Although I'm getting to know my way in Imperial threads, I am still not extremely confident in my abilities to identify them.
I've got a set of crankcases for a late Model 50 that are missing the sump plug. It's quite a small hole with very fine thread. I've carefully tried fitting various old studs and bolts and the one that goes in deepest (but not fully, about 4 to 5 mm, though that might be due to it being used) is a 3/8-20-26 stud. The 26 tpi side that is.
So it seems the thread is 3/8"-26 BSC. Could that be right?
Probably 1/8" BSP (28tpi)…
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Sump plug threads.
Hi Tim,
Yes you are correct, 3/8" x 26TPI. This section of the crankcase is quite thin so needs a fine thread. Unfortunately this is too fine for aluminium and is easy to strip the thread. A quick fix for this is to re-cut it with a 10mm x 1mm thread pitch (25.4 TPI) which is just enough to restore the fit.
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Thanks both
Thanks for your guess John, it sounded very plausible. And thanks for the confirmation Richard.
The thread seems to be in good condition, so I'll try to source (or otherwise make) a suitable bolt. It'll be drilled for lock-wiring anyway, which will help not overtightening it, which you usually do for 'peace of mind'.
If the thread eventually does fail, the M10x1 solution wil be an easy fix.
Cheers,
Tim
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Available in most engineering and Bolt Shops.
Tim,
The 1/8 BSP plug is available in most engineering and bolt suppliers. In Australia at least.
I'm pretty sure the sump plug is parallel thread not tapered thread.
They are easy to strip so be careful tightening it.
They are also very cheap , probably less than 1 pound in UK.
Don Anson
Melbourne
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Probably 1/8" BSP (28tpi)
John