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I pulled the sludge trap plug from a 160 motor only to find the threads were screwed up. It was a hex plug, so I was able to get it out. I tried to clean the threads up with a 13 mm tap, which made it unusable. I didn't realize they have a slight taper to them, I do now.

I ordered a 12mm plug from BelMetric, but it's too small. I think the correct size is 13 mm, but the taper part makes me uncertain. I am trying to avoid owning a wide assortment of plugs that don't fit. Does anyone know the correct size plug? Have a source for it? Or can cross reference it to another make/model bike that has wider availability?

Thanks in advance.

I just noticed that BelMetric carries 1/2" British plug, very close to 13mm. Does anyone know if that might fit? Thanks.

https://belmetric.com/stainless-taper-bspt-british-tapered-plug-din-906/

Hi Greg

the only plugs i run into are the M18 X 1 plugs . and they dont have a inside hexagon

Eldert

You may find it is actually a BSP plug. BSP is typically used all over the world (except the US) for this sort of fitting. From memory, even VW oil gallery plugs are BSP.

Ian

Thanks Eldert. Yes, the M18 is widely available. I do believe Lacey has plugs with the hex. I have a few.

Thanks Ian. I believe you may be correct about the BSP. I'm not familiar with them, even had to lookup what the acronym meant. BelMetric does carry some less common items in the U.S. The have BSPT DIN 906 in 1/2" tapered allen head plug, which is about as close to my size as I can find. I measured a 12mm tapered plug that I have and there is about .4mm difference in diameter between the top and bottom thread. If the taper is a similar slope on the BSP plug, perhaps it will do the trick.

I will purchase a couple and post the outcome in this thread.

IanHood wrote:You may find it is actually a BSP plug. BSP is typically used all over the world (except the US) for this sort of fitting. From memory, even VW oil gallery plugs are BSP.

A lot of hydraulic fittings are still BSP. Here in France, for example, common or garden taps are still ½ or ¾ inch .

I guess - but do not know - it's because of the problems that changing threads on existing installations would cause.

BSP in Italy too.
Maybe it's the ideal system?

Quick update. I need to do a little research on BSP sizes, because the 1/2" BSP tapered plug that I ordered is about 20mm in diameter. Way to big. The correct size appears to be 14mm x 1.25. Unfortunately, the common thread pitch for an M14 is 1.5, so my search continues. Who would have thought this would be so hard?

Another quick update. It's definitely M14x1.25, because I was able to screw an NGK spark plug into the crank. Now, I just need to find one that's tapered. The good news is that I know the correct answer, but bad news is that I don't expect it will be easy to find one.

Hmmm, BSP is actually measured in a funny way and it may be that you needed 1/4 inch BSP which I believe has a very similar thread pitch to a spark plug. See the picture attached