Valve lapping?

Hey all,
Might be a noob question, but here goes: I have my head apart at the moment, having some thread repairs and minor stuff done. Compression was 140-150 on each cylinder before I sent it out and no slop in the valve guides. It has less than 1000 miles on it since a full valve job, so what's the consensus: yay or nay on valve lapping when I'm putting it back together?
I was figuring on doing a real light lapping while I have it apart mainly just to polish up the sealing surfaces and clear off any crap that might be stuck/burnt on them. However, I've read some recent articles saying lapping has fallen out of fashion, at least on newer engines, which these are clearly not. Might be making mountains out of cow pies, but a 3 week lead time on repairs gives me a lot of time for the much-maligned "Shoulda done it while it was apart" paranoia to set in.

After 1000 miles? No, I wouldn't absent some concrete reason to do so.

Scheffy
Test the seating of the valve by supporting the cylinder head with valves assembled, hemispheres upward. Pour Gasoline or Kerosene into each inlet port and allow 20 seconds to elapse. If liquid has not passed the seating into the combustion chambers in this time, then all is well. Taken from the workshop manual.
CNN

Don't "fix" it if it ain't broke.

Really, don't disturb the valves at all.

I would do exactly as CanukNortonNut suggests, it is a good check.

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When you are too old for Motorcycles, there is always BMW.

Yup,

I would renew seals if they are old. I'm assuming the 1000 miles was in less that ten years or so?
If you did the head within a couple of years I'd just test it with kero.

Agree with above re checking valve seal. OTOH, though the mileage is low, if it's been years since the last time it was apart I'd replace the valve seals anyway. They become brittle due to age regardless of mileage.

I have to admit that despite the above, if it was me I'd relap the valves and install new seals anyway. But that's just me.

MexicoMike said:

Agree with above re checking valve seal. OTOH, though the mileage is low, if it's been years since the last time it was apart I'd replace the valve seals anyway. They become brittle due to age regardless of mileage.

I have to admit that despite the above, if it was me I'd relap the valves and install new seals anyway. But that's just me.

Click to expand...

Mike, you and Cookie just answered a question I was going to float as a new topic. Old seals, both installed and bagged. I had a head redone around 10 years ago and just boxed it up. New everything including intake seals. I slathered them with Redline assembly lube when I put it together and I think its kept them ok. Last year I put this engine together with a crankseal that was also sitting on the shelf, bagged for 10 years, and I see now that I'm running a dry primary that it's leaking. I guess that seals have a shelf life. The crankseal's gotta go, the valve seals are on probation.
A guy I know that does a lot of heads said that when he sets up the seats and valves they don't need lapping, but that you can check them with ink to see how they've settled in. If they're off it's supposed to be better to re-cut to keep the seat face width in spec.

We used to have a vacuum tester that checked our valves, with four valves per cylinder in a diesel they had to be good.
With seals you can get lucky but all that stuff ages out. In commercial service our guys rotate stuff like seals, the new ones go in the back of the bin.

After seats are re-cut concentric with new guides, a little light lapping is OK. If your head only has 1000 miles since a valve job, further lapping isn't necessary unless the leak test shows a problem. Overlapping the valves can render the seat-to-valve head juncture too wide and have a negative effect on sealing and longevity. As was said before, if it ain't broke, don't fix it.