22 replies to this topic

[mini_turbo_pete]

if you still have low oil pressure then it's probably a worn oil pump or bottom end..

[Dan]

Here's a quick and very rough paint sketch to show you what's going on.

The red passages are all unfiltered oil, the diagonal passage at the top leads to the port where oil leaves the block to enter the tube and travels to the filter head. The green circle is a cross section of the main oil gallery and contains filtered oil. The insert (shown in black) allows the gallery to cross the PRV tapping without the two parts of the oil system mixing, which it needs to do because the feed from the gallery to the rear main and cam bearings is on the outside of the PRV port. The ball or thimble then rests against the seat inside the insert, until pressure pushes it open against the spring and allows oil to flow back down to the sump. You can see that is anything has happened to the insert, if it's moved or cracked then all sorts of problems are going to arise in the oil system. As I said though it would be pretty rare and I tand to agree with the above that the problem may lie elsewehere and be more serious than a worn or stuck PRV.

Attached Files

•  oil_insert.JPG   12.68K   30 downloads

Edited by Dan, 20 March 2009 - 02:04 PM.

[Spitz]

Thanks very much for that Dan.

After thinking about it I have a theory:

If my oil pump has suddenly weakened, perhaps it could not handle my previously fine oil pressure.
The pump could very well be original (from 69 or so), as the motor still has standard bore.
When I insert the stock "thimble", the initial pressure is less and allows a higher pressure to be maintained.
When inserting the correct size ball, as a usual fix to bring up pressure, the pump just can;t handle the pressure and oil "gets by it" some how (not knowing the fine details of how a pump works).
Is this theory plausible?

I don't think either, that something in the relief valve area is broken or cracked.

[Spitz]

Maybe its not the PRV?

Update:
On someone elses suggestion, I changed the oil filter as cheap ones have been known to "fail".
My pressure shot up by about 15lbs !
This is with the stock thimble in place.

Question still remains...how/why would the correct size ball allow me to install it with a full legth spring?

[GraemeC]

You can install a ball with the spring meant for use with the thimble. Althugh the spring is longer it is also weaker.

[Spitz]

You can install a ball with the spring meant for use with the thimble. Althugh the spring is longer it is also weaker.

Waker perhaps....but I had no trouble pushing it in and the pressure dropped. (?)

[DaveRob]

For a bit of detail and 'how it works' stuff.... I think this pages is a good informative read about the oils ways in the A series.

 oil_route.jpg   659.24K   57 downloads

Rob

[Spitz]

For a bit of detail and 'how it works' stuff.... I think this pages is a good informative read about the oils ways in the A series.

 oil_route.jpg   659.24K   57 downloads

Rob

Thanks very much for that Rob! Clears it up a bit.