A diesel bike is ecconomic, a diesel bike with an overdrive is very ecconomic.

Home	I was told a few years ago that all Enfield gearboxes are identical, British, Indian all the same. How wrong that information was.

Widely available & reasonable second hand prices make this an obvious choice when combined with a longer main shaft.

On this British box the gear teeth design changed from the more fragile H type to a more robust HG type in 1959.

The Indian gearboxes had design change's from the early 1980's. The small mainshaft bearing got bigger 17mm and the mainshaft to match it, also the mainshaft had a better design to combat some weak points.

So if you have a British box it is easier to buy an Indian inner case than modify a British one.

Diesel main shafts come in two lengths 12 1/2 & 13 1/4 inch.

Trials gears are available from Hitchcock's mc's Ł85+ del and vat. 14 tooth trials gears replaces the 15 tooth standard gears.

The HG trials gears lowers the ratios for 1st, 2nd, and 3rd gears, leaving 4th gear standard. So if we up the gearbox sprocket to a 22 tooth it should bring 1st 2nd & 3rd back to normal, taking 4th gear in to overdrive. Well yes I know you can't have over drive on an Enfield box due to the way they are designed, so lets just say it's a bloody tall 4th gear.

Pre 1959 Enfield H gear set also had trials gears. A bit different to the later HG gear set as it replaced the 18 tooth for a 17 tooth small 1st gear, and the 30 to 31 tooth larger 1st gear.

Standard ratios: 1st = 2.78:1, 2nd = 1.84:1, 3rd = 1.36:1, 4th = 1:1.
Trials ratios 1st = 3.19:1, 2nd = 1.97:1, 3rd = 1.46:1, 4th = 1:1.

Best stock parts Some later version parts can stop potential oil leaks. 2002 saw a few design change's for the better, the sprocket nut has an oil seal in it, the sprocket now has a groove cut in to the back to seat an oil ring, the sleeve has changed also. The picture bellow is a late model sleeve which has plenty of room for the big bearing (between the two red dots), the green dot shows how far the grooves (left) went up on previous boxes.

If you take a look at the pre 2002 sleeve with a bearing on it you will notice that half of the bearing fits over the slots designed for the sprocket to key into, so the slots were made way too long. The upshot of this was the oil leaked under the bearing over the shaft and down the slots. I know your probably thinking, the big oil seal stops the leaks, no, it only stops oil that travels through the bearings race, and not through the big hole that fit's over the sleeve shaft, as the seal only sealed on the top of a spacer that sat on the same grooves, ergo oil down the grooves again. This gearbox was crying out for this simple design change since the 1950's and I can only think that rank complacency was the cause. Royal Oilfield was one of Royal Enfield's nick names. If you have an old Brit or early Indian box (spot the difference) you can get it oil tight by using sealant under the main bearing (well half of it), but this will come off when you slide the shafts in to position. You know how it is, in out, in out, plonk, the shafts now in position, but the sealant is now contaminated with grease or oil or just wiped off on to other bits of the gearbox that it shouldn't get to. If your careful you can do it. Better still use the latest Indian parts (or complete box) and sealed bearings & bushes of good quality.

Bearings There are many different types of bearing that can do the job in this gearbox, I don't mean manufacturers I mean types.		The normal design used in the box is known as a cheap bearing due to it's "Single race deep groove" and easy manufacture. You can go for a better design, double race deep groove like I have seen in racing boxes.
Or how about replacing those bushes with needle roller races. I've not done this but I think I'll give it ago when I rebuild the box or build one for the next project bike.		Defiantly do not use the Indian bearings or oil seals, after all why put up with 3rd rate when you can have 1st rate for around the same price. In short your being ripped off when you buy genuine Enfield bearings and seals.

Oil In a 1950's motorcycle newspaper, probably the Motorcycle news, the strip and rebuild article stated that "by no way should grease be used in the rebuild". So it looks like the box was designed to take oil in the first place, and just when grease was first introduced to it I don't know but you can bet this was Enfield's feeble attempt to to stop the oil leaks.

So we have established that oil should be used, and the general consensus is it should be EP 80 or 90, or any 20W50 engine oil, some are using thinner engine oil like a 10W, it seems that the thinner the oil the better this box works. As a precaution I have made from a sheet of gasket material a small gasket to go between the sprocket nut and the tab washer and also between the tab washer and the sprocket. It seems that Enfield India re designed the box and forgot about the tab washer.

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