Impending doom? smallblock shift spring

[SED]

Out on the Monza and about 2 miles from home the shifting becomes incredibly notchy.  Sometimes it is just greater resistance, sometimes I have to toe the lever back and forth to get it to shift.  This reminds me of the symptoms of a broken shift centering spring - but isn't that always a 100% failure?  (stuck in gear and won't shift?) 



Have the gods of Luigi given me a warning that let me correctly diagnose the problem (broken spring?) AND ride home?!  This is not usually the failure mode of spring steel. 

The linkage is not sloppy or binding, everything seems to push, pull and rotate well.  However, the shifter shaft going into the gearbox appears to move in and out a couple mm while being shifted - is this normal?  Does it indicate a failure other than a broken spring?

Thank you for your expertise.

[malik]

When my gearshift return spring broke on the V7C, it just prevented the the gear lever springing back to reset itself each gear change. I used my foot to re-position it after.each gear change (when I remembered). Worked fine for 60,000km.  Once I disassembled the gearbox, found the spring was in two pieces. The short arm was lying in the bottom of the casing.

The selector shaft has a few mm horizontal movement (in & out), but should be otherwise firm - no sideways movement.

[pehayes]

Yes, a broken spring should be a 100% refusal to return to center.  Binary failure.

I have had both shifting and brake problems related to the pivot where the shift or brake pedal pass through the frame.  It is close to the exhaust; gets hot; binds while riding.  I would immediately pull the linkage to cleand and lubricate the frame passage and then report back.

Patrick Hayes
Fremont CA

[SED]

Thank you Malik and Patrick.  While it feels like Malik describes and the solution is to reposition the lever, it is only "notchy" about 1/2 the time.  At a standstill the foot lever re-centers from both directions - so not the spring.  I pulled the foot lever and its pivot is free and well lubed (even better now).

I'm now wondering about the "shift adjusting screw" #13 (green) or the detent pawl #20 (blue).  The shift adj screw is tight, so it probably hasn't rotated, but I need to ride it to see if the problem is only with upshifts or down shifts.  What would bend the screw internally?  Any known problems with the detent pawl?

[SED]

Another shift spring question.  I have a January 1984 V65 transmission in good condition sitting on the bench.  The bike appears to have been wrecked in 1989 and taken off the road.  I want to use it (and the engine).  Should I pull the gearbox apart and replace the shift spring because of its age, or can I assume it will live a relatively long life since it appears to have few miles.

Thanks,
Shawn

[pehayes]

Don't mess with the "shift adjusting screw".  There are no internal forces to bend it or to move it out of factory original adjustment.

Did you pull the transmission breather/shift-pawl/spring?  If not, there wouldn't seem to be any reason for dynamic failure.

I'd like to hear more about the symptoms.

I'm starting to think you have a poorly functioning clutch.  It is not fully disengaging and thus creating internal drag and refusing shifts.

Do you have some slop in the clutch cable at rest?  You DO NOT want the clutch cable adjusted up snug.

Can you verify the the clutch lever arm at the back of the transmission does not hit the swingarm when fully released and also does not hit the transmission casting when fully pulled in?  Either case will give false clutch action and make rough shifting as you describe.  Also will produce costly damage relatively soon!

Look at the back end of the transmission.  At rest, the "outer throwout body" should be just about flush with the surrounding casting.  If the throwout bearing wears, the outer body will go recess.  If the clutch disc wears, the outer body will protrude.  Not too difficult to pull the swingarm and inspect the throwout parts.  Outer body is #11.  Throwout bearing is 3-parts #10





I would also recommend you browse and join the Small_Block_Guzzi discussion forum on Yahoo Groups.  Specific owners will opine there if you post your symptoms.

Patrick Hayes
Fremont CA

[malik]

I think you'll find that #20 is the breather, and #13 Is an eccentric screw which centres the return spring - and should not have been played with, so don't. If you did, return it to the position it was.

I have replaced some of my studded rod ends in the linkage, with standard rod ends (plus the appropriate bolts & washers) and have found that they work a bit better. 6mm from memory, a male & female each end, & stainless if you can get them - sorry no photo - a bit hard on the road.

There's some clear instructions on adjusting the gearbox end of the clutch by Pete Roper on this site - and again, very easy to access with the swingarm off. You get really good at it quite quickly, so no need to panic.

Mal

[Muzz]

There is another possibility which may or may not give the symptoms you describe.

The first time I had the Breva box apart I found that the stud that holds the detent spring had actually snapped off, and the nut was only held from dropping in to the workings by the bearing retainer plate. I purchased a new one and replaced the whole plate that it mounts on.

The 2nd time when I had the box apart the stud snapped off again before it was even tightened. Fortunately, I was doing the job in Steamdriven's workshop, and he happens to be an airframe technician with a set of cobalt drills. He drilled and tapped the plate and used a high tensile cap screw to replace the stud that kept snapping off.

If the coil spring is allowed to tilt sideways it MAY cause a stickiness in the gearchange.

[SED]

Thank you Patrick, Mal and Muzz.   

I will check the throwout body position and arm.  Clutch cable adjustment, lever free-play and engagement point are all reasonable, but I need to give the back of the transmission a closer look.  The sudden notchyness gives the impression that something (like the shifter spring) had broken and is not a result of progressive wear - but I need to investigate further.

Thanks for your help and ideas!
Shawn

[Muzz]

If it is the stud in question the whole box has to come apart.

I would suggest looking at every other option first, especially the clutch adjustment.

[SED]

The first time I had the Breva box apart I found that the stud that holds the detent spring had actually snapped off, and the nut was only held from dropping in to the workings by the bearing retainer plate. I purchased a new one and replaced the whole plate that it mounts on.

Muzz, I've been looking at the exploded views of the gearbox and cannot figure out which stud you are referring to.
Are you referring to #38 in this picture? (not the circle)




Thanks,
Shawn

[Muzz]

Not that one Shawn.

Funny. I went to the Stein-Dinse site and on the V50 picture it actually does not show it, although it must be there in the box.

If you go to the Stein-Dinse site and look under the '03 Breva 750 IE, in the gearbox breakdown showing the selector forks you will see on the left hand end of the selector shaft a plate #14 and a spring #13. Twice the threaded end of that plate broke off which left the entire detent location sytem free to do whatever it chooses to do.

As I said before, in my case the nut and washer stayed about in the same location trapped by the bearing retainer plate (bottom left of that diagram), so the spring stayed in the correct position.

[SED]

If you go to the Stein-Dinse site and look under the '03 Breva 750 IE, in the gearbox breakdown showing the selector forks you will see on the left hand end of the selector shaft a plate #14 and a spring #13. Twice the threaded end of that plate broke off which left the entire detent location sytem free to do whatever it chooses to do.

As I said before, in my case the nut and washer stayed about in the same location trapped by the bearing retainer plate (bottom left of that diagram), so the spring stayed in the correct position.

Must be this?  It looks like the detent has been changed from under the breather to the back of the selector fork shafts.  It may not exist in the Monza 'box.

[Muzz]

That's the one.

Never seen inside a Monza box so don't know how they work the detent system sorry.

I think Steamdriven had been inside his Monza box before he put the Nevada engine and box in and made it a Monzada.   He gave me a hand on the second time I needed to get in to the Breva box. He was the one who modified that plate after the second shaft breakage, so he may be able to shed some light on it. Send him a pm, he's a very knowledgeable guy.