What tensioner is this….aux drive shaft chain?

[Bikermike1411]

Hi all,
As part of my strip down I removed a plug on the lower-right of the crankcase - the plug/cap was in an awful state and needed replacing.




I knew it was a tensioner when it came out, which poses two questions…..

1. Is it for the auxiliary drive shaft chain? parts 10-7 below. I’ve looked through the service manual and can only fine one reference to it (same page as sight glass replacement irrc!)



2. Do I need to take the front crank case cover off to check whether it will have dropped a tooth, and therefore need to realign everything, or should it be ok? The engine hasn’t been turned since it was taken off.

Bonus round question

3. Does anyone know whether there’s a nice stainless replacement plug available?

Cheers
Mike

 

[Ian J Hartley]

It’s not a tensioner, it’s an oil pressure relief valve.

Check out the diagrams concerning the oil system.

 

[Bikermike1411]

Thanks Ian, I have read the BMW manual, and Clymer manual, repeatedly! What am I missing?

The only two diagrams linked to the oil system are these two:




Neither of which shows it.

I’ve been through the whole BMW service manual forwards and backwards, and also the bottom end section of the clymer manual. I can’t find a single reference to it. I can barely find a photo of the right side of the engine too - the default photo direction seems to always be from the left.

I’ve scanned every diagram and can’t see it anywhere. I can see the two cam chain tensioners, and the internal aux chain tensioner which is on the LHS of the engine (sat on the bike looking forwards). I cannot find any reference to what this is in any section of the manual.

If it is some sort of internal pressure valve I’d expect there to be an exploded diagram showing how to disassemble/reassemble it during an engine rebuild.

I was mistaken about it being on the sight glass page - that’s the thermostat on top of the crankcase (my joy at the time was finding the sight glass buried on the thermostat page, not finding what this thing is).

This is driving me absolutely nuts!

 

[Ian J Hartley]

it’s not mentioned in any of the servicing manuals, but is is referenced in the OEM oil system along with the oil temp bulb.

 

[theoneandonly]

oh dear .

 

[Bikermike1411]

oh dear .

Oh dear what?

 

[Bikermike1411]

it’s not mentioned in any of the servicing manuals, but is is referenced in the OEM oil system along with the oil temp bulb.



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Thanks for sharing that Ian. That’s my point - I can see it on the parts Fische, but the official BMW repair manual doesn’t even say what it is. I’m looking for what it is and how it works - the manual should show me this.

I can’t think of any reason why it wouldn’t be in there! Crank case…oil system…both would be useful places to put it.

So, I’ve removed it. How do I tell if something may have dropped inside the crank case as a result?

 

[Ian J Hartley]

The spring on the piston controls the oil pressure. I guess it’s not referenced anywhere because it never fails. Any oil pressure problems are most likely due to oil pump failure or wear.

 

[Bikermike1411]

So if I’m reading that right, the piston simply works against the spring which is held in by the plug, with nothing mechanical inside?

 

[Ian J Hartley]

That’s correct. The Haynes manual lists it.

 

[Bikermike1411]

Ian, that’s awesome, thanks for taking the time to talk me through that (and relieve a bit of stress!) I’m really grateful!

Who would have thought Haynes would trump OE BMW and Clymer for information?!