Thread for block drain

[gammakeith]

Dear all,

The threads on my cylinder block drain “cock” have just expired during this evenings flushing activity. Thus, I need to source a bolt off ebay to blank it off. Can anyone tell me what thread it should be? I’m guessing some some strange pipe thread but my knowledge of metric fasteners is proving of little help…..

Thanks,

Keith

[BRIAN MARSHALL]

Hi Keith, The vast majority of cylinder block drain holes are threaded 1/8″ BSP (British Standard Pipe Thread). I have BSP taps and dies if you get stuck. If you need to put an oversize plug in the hole you can use any thread you fancy ! The chilled cast iron of the blocks is pretty hard stuff, and cheapo carbon steel taps may have a hard time cutting a new thread, so use high-speed steel taps. (I’m assuming that it is the thread in the block you are talking about, and not the thread on the brass drain cock…)
Brian

[gammakeith]

Hi Brian,

Its the threads on the cock that have stripped. The threads in the block appear OK so I think I just need to source a suitable blanking plug (or replacement cock). The OD of the threads on the cock is approx 3/8″ if that helps?

Thanks for the offer of the loan of a BSP tap. If I need to clean the thread up in the block I will certainly take you up on the offer.

Thanks,

Keith

[BRIAN MARSHALL]

Hello Keith,
I have got some 1/8″ BSP brass plugs somewhere, so don’t go buying one. Give me a call to arrange to pop over for one. (phone number in Yowl, under Eastern Section Information). I’ve probably also got a replacement tap with good threads somewhere.
Regards,
Brian

[gammakeith]

That’s very kind, sir! I will be in touch very soon 😀 I suspect my activities will all be in vain (ie the bike will still boil over) but at least I will have eliminated everything bar the size of radiator. The bike is currently running lovely with needle is raised to its uppermost position so I am now longer concerned that its too lean. The plugs were a much darker colour and its even ticking over now. MInd you, the downside to that is that the four-stroking is now annoying at lower speeds.

Thanks again,

Keith

[Deleted User]

Hi Brian to you want to sell the tap as I have a ’27 squirrel engine with a blanking plug fitted which I have been looking for a tap for
Rgds Jim

[BRIAN MARSHALL]

At the moment it is reserved for ‘gammakeith’, but if he doesn’t need it I’ll send you a PM. You can buy new repro 1/8″ BSP drain taps/cocks quite easily, and I suggest that you have a quick look on eBay for starters.
Brian

[Deleted User]

Google vintage stationery engines ,often some 1/8 bsp drain taps on there . if no luck get in touch I have a spare. Regards D F .

[Deleted User]

Thanks for that, I am looking on ebay and through google but as yet I cannot find the authentic shape, will keep looking , if no success I will take you up on your kind. Offer, Jim

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