Royal Enfield Owners Club,  Humberside Area
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Converting a Bullet 4 speed gearbox to close ratio.
Some experiences from Pete Fletcher

I have always thought the ratios of the four speed box are not brilliant.
Bottom is, if anything, a bit too low, and third is definitely too low giving a big jump up to top.
I found this annoying as I had to rev higher in third than I would like, in order to get into the torque band properly in top.
Also, if forced out of top on a hill or strong head wind, it seemed quite a drop to third.

I don't know why RE make them like this and can only assume that the ratios are chosen for Indian roads.

After fitting the close ration conversion third gear is now fine up to an indicated 45mph, and 50mph doesn't have it revving too high.
I can then pop into top and be right in the torque band.
If forced out of top on a hill I can carry on at 40mph in third quite happily (depending on the hill of course)
Third is also now a great gear to potter round town at 30 (before I found it too low so tended to chug in top)
The new ratio in bottom gear isn't too high though I can't move off at tickover like I used too.
In all - well worth the effort.

The kit from Hitchcocks is not cheap at 150 and I had lots of second thoughts about getting it.
It is, however, very well finished and probably worth the expense.
You just get the two gears in the kit so you need a gasket as well. I suppose you should change the mainshaft tab washer as well.

While in the gearbox it might be worth replacing the kickstart pawl, and if you have a high mileage, the bearings, seals and bushes.
As mine is a relatively new bike I just replaced the kickstart shaft O ring as it had wept a bit since new.
You might think about replacing the cover screws with decent quality socket head type.

Don't be intimidated by the thought of going into the gearbox. It's only like any other mechanism and there aren't any nasty surprises like springs flying off or anything (except the kick start spring but you can easily see where that goes back)
There is nothing at all delicate about the Albion box so you are very unlikely to do any damage.

Make sure you have an exploded diagram of the gearbox and a manual to hand (Mr Snidel's is very good)
Most of the nuts and bolts in the gearbox seem to be imperial threads so make sure you have the spanners.
Get a big board ready, covered with newspaper to lay out all the bits.
I can't stress enough the importance of laying the bits out in order.

It's a good idea to fasten groups of components together with bag ties to keep them in order.
If you can get the bike lifted up to a decent height it will make the job a awful lot easier.

The first decision you need to make is how lucky you feel.
If you're lucky you can change the two gears without dismantling the clutch.

If you can't get them off in situ you need to take the clutch off in order to get the mainshaft out.
To do this you need to temporarily put the covers back on so you can get the clutch off.
I got away with it so I should try with the clutch in place first.

If you need to do any work on the clutch, or if you need to change the final drive sprocket, you might as well do the whole thing together.
If you do, I would have two component boards to lay out all the bits, one on the left and one on the right of the bike.

Take the bike for a good run to warm up the gearbox grease and drain it into a clean container. If it's not been in there too long you can re-use it. It's not like engine oil that contains contaminants and will last for ages. If you do replace the grease, I find the Silkolene stuff from Hitchcocks seems to give a better gearchange than the original Veedohl stuff.

Now follow the manual to remove the outer and inner gearbox covers.
There's nothing difficult about this but note that the nut on the end of the mainshaft is a LEFT HANDED THREAD.
You don't need to move the bolt in the middle of the inner case - it holds the inner kickstart stop and can be left in place.
It doesn't mention it in my manual but I had to dismantle the outer part of the gearchange mechanism to get to one of the case screws.

(That's the only bit I got wrong, as I lost track of which way up the ratchet block was and had to take it to bits again. The up side is I now understand a bit more of how the selector works)
You might find you have to tap the end of the mainshaft if it's a bit tight on the inner race.
Oh and watch out for that kickstart spring twanging off when you remove the bearing cover!

Now you'll see the two gears that need to be replaced.
They are supposed to be a press fit on the shafts but being RE this isn't always the case.

If you're super lucky they will just slide off.
If you're just ordinarily lucky you will get them off with a bit of heat from a blowtorch.
You can get a small 3 leg puller on the mainshaft pinion but there isn't room to get in to the dayshift one while it's in position..
The layshaft will pull out a bit so you can get a puller on while staying in the gearbox.

Both mine came off with a 3" puller for the mainshaft and a 4" for the layshaft.
Don't try too hard or you might damage the ends of the shafts.

If you're unlucky they won't move and there's nothing for it but to remove the clutch and then get the mainshaft out.
It's easier to get the clutch off if the gearbox inner cover is put back on temporarily.
There's nothing particularly difficult about this but you really need some discipline as regards keeping all the bits in the correct order and the right way round.
If you do have to take the shafts out you can hold the pinions over the jaws of a vice and tap the end of the shaft with a soft hammer to get them off. (carefully not to damage the end of the shaft - a block of hardwood helps) You might need a bit of heat to get them off.
The new pinions should tap on easily if you warm them up with a blowtorch or in the oven first. Use a big socket so you can tap centrally.

I did hear from one bloke who had to use a press to change the gears but I think this would be very unusual and I don't know if he was using heat.

For anyone who doesn't understand about this heat business, you are taking advantage of the fact that metal expands as it heats up. A gear on a shaft, being a greater diameter, expands a tiny bit more than the shaft it's on so it will come off easier. You should try to concentrate the heat on the gear and/or drain the heat out of the shaft with a wet rag or something. When putting the new gear on, you have more effect because the gear is hot while the shaft is cold (as long as you're quick getting it on) If you can get the shaft in the freezer you get even better results.
Just be careful not to get it too hot or you may alter the temper of the steel. You can certainly get it hotter than you can touch without a problem.

It's then (just) a question of putting it all back together

Make sure the selector lever engages with the inner gear operator as you put the cover on.
You might need to jiggle the kickstart shaft to get it to engage with the layshaft gear but don't push it through or you might loose the pawl.
If you've laid all the bits out properly and have a diagram there should be no problem.
If you have any bits left at the end..............  :-(

You can test to see if all the gears work before putting the outer cover back on, but remember to replace the detent plunger first or nothing will work.
Just pop the gear lever and kickstart lever on, and crank the engine round (spark plug out if the clutch is still in place) as you go through the gears.
You shouldn't need to adjust the gearchange mechanism if it was all working before you started, but now's the time to do it if the gearchange wasn't 100% before. (it's all in the manual)
I actually tested the gears before I made the joint properly with a gasket.

Make sure the inner cover faces are clean and use a bit of Wellseal to locate the gasket on the gearbox face.
I degreased the inner screw holes and Locktited the screws in. (I'm hoping not to be in there for some time)
If I'd thought about it I would have replaced the screws with better quality socket head type but as they were BSW I didn't have any.

To get the grease in, take the lid off the tin and place it in a pan of boiling water to heat up.
Decant it into an empty oil bottle (the type with the spout) and squeeze it in till it come out the level hole.

Wear gloves for this as hot grease is not nice if you get it on your hands (go on, ask me how I know)
You will find you need to top up again after the first run as the grease is distributed through the box.

I've been dissuaded from using oil in the gearbox as "someone who knows" maintains that oil will not stay between the mainshaft and the countershaft. He says it drains out at rest and can cause premature wear.
I've no idea if this is the case but the Silkolene grease gives a good gearchange and is less likely to leak out.

Have fun !!