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10 Posts

Posted - 06/09/2021 :  17:36:36  Show Profile
I am interesrted to learn of fellow members experiences of oil leaks from the rear main bearing of MMM cars and whether oil leaks only become a problem with good oil pressure or on fitting a higher delivery pump to a smaller engine. Also I am interested in whether aftermarket crankshafts using a lip seal running on a cylindrical land are better or worse than old cranks using a return scroll behind the thrower? I have been thinking about this topic as I am helping a schoolboy with a project making a replacement oil pump for a J2 engine. We have made most of the casting pattern and hope soon to cast the pump body in a good aluminium alloy.

I do not actually have a problem at present but am wondering whether I should expect one before assembling my J4 replica engine with the uprated pump we are building for the project using gears about ten percent longer than those used in N-type pumps and with a modern filter cartridge. The rods are all steel and use Triumph Bonneville bearings so there is more oil loss than with an all metalled rod.

With best octagonal regards and thanks in advance for your replies,

James Morgan

Richard Hardy

United Kingdom
1815 Posts

Posted - 06/09/2021 :  22:46:09  Show Profile

A modern lip seal running on the crank flange is the more reliable approach for retaining oil at the back of the engine.

You mention you are building a J4 engine. I assume you will be using a new banjo bolt for the rear block / flywheel housing and, a double annealed solid copper gasket between the two castings. The J type engine has a design flaw to its method of oil transfer between the two castings.

You mention making a new oil pump using an ‘aluminium’ body. Having successfully manufactured batches of J as well as P/N oil pumps in the past, I would never contemplate the body being cast in aluminium. I see this as a backward step on several fronts.

The pump body should be in cast iron or SG. Have you thought about the consequences of greater rate of expansion of the body i.e. heat opening up operational clearances which will in turn create excessive ware and, of course problems associated with running a steel spur gear in a less dense body material which again will introduce ware.

You mention that you are proposing to increase the efficiency of the pump. The J type’s oil delivery rate is more than adequate for these engines as these pumps are so over-engineered, producing an output rate which is way in excess of what the engine actually requires, excessive oil pressure regulated by a pressure relief valve.

There is nothing to be gained in going to the expense of having deeper gears machined up and generally trying to re-invent the wheel. The factory reduced the flow output on the P pumps by inserting a packing spacer,the deeper gears being used on the N type.

My advice on the pump project is, why deviate from the original design and use an inferior casting material when the factory pump was already over-engineered for its purpose. I know if a J type owner who has not regulated his pump and it is outputting in excess of 100 psi. Asking for problems!

I hope this helps.


Vintage MG Parts

Edited by - Richard Hardy on 06/09/2021 22:57:03
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785 Posts

Posted - 06/09/2021 :  22:52:17  Show Profile
I wonder why you’d make an oil pump with a higher yield than a standard J2 one?
Mine delivered more than enough and I’ve had to reduce the pressure to prevent leaks etc.
Now with 80psi no leaks from the lip sealed rear main or front

Onno "J,D,M" Könemann
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543 Posts

Posted - 07/09/2021 :  07:42:24  Show Profile
Hi James,
check the original body of a J2 oil pump, you will spott
an oil duck - cross drill - fom the pressure side to the induction side,
the works already reduced the oil deliver qunatity.
I have closed this oil duckt to see what happened, you get
160 PSI, I think it has been more that that, the instrument ends
with 160 PSI.
What you can do is, you can adjust with a situable needle screw
the qunatity and the oil pressure,but with a havy load on the
gears, my conclusion was - not necessary!

J2 4362
L2 2036
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