R1200S / R1100S cam chain tensioner

[StuRC45]

Hi all,
I read somewhere that there's a cam chain tensioner upgrade available for the R1100S that's essentionaly the same design that BMW used on the R1200S.
Has anyone got any direct experience using these or of failures to the timing gear that could point the finger at the original design being a weakness?
Cheers,
Stuart.

[Mitch1100]

This should help..did mine both sides.
http://forums.pelicanparts.com/bmw-r110 ... ioner.html

[Tapio]

I have done this mod.
I suppose you know the reason for it: if the bike sits for a day or so, the LH cam chain tensioner drains of oil, so the cam chain will clatter loudly for a second or two at startup before the CCT gets filled up with oil.
I think the mod mostly gives the owner ease of mind. That clattering sends chills up the owners spine. All surfaces still have oil on them, and it's not like you'll get piston-to-valve contact.

Strange thing is: if the oil level is low the clattering won't stop!
This is a mystery, and i don't have an explanation for it. I mean, if the oil pump is sucking oil, then you should have full pressure everywhere downstream the oil gallery?
And if it's sucking air, then you should have no pressure anywhere in the system?

There's a chance that a previous owner has done this mod. There's a quick way to find out: if i remember correctly, the old design has an 17 mm hex head, and the new design is 15 mm.

[Corvus]

What does the oil feed into the cam chain tensioners do? There seems to be a spring in there, so does the oil function more as a damper?

Is there a check valve (non return valve) in there?

Edit: or to put it another way, if the tensioner is hydraulic, then what is the purpose of the spring? Just to keep it under some kind of tension until the oil pressure gets there? If that's the case then both sides should rattle on start up, not just the left. Surely?

[Tapio]

Good question. I just took for granted that it's the oil that does the job. Question is: why is the spring there?
I'm comparing this to hydraulic valve lifters on cars. They eliminate the need for valve lash adjustment. There's no spring in them. Of course, they are placed upright so they won't drain oil no matter how long they are sitting in between the engine is running.
But if i remember correctly, the RH CCT on the oilhead boxer also has a spring. Why? It's not placed upside-down as the LH CCT.

edit: Haha! I posted before I saw your edit!

[Corvus]

.............Strange thing is: if the oil level is low the clattering won't stop!
This is a mystery, and i don't have an explanation for it. I mean, if the oil pump is sucking oil, then you should have full pressure everywhere downstream the oil gallery?
And if it's sucking air, then you should have no pressure anywhere in the system?

Does the 11s have a dual oil pump? Some section drgs seem to show this, along with two suction funnels each dipping into a separate semi sump. Is one of the pumps dedicated to the chain tensioner circuit? If it pulled from a separate sump this might explain your question? I dunno?

The priorities for the tensioners seem different to me. The tensioner, if it is truly hydraulic, would need a priority on high pressure/low flow, whereas one might expect the engine bearings to need a priority on flow rate above pressure. I dunno?

Probably completely wrong!

Edit: actually, this theory makes even more sense than I first thought and might ultimately explain the need for a spring. As well as the advantage of having two separate circuits from the point of view of the priority I mentioned, it also makes sense from a fail- safe point of view. Oil level gets low.......arrange the sumps such that the tensioner circuit gets starved first. The springs will keep the engine going and also provide a worrying audible alarm at the same time. Good theory. Be a shame if it's wrong!

[Corvus]

I forgot about the oil cooling circuit. Is this separately pumped?

[Tapio]

Yes, if you look at the oil pump: http://www.ascycles.com/Illustrated_cat ... at=11_2640
there's an Eaton pump on each side of the housing, item 2 and 5.
and in: http://www.ascycles.com/Illustrated_cat ... at=11_2632
item 13 is a suction tube and item 14 is a... that's got to be a typo!

So, two separate circuits. Maybe one of them feeds the engine, and the other is for the cooling?
Still doesn't explain why the CCT suffers from oil starvation at low oil level, while the crank/rod bearings still get oil (hopefully!).

Yes, one could argue that the rattling while hot is a reason for not to do the mod. You get notified that the oil level is low. That's a really crappy alarm system, though. I'd prefer an idiot light!

edit: Maybe item 14 isn't a typo: it's an intake manifold for the cooling
system!
edit 2: it actually says, in my first link that item 2 is for cooling oil

[Corvus]

Found these two very good resolution drgs on the attached link. It's clear that one of the pumps is dedicated to cooling and also that the tensioners are fed off the lubricating circuit. (Scroll down)

http://forums.pelicanparts.com/bmw-r110 ... age-2.html

Which makes it a little more difficult to explain why they rattle on low oil level. I think that a pump's suction head affects it's output positive head capability. (Is that true anyone?). If so, then on low oil level the pump negative suction head could easily double. Might this affect the output positive head (therefore pressure)? The tensioner relies entirely on the pressure figure to apply the correct amount of force. Dunno! Still guessing.

What pressure is the lubricating circuit meant to run at, I wonder?

I notice that the design of the later version is different to the earlier one and it is not simply a case of only a stronger spring alone. Why/how does the later design solve the rattle problem?

[StuRC45]

Looks as though it's a mod well worth doing (via up to date dealer parts as they seem to like changing their minds!) so I'll add these to the list.
I'd have been initialy tempted to just do the left hand side (to simply quieten the engine down) but after more reading it seems these engines have a tendency to blow up on the right hand side far more than the left so both sides it is, even if the right hand tensioner isn't guilty in relation to these engine failures anything that helps stabilise the valve train all round has to be a good thing
Handy links to previous posts on ADV and pelican though it doesn't help when you read through the pelican forum posts and one guys that does this mod to his bike on a regular basis(?) says the updated tensioners just have 'heavier springs' and you look back at the pictures thinking 'what bloody springs' lol

With regards to the persistent rattle under low oil situations could it be simply that if you know you're low on oil you don't rev the engine as much and by not reving as much you don't generate enough oil pressure to quieten it down?
I was advised by a world class mechanic some years ago while I was trying to limp a BMW car home (that was loosing oil at a horrendous rate, long story) and clattering like a bag of nails that it was best to try and keeps the revs up as this is the only way to get the oil pump up to speed and force it to scavenge as efficiently as possible (under low oil conditions) and generate enough pressure to keep the hydraulic tappets pumped.
It sounds completely counter to what you'd think but it worked, I got the car home and upon inspection no harm done.
Or maybe he just thought it'd be hilarious if I believed him and blew the thing to pieces

[Corvus]

It can be seen from the photo of the two versions side by side that, whatever changes to the spring rate, there is also an additional component. A piston within a piston. I assume the spring on the newer version sits inside between the two Pistons? If it's just a case of a stronger spring solving the problem then what purpose does this extra piece have? One thing it looks like it will do is greatly reduce the volume above the main piston. Lowering the time it takes to fill the chamber perhaps?

Ok, we know the mod cures the problem, but isn't anyone else curious as to the mechanism behind it?

[StuRC45]

I got the impression that the version you're referring to with the additional smalll piston was part of the first upgrade kit offered by BMW and that this kit has since been discontinued and now just has the single piston???

I noticed from the pictures that there is also a difference to the oil feed down the side of the piston so (I'm only guessing at this point) this makes me wonder if the tolerances have been tightened a little and the oil feed changed with the thinking that it could at best stop the oil draining away or at least slow it to an acceptable level?

I'll save final judgement until I order them and can take a good look at the differences.

[Corvus]

I got the impression that the version you're referring to with the additional smalll piston was part of the first upgrade kit offered by BMW and that this kit has since been discontinued and now just has the single piston???

......

Dunno. Just the photos on the link at the top of the thread. Plus I've seen the same pictures elsewhere and on u tube too. If the " double piston" idea is discontinued then it begs the question what was it meant to do and why did it not succeed?

Either way, it'd be interesting to hear your appraisal of the mod once you've got the bits. From a personal point of view (ie selfish!) not so much that it does work, but more why it works.

Cheers.

[Tapio]

With regards to the persistent rattle under low oil situations could it be simply that if you know you're low on oil you don't rev the engine as much and by not reving as much you don't generate enough oil pressure to quieten it down?

Here's what happened: took the bike for the annual summer trip. On my way back home it started rattling. More and more. Back in the garage i took both CCT's off to see what was wrong. They seemed to be OK.
Oh, and incedentally, i saw that the oil level was low. Filled it up and the clattering stopped!
Well, at least after a few seconds of running.

A bit embarrasing, but i hadn't checked the oil level. And also embarrasing that i've never thought of/heard this rattling before. It was there all along, at startup, even with sufficient oil level.
Then i googled it and found out about the LH CCT issue. So i had to do the mod. Once heard, this rattling can never be unheard.

[Corvus]

Some bedtime reading

http://www.pipeflow.co.uk/public/articl ... r_NPSH.pdf

Edit: this one also looks useful.

http://www.pumpschool.com/applications/NPSH.pdf

Edit2: and this extract is what I was looking for confirmation of. I lifted it from another, quite extensive, site:-

"The total head can be determined by adding a negative suction head to the discharge head
or by subtracting a positive suction head from the discharge head."

So, increase the negative suction head and you compromise the output head.

On the other links note the section regarding cavitation. I wonder if this also applies to tapio's scenario? As well as compromised pressure capability due to increased negative suction head.

So the sump doesn't necesarrily have to run dry to cause problems. Although that is also a big problem!