Morris Minor Owners Club

hello all, would anyone know the thread size for the bypass tube that screws into the cylinder head? it looks to be the same size as the thread size on the temp sensor hole.

thanks

Last time I checked that was a well debated question. All seem agreed that it is 5/8", most that it is a Whitworth form thread, but some say 18tpi, others 16tpi. Bet either would fit perfectly well with a bit of thread sealer. I turned one up a few years back in an emergency but I'm blowed if I can remember what pitch thread I cut.

The correct thread is 5/8" x 16 TPI UNS (Unified National Special) the same as the crankshaft bolt thread.
The problem is that the bypass hose stub is mostly supplied these days as a 5/8" x 18 TPI taper or parallel thread.
A 5/8" UNF (Unified National Fine) thread has 18 TPI.
A thread gauge I have and marked 18G 5/16 fits the current issue bypass hose stub threads.
It also fits the PG9 Tap (5/8" OD) that I have.
Sorry I cannot be more helpful.
Phil

when you say crankshaft bolt thread, do you mean the 4 bolts that bolt the flywheel on?

ampwhu wrote:when you say crankshaft bolt thread, do you mean the 4 bolts that bolt the flywheel on?

No - the crankshaft pulley bolt or starter dog bolt threads.

The flywheel bolts are 3/8" UNF.

Phil

The Mini lads don't have any problems using the one supplied by Minisport. http://www.minisport.com/12a2075-cylind ... e-kit.html

I have ordered one of the bypass stubs from Mini Sport. It will be interesting to see what the thread is!
Phil

I am pleased to report that the by-pass stub from Mini-Sport Pt No: 12A2075 has a parallel thread of 5/8" x 16 TPI.
Whether it has the same pitch angle as the UNS thread I do not know.
Phil

"Whether it has the same pitch angle as the UNS thread I do not know"

That don't matter, just jam it in with some PTFE tape

That is crude and not the way I do things.
If you need to use a sealant for sealing the bypass stub - use 'Heldite' jointing compound.
Resistant to the pressure and temperature variations found in the coolant system.

http://www.stationaryengineparts.com/He ... pound.html

Phil

A couple of added photos regarding fitting the Mini Sport bypass adapter.
Bull Motif By Pass Tube Pt No: 10M227 is also suitable and has the advantage of a hexagon to assist in screwing the stub in or out.

Just fitted a Bull Motif bypass stub Pt No: 10M227 with hexagon spanner facility to a 940 head as pictured below:-
The fit is good and it is easy to screw in and tighten with the hexagon - it does not go fully home (see picture) so would advise using 'Heldite' jointing compound or Loctite 'Lock and Seal' for securing and sealing.

If you want to block off the bypass use a Mini Sport blanking plug Pt No: 88G619.

http://www.minisport.co.uk/
The BM stub could be used for repairing a corroded water pump stub if required if you have a suitable drill and tap(s).