Gear return spring- 81 Jota

blab said:
So why is it twice the travel on upchange compared to down change ?
The 1mm to 5mm discrepancy at the internal arm has to affect this.
Click to expand...

As you have already explained, you have the eccentric at the uppermost position.  It should be at the middle position, or very close.  THAT would make throws just about even for up and down. 

If the pawls do not engage the drum correctly with the eccentric in the middle, or thereabouts, you have either the selector drum fitted incorrectly, wrong selector drum (750 and triple item are mirror-images), wrong selector shaft and pawls, or the pawls have been tampered with.  Might be even worse and the gearbox selector forks are worn/bent, selector fork axle locating pin is missing (seen that a few times!), allowing the fork axle to move and droop... all sorts of shit.  I really don't expect that sort of stuff though.

With the gearbox in neutral, a pin on the selector drum should be positioned mid-way between the pawls.  With the gearbox in gear (any gear will do), the pawls should have a pair of pins, each nestling nicely at each end, roughly equidistant between them. 

Disregard the markings on the internal and external selector drums for a start (especially if the origins of these parts is unknown).  Get the gearbox in neutral (make sure it is the true neutral!  Warning light!)  Insert the external drum with a pin at 9 o'clock, or as close as possible, the others leading clockwise from there.  This pin should then be positioned in the middle of the pawl leg when the slector shaft and pawl are fitted.

IF all is in good order, there should be no need for bending springs, welding tabs etc.  At the most, the tips of the pawls might require a bit of trimming for a smooth lever return to its central position, with the next pair of selector pins engaged ready for the next gear change.  The whole adjusting procedure should take no more than 5-10 minutes.

piet
 
This is what I have found,
With the bike in neutral and neutral light on, the mark on the inner gear is a 3 o'clock.
The mark in the selector drum is at the end most of the 4 pins.
Insert the drum with the mark at 9 o'clock and the end most pin is between the pawls.
The other 3 pins are below it ie running in an anti clockwise direction.
I can down shift to 1st then upshift through to 5th,the selector drum moving clockwise for upshifts.
Select 4th,with the eccentric at the top of its adjustment I have 1mm clearance on down shift and 5mm clearance on upshit.
Any adjustment of the eccentric give me zero clearance on down shift and even more on upshift.
Having the eccentric in the middle position gives negative clearance on downshit and stops the pawl engaging the pin.
Seems to a newby like me that eccentric or pawl arm are incorrect.
But no doubt there will be some other problem.
 
Anti-clockwise for the pin orientation is correct, brain twister on my part, sorry.

How do the pawl and the other pins match with the eccentric in the middle?  If the excessive travel is in 4th.-5th. gear only, the drum must be at fault.  The pins should be equally spaced in the drum, perhaps Luigi had a red too many... again.

Can you post some detail pics?

piet

 
Hang on, I thought once the drum was in place, mark to mark, or pretty close, it's standard procedure to have gears in 4th and then adjust eccentric to central position.
Sounds like your really close now though.
 
With this excessive travel in one direction are you SURE the actual gear levers are set up properly: the short lever at the rearset and the stub that clamps to the splined selector shaft??? if the lever angles are all over the place the travel will be different in each direction (see my previous post). If that's all god you have some other weird issue going on. The heavy spring on the selector arm isn't interfering with the eccentric screw?? Sounds bizarre to me - and 4 pages of replies to find a solution for something that takes 10-15 min max to get right??? We need pics baaad! :-\
 
Some pics and a video.
Bike in neutral,neutral light on, marks lined up,



Spring set up,


Selector arm roughly in the middle,


4th gear,


Video in 4th gear showing difference between up and down shifts,any adjustment ot eccentric makes it worse,

Should I be concerned about this crack,
 
Don't see anything out of the ordinary...

If it bugs you that much, weld up the pawls and re-shape the hooks in a more favourable position. 

Eventually, that crack is going to open up further and the thread will get a bit loose.  Time for a little welding and re-tapping/Timesert.

piet
 
sfcpiet said:
Don't see anything out of the ordinary...

If it bugs you that much, weld up the pawls and re-shape the hooks in a more favourable position. 

Eventually, that crack is going to open up further and the thread will get a bit loose.  Time for a little welding and re-tapping/Timesert.

piet
Click to expand...
What I have been lead to believe is out of the ordinary is the eccentric being at the top of the adjustment and having a 5mm difference in free play up to down.
That crack sums this bike up perfectly.
 
blab said:
What I have been lead to believe is out of the ordinary is the eccentric being at the top of the adjustment and having a 5mm difference in free play up to down.
That crack sums this bike up perfectly.
Click to expand...


Can you source another shifter shaft and pawl to compare?  The pawl must be of an incorrect length to be out of whack so far.  Maybe a 750 item riveted to a triple shaft?  (the 750 pawl engages the other side of the drum, the entire shaft assembly is different.) Can't treally tell from the pics.

piet
 
Can't say I read this whole thread but what's most important is clocking the Gear Sprocket (Cam whatever) and they where not indexed marked back then - Once you got it indexed use a punch to mark the alignment with the cam against the housing for reassembly if you ever have to take it apart again

If the gear selector spring (Tensor) is not broken, I doubt it's your problem. It's all manual clock throw - Been a while since I was there and has never failed after some 35 years except the Breganzie Tranny does have a long throw between 4th and 5th and you can hit a false neutral if you are not slow and deliberate other wise if you're Gunge Hoe you don't need a clutch and just Bang all the other 4 gears.

The Breganzie Tranny is probably the one of the biggest motorcycle transmissions I've work with - The problem is if you blow the mill you can damage the tranny with oil contamination.
 
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