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Old 08-10-2011, 09:13 AM   #1
frasermanx OP
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Location: Toronto, Ontario. Canada
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Strange Airhead engine problem solved !

Reborn BMW ! After 2 years of frustration, worry, concern, hair pulling I have finally diagnosed and repaired a terrible noise from my R80ST engine !

I thought that I was a bad mechanic and that I had not followed my maintenance schedule properly or not installed the oil filter correctly or used the wrong oil, abused the engine with high speed riding or the engine was worn out or BMW engines were not as good as advertised ! However I am glad to say that all these misgivings were FALSE.

I was not prepared - read cheap - to turn the whole bike over to an `expert` at an official beemer shop so I did take the heads off. And I found carbon buildup that was so bad that the valves were touching on the piston -- aha I thought thats the problem ... so I installed new rings, adjusted valves --- but still that horrible noise. So I bought new valve rocker arms -- no difference.

Again into the engine, I took off the connecting rods to inspect the state of the big end journals ... hmmm my micrometer reads correct specs ... the big end bearing shells look fine too .... Hey there is no shake when I pull a con rod ... if the main bearings were bad there would be at least perceptible movement !!!

Reassemble again ... same noise ... must be oil pump ,. main bearing has turned in the case... crankshaft is bent. Engine runs but is very very noisy.

Finally frustrated with the BMW entirely I try to sell it .. as noisy engine .. so I wont have to deal with it and search for another BMW ... maybe a K bike, R-series but all the bikes I try at top heavy monsters that fall over all the time and not nimble in city traffic. I have given up on the airhead engines ... Nobody will buy the bike for other than parts and I would take an unacceptable $$$ loss.

Crisis.. I buy 2 japanese BMW copies,, GS850 that are quite good but I miss the BMW panache, controls, ... everything that I like about the ST and my previous /5 ( new in `71 that I rode for 17 years before getting the ST ). I also bought a GSXR that is so scary fast that I cant ride it below 50 miles an hour without feeling out of control in the cramp riding position -- although I love the looks, the quality, the speed, the handling at high speed

A call out of the blue .. the former owner of the ST who sold it to me 10 years ago wants to buy it back !!! He had `graduated to a K bike.. then an R100gs paralever .. he tells me the horror stories of broken driveshafts, various other $$$ problems that he never had with the ST .. like falling over from the top heavy and just plain heavy bikes like the R1200RS bikes

After hearing his experiences I began to rethink my search for another BMW or another similar cruiser for in town and highway .. maybe the ST can do the job ... install my R100 barrels and heads ... hmmm

So I take the plunge and engage a pal to help extract the engine from the frame and drive 100 miles to an airhead specialist that promised to take a look at the engine, transmission and find the source of the problem without charging more than a few hours of work.

Al Blanchard, a great guy, 30 or more years of airhead riding and wrenching puts the engine on the bench (BMW school trained) ... we watch ... wondering ... he checks everything that I had already dismissed as the problem ... big ends, main bearings, pistons, barrels, valves, heads, rockers, cam followers, cam bearings, seals, oil pump, crankshaft trueness ....

But aha !!! The flywheel cum ring gear / clutch plate is riveted together and the rivet holes are elongated --- how did that happen ?? The slop is so bad that the gear that engages with the starter has been grinding into the crankcase !! In all his years Al had never seen this problem before ...... Also none of the experts who I consulted had any idea of this problem either ...

Here is a pix of the ring gear and its rivets .

One theory is that engaging the starter when the engine is running is possible if the lockout control that prevents that has been disabled by wiring changes --- so you have been warned !!

Any other horror stories with happy endings ??

good luck
Fraser in Toronto

frasermanx screwed with this post 10-16-2013 at 08:44 PM
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Old 08-10-2011, 09:54 AM   #2
One Less Harley
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dang you should have posted this problem sooner, my R80G/S had a strange problem with a noise, turns out the flywheel had small allen bolts holding the ring gear on. One very experienced airhead guy here had never seen a bolted on ring gear. It took some time to figure out the noise...not two years, but noticed it more when just hitting the starter and then after looking for the noise more i was able to cause the noise by pushing on the kick starter. Possibly the ring gear was replaced and bolted on.

flywheel problem
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Old 08-10-2011, 10:44 AM   #3
caponerd
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Quote:
Originally Posted by One Less Harley View Post
dang you should have posted this problem sooner, my R80G/S had a strange problem with a noise, turns out the flywheel had small allen bolts holding the ring gear on. One very experienced airhead guy here had never seen a bolted on ring gear. It took some time to figure out the noise...not two years, but noticed it more when just hitting the starter and then after looking for the noise more i was able to cause the noise by pushing on the kick starter. Possibly the ring gear was replaced and bolted on.

flywheel problem
After reading your story, I wonder if those bolts are adequate?

Was there equal damage to the holes in the ring gear corresponding with the damage to the threads in the old bolts?
For that kind of application, you really need bolts with some un-threaded full-diameter section to fill the holes in the ring gear tightly, otherwise, the ring gear is going to loosen up again.
It's been a year or so since the repair, is it still holding up?
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Old 08-10-2011, 11:11 AM   #4
One Less Harley
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I need to replace the flywheel. I have a replacement but haven't replaced it yet. Not ideal to have the bolts in there as I'm sure they will either loosen or elongate the flywheel holes. A little over a year since replacing the bolts. When replacing the bolts i didn't know that it wasn't originally that way so bolts were replaced. They're hanging in there, but I DO NEED TO REPLACE!!!!
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Old 08-10-2011, 02:03 PM   #5
Padmei
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I love a story where they live happily ever after.

If you didn't know your bike inside out before this you sure do now. Well done
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Old 09-01-2011, 05:25 PM   #6
frasermanx OP
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Laugh

Amen. After seeing AL check all engine parts for excessive wear I will never be afraid to go deep inside again ! He has rarely or never seen a bad bottom end that wasnt caused by oil lack ... burns on sump to give you a hint .. good to know when buying used.

Weld the ring gear together and maybe bolt it too !

cheers

Frz
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Old 09-01-2011, 11:23 PM   #7
Anorak
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My R100RS did that. I was going to weld the rivets but bought a used flywheel from Eurotech when they were near Santa Cruz. The location of the sound on mine was obvious. From what I recall, it was pretty obvious that the sound came from the clutch area.
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Old 09-24-2011, 09:26 AM   #8
PW Cymru
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Just had a look at my 80G/S and the ring gear is loose on the rivets.

Bugger :(
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Old 10-23-2011, 10:31 PM   #9
Morro
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I had the same thing on my r80g/s (8/84 model I bought new) and thought it was the timing chain. Repaced that and the noise was still there. Listened hard and determined it was in the moter gearbox join area and presumed it was the starter motor. I pulled apart the starter and lubricated it but the noise persisted.

I was heading to a rally the next weekend and pulled up for fuel and the motor made an unholy noise as I turned it off. I started it up OK but it was not right. I was about 250km from home so I rang the wife and said I was heading home and she might have to come and pick me up. The bike was running OK with no unusual noises except the ones that it made when I stopped the motor for fuel. I thought it may be the clutch but it seemed to be working fine and not slipping in any gear. Then I had a 'freeing up feeling' in the motor as if something had come unstuck. every thing was working ok so i kept riding until I puled up at home. Horrible noise as I turned it off even worse as I tried to start it bit it did not turn the motor over making me think it was the starter. When I took the cover off the starter I noticed some metal filings and then I touched the ring gear and it moved!!!

I pulled the gearbox off and the ring gear had completely seperated from the pressed steel flywheel , All the rivets had given way and the noise I could hear was the flywheel hitting the engine casing while slow but not as the motor sped up with centrifugal force holding it vetical. I got hold of a 2nd hand flywheel and got a new clutch plate (old one had about 140,000 km on it) cleaned everything up put it back together and all is fine now.
That was 3 years ago and no one had heard of it before so it may be the vintage of the bike where this may happen. Bike is still going strong and has just over 240,000 km on it. I did 1600km on it last weekend and the engine is great but now it has decided to stop charging - I got to 1km from home and it died with a flat battery. No engine light - not charging - I will start testing this week to work out what it is. I have started with the bulb and it is ok so I will have to delve deeper.

So If you have that tap tap tapping noise at idle and just above it is possibly the flywheel.


Happy riding
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Old 10-24-2011, 12:06 AM   #10
Wirespokes
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The post 81 bikes have what is called a clutch carrier, not a flywheel. And the first several years had some problems. It wasn't unheard of them coming apart or breaking. My 85 G/S got a new carrier when it fell apart on the previous owner at about 40K miles.
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Old 10-24-2011, 09:52 AM   #11
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frasermanx,

Add your ST to the ADV R80ST Registry and lets see some pictures
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Old 10-24-2011, 12:46 PM   #12
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Exact thing happened 2 weeks ago on one of my G/Ss. Brand new rebuild and after 2K miles, I thought I had a bad rod bearing or timing chain. Took the top end down and discovered why the engine was still using oil...something small must have fallen into the spark plug hole during an initial final torque..and I had a nice small groove in the cylinder and piston.ggrrrr..

Replaced that and still had the noise. Started to take the front timing cover off and was spinning the engine by hand when I heard the clinking from the rear of the engine. A big AH HA moment.

Pulled the tranny and you could wiggle the ring. Same as the rest in this thread,,ovaled out rivet holes. Slapped on a new one and the bike's a joy to ride once again.
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Old 10-24-2011, 05:12 PM   #13
azcycle
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Wow! I just disassembled my r65 last week to replace a stripped input clutch spline problem, and when I saw the clutch carrier/flywheel, I noticed the teeth had been chewed up on the inside a bit. I thought it was the starter not completely disengaging but after reading your story... I'm going to check for looseness in the ring-teeth portion!

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Old 04-13-2012, 09:18 AM   #14
chasbmw
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Is the starter ring gear on the earlier heavy flywheel bikes, one piece or bolted on?

Thanks. Charles
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Old 04-13-2012, 09:59 AM   #15
disston
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I'm pretty sure it is welded. Not prone to this problem. I have a flywheel somewhere around here but I can't find it.
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