Best Answer Spider , 13 February 2022 - 10:02 AM
Cheers for the Photos.
I may have given you a bit of a bum steer a page or so back. I did conclude that the issues you're having were in the gearbox, largely based on the fact that you could engage reverse without grinding, but now I see this, I'd say the primary gear bushes are the issue - sorry for my bad.
I'm guessing here that when you've engaged reverse, the engine, oil and primary gear have been fairly cool / cold and this would likely be why there was no grinding for reverse, but as parts and oil have warmed up, the primary gear bush has just started picking up. I think you dodged a bullet here as from those I know of who have had trouble with these bushes (and that's been everyone who's fitted them) usually don't find out there's an issue until the gear is locked on the crank, by which time, the crank is karput (eaten by the bushes). These are simply too hard - your photos here shows that clear as day.
Since the gearbox is off, may as well check it over. I doubt you'd need to dis-assemble it any further to do this, maybe even get someone experienced who's local to check it too.
As for the Primary Gear Bushes, the factory found the answer here back in 1963-ish. They did try Bronze based bushes of various allying types but settled on a steel backed soft bush for one and a deva for the other. At least when these bushes go wrong (which isn't often), it's only the bushes that let go and the crank is nearly always saved. This is one of the primary design features of any bush. The Front Bush in a Genuine type is still available, they were (are) made by Glacier, you'll see their stamp on the back (G in a box). I have Deva bushes here, however I believe AC Dodd also has a small batch made too.
Mini Mad
Posted 12 February 2022 - 06:23 PM
Moved Into The Garage
Posted 13 February 2022 - 05:48 AM
What I can see of the Gearbox internals, most looks good, I can't quite see the 1st / 2nd selector fork, it appears it may have some wear in it (I'm not sure).
The baulk rings maybe on the tin side, but again, I'm not 100% certain.
Some suspect marks on the crank which makes me think the primary gear is picking up but it's free to spin by hand?
This ^ however looks typical of the new era silicon bronze primary gear bushes - just before it eats the crankshaft.
Can you post some photos of the primary gear, so we can see both bushes ?
Mini Mad
Posted 13 February 2022 - 07:05 AM
Moved Into The Garage
Posted 13 February 2022 - 10:02 AM Best Answer
Cheers for the Photos.
I may have given you a bit of a bum steer a page or so back. I did conclude that the issues you're having were in the gearbox, largely based on the fact that you could engage reverse without grinding, but now I see this, I'd say the primary gear bushes are the issue - sorry for my bad.
I'm guessing here that when you've engaged reverse, the engine, oil and primary gear have been fairly cool / cold and this would likely be why there was no grinding for reverse, but as parts and oil have warmed up, the primary gear bush has just started picking up. I think you dodged a bullet here as from those I know of who have had trouble with these bushes (and that's been everyone who's fitted them) usually don't find out there's an issue until the gear is locked on the crank, by which time, the crank is karput (eaten by the bushes). These are simply too hard - your photos here shows that clear as day.
Since the gearbox is off, may as well check it over. I doubt you'd need to dis-assemble it any further to do this, maybe even get someone experienced who's local to check it too.
As for the Primary Gear Bushes, the factory found the answer here back in 1963-ish. They did try Bronze based bushes of various allying types but settled on a steel backed soft bush for one and a deva for the other. At least when these bushes go wrong (which isn't often), it's only the bushes that let go and the crank is nearly always saved. This is one of the primary design features of any bush. The Front Bush in a Genuine type is still available, they were (are) made by Glacier, you'll see their stamp on the back (G in a box). I have Deva bushes here, however I believe AC Dodd also has a small batch made too.
Mini Mad
Posted 14 February 2022 - 01:58 PM
No problem, thanks for all your help with it, much appreciated!
The thing I'm still trying to wrap my head around is why its worse in 1st/2nd and not 3rd and 4th - something to do with the torque I suppose? It seems to also improve when warm, maybe the clearances increase when warm?
I polished the crank with a microfibre cloth and autosol metal polish and it cleaned all the discoloration up easily. I'm thinking the clearances are too tight and this is partly the cause along with poor material choice for these bushes.
Cheers,
Moved Into The Garage
Posted 14 February 2022 - 06:54 PM
It's been my experience and that of others who've had the bad experience of running these bushes that the clearances close up when it gets hot. It maybe that from the initial hot oil soak some of that oil when warmed up, was helping, though, this material doesn't absorb much oil.
There's a few examples of how I end up seeing them in this thread;-
https://www.theminif...ry-gear-damage/
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