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camshaft sprocket timing


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I am reassembling my engine after studs pulled. When I came to the manual regarding cam sprocket alignment/timing, I am baffled, when I dissasembled the engine, i zip tied the sprockets to the chain and am pretty sure there is no slack on the non slack part of the chain. I have the camshaft slots perfectly downwards and the sprocket lining up but the stupid arrows are what appears to be 1.5 teeth off where the BMW manual says the arrows should point, how is this possible?? I locked the crank with the BMW tool and know I am at TDC, what gives?? Are the arrows less important than the key slot in the cam?? Im quite sure I have not disturbed the timing and possibly the last person to work on this bike (evident from previous thread repair on studs) switched the sprockets or something, either way it ran fine before an am fairly confident that it will run fine again, just want to know if the stupid arrows are more critical than the key slot on the cam.

 

Thanks for any ideas.

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You know I saw something similar on mine and I think I came to the conclusion that the chain tensioner would cause a "false" alighnment view. When you pull the chain taut and align the pin (careful doing this!) from the sprocket to the shaft, the arrows should fall back to horizontal.

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I put some pressure to simulate the tensioner and even with it, the key slot is still spot on (one slot up and the other down), but those arrows are not parallel to the ground, there is no way that they would be. If nobody has seen this before, ill take pictures tonight and try to attach em.

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It took a lot of torque to break that camshaft bolt, you sure it did not rotate the engine? I had no special tools except a friend and he was special" slow". We gave a gentle bump to the rear wheel in gear and re-aligned the sprocket as needed to fit the pin. Just a little rotation plus the tensioner out of slack put it right.

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Well, I had the BMW locking pin installed and am sure the engine did not turn, its possible that the sprocket turned a bit, but not that much, before I loosened the sprocket, it appeared that the arrows were not pointing exactly parallel to the ground but the key slot was pointing exactly 12o'clock and 6o'clock for the other, it just seems that the sprockets were either misaligned by someone else (and the bike ran fine) or the only thing that matters is getting the key slot in the camshaft dead at 12 and 6 o'clock.

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Install the sprockets and then rotate the crank through at least one full revolution clockwise. I'll bet they line up then.

 

Mick

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and another angle of it

 

Keep in mind that the locating slot is exactly 12 o'clock on one and 6 o'clock on the other cam and sprocket when at TDC, the mark to the inside appears to be off by a half tooth, the BMW manual speaks of an X which my bike does not appear to have, any ideas??

716468-MVC-043F.JPG.9f9680f2a3c1b5915be498e4f76a1764.JPG

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I think you're fine. If you were off a tooth you'd see lot more error than that. I suspect some slack has just creeped in. As suggested continue and then before attempting to start the bike rotate the engine by hand the proper direction one revolution. This will take up any cam chain slack, and re-check.

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Joe Frickin' Friday

You say you put some downward pressure on the cam chain to simulate the tensioner. How much pressure? Have you tried actually installing the tensioners?

 

On your right cylinder:

 

716466-MVC-039F.JPG

 

The tensioner takes up slack on the lower span of chain, which will tend to rotate that cam sprocket just a hair clockwise, bringing it to the desired position.

 

On your left cylinder:

 

716468-MVC-043F.JPG

 

The tensioner takes up slack on the upper span of chain, which will again tend to rotate that cam sprocket clockwise and bring those arrows horizontal.

 

 

The fact that BOTH cam sprockets are out of phase, each in the correct direction for its own tensioner to correct it, suggests that either the engine has moved from TDC (look through inspection port for "OT" to verify engine position), or that the tensioners will take care of it.

 

Do a visual check of engine position through the flywheel inspection report, then install the tensioners and see what those arrows do.

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Unfortunately I forgot to say that this was after installing the tensioners and rotating the engine over about 5-6 times, the pictures were taken at TDC. I think I may be a little off. Is it possible that the chain would come off of the inner sprocket?? I zip tied the camshaft sprocket but inside I suspect that it may have jumped on both chains... What do you guys think???

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I don't believe the chains can slip a tooth on the aux shaft unless you split the case and remove the slide rails.

 

Mick

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Joe Frickin' Friday
Unfortunately I forgot to say that this was after installing the tensioners and rotating the engine over about 5-6 times, the pictures were taken at TDC. I think I may be a little off. Is it possible that the chain would come off of the inner sprocket?? I zip tied the camshaft sprocket but inside I suspect that it may have jumped on both chains... What do you guys think???

 

If the chain slipped a tooth on the cam sprocket or the drive sprocket, the cam sprocket arrows would be away from horizontal in the opposite direction:

 

716616-shprockets.jpg

 

The red line represents arrow orientation if the cam sprocket is moved, relative to the chain, by a single tooth. You can see that that's not horizontal, either; it's too much adjustment. The arrows are away from horizontal by about half a tooth.

 

Regardless of how the sprocket lines up with the camshaft keyway, when the engine is at TDC, the sprocket arrows should be horizontal. An important question: were the arrows, in fact, horizontal before you started disassembly? If they were cocked off before you began, then they were stamped wrong, and all is actually right. If someone can take a quick look at their bike, or find a pic from a service manual, we can confirm that the arrows are indeed supposed to point to a tooth (and not to a valley) as your pic shows; if that's the case, then your arrows are stamped correctly. But, then, what are the odds of an incorrectly stamped sprocket? of two incorrectly stamped sprockets on the same bike????

 

IIRC, the crankshaft drives an accessory shaft at 1/2 speed via a chain drive at the front of the engine; it is this accessory shaft that drives the oil pumps and the cam chains (at 1:1). Is there a chance your megatorque during disassembly spun one of the sprockets on the accessory drive shaft??? Both left and right cam sprockets appear to be off by about the same amount; the slippage of one of the sprockets on the accessory shaft (or even on the front of the crankshaft) would explain this nicely. Manual isn't in front of me, but unfortunately, I suspect major disassembly is required to check/repair this... frown.gif

 

***EDIT: Sorry, confused you with Jerry_75_Guy. Maybe you didn't use huge torque to remove sprockets, but slippage on the accessory shaft is still a viable explanation for what you're seeing...

716616-shprockets.jpg.ed135450c65a783e7f61234fedea036a.jpg

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Agree with everything you are saying Joe. If the engine freely manually rotates, and the OP seems to be saying that it does, I'd say nothing is at risk at this point by starting it and seeing what happens. If it runs like _rap, then further investigation is in order. What do you think, start it?

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Joe Frickin' Friday
Agree with everything you are saying Joe. If the engine freely manually rotates, and the OP seems to be saying that it does, I'd say nothing is at risk at this point by starting it and seeing what happens. If it runs like _rap, then further investigation is in order. What do you think, start it?

 

Sure, it ain't my bike! dopeslap.gif

 

All kidding aside, the camshafts appear to be lagging behind the crankshaft, so valve events will be delayed from spec. You'd expect crummy breathing and overfueling when in open-loop operation.

 

A possible problem: if one of the accessory shaft sprockets has in fact been spun, its key is sheared off and it is now vulnerable to spinning even more (or possibly in the opposite direction), either suddenly or gradually over many 1000's of engine cycles. So even though the valves may not be hitting the pistons right now, I'd worry that they might in the future, making the damage REALLY expensive. If it's gradual, then OK, the bike runs like crap right away (see previous paragraph) so you shut down before anything disastrous happens; but if it's sudden, the valves will hit without warning. If this were my bike, I'd have real serious reservations about hitting the starter button without checking this out more thoroughly.

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How does hydraulic pressurization of the camshaft chain tensioners play into this. It looks like both sprockets are "off" by the same amount. If the sprockets had beed tie wrapped as indicated and the sprockets fell back onto the pins then there can be no misalignment.

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Joe Frickin' Friday
How does hydraulic pressurization of the camshaft chain tensioners play into this.

 

At rest, the spring force is enough to maintain proper cam chain/sprocket positioning. When I'm checking the valves on my RT, with the engine at TDC the cam sprocket arrows are dead-horizontal.

 

It looks like both sprockets are "off" by the same amount. If the sprockets had beed tie wrapped as indicated and the sprockets fell back onto the pins then there can be no misalignment.

 

Correct, the cam sprockets should be properly synched to the camshafts. But if the cam chain drive sprocket on the accessory shaft has been spun on its shaft, then none of that matters.

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the BMW manual speaks of an X ...

The X is just a text reference for the timing mark in the picture.

 

However, the 1150 manual shows both sides with the arrows pointing to a tooth tip and specifically talks about the tooth tip aligning with the mark. On your pictures, your left-hand sprocket has the arrow pointing to a valley. Can someone check the 1100 information?

 

As the manual talks about exactly aligned (BMW's bold, not mine) ...

 

It has to be less painful to check the timing through the main and auxilliary chains now, rather than towing a wrecked engine later. Notwithstanding a difference between the 1100 and 1150, something is not right.

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Joe Frickin' Friday
Can someone check the 1100 information?

 

Same thing.

 

Right:

rt.jpg

 

Left:

lt.jpg

 

Also look at this pic of the front of the engine:

 

ft.jpg

 

The small pulley on the crankshaft is locked on with three bolts and can't possibly spin on its shaft (unless you are somehow able to shear three bolts), but the large pulley on the accessory shaft appears to be held on by a single center bolt, and possibly a flat side on the shaft; it's possible this could have spun when the cam sprockets were being removed.

 

I'd recommend inspecting this area. Doesn't look too bad to get to:

 

-pull alt belt cover

-pull alt belt

-pull alt belt drive pulley

-pull HES

-pull alt support (front engine cover)

-remove sprocket on accessory shaft, inspect for signs of slippage. If it didn't slip, it'll be easy to put back on in the right orientation, as any flat or keyway will be undamaged. If it did slip, AND if you're lucky, the shaft is fine and the sprocket hub is damaged; replace the sprocket. If it did slip, AND you're UNlucky, the shaft is damaged, and you'll have a lot more work to do.

 

Let us know what you find. thumbsup.gif

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Joe Frickin' Friday
All kidding aside, the camshafts appear to be lagging behind the crankshaft, so valve events will be delayed from spec. You'd expect crummy breathing and overfueling when in open-loop operation.

 

eek.gifdopeslap.gifdopeslap.gifdopeslap.gifblush.gif

 

I got this backward. We're looking at the back of the engine. Engine viewed from backside spins counterclockwise; so from the pics, the camshafts are actually leading the crankshaft. Not only will breathing/airmass not be what the Motronic is expecting, but with early IVO there is potential for backfire as substantial quantities of hot exhaust gases get driven back into the intake tract.

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Well... my cam sprockets came off with ease for a 65Nm torque value, no real trouble there-so I'm hoping I did not disturb anything. I've rotated it by hand several times and can see/hear no problems, so I'm tempted to start it. Of course, I may just pull the front cover and take a gander.

 

Thanks for all of the ideas, much appriciated

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Be careful when re-installing the cam sprocket. It IS POSSIBLE to install the sprocket without getting the keyway and key aligned perfectly (I've done it) grin.gif . And if this happens, the bolt and washer will obscure the fact from view. Torquing the bolt will feel a bit mushy, but if you aren't paying attention, you may not deem it important enough to investigate.

 

Pat

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Joe Frickin' Friday
Be careful when re-installing the cam sprocket. It IS POSSIBLE to install the sprocket without getting the keyway and key aligned perfectly (I've done it) grin.gif . And if this happens, the bolt and washer will obscure the fact from view. Torquing the bolt will feel a bit mushy, but if you aren't paying attention, you may not deem it important enough to investigate.

 

All true - but even if this is messed up, with the engine at TDC and the chain having NOT slipped on the sprockets, the cam sprocket's arrows should still be dead-horizontal.

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Well I got it all back together today and it started with a bit of chain clatter for about 2 seconds (tensioner buildup), then it ran just fine. Aside from all of the residue and oil burning off I would never know that my bike was just gutted for stud repair. I flushed the crankcase a couple of times and will probably do an early oilchange because of all of the shavings from the engine company that did the inserts.

 

Maybe later I'll get it to TDC and check the cam sprocket position. Right now, with the way it started and runs I just cant believe that theyre off.

 

Thanks again for all of the insight and help.

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mikefigielski

Those cam sprockets are known to have their locating tabs as much as 6 degrees off. I have taken quite a few of them off where one or both sides are what appear to be half a tooth off. All of these bikes ran fine. As was stated earlier it is very easy to put the sprockets on slightly off and then mash the locating tabs when torquing the bolt. Since yours is an early bike it may have had the head gaskets replaced and there would be an opportunity for the sprockets to be installed slightly off. Glad it is running well again!

Mike

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