MG T-ABC

Hi,

Looking for the hot low pressure problem, I have noticed that my rocker assembly does not have shims under the pillars. It is obviously wrongly installed!
Can the pressure drop for this reason?

Thanks for your help

Only if there is a leak from there. Some people block the holes on the top of the rockers to bring the pressure up. You do have the gauge take off on the block and not the head, I assume.
Ian

There should be NO shims under the rocker pedestals - this is an urban myth started MANY years ago, which persists to the extent that dealers still sell them. A guy in Norway (forget his name) wrote a whole thesis on rocker geometry while he was in college, to disprove the myth!

Ian is right to point out the incorrect pressure gauge take-off problem, but there are many other reasons for low oil pressure, all discussed on here and other forums. But whatever the actual pressure, the flow rate is considerable. In fact too high a pressure can be damaging to the crankshaft shell bearings!

Roger
TC0978

It could also be the brand of oil you are using. How long since last change. I had a car that would have great oil pressure after I changed it. But in a few months it would start to drop when hot. Changed the brand of oil I was using and problem solved.

Ed

My theory on the high volume of oil pumped up to the rocker shaft is that it drains down over the camshaft and followers. When cold the volume of oil in the rocker cover will almost reach the top but as the oil gets hot and thinner it drains down.

Only a theory, you can now all shoot me down

Modern car engines keep the oil temp up around 220*+ F, to boil off water vapor. I have never measured my TC oil temp over 180*F on a long drive in hot weather. Another reason to change the oil often, and prior to winter storage.

No pedestal shims in my XPAG.

Shim are for when you cut the head to keep the alignment of the rockers correct. Not needed on a un-cut or mild cut head

EdCallo wrote: ↑

Mon May 16, 2022 7:21 am

Shim are for when you cut the head to keep the alignment of the rockers correct. Not needed on a un-cut or mild cut head

Yes. At the 1/2 to 2/3 lift point, the rocker arm's pivot axis should be at 90 degrees to the valve stem and in perfect alignment with the centre of the ball and the tip.

Has anyone here seen improved XPAG performance with after market rockers?