gearbox

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flanker850

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Feb 6, 2012
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OK so my 850 1974 mk starts up super well and sounds great!!! I have some shifting issues that I alluded to earlier. most specifically, i can go down to 3rd and 4th but coming back to 1st and neutral does not happen. it truly freezes up. So the advice i got was was to check the chain, clutch and gearbox. the chain seems sorted. so i decided to tear into the gear box first. i also bought barnett clutch plates to replace the stock. i plan on doing that tomorrow.....

THE GEARBOX
I removed the inner and outer covers. The gears looked pretty good. no issues with the shaft and the i went though the gears pretty well by rotating the wheel and moving the quadrant. So i oiled/cleaned what i could and put it back together. Well sort of.... the whole thing went back together and i was rolling, but the outer box will not slide into the ratchet plate when it is connected to the knuckle pin roller/ quadrant. The outer cover fits without the ratchet plate and the knuckle ratchet plate and neighboring rod connect well.

The spring is pretty twisted I need a new one.

My question is can the ratchet plate be bent? or is there some trick to getting the outer cover back on. I was thinking heat, but it should fit right. im certain the pawl is in place and not blocking reassemble. The ratchet plate goes halfway into the outer cover and refuses to go any further. any ideas????? Rob
 
I probably need to tear into a gearbox to actually visualize how that all fits together. I rebuilt mine a couple of years ago and had the outer cover on and off a number of times because I was shimming for the new layshaft bearing I had put in. I don't recall now anything needed other than a tap with a soft mallet. I am sure somebody here has a better memory than I and will set you right. Otherwise, I have another gearbox sitting that needs to be torn down. I could use this as an excuse to get in there.

Now...mentioning that layshaft. You did check yours to make sure it has been upgraded? Right?

As for the shifting problem, I was not sure from your description...it is the primary chain tension which tends to cause problems with this not necessarily the drive chain.

Russ
 
Make sure you have the correct clearance between the pawl & the spring. It may have to be bent to obtain this.
The spring can be barely touching each side or a very small clearance. New ones require bending.
Information in workshop manual or on Oldbrits site.
Just done mine last night.
 
flanker850 said:
Flo said:
Most probably the pawl spring.
Click to expand...

yep i ordered one! but that should not keep me from putting on the outer case????
Click to expand...

Yes, my mistake!
# 4
This spring may be on backwards or flipped so to speak. It only work one way. The wrong way will cause the effect you speak of being able to shift up but not down. Hopefully someone may enlghten as to which way the offset goes.
http://www.oldbritts.com/1973_g8.html
 
According to my workshop manual,

"An examination of the spring will show that one leg of the spring is straight, the other spring leg is cranked. The correct spring location is with the straight leg of the spring in the uppermost position. Position both spring legs on each edge of the rocking pawl."

As I remember there was a bit of clearance between the spring and the pawl, and the crank had to be just right, but some expert will chime in

Dave
69S
 
Just wanted to check that the lay-shaft bearing has been up-graded.I used the OldBrits instructions which were a great
help. There is a whole section on the problems you are having.
YING
 
flanker850 said:
OK so my 850 1974 mk starts up super well and sounds great!!! I have some shifting issues that I alluded to earlier. most specifically, i can go down to 3rd and 4th but coming back to 1st and neutral does not happen. it truly freezes up. So the advice i got was was to check the chain, clutch and gearbox. the chain seems sorted. so i decided to tear into the gear box first. i also bought barnett clutch plates to replace the stock. i plan on doing that tomorrow.....

THE GEARBOX
I removed the inner and outer covers. The gears looked pretty good. no issues with the shaft and the i went though the gears pretty well by rotating the wheel and moving the quadrant. So i oiled/cleaned what i could and put it back together. Well sort of.... the whole thing went back together and i was rolling, but the outer box will not slide into the ratchet plate when it is connected to the knuckle pin roller/ quadrant. The outer cover fits without the ratchet plate and the knuckle ratchet plate and neighboring rod connect well.

The spring is pretty twisted I need a new one.

My question is can the ratchet plate be bent? or is there some trick to getting the outer cover back on. I was thinking heat, but it should fit right. im certain the pawl is in place and not blocking reassemble. The ratchet plate goes halfway into the outer cover and refuses to go any further. any ideas????? Rob
Click to expand...
Its tricky u have to fuss with it wiggle, jiggle, etc... tap with rubber hammer "patience" no heat required. {is your quadrant lever at top position?} Dox
 
I have trouble with the outer cover sometimes too. The ratchet plate (3), has to line up with 2 items, the gear shaft inner bush (25) which is installed already in the inner cover, and the hole in the shift roller (5) which wanders around while one is trying to put it in. Maybe some thick grease on the shift roller would help keep it in place while pushing on the outer cover. For me it's a trick, but when it goes, it just goes in. http://www.oldbritts.com/1971_g6.html

Dave
69S
 
Depending on if you load the pawl ratchet plate into the cover before loading all into the inner cover, the shaft can 'hydraulic' lock in the inner cover bush if you have to much oil there and the shaft to bush is a really neat fit. Keep at it it will go.
Regards Mike
 
Wow all these posts are relevant!!!! I got it to work and to my astonishment, all 4 gears and neutral are obtained!!! pretty happy about this. however they do slip a little. i did not tighten the cover so there is some play, it gets stuck between gears for a small time period so Ive ordered a few new parts and i will do a partial gearbox rebuild. I think the spring is pretty dodgy! but it does shift which is pretty assuring!!! Ive labeled the gearbox adventure a 90% success.

the gears look great! i left the layshaft bearing alone, but i'll go back to that. since the gears and other parts in that area looked so good i wonder if that is my problem....

Now the clutch.... lots of controversy surrounding barnetts. Ive read the old brit stuff and apparently an extra plate can be obtained to rectify this in a 750. I have an mk 850 1974, which already takes five plates. i wonder if i need another, but i probably have to look to find out. has anyone had a positive experiences with barnett.

I have to say this has been a much better experience then the old ducati, and i havnt even really road the thing yet! Thx again for all the help, I hope I can repay it when i get a few more years under my belt!!!!! Rob
 
Oh yeah Dox, I found it easier to move the quadrant to a lower position??? Im not sure if this is correct but thats how it went together easiest! Rob
 
flanker850,
I did not mean to imply that the lay-shaft bearing was giving you any problem but as you have it this far apart,I would
check to see if it is the one with the brass cage for the rollers that was made in Portugal.I also have a 74 and replaced
mine with the up-grade after reading all the horror stories of these coming apart.My gear box was not giving me any
trouble at all,I just wanted to replace the bearing before it went.Just my own two-cents.
YING
 
YING said:
flanker850,
I did not mean to imply that the lay-shaft bearing was giving you any problem but as you have it this far apart,I would
check to see if it is the one with the brass cage for the rollers that was made in Portugal.I also have a 74 and replaced
mine with the up-grade after reading all the horror stories of these coming apart.My gear box was not giving me any
trouble at all,I just wanted to replace the bearing before it went.Just my own two-cents.
YING
Click to expand...
yeah im just lazy!!!! thanks i'll change it!!! Rob
 
I'm doing my box now too. Last summer it was all I thought about, worrying about the lay shaft bearing coming apart. I bought the super blend bearing.
Have yet to put it in as I am still stripping the frame as time allows.
But, yeah. Do that bearing, check all your bushings and seals.
I had a lay shaft snap about 20 or so years ago because of that bearing.
What a bitch getting that stub out of the case. I still have that shaft in my tool box as a reminder.
 
Guido said:
I'm doing my box now too. Last summer it was all I thought about, worrying about the lay shaft bearing coming apart. I bought the super blend bearing.
Have yet to put it in as I am still stripping the frame as time allows.
But, yeah. Do that bearing, check all your bushings and seals.
I had a lay shaft snap about 20 or so years ago because of that bearing.
What a bitch getting that stub out of the case. I still have that shaft in my tool box as a reminder.
Click to expand...

yep i just got the layshaft bearing out! waiting for the superblend! replacing most bushing seals and warn parts! cleaning everything else. basically a new gearbox.

installed a barnett cluch too!!!!
 
Looks like you and I are in the same state of repair. I just opened my box last night and as it turns out I have never opened this box up.
I have 2 bikes, one is a 73 and this one is a 74. I've had this one since 1979. It was the other one that snapped the lay shaft.
To my surprise this one had the super blend bearing and the 3 bushing set up in the sleeve gear but the main shaft bearing is all crunchy feeling.
I have both 1st gears to replace, the main shaft, bushings and bearings.
Now I just have to figure out how to shim the layshaft as it wasn't done and thats what ate up my first gears.
 
Guido said:
Looks like you and I are in the same state of repair. I just opened my box last night and as it turns out I have never opened this box up.
I have 2 bikes, one is a 73 and this one is a 74. I've had this one since 1979. It was the other one that snapped the lay shaft.
To my surprise this one had the super blend bearing and the 3 bushing set up in the sleeve gear but the main shaft bearing is all crunchy feeling.
I have both 1st gears to replace, the main shaft, bushings and bearings.
Now I just have to figure out how to shim the layshaft as it wasn't done and thats what ate up my first gears.
Click to expand...

yeah i just finished the gearbox. Ive never done that before! but it was a great project. finding all gears well now. I put in the barnett clutch it seems pretty tough to pull, but i think it needs to be broken in.

lucky to have the super blend already. but once i did it, i think the next time will be much easier!!

Im in venice! i cant wait to take it in the canyons? Where do you ride usually? Keep updates on your project. cheers, Rob
 
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