less lash clearance set on the s/steel would co-inside with what would be happening in the combustion chamber of heat, if the valve was working it's way up to 16 and the block cast 10.8 and if by being a hole, by theory the valve seat opening would go larger and the valve growth is larger again so the valve would ride higher rather than lower to close any lash, stem and push rod spot would only have to content with the lower heat range and less expansion.
I'm not sure that this isn't a case of "overthinking" a situation. About the only time I ever set/adjust valve lash, or clearance, or whatever you want to call it, is upon completion of a "valve job", which usually entails cutting new valve seats by hand with modern carbide cutter equipment, and then refacing existing valves, or replacing with new stainless steel valves. And at that time, I set them all at .015" and forget about 'em! I mean,.....it's just a Model T Ford, right? I think the important thing to remember is that a thousandth or two too much clearance is no big deal, in fact, for safety, maybe a good idea, however, a thousandth or two "TOO LITTLE" clearance really is a big deal, especially for the hotter running exhaust valves! (....read, burned valve). FWIW,....harold
O.K.,....maybe I'm "overthinking" this stuff too, but not entirely. Here's one thing I'll add that I feel is very important:
When grinding valve stems for proper valve lash, the end of the valve stem must be perfectly flat, and exactly perpendicular to the valve stem. To do this, I make a jig by drilling a hole thru' a block of wood which holds the valve exactly perpendicular to the edge (side) of the grinding wheel. (double-check this with combination square) In other words, make at least the last cut by grinding the stem against the perfectly flat side of the grinding wheel. A violation of good, accepted grinding procedure, I know, but I know of no other easy way of doing this for us "shade-tree mechanics" without expensive machine tools.
If the end of the valve stem is not perfectly flat, it will make "point contact" with the surface of what Ford calls the pushrod, which I prefer to call the valve lifter, or tappet. And point contact will soon wear a crater in the flat surface of the tappet, and also quickly wear the end of the valve stem, and there goes your accurate valve lash! (....again, read burned valve)
I shoot for .010, or as Anthonie says .01, on the intake and .012 for the exhaust.
Setting intake and exhaust both at .010 seems to work just fine and you won't get a noisy valve that way.
If you set them at .012 and you get a noisy valve or two just turn up the radio a little and ignore it. Or get yourself some ear muffs.
I'm gonna fully support the notion that this topic is gettin overthunk! ;)
In reality cold lash numbers are estimates of expected heat growth in the valve train. These clearances can be adjusted for any number of reasons. The main reason for me is to fine tune the cam specs. If you have a .250" lift cam and you have .0125" of lash when hot... That's 5% of available valve lift wasted by having excessive safety cushion. This lash will also affect the degrees of valve open duration and overlap.
An engine doesn't need any more than .001" of valve clearance that it doesn't need. I run .006" on my intakes and .008" on my exhaust without problems.
.010 intakes and .012 exhaust