No oil pressure

[Pukmeister]

The oil pressure relief valve is there to bleed away the excessive oil pressure which can happen on a cold engine. Its unlikely to open in a hot engine, so shimming just risks oil seals getting blown when the engine is cold.

OP stated his relief valve looked ok when inspected, my suggestion was a temporary means of seeing if the spring pressure was too weak. Clutching at straws really without being able to see the symptoms directly.

Agreed that an oil filter change is worth doing to eliminate the easy stuff, but the OP mentioned cutting open filters so presumably he already fitted a new filter.

Pumps create flow, restrictions create pressure. There is a lack of restriction somewhere causing a drop in pressure, it's the finding and fixing it that is difficult.

 

[Steptoe]

He's been running the bike with too thin oil for too long in hot conditions. Could be the big ends have lost some surface, hence the low pressure.

Next time use 20/50 and stick with it.

 

[birdseye]

Looks like the engine is ####ed fitted an oil pressure gauge, not easy as there's not much room. Oil pressure when cold is 80psi and out the road when warm is about 40psi with 3 bars showing at 3000rpm however if I run it in the garage with 4 bars showing it drops to about 5 to 10psi at 3000rpm and at 5bars showing it can hardly register anything!

what is the BMW oil pressure spec?

 

[rust bucket]

Hi Pukmeister I changed the filter and I removed the shim after it made no difference.According to the Haynes manual it should be 50 to 87psi warm but doesn't say how warm. I think the damage may have been done before I got the bike and using 40w oil has probably made it worse. I could always try 20w/60.
Going to keep using it till I have to do something,there seems to be plenty of crank and rod sets on ebay so i'm not worried if I score the crank.
If it get gets drastically worse I'll let you know I'll keep an eye on the pressure. Thanks for everyones input.

 

[birdseye]

I wouldnt worry too much about the pressure at 3 bars - 40 psi is sufficient to circulate the oil which is what the pump is for. And in any case you dont know how accurate your guage is. Nor would I worry about the pressure at 5 bars - all engines suffer an oil pressure drop when overheating which is what 5 bars are. The bit that would concern me is the idle pressure at normal temps. It does suggest crankshaft bearing wear.

Unless you are going to pass the problem onto another owner, it will be way cheaper to sort it now rather than wait for somethingnasty to happen. Replacink crank bearings is a diy job if you have somewhere to work on it

 

[Pukmeister]

If it is just the big end shells that have worn its a relatively simple repair. If however you start wearing the big end and main crank journals then it is both expensive and a pain in the arse to do and would probably work out easier to just replace the short engine with one from a breakers.

 

[Steptoe]

I could always try 20w/60.
.

Rock oil do a 20/60 fully synthetic, i use it in a couple of my own bikes.

 

[rust bucket]

Hi, can you replace big end bearing after removing the barrels? I didn't know if there was enough space to remove the rods.
I'm hoping to keep the bike running through the summer and if possible i'll remove the rods check the oil pump and if i can see it with the rods out check the oil strainer.
In the meantime I'll see how it goes with the 20w/50 and I'm going to get some 20/60 as I'd like to keep the bike on the road for the summer.
I'm off to try the bike out with the 20/50 in as I've only run it in the garage.

 

[Pukmeister]

According to the book, you can remove rods via the opposite crankcase once the barrels are removed. Never needed to do it myself. You can also remove the oil pump with the engine in the frame via the front timing cover. Oil pump strainers require engine removal/cases split.

You can't get in to accurately measure the crank journals with an external micrometer however (requires engine removal and splitting the cases) although I guess you can inspect the bearing shells and plastigauge the running clearances.

Big end bolts are stretch type and cannot be reused. Conrod caps are 'fractured' so keep the caps the same way around (mark before undoing). Big end bearings are sized by colour markings.

 

[Daffy]

Conrod caps are 'fractured' so keep the caps the same way around (mark before undoing). Big end bearings are sized by colour markings.

When you undo them, make sure you bolt them back together as soon as possible, you only have to nip them up, it maintains the integrity pf the rod end. The eye of the rod will go oval if you leave them separate for more than a few hours. ( and you will not get them mixed up)

 

[rust bucket]

Went out on bike yesterday and couldn't beleive how much quieter it was starting from cold with 20/50 and the oil light went out immediately instead of taking a second . It was fine as long as you don't push it too hard but gave it a quick run at 5000rpm on a dual carriageway for a few miles and it soon dropped to 30psi even though the temperature gauge was still showing 3 bars, so looks like the big ends may be a bit worn, mind it was boiling hot probably above 24c
Thanks for everyones help it looks like I'll be busy this winter taking the barrels off and checking the big ends and oil pump.

 

[Pukmeister]

Only thing to worry about then will be the mains, depending upon what you find with the big ends.

 

[tanneman]

Looks like your bearings as suggested before. The thicker oil might be a temporary fix to keep lubricating the bearing when the clearance has increased ie worn. However as you build revs the pressure on the bearing will increase trying to squeeze the lubricating film out until such time it does. That knock you are hearing is the metal to metal contact. The thicker oil might have better lubricating properties but will also cause a slightly higher oil pressure readout due to the fact it offers more resistance to flow.

 

[Bendy toy]

Put some Wynnes in there until you can do the work but ideally avoid using the bike.

This has probably already been said but anyway --

The bearing shells will wear if oil pressure is too low, but are replaceable. However, the crank will be damaged if they wear too much. It probably has specially hardened journals and not repairable. If you keep using the bike, even for a few weeks, you could end up needing a new crank as well as the bearing shells.

If it was mine I would be looking to replace all of the crank bearings though the state of the cam bearings might give a clue as to how much overall damage there is.