My day goes from bad to worse

[schrader7032]

Is the sound you're hearing coming from the front of the engine or near the rear? You said where the "shaft enters the engine case"...that's a bit unclear to me...there are shafts all over this bike . Maybe you can provide a link to one of the on-line fiches that you were looking at.

When you take off the front engine cover, the ends of two shafts stick out. The lower one is the camshaft and has the points and advance unit mounted on. The upper one is the crankshaft and has the alternator bolted to the front of it. There's another part of the engine behind this that is about 3 inches in depth and covers up the gears and timing chain.

Then of course is the engine block itself. The transmission is bolted to the rear of the engine block. Between these two is the flywheel and clutch assembly. The clutch transmits the motion to the tranny through a splined input shaft. Sometimes, after poor maintenance on the input shaft, the splines shear off, making bad sounds. At that point, the engine will run but when in gear, the bike won't move forward.

You said the engine shuts off and starts coasting in 4th gear. Engine compression would slow the bike down pretty quick if the timing gear was still attached. But if you started it for a few seconds, then the timing gear still had to be attached otherwise it would not have started. If the timing gears jumped a tooth, you could easily get to the point of bending a valve if the valve timing gets too far out of whack.

First, I'd make sure I had isolated the noise. Then, I'd probably perform a static tune up just to check the basic settings, checking timing and valve settings. Remove the plugs, tranny in neutral, try turning the engine with an allen wrench in the alternator bolt. You could also try keeping the plugs in, put the tranny in 4th, and turn the rear wheel by hand. Observe what does or does not happen.

If the noise is up front, I'd have to think it's something associated with the timing chain. I've heard of them making a bit of noise that can be heard above the engine idling as you rev the engine. This is usually a loose chain that is slapping the inside of the engine case. Not horrible, but not good and needs to be fixed.

If the noise is in the middle of the engine, then you make have a damage lower end bushing. You can investigate this by completely removing the top end of the engine and evaluating the looseness of the conrods attached to the crankshaft.

Let us know what you find out as you begin checking on things.

Kurt in S.A.

[armymutt]

Sorry for the confusion. The sound is coming from the right rear of the engine case where the rear drive shaft enters the case. Right now, I'm thinking it's either a part that connects the drive shaft to the tranny, or something further forward of that point in the train. It basically sounds like something has broken loose and is either still attached at one point while the gears are spinning around, or it's loose in there and is being knocked around. Another symptom is that the shift pedal isn't returning to the normal position - it's like a return spring is broken or something is binding it to the point where it stays. I think we got it back in neutral last night through manipulation of the kick starter and the shifter.

[schrader7032]

Ahh...I bet what happened is one or all of the four bolts that connect the driveshaft to the output shaft of the tranny have come loose. If that happens, you'll coast and with the rear wheel turning it'll make a bunch of racket. I think you're looking at #1-3 on this:

http://www.realoem.com/bmw/showparts.do ... g=26&fg=05

You should see the rubber boot that covers this joint. There's a clamp that connects both ends. Remove the clamp and peel back the boot. See what's there.

Or do what I suggested earlier. Put the tranny in gear (if you can), take out the plugs, and turn the rear tire. Does the engine turn over? If not, then things are disconnected. You can also put your fingers or over the rubber boot (even before you remove it) and feel the driveshaft turning and count the number of bumps...should be four. If it's not connected, you may be able to push the end around with your fingers.

Another thing it could be is the tranny output flange taper has come loose from the back of the transmission. This flange is typically held on with quite a bit of torque but can come loose in unusual situations. Sometimes those situations are bump starting the bike while in gear...the reverse torque can pull the output flange off.

If the problem is the first one, it wouldn't take much to fix things up. You might need to remove the driveshaft housing and make sure it's all clean and there's no metal debris. You'll need new bolts...BMW switched from long bolts with lock washers to short ones. The lock washers sometimes would break, thus relieving the tension on the bolt, allowing it to work loose.

If the problem is the second one, the tranny will have to come out and possibly opened up to inspect for damage, bearing replacement, etc. Generally, tranny surgery needs to be left to experts.

Look under the boot and see if the driveshaft is connected or not. That's the first place I'd check right now.

Kurt in S.A.

[armymutt]

Well, turns out that the rear wheel hub failed. Inside, it is riveted together and a couple of the rivets sheared off. There don't appear to be any more issues, but we won't know until we get the new wheel in place. I think I'm just going to get a new wheel since a hub is running around $400, spoke kit is about $70, and the labor is $100.

[schrader7032]

Good that you've isolated the problem. Be sure that the wheel splines and final drive splines match up well. Hansen's BMW in Oregon is one of the better places when it comes to this sort of thing.

Kurt in S.A.

[VBMWMO]

So after disconnecting the tach cable (see post below), I put everything back together. When I went to leave for the day, I found the turn indicators no longer work. Not a big deal, as I have fixed that problem before. I continue riding and about a mile from my house, I hear a loud "clunk", the engine shuts off, and the bike starts coasting like it's in neutral - it was in 4th gear. After getting it back to the house, my buddy (a Brit bike mechanic) did some initial testing to try to ID the problem. When the engine is running, there is a clacking sound coming from the area where the shaft enters the engine case. We didn't run it longer than a couple of seconds to minimize the damage. Looks like I've got a way to spend my tax refund now. Anyone ever repaired this area? How technical is it? I've looked at a couple of cut away diagrams and it looks like a lot of gears.