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Valve seat width?
Posted: Mon Apr 09, 2012 1:41 pm
by Oland
Now I've come to the valve seats on my disassembled M38 engine.
As the exhaust seats were in pretty bad condition, I'm grinding them with my hand grinding set.
Question: What is the specified seat face width? I cannot find any reference in the manuals and didn't find any topic here on the forum either. I measured the old seats and it seems they are approx. 0.080" wide. Is that a good value?
Before...
And after...
Grinder
Posted: Tue Apr 10, 2012 5:41 am
by danrothe2001
Manual for the M38A1 states .093 to .125. However, .080 seems wide enough and using a single angle cutter like you are, they will definately be wider than they were. If they clean up at .080, I would run them.
Dan
Posted: Tue Apr 10, 2012 11:23 am
by Oland
OK, thanks Dan.
They have come out a bit wider than .080 after grinding so I think I'm rather within the limits .093-.125.
I have a 20 and 70 degree grinder so I can adjust the width if I want. Should I reduce it to .080 or leave it a bit wider?
/Oland
Posted: Tue Apr 10, 2012 10:00 pm
by danrothe2001
I would probably keep it to the low side of around .090.
Dan
Posted: Thu Apr 12, 2012 9:22 pm
by artificer
Find a picture of the valve nomenclature somewhere on the web....
The valve after grinding/machining must have margin of about 1/5 the seat width.
The actual valve seating should be about 1/3 of the total valve seat width & in the middle.
This is achieved by crowning & throating the block/insert/seat using 30* & 60* cutters to achieve both width & central position.
Posted: Fri Apr 13, 2012 1:39 pm
by Oland
Yes, I agree all this makes sense. However I doubt the original seats were so carefully machined. It seems more like they ground 45 degrees out of the block and then made a very small 20/70 degree chamfer (or none?). At the factory they of course had big solid grinders who gave a very uniform result.
I put paint on my valves and checked the the position of the seating, it seems reasonably centered.
/Oland
Posted: Fri Apr 13, 2012 2:22 pm
by wesk
The procedures mentioned above are not that futuristic or complex. I have used them with good ole quality Sioux Valve grinding equipment for years. Odds are the type of field grinding you just described wpouild only be fpound ion Bubba's private garage or under Bubba's tree out ion the yard. The military used the same Sioux type equipment for the last 50 years as well.
From the looks of that block deck very little professional work has been done to that engine in a very long time.