oil pressure question

[scarf100gs]

I have been slowly improving my ST, 1000cc conversion, twin plugged, twin discs, ohlins, refurbished carbs, valves set,etc. The bike is low mileage and runs very smoothly but after a recent oil/filter change (everything measured with no shims needed, pressure relief valve in canister looks okay), I noticed on cranking that the oil pressure light comes back on after only 3 secs wait. Replaced the sender unit but still the same so did a pressure test which settles at around 40psi when warm increasing to over 90psi when revving to 3000rpm+. A compression test gives a good 150 psi in each cylinder. No apparent oil leaks, everything seems good apart from the cold cranking test which suggests pressure is escaping from somewhere. Any ideas much appreciated on where to go next?

 

[scarf100gs]

I have been slowly improving my ST, 1000cc conversion, twin plugged, twin discs, ohlins, refurbished carbs, valves set,etc. The bike is low mileage and runs very smoothly but after a recent oil/filter change (everything measured with no shims needed, pressure relief valve in canister looks okay), I noticed on cranking that the oil pressure light comes back on after only 3 secs wait. Replaced the sender unit but still the same so did a pressure test which settles at around 40psi when warm increasing to over 90psi when revving to 3000rpm+. A compression test gives a good 150 psi in each cylinder. No apparent oil leaks, everything seems good apart from the cold cranking test which suggests pressure is escaping from somewhere. Any ideas much appreciated on where to go next?

Further examination, pressure-relief valve on crank seems to be okay so went back to the old favourite, the oil filter!. Measured canister rebate again and still good but will add extra shim for good measure. Prodded the bypass valve ball, difficult to see in there when you are on your knees, oil is dripping down your arm onto your torch, your specs are misted and you wish you had three hands BUT noticed some movement on the retaining plug which holds the ball and spring in there. Managed to get a screwdriver in, the plug is loose and turns half a turn and doesn't budge so I have no valve as the ball isn't seated so oil just bypasses the filter and flows into the sump, think the spring may have broke. Not sure how I missed this on first examination!!!?? Relieved to have found this which may solve my problem if I can fix! No info anywhere about this, motor-works don't stock any of the valve bits, guess it is not a common problem!

 

[mikeyboy]

I’m not sure you fully understand how this part operates.
The bit you are describing is not the oil pressure relief valve.
It’s the bypass valve.( as you state)
It’s purpose is to open if there is excess pressure differential across the oil filter element.(ie.blocked filter)
In normal use ,the filter should have normal pressure on both sides of the element,if the filter is blocked or collapses this valve will open and allow unfiltered oil through the canister,the theory being,unfiltered oil is better than no oil.
It does not dump the oil to the sump and will not affect oil pressure.
The spring fitted is very small .
Motobins stock the parts if you really want to change it or they are available direct from bmw .
The slotted part you see is factory peened and although it may move slightly ,undoing it completely may prove to be a different story.
We normally remove these for blast cleaning but only attempt removal with the whole block heated to 100 deg.
The oil pressure relief valve is mounted to the front main bearing housing under the front engine cover.
As you suggested, try with another shim fitted .

 

[Mad Hatter]

What canister depth measurement are you getting? It should be around 3.5mm

 

[scarf100gs]

I’m not sure you fully understand how this part operates.
The bit you are describing is not the oil pressure relief valve.
It’s the bypass valve.( as you state)
It’s purpose is to open if there is excess pressure differential across the oil filter element.(ie.blocked filter)
In normal use ,the filter should have normal pressure on both sides of the element,if the filter is blocked or collapses this valve will open and allow unfiltered oil through the canister,the theory being,unfiltered oil is better than no oil.
It does not dump the oil to the sump and will not affect oil pressure.
The spring fitted is very small .
Motobins stock the parts if you really want to change it or they are available direct from bmw .
The slotted part you see is factory peened and although it may move slightly ,undoing it completely may prove to be a different story.
We normally remove these for blast cleaning but only attempt removal with the whole block heated to 100 deg.
The oil pressure relief valve is mounted to the front main bearing housing under the front engine cover.
As you suggested, try with another shim fitted .

Spot on Mikey, I really have no idea and taking beer into the garage maybe not a good one!

Just been looking and the bypass ball valve was flush with the canister bottom, it seems to have worked its way out so the ball is not sealing on the retainer, no spring pressure. This block has been blast cleaned sometime in the past and I guess the retainer was not peened or loctited in there properly and has worked loose. I have screwed it all the way home, about 5mm further down and the ball is now tight but not a lot of movement, wondering if the tread goes to the bottom and the spring is now fully compressed. No idea how far to screw this in as it obviously affects the release pressure also would be very difficult cleaning the treads to loctite it in any position. Any ideas?
The oil pressure relief valve seems fine with the piston moving okay. I have dismantled it and the spring looks good but will order another one.
Re-measured the canister depth to an average of 3.7mm so one shim(0.3mm) will compress the white gasket 0.6mm which seemed okay as the gasket came out with a flat (I did put one in!!!). Will put another shim in for good measure.
Will try and get it back together and test but don't think it will have improved, I suppose crank bearings may be next!
Cheers

 

[mikeyboy]

Ok,
The bypass valve has no effect on your oil pressure.
It should just be level on the lower surface of the housing.
You will see ,two marks on the casing from factory peening.
Align the the slots on the screw and re peen with a screw driver or chisel

 

[scarf100gs]

Ok,
The bypass valve has no effect on your oil pressure.
It should just be level on the lower surface of the housing.
You will see ,two marks on the casing from factory peening.
Align the the slots on the screw and re peen with a screw driver or chisel

Thanks Mikey,
I get the oil pressure thing was my bad but now okay, now sober and thinking.......just
When level on the lower surface the ball is not contacting the retainer, it flops about so valve open and will stay open under normal conditions if the differential pressure is zero. It maybe a knackered spring but I will adjust until it is closed and opened with slight pressure.
Not too bothered now, will put back together, run it and take the consequences. From pressure test readings it seems the oil pump is good so lubrication is fine when moving, seemed to run okay with similar power to my old bumble........will never be the same but that's life........maybe a Honda is calling, quite fancy a cub at my age just to get me down to the shops
Much obliged for all your help