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MG MGB Technical - Oil Galleries ???

Hi All,

I've just finished rebuilding an 18V engine for my car and noticed that on the manifold side of the engine block, just below the rear side cover, there is a "boss" (bump) in the engine casting. It appears to be an access port of some kind, to the oil gallery that runs internally, the length of the block. I believe this is the low pressure gallery that supplies oil to the distributor drive gear off the camshaft.

My question is twofold:
1. Can anyone tell me what the actual oil pressure is in this gallery that is "Low Pressure"?
2. The "boss" (bump)I mentioned appears to have been sealed off, but I am unsure with what. Is it a bolt, a copper plug similar to a frost plug, or a "driven in" plug?

Any help with this will be gratefully accepted.

JR Jim) Ross

I'd leave well alone.
paulh4

It's left over from when the engine was machined at the factory. It carries the same oil pressure as the rest of the engine's lubrication system. RAY
small

It is a driven in brass plug and it seals the end of the drilling between the gallery and the oil pump drive gear bearing.

It is fed from the drilling from the main gallery to the centre main bearing and since the flow into the bearing is reasonably high I would expect the pressure in the low pressure gallery to be around 10 psi lower.
Chris at Octarine Services

Hey All,

Just for future reference:

I took a chance and started the engine with this gallery left open.

Since the oil only "ran" out, and wasn't "pumped" out, I assume that the low pressure is just that; "low pressure"(less than 10 lbs.)

My local engine machine shop tells me that this hole is there to act as a "clean-out" for the oil gallery, and as Chris stated, it is closed off with a driven in plug.

I assume that the existing plug was dissolved while the engine block was immersed in the hot acid bath, prior to machining.

It's my fault that I didn't notice the plug was missing before assembly and re-installation of the engine.

In any event, I was able to plug the hole with a new plug made of a two part metal paste. without having to remove the manifolds. It was difficult due to the position of the hole in behind the exhaust manifold, but achievable.

The engine runs smoothly with no loss of oil pressure, and no oil leakage.

Thanks for the input. As always, it is greatly appreciated.
JR Jim) Ross

Lol - your local machine shop is talking out of its bum... the hole is simply where the oil drilling was made to connect the gallery to the vertical drilling for the oil pump gear spindle, having connected the two in the machining of the block it was sealed off.

Normally all such plugs are removed in the reconditioning process to gain access to all the drillings so that they can be cleaned out but that is not the prime reason for the plugs - they simply stop the oil falling out.
Chris at Octarine Services

Thank you Chris,
You provided a much more logical reason for the "hole" being there to begin with, and your description of the "oil falling out" confirms my suspicion that there is very little pressure "behind" that plug. This, in turn, removes my concern about my "plug" being forced out.
Thanks again.
JR Jim) Ross

This thread was discussed between 04/03/2017 and 08/03/2017

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