Sump drain size

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Sump drain size. Does anyone know what size socket the sump drain is? I have been using and adjustable wrench. Caveman I know but it works.
I would like to get a real socket for it. I know its big. Larger than 1 inch. My bike is a 71
Thanks MikeM
 
MikeM said:
Sump drain size. Does anyone know what size socket the sump drain is? I have been using and adjustable wrench. Caveman I know but it works.
I would like to get a real socket for it. I know its big. Larger than 1 inch. My bike is a 71

Why not just measure it?

However:
 
Last edited:
Mike

The size of hex head nuts (and the proper socket) is given by the width of the head (in inch fractions) measured across parallel flats. US and metric bolt/ nut sizes refer to the width across the flats (inch fractions or mm resp.). Whitworth spanners refer to the thread diameter, so the spanner opening is much larger.

You can set your adjustable spanner on the head, then remove and measure the opening.

Off the top of my head, the sump drain is 1 1/2, but measure yours before buying a socket on my recommendation.

Slick
 
Last edited:
Mike,
I have 75 MK3. Plug is 1.5" SAE. Which happens to be the same size as the front drive sprocket nut. I purchased a 1.5" deep socket, cut it in the center and welded in a piece of pipe ( standard socket was not deep enough).
 
Deets55 said:
Mike,
I have 75 MK3. Plug is 1.5" SAE. Which happens to be the same size as the front drive sprocket nut. I purchased a 1.5" deep socket, cut it in the center and welded in a piece of pipe ( standard socket was not deep enough).

Yes, same size as gearbox sprocket nut. I use the gearbox sprocket nut box spanner on my sump plug.
 
Be sure to grind the chamfer from the socket/box wrench/ring spanner, that thin hex will be held more secure if you do.
 
MikeM said:
Sump drain size. Does anyone know what size socket the sump drain is? I have been using and adjustable wrench. Caveman I know but it works.
I would like to get a real socket for it. I know its big. Larger than 1 inch. My bike is a 71
Thanks MikeM

You should have a 20M3S engine, you will find no one yet has the correct answer except in the thread LAB has provided.
The size is 1.474" and as such is a 1" BSF/7/8" BSW.
2xxxxx 750 had none
The 1-1/2" started with the 850's . If yours is 1-1/2 then it (engine or drain/filter) was replaced at some time.
 
dynodave said:
The 1-1/2" started with the 850's . If yours is 1-1/2 then it (engine or drain/filter) was replaced at some time.

It started earlier than that.
I have a set of dommie cases with that large sump plug.
Its 500cc and 1950s, on a generator engine.
Swaps with 850 parts not possible.... (as in swapping cases).
 
Just happened to have some cases in the basement.

Trying to show the difference. Left 850, nice 1-1/2" hex condition, center 750 rather chewed up!, probably 1-1/2", right from an 88 engine has the slightly smaller BSW hex size.
The Commando plugs are steel, the 88 is brass. The threads into the crankcase are the same. All have the brass mesh and retaining clip.

Sump drain size
 
Bob Z. said:
Just happened to have some cases in the basement.

Trying to show the difference. Left 850, nice 1-1/2" hex condition, center 750 rather chewed up!, probably 1-1/2", right from an 88 engine has the slightly smaller BSW hex size.
The Commando plugs are steel, the 88 is brass. The threads into the crankcase are the same. All have the brass mesh and retaining clip.

Sump drain size
Not a fair comparo, example #2 clearly showing pipe wrench marks :shock:
 
I use a trailer hitch wrench (1.5 inch) from Walmart ($10) on my 1970. Works great.
 
baldy said:
I use a trailer hitch wrench (1.5 inch) from Walmart ($10) on my 1970. Works great.
aceaceca said:
I have a 71 Commando and use a 1 7/16" six sided socket.

No complaints from my 1 1/2 af ring spanner either. Size matters only when it doesn't fit!

J
 
auldblue said:
Sump drain size

1.5 AF or 1 1/2 AF but some I have taken out have had the cold chisel and hammer job. Effective but agricultural!


I remember you. With all the disrespect I can send, I have no respect for you or any of your opinions.
Your wrench will certainly fit in a place that I cant mention. Perhaps this should be in the pub.
 
Rohan said:
dynodave said:
The 1-1/2" started with the 850's . If yours is 1-1/2 then it (engine or drain/filter) was replaced at some time.

It started earlier than that.
I have a set of dommie cases with that large sump plug.
Its 500cc and 1950s, on a generator engine.
Swaps with 850 parts not possible.... (as in swapping cases).

I just tried one of my MKIII commando 1-1/2" sump screens in norton engine H12 50131 which is a 1953 generator case, and the brass domi sump went right into the E-start motor? Seemed to fit OK both ways.

E12 27614 (1950) is like the combat cases 72-73 with a drain screw only.
from the parts books shows these sump filter bodies #
1953 part = 16945 works in my 1952 also
1963-1970 part = 16945
1971 part = NM16945 (73+74 850)
1975 part = 06-7676 IPL also shows original # NM16945
They are all functionally the same, possibly the NM was added in 71 and OEM was then increased to 1-1/2" hex
 
Think we are talking at crossed porpoises here.

Your post didn't really distinguish that you were talking about the whitworth type large sump nut giving way to unified sized large sump nut.
i.e. slightly less than inch and a half and a full inch and a half.
It read like you were denying there were large sump nuts before the 850...
 
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