ET: Engine (Twin) Rapide Gearbox - Very 'tight' gearchange

[greg brillus]

Whilst that gearbox jig in the picture above might seem like a useful tool, the best jig of all is the actual engine and gearbox components themselves, as no two are exactly the same. They can take the same fettling as a timing chest to get all working ok...............Try setting up the gearbox after you've machined 20 odd thou from the mating faces of the cases, that takes some sorting due to loss of running clearances (end float). It sounds like your cover plate layshaft bearing is not fully home, perhaps the shaft is a bit too snug in the bearing and when you remove the cover it is pulling the bearing out, lininsh the shaft a small amount so it slides into the bearing without grabbing. Try installing the cover plate with just the lay shaft in place including it's gears and with the input shaft removed, put your finger through the bearing center to see if the layshaft spins freely and fee some end float on the gears. if you isolate things like this, you can sort where the problem is.

 

[Bill Thomas]

Whilst that gearbox jig in the picture above might seem like a useful tool, the best jig of all is the actual engine and gearbox components themselves, as no two are exactly the same. They can take the same fettling as a timing chest to get all working ok...............Try setting up the gearbox after you've machined 20 odd thou from the mating faces of the cases, that takes some sorting due to loss of running clearances (end float). It sounds like your cover plate layshaft bearing is not fully home, perhaps the shaft is a bit too snug in the bearing and when you remove the cover it is pulling the bearing out, lininsh the shaft a small amount so it slides into the bearing without grabbing. Try installing the cover plate with just the lay shaft in place including it's gears and with the input shaft removed, put your finger through the bearing center to see if the layshaft spins freely and fee some end float on the gears. if you isolate things like this, you can sort where the problem is.

Or after the Boss has been welded !, We did one years ago and we found not all camplates are the same,
We found the best of 3 and did a small bit of grinding.
If I was to do it again, I would weld up a steel Boss and bolt it to the top of the cases with oversize holes,
So I could jiggle it about a bit !. Cheers Bill.

 

[Phil Arundel]

Morning Phil, What did you do to change the problem from the high gears to the low gears ?.
That bearing does not sound right, Just checked my spare, Mine is 20 thousands of an inch proud, Is yours the right bearing ?, Check the numbers on the bearing with the book.
As Vibrac said, The ends of the layshaft are not the same !, The right gear has to go on the right end !.
If you put it the wrong way round, The outer cover does not go in far enough.
Cheers Bill.

Hi Bill, to achieve 3&4th gears I freed up the mainshaft selector arm which was binding on the camplate. After this neutral & 1st became impossible.
Also when I secure the coverplate things do tighten up - so it sounds like the layshaft bearing is too wide making solving the problem more difficult.
Would it be possible for you to measure the thickness of the layshaft bearing you have to eliminate this as an issue.
Thanks very much Bill
Cheers, Phil

 

[Phil Arundel]

Whilst that gearbox jig in the picture above might seem like a useful tool, the best jig of all is the actual engine and gearbox components themselves, as no two are exactly the same. They can take the same fettling as a timing chest to get all working ok...............Try setting up the gearbox after you've machined 20 odd thou from the mating faces of the cases, that takes some sorting due to loss of running clearances (end float). It sounds like your cover plate layshaft bearing is not fully home, perhaps the shaft is a bit too snug in the bearing and when you remove the cover it is pulling the bearing out, lininsh the shaft a small amount so it slides into the bearing without grabbing. Try installing the cover plate with just the lay shaft in place including it's gears and with the input shaft removed, put your finger through the bearing center to see if the layshaft spins freely and fee some end float on the gears. if you isolate things like this, you can sort where the problem is.

Hi Greg,
I have checked to see if the layshaft bearing is fully home and it is - maybe I need a narrower bearing? I will try your suggestion of fitting the layshaft only to see if it tightens up.
Thanks, Phil

 

[Phil Arundel]

Just found that spacer G20 is missing from the mainshaft! I will order one & see what effect this has.

 

[Bill Thomas]

Hi Bill, to achieve 3&4th gears I freed up the mainshaft selector arm which was binding on the camplate. After this neutral & 1st became impossible.
Also when I secure the coverplate things do tighten up - so it sounds like the layshaft bearing is too wide making solving the problem more difficult.
Would it be possible for you to measure the thickness of the layshaft bearing you have to eliminate this as an issue.
Thanks very much Bill
Cheers, Phil

Hello Phil, I make it 9/16 ", = 562 thou' That's the one that goes in the outer cover under the clutch.
I also make 550 thousands, Deep for the hole it goes into, So it would be 12 thou sticking out, I said 20, But that was a guess. There is a number R and M bearing, 33k3 and 33j3 stamped on the bearing. Cheers Bill.

 

[Phil Arundel]

Hello Phil, I make it 9/16 ", = 562 thou' That's the one that goes in the outer cover under the clutch.
I also make 550 thousands, Deep for the hole it goes into, So it would be 12 thou sticking out, I said 20, But that was a guess. There is a number R and M bearing, 33k3 and 33j3 stamped on the bearing. Cheers Bill.

Thanks Bill - I’ll check it.

 

[oexing]

When messing around with gears I try to get max overlap with drive dogs. As you can see close to the 2 of the 82 number I welded a bit of hard steel on one side of the slot and dremelled the opposite side of the slot to free the selctor pin to prevent it getting stuck. There is a lot to be gained in that respect so check all positions for possible additional overlap, it may help avoiding gears to jump out of engagement with wear.
As to troubles with gear changes, have you checked that the pins move freely in their slots ? I found places in camplates with tight slots so new pins won´t go easily.

Vic

 

[Bill Thomas]

I have a little trick I do with a twin gearbox, When the cover is done up tight, I like to push /pull the mainshaft,
And feel a little slack, That slack is made tight when the clutch is fitted and done up tight.
The chain sprocket must also be done up tight, Which gives a small gap between the final drive gear, To let oil in to lube between the final drive gear and the mainshaft, Most important !.
We did one a few years ago, There was no slack !, We found someone had fitted the 32thou shim, But there was some worn shim they had not seen already in there, Just a small ring, But it took all the play out, Not good !.
The shim fits on the main shaft and touches the bearing where it goes through the outer cover.
Cheers Bill.

 

[Phil Arundel]

Hi Bill, to achieve 3&4th gears I freed up the mainshaft selector arm which was binding on the camplate. After this neutral & 1st became impossible.
Also when I secure the coverplate things do tighten up - so it sounds like the layshaft bearing is too wide making solving the problem more difficult.
Would it be possible for you to measure the thickness of the layshaft bearing you have to eliminate this as an issue.
Thanks very much Bill
Cheers, Phil

Thanks Bill - I have the correct bearing & seated it fully.
I have spent some time polishing the camplate slots & seem to have found the layshaft selector arm slightly binding on the mainshaft selector arm.
I have sourced spacer G20 & fitted it.Tomorrows job is to assemble the gearbox (without the crank) and see if any progress has been made.In the meantime thanks so much for your advice.
Cheers
Phil