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Answers for DOAX and some other dave.
First SOD.
One way to retorque them is to just put them exactly where they were when you started. 10 foot pounds is 20 pounds on a 6 inch wrench. I find with the regular wrenches it's a pretty good pull and have never had one strip, pretty strong material. I usually break them loose with a palm whack to the wrench and go back to exactly the same spot when tightening.
Second DOAX.
I can not remember a valve lash adjustment where the valves wore to a larger gap. Most of the wear (assuming the engine was decently cared for) is the valve to seat interface on the exhaust valves. This is especially true on air cooled motorcycles. My GZ250 was at the minimum tolerance at 5200 miles, so I adjusted to .001 above the maximum tolerance (.006, versus .005). I can hear the valves more than before from .003 to .006 lash. I did go one over max in order to avoid doing adjustments at the recommended intervals. Every valve on my VX was in specs at 62k miles, never having been adjusted.
The only case where the valves wore open that I can remember is the early Nissan Z cars that had a spray bar for the camshaft. Later ones had a hollow cam with holes for each lobe. The early spray bar type would get clogged up and wipe out that cam lobe, but that was just neglect, not good maintenance.
In most vlavle "adjustments" if you check the recommended service intervals, it calls for a valve lash "check". Basically this means, even though on my bike the exhaust valves were at the minimum spec, they would still "check" OK if the tech was not very scrupulous he would not attempt an adjustment.
I always checked the balance of wheels when I was asked to do an rebalance. If the wheels were in balance I charged less for the check since it was less work.
When doing a valve adjustment, I set every valve to the spec that would allow it to go the furtherest distance before requiring another adjustment. On my 73 Alfa GTV, which required removal of both cam shafts (DOHC) a micrometer measurement of the shim which was below the bucket that rode the cam lobe and a replacement shim that got you the proper lash at 58k miles. 100k later and every valve had tightened by exactly .001. All 8 valves were exactly the same. The engine was liquid cooled with hardened seats. I think the exhaust valves were sodium cooled.
regards
Mech
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