Valve lapping. On a long list of moto-related jobs I've enjoyed in the workshop that is right up there. It's just so damn satisfying. Here's a before -
Hooked up a brass wire wheel to the bench grinder, being careful not to brush the actual seating surface too much, or above the join where the valve meets the stem. They clean up pretty good -
Some grinding compound on the valve and its corresponding seat, a minute or so spinning the lapping tool - lifting the valve up and off the seat and rotating it through 180 degrees every now and then - and they come out looking like this -
That's what you're looking for - an even grey ring around the valve. Anyone unfamiliar with the valve geometry (as I was) - note that the seating surface is pretty narrow. There are a few angles to the valve, one of which is the actual seating surface (please correct me if that's wrong), and that's the angle you're lapping. The band isn't wide - from my understanding it's around 1mm. So softly softly catchee monkey kinda deal when you're lapping. I did it by hand - there are vids out there showing guys with drills but that all looks a bit aggressive particularly if it's your first time doing it. Lapping by hand gives a really good feel of the process, plus you can hear the grinding compound breaking down too, which is good.
Here's a before of the valve seat -
And here's an after -
I sharpie'd the valve and the seat after lapping - spinning the valve in its seat then shows any high/low spots where the sharpie has not been ground off. Again, that clean grey ring is a good indicator that your valve is lapped and seating well. Next - rebuild the valves and do the leak test, but that's for another day.
Also, I don't know what I was thinking. Looked at the cylinder block, looked at the gasket set I'd received in the mail and pulled it. I mean, shit. Got this far, may as well do it properly. Block came off without any drama -
- and I could then give the pistons a decent clean -
Decent enough anyway. I'm not going to remove the pistons I don't think, but all the rings are off and bagged - I'll check out the gaps but all being well they're within spec and re-useable. The block will get a hone - would it be a good idea to glass bead clean the block too? Seem to remember reading somewhere that media-cleaning blocks may or may not be a good idea.