got oil pressure problems at idle.

here are the details:
- freshly rebuilt 1330. just been done
- idle speed on cold engine low (havent put a tacho on it)
- idle speed on warm engine higher - little bit too high (havent put a tacho on it)
- oil pressure at idle on cold engine 50psi
- oil pressure at cruising on cold engine 65-75psi
- oil pressure at cruising on warm engine 65-75psi
- oil pressure at idle on warm engine 20-25psi at lowest
- I have another 1275 with very similar engine specs that the oil pressure sits on 50psi at idle and 75psi cruising hot or cold. also freshly rebuilt with the same engine builder and same oil 20w50

So as far as i can work out, my oil pressure is all good untill the engine is warm and i drop down to idle, then turns to poo.

I do not think increasing my oil pressure relief will do any good as my problem is at idle only and my research tells me that idle oil pressure is down to engine tollerances and oil viscosity

Can anyone shed some more insight onto my oil pressure problems and recommend a fix? 20-25psi at idle on warm engine is worrying me especially when my other mini with near on exactly the same engine specs and the same oil is running 50psi at idle, hot or cold.

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- '74 Clubman Ute project

Could be the relief valve plunger is not seating properly. If so it affects idle pressure mainly. Pull it out and check its condition, also shine a torch in there to check the seat it sits in.
If the plunger is dodgy replace it.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

What I did try today was taking the plunger out. Had a look at it, It was badly worn on one side only.
I swapped it out for a pot joint ball, and this is what happened.
The overall oil pressure increased to 75psi all the time but the idle pressure still remained at 20-25psi.

Doc, could i have a seat problem?

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- '74 Clubman Ute project

The ball seats perfect compared to the plunger. Your problem is elsewhere-
Were the cam bearings replaced? If not that could perhaps be the source of leakage. The oil is going somewhere.

If you decide to keep the ball, cut a bit of 5/16"/8mm steel rod, chamfer the ends and put it inside the spring. Otherwise, the spring can bend & push the ball sideways off the seat- you then have 10-20psi at any speed until you take it out and refit it. I use the ball, but IMO a good plunger is more reliable.
[edit] the bit of steel rod is 40mm long.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I'll get a bit of 8mm rod and do that just in case.

Unsure if the cam bearings were done or not. I was leaning towards maybe some clearances internal to the engine being too much.

What effect could the cam bearings have?

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- '74 Clubman Ute project

that idle oil press shouldnt really be any problem

lotus twin-cam escorts have 35lbs max,,, while reving

don`t be too worried

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

If worn you will lose some oil pressure at idle. The front one and middle one get the same pressure the mains do. The front one wears more than the others do.
As Matt said 25psi is fine, mine is that on a hot day after a run. The oil pressure light on common Minis comes on below 8psi...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I agree 25 to 30 lb at idle is quite normal if the clearances of crank or cam are a tad worn
My Cooper S with over 100,000 miles was running at those pressures until the last build when I had the crank ground to the next size. Bearings were fine, I just wanted to grind the crank to the next size cause I felt happier with more pressure. But I think it is just a mind set, not really any technical or mechanical issue

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Sounds perfect to me... If you want to jack it up a bit add a washer under the spring inside the relief valve cap.

10psi/thousand revs is generally considered adequate by people like DV (this is probably for race motors that don't idle at 700 rpm ).

Cheers, Ian

Cam and crank bearings are all new with fresh grinds on all including a fresh grind.

Whats the chances of maybe a sticky oil bypass in the filter head causing the lower pressure at idle?
Or what about too muh engine assembly lube used?

My other 1275 same everything has 50psi at idle. Could it be slightly incorrect bearing clearances?

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- '74 Clubman Ute project

What oil are you using- is it the same in both? Some oils eg Castrol GTX are notorious for dropping pressure when hot.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

what oil am I using Mitch?

Its actually mitchell_evans mini in question, not mine. I'm helping to fix it

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- '74 Clubman Ute project

The oil is gulf western just cheap stuff while running in 20-50
I bought some 20-60 penrite today will see how that goes

Did the oil change today sits at about 55 when warm
Warm idle is still about 25
What do you guys reckon? Thanks

I would fit a new plunger & Cooper S spring. Shim inside the spring cap (if needed) to get 70psi normal running, hot. That 25psi at hot idle is OK. What is the idle speed?

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.