BMW K bikes (Bricks)

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Banzaibob

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K100LT with 48,000 miles. Bought it after is has sat for 5, maybe 10 years...who knows. Cosmetic condition is poor, overall I'm still evaluating this bike to see if it is worth restoring. Finally got the fuel pump issues sorted out and got it started today. At just over idle (and intermittently during idle somethings) there is a sort of slapping sound. It is not the deep resonant knock of a bad rod or the thin ticking of a loose valve train, but a clacking sound. My first thoughts? Cam chain. After removing the cover and exposing the cam chain everything looks rather normal. However, it appears that the automatic adjuster can be pushed back with finger pressure. Is this right? Also when turning the starter motor over is the cam tensioner device suppose to hold the chain taut?

    

Holister

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.... it appears that the automatic adjuster can be pushed back with finger pressure. Is this right?
No
.... is the cam tensioner device suppose to hold the chain taut?
That's what a chain tensioner does. It may have been replaced without being properly reset. But seeing as you can push it in with your finger I suspect that the ratchting teeth inside are very worn or missing or possibly the follower that runs in the helical key way has broken off.


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1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

Banzaibob

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Caveat: I know virtually nothing about K bikes, airheads are my specialty. I was under the impression that the k bikes of that era used a cam chain tensioner that used oil pressure to drive the shoe outward. You're saying that there is a ratcheting mechanism that holds in in place? It has maybe 2mm of inward movement....I take it that that's bad?

    

RicK G

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That is not bad, the oil pressure will push the correct tension on the chain as soon as the engine is running and 2mm is about normal when not running.
I thnk you will need to look at the rubber dampers in the main output shaft as one or more may have been damaged due to standing for an extended period.
Part #13


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If everything seems under control then you aint goin fast enough:- Mario Andretti
Bikes 1986 K100RT, 1993 K1100 LT, 1994 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 & 1976 SR 500 Yamaha for now
    

Banzaibob

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Ewww...it take it that access to the output shaft is not a light undertaking? Listening to it running with the stethoscope, I placed the noise more forward in the cam chain area.

    

RicK G

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It is difficult to diagnose a noise by description but one other thing is to check the rubber damper blocks on the alternator drive.

Does the noise go when the clutch lever is pulled in?
Using a long screwdriver as a stethascope with the handle to your ear and tip on the engine case can help narrow the area down.


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If everything seems under control then you aint goin fast enough:- Mario Andretti
Bikes 1986 K100RT, 1993 K1100 LT, 1994 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 & 1976 SR 500 Yamaha for now
    

Banzaibob

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I haven't listened to it run with the clutch pulled in. I'm going to put it back together tomorrow and listen for that.

While cranking with the starter motor, should the oil pressure be enough resist me pushing it back in? While cranking, I can easily push the tensioner those 2mm or so.

    

RicK G

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Banzaibob wrote:While cranking with the starter motor, should the oil pressure be enough resist me pushing it back in? While cranking, I can easily push the tensioner those 2mm or so.
I would say it's unlikely


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If everything seems under control then you aint goin fast enough:- Mario Andretti
Bikes 1986 K100RT, 1993 K1100 LT, 1994 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 & 1976 SR 500 Yamaha for now
    

Holister

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BanzaiBob... you said it could be pushed back with your finger.... Now its just 2mm. Well I'd agree with Rick. That's not too bad. I think mine might depress about 0.5 to 1.0mm

With the timing chain cover off and just cranking, I doubt you would get enough oil pressure for anything. Besides, just imo, I can't see how oil pressure plays a major part in tensioning the timing chain. All it does is provide some hydraulic dampening and lubrication for the mechanism and pressure surfaces.

Bottom line is that there's probably nothing wrong with your tensioner, but I think Rick's on the right track with the noise.

Cheers


__________________________________________________
1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

10Back to top Go down    Here is the noise in all of it's glory on Fri Nov 04, 2016 3:48 pm

Banzaibob

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Hopefully this will shed a little more insight.

    

Banzaibob

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ALSO: I let it warm up a little more and run. The idle is erratic with #1 cylinder either very out of sync or a partially fouled plug. However it appears to rev strongly, etc. At idle the noise pretty much disappears. Just off idle, at perhaps 2000rpm or so, it starts that intermediate "tapping". Once at about 2500-3000 the "tapping" is consistent. Again, using the mechanics stethoscope and simple dead reckoning I can pretty much pinpoint the noise to the front left quadrant of the engine....near the camshaft gears. Visual inspection of the chain revealed about 6 to 10mm of "play" in between the two cam gears. At first I attributed this to....well, I don't know what I attributed it to.

Bottom line: This is my first experience with a K bike, having much experience with many other types of motorcycles. If this is an output shaft problem the noise is manifesting itself in a specific part of the engine that would lend me to believe it is a cam chain problem. Is that possible?

I am trying to evaluate whether or not I should simply part it out, keeping choice pieces for my customized airheads. I just had a friend buy one of these for around $1800 which appears to be typical for a fair bike. Like I said earlier, cosmetic condition is poor, the fairing is pretty mashed up.

    

12Back to top Go down    Additional photos on Fri Nov 04, 2016 7:19 pm

Banzaibob

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In the first photo a small screwdriver is inserted to demonstrate the slack between the 2 camshaft gears. In the 2nd photo, this is demonstrated with fingers. I was able to run the engine with the valve cover removed (my shop is now covered in oil). I was able to slide a small dowel underneath the cam chain and that top guide to take up that slack while it was running. The noise persisted regardless.

    

Holister

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That looks to be too much deflection of the chain between the camshaft drive sprockets. Would be better if you could post some pics or video of the chain tensioner itself.

Its possible that if the chain has been replaced, one of the camshafts has moved. I'd do a compression test before anything else and then check the valve clearances just to make sure you aren't doing any damage while running the engine.
It could be one of the drive sprockets is loose. They should be torqued pretty tight.
Tensioner could be busted or not set correctly or the chain is totally stretched.

I wouldn't be running the engine with that noise and definitely not without the covers. You won't get enough oil pressure for proper lubrication.


__________________________________________________
1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

Banzaibob

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Pretty exciting noise, nonetheless, right? I run the engine w/o the valve cover for durations no more than 15 seconds. When I first started yesterday it appeared to not be running (or running weakly) on #1. The exhaust only got lukewarm. I did a compression test on #1 and cranking compression was about 100psi. Not knowing what the pressure should be, I assumed that that was at least good enough to run. Although I didn't check the actual clearances, both exhaust and intake buckets could rotate easily therefore denoting that there was at least some clearance.

    

Holister

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You can see that the sprocket timing marks are aligned with each other so that's good.
I'd would've done a compression test on all cylinders. that would tell you more if one was different.
After its run, what do the plugs look like?
I think the loose timing chain needs to be addressed regardless. How far can the tensioner guide be moved with your finger. Pic or vid would be good. The fact that there is even a little slack in the chain means the tensioner is not working as it should.


__________________________________________________
1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

RicK G

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The chain is shagged and slapping on the return run. Possibly the tensioner blade is broken also.
Take the cover off and the guides and chain out for some year book pics.


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If everything seems under control then you aint goin fast enough:- Mario Andretti
Bikes 1986 K100RT, 1993 K1100 LT, 1994 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 & 1976 SR 500 Yamaha for now
    

Banzaibob

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Pictures of the cam chain tensioner. One possible area of concern is the teeth on the ratcheting wheel appear rounded off somewhat. Holding the entire unit together with fingers, there appears to be about 1mm of up and down play.

    

Banzaibob

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Oh and by the way: Compression is even on all 4 cylinders. Cranking with an old battery, each cylinder was around 120 psi. A quick valve clearance check revealed each valve had at least .007" of clearance.

    

Holister

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That tensioner is Kaktus. Probably caused by an excessively stretched chain, tensioner at its limit and chain slap stressing the ratchet teeth. Good news because its a simple fix, but you'll need to scavenge a used tensioner off a wrecker. I've not seen one for sale anywhere.
You can get a timing chain kit from Motorwork or Motobins. The Motorworks kit does not include the cranksft seal for the cover. Plenty of posts about changing the chain and guides on the forum, just use the search on the portal page.
My initial thought was that there was something wrong with the camshaft drive train, so check for valve damage. That seems to be ok if you have compression and clearance. Worth doing a proper valve clearance check while you have it open.

EDIT: From memory..... that spring does not look Kosher. The tensioner tends to fly apart if you don't know how it comes out. The PO probably lost it. This is probably why the tensioner was not working properly causing wear and slap.
I just checked some old pics of mine when it was out.... Yours looked a little light at first but I think its ok. I've not seen that piece in the end before.



Last edited by Holister on Sat Nov 05, 2016 7:09 pm; edited 2 times in total (Reason for editing : added last para)


__________________________________________________
1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

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