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Crankshaft oil supply tube

I’m restoring my 44 m20. I found the rod bearings were badly worn,so i’m looking for the cause. The timing cover had no spring for the ball valve. Does anyone know how strong the spring has to be? Does the ball act as a high pressure release ? Or does it work only as a check valve? Also the crankshaft oil comes from a oil tube extending from the timing cover. The tube is about 3/16” in diameter. It slips into the crankshaft having a bore of about 9/32 so it must dump 1/2 the oil back into the timing cover. My Triumph has a oil seal in that location which makes sense. I looked threw the parts manual but found nothing. It seems like something is missing. I would appreciate some help. Thanks, Ken

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Re: Crankshaft oil supply tube


The M20 has all roller bearings that does not need a high oil pressure. You don’t specify what type of Triumph but my Bonneville has the same seal in the crank oil feed. This is due to not having roller bearings thus needing a much higher oil pressure.

Make sure however that the quill that feeds oil into the crank is seated properly in the timing cover so that it doesn’t break.


Re: Crankshaft oil supply tube

Simon is right, just a dribble of oil will keep the rollers and balls lubricated unlike the pressure needed for shell bearings. The timing cover ball and spring is available from all the usual BSA dealers for 2 or 3 Quid :- Russell's, Draganfly, C&D Auto's etc. and probably ebay. Ron

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Re: Crankshaft oil supply tube

There should be a light spring in the side cover, very important.
And also the right size ball.
The oil pipe (quil) is ok, it needs some room, not to touch the crankshaft.

My Triumph 5t from 1955 also has a sealing there, a later modification.

Re: Crankshaft oil supply tube

Hi Ken,

Oil feed from the timing cover quill is drawn to the big end due to the centrifugal affect of the rotating fly wheel, it's more about volume than pressure. Without seeing the wear on your big end bearing I'd say it's probably down to mileage or lack of regular oil changes. What is the condition of the rest of the engine components?

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