Can someone tell me what the thread is in the head for this bypass fitting
The one the connects to the water pump
I have a new fitting here that is 5/8" x 16 tpi and i can not find any reference to this thread
can someone confirm that this is the thread

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1970 MK2 Cooper S

Yes, it is an odd-ball. It is also used for the crankshaft bolt.

It is 5/8-16 Whitworth apparently, but I reckon a 5/8-16 UNS will be close enough even though the threadform is slightly different (55 deg v's 60 deg) given the low torque/load on the fitting.

I am about to change that fitting myself.... once my new tap arrives from China

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Don't listen to what I am saying... just understand what I mean.

I drill the remains 9/16" then run a 5/8 18 UNF tap in, it takes hardly anything out (except the old fitting's thread). There are only about 3 or 4 threads in there!
I make new fittings from 5/8 UNF [RH] oxy hose joining nipples. Just turn one end down and shorten the other end a bit.
Never rust, last forever.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Well with the use of a thread file and a die grinder i managed to revive the thread and get the fitting installed
Only problem is that the fitting was just plain round and no hex
So a little butchery to get it screwed in

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1970 MK2 Cooper S

The plain round ones that I have seen have two little notches in the hose end of them so you can fit a big screwdriver in and screw it in tight that way. You could mod yours with a hacksaw.

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Find a job you love and you will never have to go to work !