Oil pressure baffling me!

Hi all,

I hope someone might be able to give me some idea of where to go next. appologies for the essay but i figured you'd need the info.

Bike - 1983 R65

Problem - intermittent low oil pressure after engine rebuild.

notes - Siebenrock 846cc kit. engine stripped to bare block. crank, thrust washers, main bearings, cam shaft and conrods are original. new seals and stretch bolts throughout. 20w50 oil. Mahle filter. No oil cooler.

i stripped the engine getting on for 2 years ago to the bare block, which i sent away for aqua blast cleaning along with the heads and engine covers. I then proceeded to rebuild the engine with new gaskets and seals throughout. Now because of the 2 years between rebuilding and actually firing the bike, i cannot for the life of me remember what i did internally regarding checking end float of crank and cam although i cant see how either would attribute to the problem i have.

I do remember visually inspecting the big ends as they appeared like new, i also bolted them upto the crank on the bench and the operation was smooth and im pretty sure i would have checked the clearances too.

all components were manually oiled on rebuild.

The problem i have is that it takes 20-30 seconds of turning or running the engine before i get pressure registering on my oil pressure test gauge. Then, when i do get pressure, (which is good at around 30psi at 1000rpm tickover rising cleanly with revs upto approx 85psi), it cuts drops off a cliff at around 90psi, which i could attribute to one of the pressure release valves opening, but then it doesnt come back!

i have spun the engine 3 ways;

1 - actually running the bike (which alerted me to the problem initially as dash oil light came on).
2 - plugs out, fuel off, turned with starter.
3 - timing chain off, turn the cam only with a cordless drill.

i have turned the engine with the drill with the oil filter out and oil absolutely floods into it, I have also checked all oil pump clearances which are perfect so i have eliminated the pump itself.

I have removed the pressure release valve in the canister and cleaned and inspected. the spring is in decent condition, no pitting to the ball bearing and the screw is good. however, to eliminate this as the weak point, i have screwed the cap down till it lightly seats on the bearing.

the pressure release valve by the timing chain has also been checked and passes.

the canister depth is 0.188'' / 3mm . i use a new white oring and one shim. no gasket.

i have a siebenrock deep sump kit with the strainer extender. i removed this and checked for correct installation and a clear pipe. all is good.

Oil level covers the strainer by at least 50mm. (i have turned bike over with starter with sump dropped and can see the level drop once pressure gets up)

oil has got up to both sides rockers although less to the right than left.

no external oil leaks are apparent.

engine is currently stripped with only conrods and crank left attached, i have checked everything during strip down thus far and can find nothing of note.


Any pointers on where i can look? i am stumped!!!

Ok, this is a real stab in the dark but are you sure your oil pressure gauge is ok?

have you read through this http://bmwmotorcycletech.info/oil.htm

sounds like you haven't put the oil filter assembly together properly http://www.largiader.com/tech/filters/

When the engine was aquablasted did you remove the mains?
Also the 3 gallery plugs and the upper two timing chest studs.
You seem to imply they are original?
I’m struggling to see how the block could be reliably cleaned with them still in.
I’m wondering if there may be some blast media knocking around poss causing the oil pressure relief valve to stick.
I’d be removing the Conrods to check if any media has gone through them.

mikeyboy said:

I’m wondering if there may be some blast media knocking around

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Does sound as though it could be to do with the oil filter, if its a "bendy" type putting it in the wrong way round could cause similar problems

Thank you all for your replies.

I have checked my (new) guage with an airline. That was one of my suspicions. It Instantly responds. I also used a new oil pressure switch (oe) and tested the oil pressure with that to be sure. Same problem, 20 seconds till pressure then, if I stop turning the engine and then start again within 10 seconds the pressure has gone.

I have read snowbums and mr largiaders sites until I can recite from memory and I reference them constantly (brook reams also)

The aqua blasting media may well have found its way into the gallery’s during the clean but I definitely cleaned them all out when I received it back. The screws and studs were removed before cleaning . I have found no trace of media or other particles anywhere, the pressure relief valve was removed, solvent cleaned and refitted and I have seated it. No oil is getting past there !

I even cut the filter open to check for detritus. Nada.

Oil filter is the solid type and brand new.

Tonight I’ve removed the con rods and crank and found nothing of interest. Checked all the oil ways, removed all the gallery screws, blown gallery’s through with airline, checked casting for cracks and double checked the pressure relief valve and canister depth and that the white o ring was cover side and the steel washer to the canister.

As I’ve used new mineral oil which is green it’s easy to see that the oil has got to everything but it just doesn’t have enough pressure.

One thing I did notice is that the strainer/ oil pick up is close to the bottom of the sump. Around 5mm... is that about right?

tomkite said:

One thing I did notice is that the strainer/ oil pick up is close to the bottom of the sump. Around 5mm... is that about right?

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Its probably OK, but does seem a little on the minimal side - I would email Seibenrock and ask them. When you rebuilt your engine, did you rebuild the oil pump, and if so did you use the BMW OEM pump rotor?

Thanks. I’ll get in touch with them. Although thinking about it, the problem was still present when I ran it with the sump dropped by 10mm so it’s unlikely.

Yes I used the oe pump. I have checked all the clearances with feeler gauges and they are well within tolerances .

Sounds like your oil pressure relief valve is shagged.

+1 on the pressure relief valve, from the information in the first post.

Are you talking about the one in the canister or timing chest?

I’ve screwed the one in the canister in well past flush so it sits hard on the ball bearing. Oil cannot pass.

The one in the timing chest holds correctly. Once I get pressure, I can see the oil slowly exiting the front main bearing as you would expect and only a tiny weep from the relief valve.

One thing I’ve just found though is a 1 or 2mm diameter hole at the back of the oil pump housing. Output side. It goes directly back into the crank case. It’s almost certainly been drilled. Have I found my problem or is this factory? I haven’t read mention of it anywhere..

tomkite said:

One thing I’ve just found though is a 1 or 2mm diameter hole at the back of the oil pump housing. Output side. It goes directly back into the crank case. It’s almost certainly been drilled. Have I found my problem or is this factory? I haven’t read mention of it anywhere..

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IIRC that doesn't sound right. On the ones I have seen, there have been the two "Slots" (for want of a better word) to the right and left of the housing (and I presume you mean the housing within the block casting)- and thats it. I dont ever remember seeing extra holes etc but I suppose it is slightly possible that there may be a model or engine type variant where it might be a factory addition. It certainly may well account for the symptoms you describe if you have a bypass drilled in for some unfathomable reason (oil pressure too high in the past due to stuck pressure relief valve - who knows.....) Smacks of a bodge.......

The reason I previously mentioned the oil pump BTW was that the later BMW OEM rotors are made differently to the earlier ones - BMW for some reason now incorporate a sharp edged slot in the outer rotor surface which can cause damage (so ive heard) to the block surface and rather spoil the pump housing - result crap oil pressure....A Moorespeed variant is the way to go now, apparently.

The one in the canister is a filter bypass valve nothing to do with oil pressure. 30psi at 1000rpm is bad, thats what you would expect from a worn engine on a hot day. the hole in the oil pump housing is std approx 1mm it is a squirt jet for the camshaft. with 20/50 oil on a cold engine at 3000rpm plus the relief valve cant cope so you can get 120plus psi. you have a big internal leek. MAINS ? BIG ENDS ? PRESSURE RELIEF VALVE ?

If everything checks out have a good look at the oil pick up pipe to see that it’s properly sealed and not damaged as it will draw air easier than oil.

The fact that the oil pressure takes a wile to build could indicate that its drawing air, this would also account for the fact that when only stopped for a short time it needs to draw oil up the pipe when it shouldn’t be empty.

I don’t know the design of this engine but it’s worth checking.

So were the mains removed and replaced with new or the old ones left in situ when blasted?
It sounds as Richie has suggested above that it’s dumping a fair amount of oil pressure somewhere

The mains are original as is the crank. Front was removed with the housing. Rear was left in and covered . They did not directly aquablast in or around the flywheel area.

I’m going to try and pressurise the gallery between the pump and the pick up today with the pick up bolted on, see if get any leaks.

I’m also going to do some measuring of the crank, mains and Big ends.

I read last night on Snowbums site that Bmw states official figures for pressure at the oil switch of 30psi-50psi.

The hunt continues! I’ll update with any findings.

Ahhhhhh.... I love motorcycles.

I have found the problem. With some help from my dad. Also known as the oracle when it comes to engines.

We refitted the cam and pump and fitted a clear tube up the strainer hole which I put in a pot of oil. Spun with drill. No suction. Hmmm... checked pump clearances again. All as expected. Bolt the cover back on. Dad asks... is that flush to the case?” Feeler gauges out.... no it is not. So we take the seal out, bolt it up flush. Cam is not binding. Turn it. Bam. Instant suction!!! Even by hand.

Turns out I fitted the fatter black flywheel seal in the oil filter cover. Doh!!! Dig around in my spares box. Found a lovey new unused thin red seal. FFS.

I’m going to Put it down to inexperience. Or being drunk.

Obviously it’s annoying that I made the silly error in the first place but I’m a glass half full kind of guy, so I’m pleased that not only have we rectified the issue before any damage has occurred, I also now have a much more thorough understanding of the boxer engine , especially the oil system.

Ok so it turns out I didn’t need to strip it but hey, it’s given me the opportunity to replace the crank gear and outrigger bearing and double check all aspects of the build. I’m now utterly confident the engine is as healthy as it could be.

Thanks for all your input. Highly appreciated. Now to finish building the bloody thing.

Glad you've found the problem. . . .you may or may not be aware but you've also had the benefit of some extremely erudite contributors from the airhead world