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MG TD TF 1500 - Banjo bolt orifice size

I am currently tearing down my engine to replace the cam and followers and I am inspecting parts as I go along. So far this is leading me to an oil pump rebuild, and a oil line replacement. (Early TD).

The banjo bolt for the oil feed line in the head has the fitting thread for the oil pressure gauge. This banjo bolt has been restricted and has an outlet hole of just less than 1/16th of an inch. I cannot fit a 1/16th drill bit in this hole, but its close.

What size is this restriction hole suppose to be?

I am tempted to remove the restriction altogether, even if the gauge will read low. (I can't see how it would, at least the same as it would taken off the upper bolt anyway).

I know I have seen this info somewhere , but I just cannot find it. I am getting more and more Senior moments.... I think!

...CR
C.R. Tyrell

CR - You are correct in thinking that the restriction should be removed from the banjo bolt. That was a practice many years ago to "improve oil pressure". The problem with that approach is that it greatly reduces the amount of oil delivered to the rockers on the head. The problem of "low oil pressure" is the result of taking the oil gauge line from the banjo fitting at the head. Remove that banjo fitting and move it to the output point on the block, taking the oil pressure gauge line off at that point, remove the restriction in the banjo bolt at the head and you will find that you have full oil pressure being displayed on the gauge, while supplying plenty of oil to the rocker assembly on the head. Cheers - Dave
D W DuBois

Thanks Dave. I am thinking that the various oil delivery issues were mostly responsible for the lifter failure... leading to cam failure, etc. in the engine. I am starting to believe that although their was oil delivered to the rockers, I don't think that their was enough.

Some of the issues I have found so far....

- worn out bushing in oil pump driven gear.
- paper gasket installed under pump outer cover.
- worn outer cover.
- PO had put a replaceable canister filter adapter on engine (which is great), but bent the oil line to a new configuration and collapsed the line causing a restriction.
- less than a 1/16th orifice for oil passage in the upper banjo bolt.

This , I am sure is just the beginning. I just hope that their is not going to be main bearing issues. Keeping fingers crossed!!

....CR
C.R. Tyrell

I wouldn NOT open the banjo bolt hole. More is not always better.
Pumping uncontrolled flow of oil to the head can rob oil and oil pressure from the bottom end for one thing.
The rockers get a healthy supply of oil and if you've ever fired up an engine without the cover, you'll agree there's plenty of oil spraying and misting the valves.
A superabundance of oil accumulating on the head can aggravate leaks around the valve cover.
An excess will wind up increasing the oil finding its way down the valve guides, with blue smoke coming out of the tailpipe, giving the impression the engine is worn out.
Oil picks up a great deal of heat pumping through and then draining down the engine. It needs a break in the oil pan to cool down. If oil is needlessly run through the engine, it will spend more time getting hot and less time cooling off, thus getting thinner than it should and oil pressure suffers.
The speed of the draining process is at mercy of sticky oil under gravity alone- in other words, it is slow. The Ford SOHC 427 had such large heads and drained so slowly, tehy found the series 1 protype actually ran low on oil at high rpms, so the production heads and those FE blocks required extra drainage.
My wife ran 3 laps around Michigan International Speedway at 75mph with 5:12 gearing. When we got back into the pits, it only had 10 psi pressure at idle. THe water temp did not get abnormally hot. After it set for a while, it was back up to 30-40 psi at idle.
Opening the hole will also reduce the backpressure on the banjo bolt below where the gauge reads the pressure; it will show less pressure than the block's oil gallery and may give the false impression the bottom end needs an overhaul.
Are those enough reasons?
JRN JIM

JRN Jim, are we at cross purposes here? As I understand it, CR is talking about restoring the banjo bolt orifice to the original size set by MG, not enlarging it. This seems sensible. I've read on this board of people who've introduced restrictors in the top banjo and have suffered major valve gear wear.

Regards, David
D A Provan

Factory manual quote:" Commencing at Engine No.31943, the lower banjo coupling on the oil pipe (gallery to head) has had the internal diameter reduced to .055in. (1.39mm)... So I think the bolt hole should be at least that size. That small, a little sludge build-up would pretty much kill oil flow to the head. With the rash of cam/lifter failures these days, I'm in favor of lots of oil flow. Restricting would mask worn rocker shaft/bushings and a loose/worn bearings or oil pump. Been around this before, but the only oil pressure that matters to the bearings is that in the main oil galley, which is what is read off of the lower fitting. George
George Butz

I cleared out the restriction in the banjo bolt. I have decided to switch bolt positions so that the gauge will read from the lower location. The oil pipe that feeds the head is of sufficient reduction to provide sufficient oil flow to the rockers, etc.

Does the braided flex oil line have to be extended to reach the lower position, or is it of sufficient length?

Moss only shows one line for both applications.

Having a chance to examine wear on the lifters and cam, it looks like most of the issues have been caused by insufficient oil flow. I think that their must have to be "lots" of oil wash out of the rockers to flow down to fill the lifters on the return to properly lubricate the tappets and cam.

I also found that the oil pump was sufficiently worn to affect oil supply as well. .001 extra clearance at gears and pump cover. Not enough to have it fail, but enough to have some by-pass of oil in the pump. Not to mention a .002" gasket was installed under the cover. Modern oils are indeed a blessing.

I was very lucky not to have any of the metal bits shed from the tappets go any further than the filter. Mains are in perfect condition.

My vote is to get rid of that restriction in the head banjo bolt!
....CR
C.R. Tyrell

Flex line should be fine- if what you have is the correct one. Oiling issues aside, search/read in the archives for the cam/lifter failure problems. More than you would like to know in there, all kinds of theories, etc. George
George Butz

George, I think I have read everything available regarding cam/ lifter failure. I got my best clues from the parts/pattern of wear etc. of the actual parts when I removed them from the engine. I do believe that the restriction that was in the upper banjo bolt ( according to the WSM service Notes was a modification to stop or reduce oil pressure hammer) Is the major culprit in my situation. The drill size that was used on mine was less than what is specified in the WSM. I do believe that this reduced the oil supply sufficiently to not adequately lube cam/lifters.

.... CR
C.R. Tyrell

This thread was discussed between 21/01/2015 and 28/01/2015

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