850 Mk3 Primary Drain Plug

Mart UK · Dec 9, 2022

This question may be "how long is a piece of string"!

The drain plug hole in my primary cover has been helicoiled at some point. The helicoil is loose and starts to spin just as the plug gets to the nipping up stage. I've prevented a leak by using a thin smear of Wellseal on the plug and washer faces. I may get away with it at the coming oil change, but would like to replace the helicoil.

Is it possible to get the old one out and just replace with the new one? If so, does anyone have a view on what the size/spec of the helicoil is likely to be!? It is using the standard drain plug.

L.A.B. · Dec 9, 2022

Mart UK said:
Is it possible to get the old one out and just replace with the new one?

If the Helicoil is turning with the drain plug then the case thread must be stripped so replacing the Helicoil with an identical one is going to do the same.

Mart UK said:
If so, does anyone have a view on what the size/spec of the helicoil is likely to be!? It is using the standard drain plug.

The standard thread is 1/4" UNF. Item 13;

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kommando · Dec 9, 2022

Go for a solid repair type such as a Timesert, these have a bigger OD so a loose helicoil size will not be a problem.

L.A.B. · Dec 9, 2022

Or Big-Sert.

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Mart UK · Dec 9, 2022

That's great. Will try one. Thank you.

L.A.B. · Dec 9, 2022

Easier/cheaper to just tap it oversize.

N0rt0nelectr@ · Dec 9, 2022

When I bought my Norton back in 76 my dealer said that as I (or anyone else) adjusts the primary chain the transmission rocks back. When it rocks back the level hole will get lower. He said to look in the filler hole and make sure the kickstart return spring is half covered. Simple and easy.

Mart UK · Dec 9, 2022

L.A.B. said:
Easier/cheaper to just tap it oversize.

I did wonder about that, I have a range of taps. I just wondered how well a wider hole will seal at the face, I guess no different to the big sert...

Mart UK · Dec 9, 2022

N0rt0nelectr@ said:
When I bought my Norton back in 76 my dealer said that as I (or anyone else) adjusts the primary chain the transmission rocks back. When it rocks back the level hole will get lower. He said to look in the filler hole and make sure the kickstart return spring is half covered. Simple and easy.

I think you're replying to the gearbox level plug thread?

L.A.B. · Dec 9, 2022

Mart UK said:
I did wonder about that, I have a range of taps. I just wondered how well a wider hole will seal at the face, I guess no different to the big sert...

You could drill and re-tap it slightly off-centre from the original hole and extend the flat face area inwards.

Mart UK · Dec 9, 2022

Yes, that would be a good solution. I don't have a pillar drill / clamps to hold it properly for that. I'm out at a Christmas dinner with riding mates tonight. I will see if any have the right set up.

Thanks.

Torontonian · Dec 9, 2022

I've never used the MK111 drain screw ever , after all you are likely going to take off the cover to do work or cleanings . I could see the need for an oil flush using it . It protrudes too much and can hit the L .H . pipe. I reversed the screw to avoid this , putting the head inside the outer cover with a good copper washer. Another option would be to aluminum weld up the hole forever. Likely not what you wanted to hear .
Enjoy.

850 Mk3 Primary Drain Plug

Mart UK

L.A.B.

Moderator

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

kommando

L.A.B.

Moderator

++ BIG-SERT Oversized thread repair kits ++ thread repair kits for oversized holes, previously repaired threads oversized holes

Mart UK

L.A.B.

Moderator

N0rt0nelectr@

Mart UK

Mart UK

L.A.B.

Moderator

Mart UK

Torontonian

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