Any engine machinists on here? Valve seat questions

Yamaha Raptor 350 & Warrior Forum

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Jul 6, 2022
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Tearing into rebuilding a '87 head. The intake valve mating surface seemed too large. Measured 2.1mm, when .9-1.1 is spec. Upon further looking, the intakes 45 degree mating surface is lopsided. Measures 1.8mm on one side, and 2.8 on the opposite. Clean cut with no hammering effect visible.On the thinner side, with a new valve, I can barely see light shined through. My thinnest .0015" feeler will not go through, but it leaks when tested with isopropyl alcohol. Yes, I did thoroughly clean all the carbon off. I installed the new valves with the inside spring to keep some seat pressure.

Is it normal for a factory seat to have been cut this way? Or did someone do a hack job on it?

When I got the old warrior, they said it was a completely rebuilt engine from a shop(red flag?). I found other things wrong, after it blew up, during teardown. Mainly, nothing was torqued to spec. All the bolts where all over the place, when it came to torque.

The exhaust side leaked, but there is mild burning visible on the seat. That was expected.

How far can you cut valve seats before they just need replaced?

I have access to a engine building shop for a quality valve grinding machine. I will be honest in saying I have no idea on this subject. All of the heads I have rebuilt, big and small, have been okay or I took to a machine shop. Like any builder, I'm always learning.
You can see the difference in the cut between the two pics.

I'm rebuilding this head for a 2007 Raptor 350. I will have dyno numbers, when it is done. I got to the dyno, with the current head making alot of bad noises. Pig rich it made stock hp. Going to clean up the ports. Has a mild cam. Just making a decent, cheaper, set-up for yard, trails, and a couple trips to Silver Lake in Michigan
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