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Old 10-28-2012, 09:14 PM   #34
Aspiring human
Zombie_Stomp's Avatar
Joined: Jun 2007
Location: SE Portland/ Carrboroland NC
Oddometer: 2,231
^^^ I got paranoid enough about that issue that I bought a brand spankin' new oem factory head. The one in the first engine on my XL got so overheated by a PO that a valve seat dropped and was rattling enough to cause wear in the aluminum. Later found cylinder sleeve dropped in the aluminum as well. I never got it started with that head in there. I wonder if it would have run at all if I had gotten the new stator it needed first. I think XRs only does that service. I heard they do it at the factory with a certain tolerance machined then use liquid nitrogen to shrink the steel insert. One machinist at the auto parts store I was using was talking about making little ding marks all around the head where the valve insert goes, then a bunch of ding marks (with a center punch) around the valve seat steel insert, then using red loctite, pressing it in. I asked my retired, formerly fulltime self employed machinist friend about this procedure and he said "those guys are kind of a bunch of yahoos", at which point he explained how that would fail in short order, and how they do it at the factory. That got me asking all kinds of questions, like, can any used head ever be trusted knowing this?

The point of my long story about my experience with bad valve seats is:
1) take the valves out at least to see if the valve seat has obvious signs of overheating or any wear around the outside, and to see if the valve seat just friggin falls out.

2) don't take the head to any yahoos. Use a motorcycle-specific shop.

3)Don't get too paranoid. It is most likely fine and will be unless you overheat the shit out of the engine.

P.s. there is a test you can do to check valves too. Tilt the head with exhaust ports toward the sky and try pouring solvent in there and see if it leaks past the valves. You can try petroleum based liquids of various viscosities to see if they leak, do this for intake side as well.

Hopefully you honed the cylinder and a new set of rings, that's pretty important once they have seated they can't really find their original seal again once disassembled.

And of the valves one more time, bar minimum take them out and replace the seals, before that, lap them with valve lapping compound and check to make sure there are concentric wear patterns all around the valve. Better one step than this is replace the valve guides too, but IIRC you are on a budget.

You can lap the head mating surface on a piece of double-thickness glass with very fine sandpaper and something wet like mineral spirits. Same for the cylinder, but that's (hopefully) already on with it's nice hone job and set of piston rings.
1982 4x4 longbed, a rolling daily driver work-in-progress...
1987 Yamaha XT600 2KF (German)
STOLEN: RED XL600 in Portland

I do heavy-duty textile repair, upholstery, and design/manufacture bags.
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