Single angle Valve Seat

1952 - 1968, M38A1, M170, questions, discussions, regarding anything related to the M38a1 series.
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Single angle Valve Seat

Post by delta31 » Thu Mar 16, 2023 11:30 am

This jeep is not intended to be a daily driver.

I replaced the exhaust valve guides in an F134 engine which went well. Purchased 4 new exhaust valves and will need to get a 0.375
reamer to get the valve to go into the guides. The seats don't look bad but I concerned if they will be concentric with the new guides
and might not lap in well. I was thinking of just buying one New Way seat cutter which I think would be 46 degrees as the valve is 45 degrees.

My main question is, is it that important to do the 3 angels on the valve seats? Or, will just the single angle be sufficient?


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Re: Single angle Valve Seat

Post by parker007 » Thu Mar 16, 2023 1:37 pm

after new guides you must cut the seat, 45,46 will work. no need for 3 angle but you need to get the right contact width.

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Re: Single angle Valve Seat

Post by dpcd67 » Fri Mar 17, 2023 5:02 pm

Right; lap them after grinding; and the 3 angle thing is a modern concept. On Jeeps you only need one angle.
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Re: Single angle Valve Seat

Post by Wolfman » Sun Mar 19, 2023 5:55 am

The 3 angle seat is used on newer engines with hard seats and valves. The idea is, the narrower seat face would break up any carbon deposits that were caught between the seat face and valve face. Less seat face contact area creates more pressure on the smaller contact area.
If you still have the seats cut into the cast block, a little wider seat face would give more contact area and spread the pressure on the seat face out over a larger area. Better wear and longevity.
More important is the upper edge of the seat and where it is on the valve face.
When the seats are ground, the upper seat face edge moves up and out. Don't want the upper contact edge of the seat face too close to the outer edge of the valve face.
On a 45' valve, if the seat contact edge is too high, the seat needs to be top dressed with a 30' stone or cutter to move the upper seat edge back down on the valve face to the proper position.
After top dressing the seat, if the seat is excessively wide, I bottom dress the seat to narrow it up.
3 angle cutters do 3 angles with one cut. top 30'. seat face 45' or 46'. and the lower angle 60'.
Going to need a different 3 angle cutter for each valve and seat size you plan to cut, and they are not cheap.
One more thought.
If doing what I just said ends up with the top cut area being wider than the O.D. of a replacement seat. STOP.
The seat is beyond grinding. Time for replacement seats.
Comes under the heading of self induced grief if you keep grinding.
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