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MG MGB Technical - Oil Cooler Thread Size?

I can't seem to remember or locate the thread sizes for the oil cooler lines. Anyone else know off hand?

I also have a Mocal oil thermostat installed, as purchased from Moss 20 years ago. It appears to be the same thread but I'm not positive. Anyone know for sure?

Thanks!
Steve Simmons

Probably 1/2in BSP. (But may be 5/8!!)

CP

Colin Parkinson

A very good question. I would also like to know what size the threads are on an oil cooler. Is it AN like Aeroquip,or NPT, or BSP?
ASH Andrew

Oil cooler fittings are 1/2" BSP. You can buy BSP to AN adapters from www.PegasusAutoRacing.com
They also sell BSP barbs so you can use high quality push on hose.

Clifton
Clifton Gordon

Thanks Clifton. I suspected BSP but now I know for sure. I'll write it down this time!
Steve Simmons

I think you will find the oil cooler hose threads are 13/16" X 14 thread - a UNF fitting I think. The same thread for the hose connection to the oil filter adaptor and the hose fitting at the block, though don't recall whether the same thread size mounts that fitting into the block.

Regards
Roger
Roger T

I'm not sure if there is a 13/16 x 14 UNF size. All references and searching only come up with a 13/16" x 10.

In In Appendix 7 page 347 of Lindsey Porter's MGB Purchase and restoration Guide;

British Standard Pipe
In the applications listed below, BSP threads are used. These ARE NOT compatible with any American threading system, and the proper BSP screws and fittings MUST be used.

Uses of BSP on MGB.
Oil Cooler and fittings 1/2BSP
Oil Pressure relief valve 1/2BSP
Oil outlet rear 1/2BSP
Others are listed.

note at the bottom.
Most of these BSP applications require the use of BSP/BSW wrenches or the use of a good quality adjustable wrench.

I would have scanned this information and posted it as an image but there is a copyright warning in the Dedication page.

Clifton
Clifton Gordon

G'day Clifton,

It's interesting to see what Porter lists. My eye caught this subject because of some recent research into alternative oil filters and adaptors where thread sizes were central. My contribution was based on a concern that people may avoid investing time and money in obtaining fittings that wont fit. The reference to 1/2" BSP didn't sound right based on that research.

Prior to posting I went out to the garage to take some measurements of a discarded oil cooler hose fittings and an oil filter adaptor not on my car. I did not go looking for the disconnected oil cooler because those hoses have the same fitting at each end and the filter adaptor gave me a viable external thread to measure. That measurement is 13/16". That is by micrometer at the outside of the thread cut. That hose fits neatly onto that adaptor thread. The TPI figure of 14 was by thread measure tool fit.

Testing that measurement, I offered a known 3/4" thread up to the hose fitting. Screwed in but was very sloppy, as you would expect. Would never be a secure fit.

Can't accept Porter's figure. Have to go with my measured 13/16" for that thread.

As to whether its a UNF or BSP thread, open to advice but I note the following.

The UNF size of 13/16" did exist, though I am happy that it is difficult to find reference on contemporary thread size charts. I believe it is now known as a 'non-preferred' size - one of a handful of the originally agreed sizes that has fallen into disuse and which is actively discouraged. I imagine this has probably happened this side of the 1960's, which period saw the continuing take-up of the UN system.

Interestingly there is an active 13/16" size on the UNEF charts, but this has a TPI of 20, as do all from 3/4" to 1" in that system.

The reason I thought/think the thread is UNF has to do with the cut of the (internal) threads inside that (original) oil hose fitting. They display a distinct flattening to the top of the thread cut which is a feature of the UNF standard. The BSP thread, on the other hand, has a marked curve to this part of the thread cut.

The TPI figure of 14 is between the 16 for the 3/4" and the 12 for the 1" sizes in the UNF system. It is the same as for the 7/8" size - which is in contemporary use.

I acknowledge that in the BSP system a TPI of 14 runs from the 1/2" to 7/8" sizes, so would I presume apply to a 13/16" BSP size.

So, based on measurement and observation, my offering of a 13/16" X 14 UNF thread. Happy to be corrected in the interests of greater accuracy for us all - as well as for those who will access archives for research in the future.

Regards
Roger
Roger T

One would have to measure the included angle of the threads to be sure what it is. Since a 1/2 BSP and a 1/2 NP have a thread count of 14 TPI, the only difference would be the profile of the threads. Also, a 1/2 BSP measures 0.8250", a 1/2 NP measures 0.8230" and 13/16 UNF would measure 0.8125". This all boils down to the thread profile for determining what the actual thread, but from what I have found in the MGBs, my bet is that the thread is 1/2 BSP. Cheers - Dave
David DuBois

David,

Yes, major diameter and thread pitch do provide another way of looking at this. I would never have thought a 1/2" BSP thread would be that far up the UNF scale. It would also make sense in terms of the block drilling into cast iron, to take the hose at that end.

On that basis Clifton I owe you and Porter both an apology.

On the up side I may have found a way to a solution in my quest for an alternative filter size on my B.

Regards
Roger

Roger T

Hi,
To be able to use JIC fitting, 3/4x16, dash8, aluminium anodised made,teflon braided hose, I built my own adaptor. The other adaptors, the radiator with JIC output are available in trade.
Regards

mw michel

I've always been led to believe that the oil-cooler fittings were 1/2" BSP
Dave O'Neill 2

On a related note, does anybody out there know what size the fittings on the oil filter stand are?
Neal Glick

On the mgb, to the original equipment all raccords and fittings for the oil cooling system are 1/2 BSP
Regards
michel

BSP (British Standard Pipe) is a parallel thread. Like NPT (National Pipe Thread (tapered) used here in the US) the size listings were based on the INSIDE of the pipe when they were made from cast iron - many moons ago. As materials improved (better cast iron and then steel) the ID of the pipe got larger, but the OD remained the same. Otherwise all of the fittings would have to change - there would have been no backward compatability. That's why the sizing doesn't seem to make any rational sense.

1/2" BSP has a thread major diameter (the OD) of .825". That's pretty close to 13/16" (.8125"). Often threaded items are not made to the nominal dimension so there is some clearance between the male and female threads.

The standard thread pitch for 1/2" BSP is 14 threads per inch and is based off the Whitworth 55* thread.

And just to confuse matters a little more, the current designation for BSP is "G" thread!

HTH,
Tom
Tom Sotomayor

Neal, MGB oil filters are 3/4" x 16 threads per inch. It's very common size for oil filters.
Clifton Gordon

Tom,

Spot on and the nub of the mistake I made. No excuse really as I have replaced the pressure relief valve on our water heater any number of times over the years, and you will know exactly the thread size without me mentioning - 1/2" BSP.

A suitably humbled contributor promising to try to remember the potential for error in untested assumptions.

Regards
Roger
Roger T

This thread was discussed between 28/08/2007 and 06/09/2007

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