fbekholden.com

Ok mate well I’m going to trust what you saying and as they say it… Send it!

I’m happy to feel reassured that it’s ok.

Well I hooked the pipe work back up and got it warm.

Penrite 15/40 running in oil being used

About 22-24psi @ 1200rpm
And 20 psi even @ 500rpm (very low idle almost stalling)

When revving to 3000rpm the max it seems to build to is about 28-30psi.

I pulled the rocker cover off to see what what going .
Wiped the front 2 rockers dry and at very low idle start it up.
Took about 10 seconds for a dribble of oil to flow.

Mind you the rocker tube was already full of oil.
I suspect it will take longer to flow on a cold start.

Seems there is enough oil up the top end.

What’s your thoughts on it being below spec on 22-24 psi at 1200 revs?

The spec is 29 psi +/- 2psi. 27 would be low, 24 is a fair bit underspec.

To be honest, I reckon there are a lot of greys out there at that pressure (or lower). If you were just tootling around, it probably won't hurt anything. If you really want to lean on it, then 24psi could catch you out.

You could try shimming the relief valve. Relatively easy to get at, and cheap. That might give you a few more psi. If you go down that route, then check pump clearance whilst it is in pieces:


Can't remember if you rebuilt the oil pump on this. There are rebuild kits available, but you may need to sell a kidney to afford one:
https://www.autosurplus.com.au/oil-pump ... ek-ej-grey

Cheers,
Harv

How much of this low pressure issue would I account for with the 15/40 oil do you think?

Oil pump work means sump off / motor out.

Yes I did rebuild the pump and checked all the clearances which were all on the tight side of the specs.

Had a play with the relief valve as I mentioned and stretched the spring out- which now could be a questionable move.

Only try thing I have left to try at this point is thicker oil.

Or is thicker oil only masking the problem ?
Would you expect correct pressure with 15/40?

A thicker oil may help, though hard to gauge exact result. My understanding of various lubeoil grades is sadly lacking.

Cheers,
Harv

Have you another oil pressure guage just as a crosscheck.

Hi Drew

I think I have some gauges home if you’re looking for a second one as ehsv6 suggests.

Regards
Stephen

ehsv6 wrote: Thu Dec 22, 2022 3:03 pm Have you another oil pressure guage just as a crosscheck.

That’s a god idea!

In the Shed wrote: Thu Dec 22, 2022 3:34 pm Hi Drew

I think I have some gauges home if you’re looking for a second one as ehsv6 suggests.

Regards
Stephen

Hi Stephen. Yes please that would be great to borrow it.
Drew

Some more thinking. This is what I think your system is doing.

At low revs (0-1200rpm) the relief valve is shut, and pump is delivering all the oil it is sucking up. You get some pressure drop across the filter, and end up delivering 24psi to the galleries. The galleries are still getting the same amount of oil that they would have without a filter (because the gear pump puts out a set volume). They are fed at a lower pressure though. This should be fine - if the oil is flowing the same volume, then the bearings are getting what they need.


As revs increase pump pressure gets higher and higher. Somewhere above 1200rpm but less than 3000rpm (lets call it "X" rpm) the filter becomes restrictive enough that the relief valve lifts at 40psi. Some of the oil goes to the bearings, and some cycles back to the sump. You end up with 30psi at the galleries.

As revs increase more and more (up to 3000rpm, or higher) you will get no more oil pressure. The relief valve stays open, holding the pump at 40psi and the galleries at 30psi.

The engine is safe all the way up to "X" rpm. At every given speed, the pump is delivering the same volume oil that GMH thought it should. The risk comes in above "X" rpm when some oil goes to the bearings, and some to the sump. You're getting 30psi above "X", but no idea of how much flow. 29-30psi was fine at 1200rpm, and may well be fine above 1200rpm too.

I reckon a standard grey motor also plateaus like that. To test the theory, take a standard grey motor in good condition and measure the oil pressure from 0 through to the redline. If it plateaus around 30psi or so then I reckon you are OK.

Cheers,
Harv

Certainly an interesting issue this one. Here are the gauges I have Drew. Do you also need to borrow my grey motor Ute too

Stephen

Umm yep those gauges look like I’ll need to put my thinking cap on to get them connected!
Yes please Stephen maybe you could come over and I’ll throw my oil pressure tester on your bus and we can see what it tells us.

Harv what I’m thinking is I’ll bypass the filter and check pressures as cross reference.

I’ll then remove the dizzy, block the oil outlet pipe and spin the oil pump with my drill through the dizzy hole. I’d expect the pump to max out immediately and tell me what pressure the relief valve is relieving at.

This should give me an idea on how the oil pump is behaving.

Also I can gather the 2 or 3 spare oil pumps that I have and rig up an oil outlet pipe, sit it in a bucket with clean oil, drill the pump so the oil circulates and do some static pressure testing in the shed so I can get a good understanding of what is going on before I consider pulling the motor out and going for a sure fix.

Sent you a PM Drew

Thanks Stephen, I got the gauges from my front porch.

I went for the first step in diagnosing the low oil pressure.

I removed the dizzy, connected the tester to the oil pipe outlet direct from the pump and spun the oil pump with a drill.

Pressure was 50 psi which I am more than happy with.

I looked up the Milwaukee website at the drill spec is max revs of 2000rpm.

So I know the pump can produce 50 psi at 2000 rpm

So for now I’ll pass the oil pump as ‘OK’

I was really hoping the pump would be stuffed as it would explain the low pressure… now I have to dig deeper

With tester connected to outlet of the filter.

50 psi…