More on Valve Guide Clearances.
I have detailed my cylinder smoking problem earlier in the forum item below:-
https://www.a7a10.net/forum/index.php?topic=13316.msg107462#msg107462A quick summary - after running for 40 miles, the GF is smoking severely on the Left Pipe. It was excessive and wasn't settling down, so I have taken off the Cylinder block and head. The compression test implied glazed bore on the LHS.
I certainly think that I have glazed the bores due to lengthy problems getting it to run enough to ride it.
However, the valve guides were something else.
There was one odd type with a non-tapered top, and all 4 had been "knurled" inside - like there is a thread in each guide presumably to enlarge the ID of the worn guides, not cut but rolled in and then reamed to suit the valve stems. I believe this was sometimes done to lengthen the life of the guides at little cost, but was never intended to last very long. I imagine this would also accelerate wear on the valve stems due to reduced surface area.
Anyway, I measured the clearances - all are at least 8 thou, and the Left exhaust is at 10 thou.
I would say R**ted.!
That probably explains a lot of the smoke. I measured the valve stems, and they are all worn a little - the clearances compared to a new uninstalled guide (5/16" = 0.3125") are all from 2.5 to 3.5 thou. That suggests valve stem wear of 1 to 2 thou. Stem ovality is good I think, the worst being about 0.6 of 1 thou.
I will replace the guides with new Cast Iron Guides, but am wondering whether the new guides when compressed to fit will be a little reduced in Inside Diameter - just a thou or two would do. I hope I don't have to buy new valves. I'd like to know whether I should go look for new valves now or wait until I can measure the installed guides which may be a few weeks.
Does anyone have experience whether the guides ID will shrink a few thou when installed.??
Cheers Colin