Cylinder head/Barrel through studs

Maybe this: https://www.rgmnorton.co.uk/buy/single-cylinder-head-barrel-through-stud-6-5-8-st-st_162.htm may help?

Fritz

I would have expected the threads in the crankcase to be Whitworth (BSW), although that RGM link shows both ends to be Cycle.

Unusual for a stud screwed into alloy to be that fine.

If you hover over the picture on the RGM site it zooms in and looks clearly like one end thread is courser than the other. As Ian S' says it would be unusual to have cycle thread for a stud going into alloy. Whitworth is much more likely. Mike Pemberton could probably give you the definitive answer.

Ian

If the female threads in the crankcase are good you could get double diameter studs made up but if you don't have access to a lathe yourself it may be pricy.

The crankcase end is almost certainly BSW (Whitworth) then - 16tpi.

I've used these before: http://www.uni-thread.com/tr_bsw_kits.php - less than £30 for a kit.

If I was doing the job I wouldn't attempt it with the crankcase in the frame as due to the length of the studs alignment needs to be pretty spot-on. In fact I'd probably split the crankcase as well.

If the original threads are BSW, at 3/8 they are 16 TPI. At 7/16 they are 14 TPI. The tapping drill for the helicoil will not clear the 7/16 thread and the helicoil tap will cut across the thread remainder resulting in an incomplete thread for the insert. Risky!

This sounds like an awful lot of work, risk and hassle for the sake of ten minutes with a gasket punch or razor blade!

Colin

That's a good point. Timesert or similar (or even making up brass inserts) may be a better option.

If you did the latter, 1/2" BSPT is also 14 tpi.