MTFCA Forum

Which angle of cutter is used to just clean up valve seats ?

Original Model T valves are at a 45 degree angle which means the seats get cut at 44 or 44.5 degrees. Hope this helps!

Thanks Tim, where would a guy find the tool? I don’t think the Vendors sell things like that

With out spending a fortune, Ebay has sets made in India, work OK on cast iron but not to flash on hardened seats.

Thanks Kerry

GG Gregory wrote: ↑

Tue Aug 09, 2022 7:34 am

Thanks Tim, where would a guy find the tool? I don’t think the Vendors sell things like that

It really is not that easy IMO. I say this coming to you as a professional engine rebuilder near you however this tool that is referred to requires other things IMO. To begin with, I am unsure if you are touching up seat faces or whether you are cutting seats to remove damage. Cutting a seat face requires a carbide cutter that has rigidity. You really do not get that with a cheap-style cutter, and what you often get using these is a seat that has chatter marks that often leads to the valve's face not sealing well to the seat. More on that below.

If you are only touching-up a seat, then using a rock to stone the seat is the quickest way to a nice finish however you must also have a mandrel to pilot from. These pilots use the valve guide area of the block to center with, and I feel you need mandrels in multiple sizes (+/- around 0.001" - 0.0005" in oversize) to find the best fit. Then you really need a gauge to verify the concentricity of the valve seat so you will know how the valve's face will seal. This is especially important if new or refurbished valves are being installed. My suggestion is to see if you can find a professional shop in the Knoxville area that can do the seats for you. Valve seating is an area that is often overlooked. Model-T engines need a good sealing valve to make power, and one that is even leaking slightly quickly causes a power loss,

A single 45 degree cut makes for a wide seat which is not optimal for long life. Done properly, the seats need to be narrowed to around .060" & positioned above the center line of the valve face. This is done with 30 & 60 degree cutters/stones then lapped & seal confirmed. If the seat is getting too deep, then new seats are needed. This takes expensive equipment. Best done by an experienced person.

Thanks Brent. Yes we’re not that far away from each other. I think you know a friend of mine, Jim Eubanks. Sounds like this valve job is more involved than I have the talent or tools.

I totally agree with speedy except I shoot for about 080 to
0 90 inch width of contact. Lapping is important in my opinion.

I've put many a seat in and have never lapped any but it takes experience to know what to look for. .060 width is good for gas motors. You could put a larger valve in to deal with the worn seat but it requires more seat grinding of various angles to get the seat width and diameter right. You also don't want a valve seating on the outside edge of a valve where it can burn.