New Airhead

[kmkahuna]

Thanks guys!

You guys are great... Don't worry: like I said...I know today I feel this way for awhile.. and tomorrow I'll get back on the horse. But man, what a kick in the pants. All that work, money, etc... and the bike sounds beautiful...like a sewing machine with that new ignition...and the transmission is tight and smooth now...
But that stubborn lurch remains.
Ah well...
You've all inspired me: so here's the goods.
1) Like I said...that new ignition? Wow, the bike purrs even though it's cold. Amazing.
2) No oil coming out of the front end anymore, and every seal on this bike is now officially done. She's ready for another 60,000 miles.
3) That transmission: I only rode for a few minutes, but it is completely different, and smooth as butter.
My neighbor Marc and I wondered about the torque curve: If that flywheel is so light, it allows the clutch to skip, but only at a very high torque... would that explain the 2nd gear lurch? The clutch lever is good: has about a 1/4 inch play.

Mike: that grease is from a before picture, it's all clean now. And yep, we'll get er done...
Night guys, and thanks for the encouragement.
K

 

[20774]

You continue to mention 2nd gear and issues with it. I would do some tests to convince myself it was just 2nd gear. You mention high torque in 2nd gear. At what RPM/speed? You can get that same torque in 1st gear, right? Try holding everything else constant, but just be in 1st or 3rd. If it was ignition, you would think that it would happen in any gear when the other parameters were the same - speed, RPM. Maybe that will help isolate the problem.

 

[kmkahuna]

You continue to mention 2nd gear and issues with it. I would do some tests to convince myself it was just 2nd gear. You mention high torque in 2nd gear. At what RPM/speed? You can get that same torque in 1st gear, right? Try holding everything else constant, but just be in 1st or 3rd. If it was ignition, you would think that it would happen in any gear when the other parameters were the same - speed, RPM. Maybe that will help isolate the problem.

Kurt, I'm pretty confident now after riding it for 1500 miles after the rebuild that I've done what you mention above enough times to eliminate the possibility that it's happening in another gear. Lots of experimentation at the beginning, because I didn't want to go down the road of tearing the bike down again and rebuilding the transmission unless I had to. Ignition became an issue only because after the latest tear down the rotor assembly was bent when it came back from the shop; I'm very confident it's not ignition; that would be a loss of power, whereas this symptom is as if it comes out of gear for a microsecond...the engine surges in that microsecond because there's no load on it.

The symptoms are: as I accelerate out of first gear, there is smooth, strong acceleration. Once I hit second and roll onto the throttle ( I open the throttle up), the bike will lurch three times from 1000rpm to 3000 rpm, in a rhythmic manner....one lurch....two lurch.....three lurch....as if a gear is missing a tooth, or the clutch is slipping for a micro second.
All the rest of the gears are fine, with the throttle wide open, getting up to speed, all very smooth and strong.
For anyone who doesn't know the bike, this is a fully restored bike now: rebuilt transmission, new heads, rebuilt carbs, resurfaced clutch, new clutch installed by Dave Campbell in Santee, new drive shaft (Dave Campbell again), new drive shaft bolts, clutch cable has freeplay in it, so I'm not dragging the clutch, it's fully engaged..

It's a mystery right now, but here's some questions for the old hands out there, who might have seen something like this..
What about the clutch spring?
Would the lightened flywheel make the difference, but only in second gear?

I have a GoPro at home, and I'm going to make a video of these symptoms while I'm riding, and start a new specific thread for this lurching...see if the crowd here on forum can help me solve this very stubbon ghost in the machine...
See? I told you....I'm fine today. And no....my bike is not for sale!

 

[20774]

Kurt -

I thought you'd probably done some evaluation to eliminate the issues.

How close in time are the lurches? I would think that the gears are spinning pretty fast in the box, so if there was a missing tooth, it would happen very quickly. Hard to believe that a tooth is missing. Maybe someone can analyze the "flow" of power from the input shaft over to the shaft that the 2nd gear is on and then out the output shaft...maybe there's something unique about that?

Looking forward to the movies!!

 

[lmo1131]

chiming in...

... over the course of the last year, two people at the Tech Day here in SD have the same problem, and cannot get rid of it..even after a tranny rebuild.

Curious. Are they running lightened flywheels as well? The "lurch" is as if you were pulling in, and releasing, the clutch slightly (just enough to break friction)?

Any chance you can lay hands on a "loner" gearbox to see if the condition is the same with a different box? Or a different flywheel? A PITA, but it might shed some light.

I was planning on installing a lighten wheel that I have, but now you've got me spooked.

edit -

just re-read:

t I didn't replace the disc and the spring while I was in there, but it still had plenty of life in it; maybe the material is contaminated and I didn't catch it? Any ideas?

Any comparative feedback from the other two guys on this? .... just a thought.

 

[mneblett]

The symptoms are: as I accelerate out of first gear, there is smooth, strong acceleration. Once I hit second and roll onto the throttle ( I open the throttle up), the bike will lurch three times from 1000rpm to 3000 rpm, in a rhythmic manner....one lurch....two lurch.....three lurch....as if a gear is missing a tooth, or the clutch is slipping for a micro second.
All the rest of the gears are fine, with the throttle wide open, getting up to speed, all very smooth and strong.

How quickly after the shift to second and application of power are you getting the "lurch"? Instantaneous/during the clutch engagement?

How much are you opening the throttle? Getting on it hard (i.e., max torque output?)? Does it "lurch" when shifting up into 2nd with more moderate/relaxed shifting?

The reasons for my questions: I'm wondering whether the tranny input shaft torque protection mechanism (the mating cam/ramp and spring arrangement) is seeing enough input torque to cause the cams to override the ramps 2-3 times at lower speeds -- at least until the bike is going fast enough to take the torque before the cams top the ramps. A weak or broken spring could allow enough axial travel of the cam ring to let the tips top the ramps.

 

[30064]

Lew,

I almost posted some questions to Kurt right in line with your comments. One of those 2 fellows Kurt mentioned was Chuck, wasn't it Kurt? I seem to remember visiting with him at one of the past sessions and discussing this issue.

Maybe a post to "AskOak" or the Airlist is in line for some input from the Gurus?

I wish my transmission experience exceeded hypoid changes to add some insight, then again - is it the transmission?

One would assume if the clutch is disengaging for a fraction of a second in 2nd gear...it would repeat in other gears if like loads are being applied.

??????

 

[lmo1131]

Good point Mark. I think this is definitely an "Oak-able" question; nothing mundane, or "how do I ...?" about this problem.

 

[kmkahuna]

One of those 2 fellows Kurt mentioned was Chuck, wasn't it Kurt? I seem to remember visiting with him at one of the past sessions and discussing this issue.

Mike, I remember that Gary had the problem, and a fine crusty old gentleman out in the parking lot had the same problem, but I can't remember his name!

Maybe a post to "AskOak" or the Airlist is in line for some input from the Gurus?

This is gonna be fun!

How quickly after the shift to second and application of power are you getting the "lurch"? Instantaneous/during the clutch engagement?

Mark, this happens about a second or two after the shift..probably closer to one second than two... clutch lever is completely disengaged and loose.

How much are you opening the throttle? Getting on it hard (i.e., max torque output?)? Does it "lurch" when shifting up into 2nd with more moderate/relaxed shifting?

Throttle is probably around 3/4. I can completely eliminate the lurch by babying it all the way through 2nd gear; but this is obviously not what's needed when you're trying to accelerate onto the freeway.

The reasons for my questions: I'm wondering whether the tranny input shaft torque protection mechanism (the mating cam/ramp and spring arrangement) is seeing enough input torque to cause the cams to override the ramps 2-3 times at lower speeds -- at least until the bike is going fast enough to take the torque before the cams top the ramps. A weak or broken spring could allow enough axial travel of the cam ring to let the tips top the ramps.

Partial Swahili for me there, Mark. I had the transmission completely rebuilt with new bearings and checked out, which is why this is such a brainteaser...

Are they running lightened flywheels as well? The "lurch" is as if you were pulling in, and releasing, the clutch slightly (just enough to break friction)?

Yes, Lew that is exactly it.... as if the clutch slips, and then catches drastically...three times, from 1000 to 3000 rpm. Hopefully the video will show you guys exactly where it's happening.
and YES, what a good question! I don't know if their flywheels were lightened. But you can be damn sure I probably have one of the lightest flywheels out there, huh? Damn thing looks like swiss cheese...

Any chance you can lay hands on a "loner" gearbox to see if the condition is the same with a different box? Or a different flywheel? A PITA, but it might shed some light.

Barley Therapy at Gary's is coming up...

How close in time are the lurches?

About a second, Kurt, maybe less.

Thanks again, everyone: spoke to Dave Cambell about all this, and he says he's seen this before, and it's in the transmission: that clearance between the gears and the casing might be the issue. I'm speaking in the blind here, because I only have a basic understanding of the physical situation he's talking about... Will get the video up, and am going to call Mike at MotorWerks who did the work. Hey, Mark: does this jive with what you're talking about inside the box??
K

 

[mneblett]

Hey, Mark: does this jive with what you're talking about inside the box??

No -- completely different mechanism, but actually more likely than my thought.

Dave's talking about excess axial clearance on the main shafts which allows too much axial movement of the intermediate shaft or output shaft when under load. When that happens, there is the possibility for the dogs to not fully engage their corresponding holes to lock 2nd gear to the shaft when the shift fork slides the engagement ring toward 2nd gear. The pop, pop, pop would be the dogs jumping out of their holes.

The same symptoms/problem (dogs skipping) can have more than one cause -- dogs jumping can result from excessive axial shaft play in the case, worn dogs, a bent shift fork, a shift drum with worn grooves, etc., or some combination of the above. All need to be checked when Dave opens the case again.

 

[20774]

I checked my listing of Oak's articles...not his Tech Index, but "Kurt's Index of Oak's Articles":

Jul 2003 - Lunging in Second Gear
Writer said something like when accelerating hard in 2nd gear, the torque will change the and the bike will lunge. He had a '81 R100.

Oak said could be clutch slippage, especially if the spline lube was excessive (writer mentioned having to do some lubing recently). He also said could be a defect in the cluster gear, a defect in the output flange slipping on the shaft, or the shift dogs may be worn enough to pop out on a given gear, but pop back in on a different gear. Oak said he had the older shift mechanism which could be updated to resist overshifts and false neutrals.

Feb 2010 - Transmission Lurching
Writer had a '74 /5 5-speed transmission lurched after being shfited into 2nd gear, then it worked fine...didn't happen in other gears. He said it was supposed to have been rebuilt but was unsure of the engagement dogs as the tranny had seen sidecar use.

Oak said the tranny might need proper shimming...axial end play might be wrong. Also mentioned a gear might be slipping that was pressed on the shaft...rare, though. Mentioned the output flange torque...be sure it was properly done. Agreed that worn shifting dogs could be the problem but there would be noise with that as well.

Some common problems there...I wonder about the shimming...that's an important part of tranny rebuild, to be done by experts.

 

[kmkahuna]

All need to be checked when Dave opens the case again.

Thanks, Mark.
Well, got off the phone with Mike from Motor Works
http://www.motorworkspromach.com/

and turns out our SOCAL airmarshall Gary Jackson, Chuck Thomas and I all have something in common: all of us have the same ghost in the tranny! Mike's familiar with both of their stories, and wasn't too hopeful that something can be done about this. That being said: my bearings were toast, so no matter what, I'm glad I had the work done.
Mike will be more than happy to crack open the case again, but he's pretty vexed himself.
Dave C. and Mike are going to compare notes... I'll let everyone know if something comes of it.
5:00 pm PST:
Okay, here's the video...
http://www.youtube.com/watch?v=KIHh1UUtTxk
Notice the very first takeoff I was already in second gear..

 

[lmo1131]

That is a p-r-e-t-t-y cool diagnostic tool Kurt.

I guess I didn't read about the pop-pop-pop associated with the lurching. If it was just slippage there would be no other sound. I was thinking along the lines of maybe that flyweight flywheel warping under certain torque conditions, maybe allowing the clutch to slip ... a bit of a reach, but one never knows, does one?

It's isolated to 2nd gear operation; it's intermittent ... in your video when you first took off it skipped three times, it occasionally just skipped once, then twice... and as the load drops it doesn't skip.

I'm with Kurt; dogs/shims. What else could it be?

 

[kmkahuna]

5:00 pm PST:
Okay, here's the video...
http://www.youtube.com/watch?v=KIHh1UUtTxk
Notice the very first takeoff I was already in second gear..

Okay everyone; here's Marc, my neighbor, who has just done another ride on the bike...here's his comments:

"Well hell, if you had bought a damn Guzzi.... in any case, after riding the bike around and listening to the transmission I'm thinking that the shift fork is worn/bent or the dogs on second gear are messed up. I would think that someone who does transmissions for a living would spot this kind of problem easily when inspecting the parts."

 

[lmo1131]

I would think that someone who does transmissions for a living would spot this kind of problem easily when inspecting the parts.

ouch!

 

[mneblett]

ouch!

Have to admit I was thinking the same thing -- I was just too polite to say it

Listening to the vid, I'm more certain now that it's dogs jumping, for a couple reasons:

-- when the drive train re-engages, it's abrupt -- not like a smooth/quick re-engaging slipping clutch plate -- more like a dog re-entering a slot and immediately transferring torque to the gear.

-- the length of the "jump" is pretty constant -- actually within a rather narrow time-window each time -- suggesting the dogs are re-engaging on a pretty consistent basis. I would expect a slipping clutch's re-engagment to be more variable, in partlcular more in line with release of the throttle to remove torque from the driveline.

One additional test to consider, which may or may not be useful: Next time you upshift to second, hold the shift lever firmly up -- do not release it while you open the throttle. The objective is to see whether it stays in gear.

If it doesn't, the test doesn't tell you much.

If it does, it's an indication of a possible bent shift fork -- the theory being that when held by your toe it keeps the sliding ring all the way over and the dogs engaged, but when the toe releases a bent fork can draw the sliding ring back just a hair, enough to let worn dogs slip out of engagement.

 

[gch71]

Get a loaner tranny, or loaner stock flywheel, and do an individual swap and test run, after seeing those pics of the flywheel I'm very surprised it hasn't come apart yet, I bet if you did an NDT inspection on it you'll be surprised...(none destructive type test) ie, dye penetrant or eddy current type of inspection. I don't know how it's not warping flexing etc under torsional loads etc. I can appreciate the lighted flywheel concept but I think this particular one was done by someone that was a little to ambitious, lacking technical thought of the consequences.

 

[kmkahuna]

Get a loaner tranny, or loaner stock flywheel, and do an individual swap and test run, after seeing those pics of the flywheel I'm very surprised it hasn't come apart yet, I bet if you did an NDT inspection on it you'll be surprised...(none destructive type test) ie, dye penetrant or eddy current type of inspection. I don't know how it's not warping flexing etc under torsional loads etc. I can appreciate the lighted flywheel concept but I think this particular one was done by someone that was a little to ambitious, lacking technical thought of the consequences.

Well, if that flywheel is the problem, it sure would fit in nicely with my airhead experience so far...
All that's left to do is to replace the frame, wheels, camshaft, connecting rods, pistons, main engine assembly, seat, fenders, headlight, instrument cluster, front forks, gas tank, and the panniers and I'll have a top notch bike.
Over a year ago now...my neighbor warned me:
"just get her running and ride her around for awhile...don't take her apart"...

For anyone who's trying to figure out the entire transmission thing to begin with: there are some great resources out there: I suggest taking a look at the animations at John Lawrence's site:
http://www.gadgetjq.com/transmission.htm
He said to drop him a line if you link to his page, but I can't find an email for the life of me on his site...so John! Hey, it's Kurt! I'm linking your site!!!
Snowbum, of course (who's the origin of that link)
http://bmwmotorcycletech.info/transmission.htm

Excellent pictures of the actual gears:
http://w6rec.com/duane/bmw/trans/

 

[30064]

Kurt,

Call Stoner. He may have an extra transmission laying around that he's willing to loan to you. It may be worth a try. Process of elimination...

(good call Lew [ref: post 325])

 

[lmo1131]

One additional test to consider, which may or may not be useful: Next time you upshift to second, hold the shift lever firmly up -- do not release it while you open the throttle. The objective is to see whether it stays in gear.

Have you tried Mark's suggestion yet?