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MG MGB Technical - Rocker Arm Oil Flow?

Hi All, It's been a while since I posted. Problem: '71 B, Newly rebuilt engine, 600 miles. Oil flow good to rockers when first cranked. Now I get miss at speed 3000-4000 RPM after about 30 minutes steady driving. Chased Lucas Ig, SU's etc. Finally decided it was sticking Intake valve. Could slow down momentarily & problem would self correct (assume a momentary cool off), once again hitting on all four. Pulled Valve cover again (Already did the 500 mile oil change, retorque and valve adjust but did not check oil flow to the rockers at the time...ass-u-me.) Just tonight pulled cover and ran the engine and no oil to the rocker shaft. Pulled the rear pedistal plug & ran the engine at idle---no oil up through the port. Blew high pressure air back through the pedistal (I can see the port) Ran a pc of safety wire down the passage and could get it about half way through the head toward the block. (oil pressure shows to be 50-55 psi at idle) Am I to assume that the rear cam bearing has rotated blocking the port down in the block? Is there any other possible cause? (Prehaps something easier than pulling and tearing down the engine again?)
Thanks in advance,
Ron
Ron Stuckey

The oil drilling to the rockers goes through a number of turns and you will not get a wire past the first one just above the head lower surface.

The oil is fed by the cam intermittantly and blowing with the air line won't work if the cam groove is not lined up with the hole.

It is possible but unlikely that the cam bearing has rotated - but it will also have cut off the oil feed to the rear cam bearing as this comes up from the main bearing.

The problem could also be due to dirt dislodged and blocking an oilway or to a large clearance on the rear main which will allow the oil to escape rather than go up the drillings.

Looks like a tear down to me!
Chris at Octarine Services

Thanks for the reply chris.
Is the oil passage in the block straight to the rear cam bearing or does it snake its way as well?
(This is very frustrating as this motor is totally "new" including turned crank, main & rod brgs, cam and cam bearings etc... Not only that it is Spring in Mississippi and I should be riding in it not working on it.) I'll pull the head and try to use air while rotating and see if I can make a difference before I do a full teardown. But with my luck.....!
Thanks again Chris,
Ron
Ron Stuckey

Wasn't there a change in the rocker pedistals when the 18V engine was introduced. If you have the wrong head /pedistal combination then the oil supply drillings don't line up.
Paul Hollingworth

Thanks Paul for your response.
This is a "G" engine using the same head and rocker pedistals it came with. (PO notwithstanding) The oil holes do line up. I had good oil flow at the rockers when the "New" engine was cranked first after the rebuild.
Ron Stuckey

Hello Chris & Paul,
Thanks again for the responses. Now! Is my face red!
Two weeks ago I replaced the head gasket chasing what turned out to be a Lucas electrics problem & while replacing the rockers I inadvertantly placed one of the shims under the rear pedistal. This stopped all oil flow to the rockers. I just finished removing and replacing them, retorquing the head & resetting the valves. Now everything is fine. The rockers are once again oiling and thankfully I will not have to pull & tear down. Our discussions helped me to remember the shim as a possibility. Thanks again,
Ron
Ron Stuckey

This thread was discussed between 25/03/2004 and 26/03/2004

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