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Tricky Dickie 
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Joined: 05 Nov 2009
Location: North Yorkshire
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 Topic: hard valve seats
Posted: 06 Apr 2010 at 4:20am |
I've got the heads off my 25-40 Threshermans Special at the moment. The valves need grinding in, but those seats are hard suckers! Anybody know what kind of compound will cut them?
Tricky Dickie
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PaulRoidt(WI)
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Joined: 11 Sep 2009
Location: Montello WI
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Posted: 06 Apr 2010 at 7:46am |
Tricky,
I would grind the valve and dress the seat with a seat grinder. Then lap it in with some lapping compound.
If you are trying to just lap them in, it will take a long time, especially if they have any amount of wear on them.
Paul
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Tricky Dickie
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Posted: 06 Apr 2010 at 11:01am |
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Thanks Paul, I think that will be the best way forward as I'm getting nowhere by just grinding with paste.
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PaulRoidt(WI)
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Posted: 06 Apr 2010 at 12:01pm |
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Dick L
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Location: Edon Ohio
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Posted: 06 Apr 2010 at 12:53pm |
No where is where anyone really gets trying to do a valve grind with grinding compound. Some where over time the reason for lapping got mixed up with the actual grinding of valves and use of the lapping tool.
I have the hand equipment/tools used to face valves and cut new seats on Model T type engines. I need to take some pictures of them. After looking at the pictures of how it was done it is easier to understand why it was necessary to do quite a bit of lapping.
It would have still been after facing valves and cutting seats with what they had to work with at the time.
Also could be that in watching the lapping done and not the first part that some could get the idea that lapping was all that was done.
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Brian Jasper co. Ia
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Posted: 06 Apr 2010 at 1:02pm |
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I don't know for sure, but they may have put hardened seats in it from the factory. All of my oldest Wisconsin engines from the 40's have hard exhaust seats in them. Sometimes they have a Stellite exhaust valve too. If there's any real wear, just bite the bullet and have them ground.
Edited by Brian Jasper co. Ia - 06 Apr 2010 at 1:08pm
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"Any man who thinks he can be happy and prosperous by letting the government take care of him better take a closer look at the American Indian." Henry Ford
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Brian Jasper co. Ia
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Posted: 06 Apr 2010 at 1:08pm |
I'll add to what Dick says in that when I grind valves for my small engines, I find that I can get a better seal, plus the location on the valve face can be seen so I know if I need to widen or narrow a seat when I lap them in when done. The tools aren't cheap, but that's what it takes to make them seal. Another reason to take the heads in is if the guides are loose, they can be knurled to restore proper valve control. Sloppy guides will beat the seats out of round and then they leak.
I got lucky on evilbay and bought an old Sioux valve grinder and hard seat grinder very reasonable. They're old, but still work well.
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"Any man who thinks he can be happy and prosperous by letting the government take care of him better take a closer look at the American Indian." Henry Ford
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Brian Jasper co. Ia
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Posted: 06 Apr 2010 at 1:10pm |
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Dick, are your Model T valve tools hardened cutters run by hand and not stones?
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"Any man who thinks he can be happy and prosperous by letting the government take care of him better take a closer look at the American Indian." Henry Ford
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Dick L
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Posted: 06 Apr 2010 at 1:15pm |
Yes, run by hand and no stones.
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mlpankey
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Posted: 06 Apr 2010 at 1:36pm |
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Valves and seats need to be ground with a valve grinding machine then lapped in for the smallest margin. IF you have a seat thats being aggravating to remove and you want to remove run a heliarc ring around the seat it will fall out. welding causes metal to draw.
Edited by mlpankey - 06 Apr 2010 at 1:38pm
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Dick L
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Posted: 06 Apr 2010 at 2:12pm |
Tricky,
Are the seats inserts or just part of the head?
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Ages Cat
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Posted: 06 Apr 2010 at 7:32pm |
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The seats are replaceable. Typically the seat is ground for uniformity and the width of the seat determines the ability of the valve to transfer heat to the head. Water cooled engines are not as critical as the air cooled cylinders. The use of Prussion blue to determine seat uniformity and width is of great help. Once the seat is uniform, center of the valve face 25-30% of the width of the face of the valve, lapping compound will provide a great finished product.
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Tricky Dickie
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Posted: 07 Apr 2010 at 12:04pm |
The seats are replaceable and are made from some alloy steel which is ultra-hard. Thanks for all your advice guys; I think that I will have them recut professionally.
Tricky Dickie
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