Forum:
While adjusting the valve clearances,I got dirt on and in the rocker cover bolt threads, was interrupted, then, short of time, put it back together in a hurry without remembering to clean up the threads, releasing dirt into the engine.
Of course some damage will already have been done, and there'll be some abrasive that won't be removed by anything short of a full strip-down (embedded in the soft metal bearing shells, for example) so the best I can expect is to limit rather than eliminate it.
I'm thinking I might just do a DIY engine flush to remove as much of the silt as I can.
The basic idea is to use 3 changes of 30% 2-stroke as a flush while turning the non-firing engine over with the plugs out, then, after changing the oil filter, do a couple of close-succession changes (say 100 miles or so) with Delvac 15W/40 and (very old) Mobil Special 20W/50, before resuming normal oil change intervals. I'd have to watch the very old Mobil Special for signs of short-term instability, but, unlike current-spec oils, at least it'll have a decent amount of zinc in it.
I'm assuming that, while 30% 2-stroke is probably a relatively poor lubricant, it won't be too damaging in a non-firing engine, and may flush out grit that would be retained by thicker oil. 30% is still a high oil % compared to a typical 2-stroke engine running at, what, 2-5 % 
Seals are presumably made to withstand some petrol contamination of the oil, (though of course not that much) and they won't be exposed for long or at very high temperature.
Possibly, perhaps after filtration/settling, the 30% petroil mix could be diluted further and burned in a 2 or 4 stroke engine.
Comments?
Safe-ish or guaranteed fatal?
Contamination
In engines I have worked on I would not have worried too much about some grit contamination on rocker cover bolt threads. Any of it that escaped from the threads and got into the rocker box should have been washed down into the sump. As the bearings are pressure fed with filtered oil there shouldn't be a problem.
YRV Tony
I think you are looking into
I think you are looking into it far too much and don't need to be overly concerned.
Drain the oil, leave filter on, and use normal oil like you normally do. Then change it again after a short while, But with a new oil filter.
You mean I think too much?
Sorry, but we expatriates get that all the time in Taiwan.:)
My rationale for using 2-stroke is I already have quite a lot of it, (likewise the Delvac and the old Mobil) and it should allow me to produce a large volume of flushing oil at fairly low cost. (No cost if I can later burn the petroil mix in an engine).
I'd expect the efficiency of flushing to increase with the volume / number of changes.
After about 40 klicks on the motorway, when it dawned on me what I'd done, the oil film had a greyish appearance, suggestive of very rapid wear, and after sitting for a couple of weeks, metal slurry has settled out on the dipstick.
I'd done an oil and filter change about 600 klicks earlier, with Mobil Delvac MX, which I'm going to stop using long term because of the lowered zinc levels in current-spec oil.
I suppose its possible the petroil mix wont be viscous enough for the oil pump to develop pressure, so it wont reach the top end.
Can't think of any other gotcha's with using 2-stroke at the moment, but I've never heard of anyone doing it, so if anyone else can I'd be glad to hear them before its too late.
Relying on the filter
Depends how good the filter is. My understanding is that "standard" full-flow oil filters aren't very good, and don't remove fine contamination.
This oil filter was a fresh one, but it was some Chinese brand of unkown quality (its difficult for me to find good stuff here, partly because I don't speak Mandarin or Taiwanese) so might well be worse than standard.
I'd "parked" the bolts in holes in the rocker cover that were contaminated with congealed oil. I think they picked up quite a lot of fine oily silt, evident as streaks when I later took the rocker cover off again.