Valve adjustment

[Guest F37Olds]

I recently rebuilt the 6 cylinder engine in my 37 Olds and upgraded to hardened valve seats and stainless steel valves. Given that the original valve clearance specs were created for regular steel valves, do I need to compensate for the change to stainless steel valves due to any difference in the expansion between stainless steel and regular steel valves?

[HarryJ]

F37Olds....I don't know the difference in expansion ratios between stainless steel and the steel origanally used in your Olds; however, I do know too much gap is better than too little. There are tables giving these ratios in expansion rates. I would reference these at your local library. I don't believe there will be much difference in a distance equal to the length of these valve stems. Obviously, the gap should be adjusted to add a little if the rate is greater or subtract a proportional amount if smaller. The original valves may have been silicone or possibly tungston steel; so the rate of expansion will be different from carbon steel.

[Guest JT]

As long as you set them hot it should make no difference.

[Guest Ken G]

It obviously depends on the particular design of engine and of the materials employed, but the instruction book for my 1925 Rover says "temperature variation of engine causes no more than 1 1/2 thousandths of an inch difference in valve clearance. Rise in engine temperature increases (in italics for emphasis) valve clearance". This means that for this engine it is correct to adjust the clearances with the engine cold (when the clearance is set to 1 1/2 thou).

I grant that if you change the materials from those originally used, the change might be different, and conceivably even in the other direction. I hope not, because I had new exhaust valves made, with modern materials, and until now it hadn't occurred to me that the procedures for adjusting the tappets might change. The new exhaust valves use fancy stainless material for the business end (a non-magnetic alloy, unlike the originals) but fairly stock material for the stem; since the bulk of any dimensional change with temperature will occur along the stem, I think it unlikely that the behavior of a new valve will be significantly different from that of an original. However, perhaps I should check the clearance cold and hot and make sure that indeed it does not decrease.

Ken G, 1925 Rover 16/50 (San Francisco)

[Guest F37Olds]

Thanks everyone for the input and comments.