pulled my valves last nite,all the intakes look pretty good and are .312,the exaust are .325?? and are shot,so is .325 right? thinking about going up one size. the seats look ok but i'll have someone else have a lookie see.i'll cut the seats probrobly just to be sure. will replace all as they are 2 peice. measured with 2 indicators
The valve stems originally were .3125" (5/16") diameter. It is best practice to ream the valve stem bores in the block true and oversize the valve stem to achieve desired fit up to 11/32" diameter. At that point you would need to install a valve guide bushing or guide liner, often referred to as "installing valve guides". Installing replacement valve guides is difficult to do properly with the engine in the car.
The cast iron block is the best valve guide as long as you can keep the stem diameter at or below 11/32".
As with the guides, the best seat is the block itself. You can install larger diameter valves to compensate for years of valve jobs. The valve should sit proud of the block about .063" for best flow. The contact area of the valve to seat is critical. In days past it was typical to perform a three angle valve job to control the contact patch. This is still adequate for Model T engines, and needs to be done at a minimum.
In your part of the country there are lots of Nascar and ARCA engine builders who might recommend a radiused cut on the valve. This is great too, but might (or might not) be more expensive. In any case if you install oversized diameter valves be sure to check for clearance with the head and head gasket before tightening the head bolts.
.312 is standard size. I had my guides resleeved to that size and then put stainless valves in.
.327 is the next (.015) oversize
W. L. V.
I almost hate to see the term "stainless" when it concerns valves, as it does not mean anything. There are soooo many grades of stainless, and some are unsuitable as exhaust valves. And no, a magnet does not distinguish between stainless and not stainless, as there are both austenitic and martensitic stainless steels, and then there are superalloys, which are mostly nickel based and have practically no Fe (iron) in it.
Before you go reaming new valve guides. You say the valve stems measure .325. There is no "good" or "bad" about that. All that matters is how much larger the valve guide holes are. In other words, how closely do those .325 stems fit in the block? The 2 piece valves should, as you say, be replaced. However, if you can get oversize stems and they fit well, there's nothing wrong with .325 valve guides.
A fairly easy solution is to use Chevy 350 exhaust valves (easy to buy at any parts house locally) with valve seat spring retainers for the Ford 8N Tractor intake valves also (available locally). Use standard Model T springs. The 350 valves have a slightly larger head to make it easy to fit into a fresh ground seat in the block without being recessed into the block. These valves are .030 (.342) oversize so the guides need to be reamed to fit. Then use adjustable lifters and you are good to go. I believe that Lang's also sells these valves as "modern style valves" with all of the parts needed to use them.
I have used these valves in every engine I have rebuilt and driven thousands of miles with excellent results.
This engine had many thousands of miles on it when I took it down last fall to repair some other Items, the Chevy valves still look great!
This is a fresh engine with Chevy valves.
I was going only by what the box said. I'm not a metallurgist, so they could be anything. LOL
That ambiguity is a little scary.
If using valves made for modern engines, I feel a lot better that the material would be up to the task in a T.