Enfield 4 Speeder - Close Ratio Gearset fitting

[Diesel Dave]

For those running the 4 speed Enfield gearbox and fed up with the huge gap between 3rd & 4th gears, it's manageable on a petrol bike but on a diesel the slightest hill's gonna kill you. What you need is a nice close 500rpm gap between 3 & 4 - read on!

Hitchcock motorcycles in the UK sell the 2 gears required as a kit at a cost of £150 in 2008.

Although not a beginners task it should be well within the capabilities of someone with 2 years Enfield ownership who has done his own spannerwork.

You will need to beg/steal/borrow some 3 legged pullers or a bearing puller to get the gears off the shafts in situ - if you remove the shafts from the box a vice can be used.

Converting a bullet 4 speed gearbox to close ratio.

In addition to the two gears in the kit, you will need a gasket, mainshaft tab washer and the kickstart shaft O ring. While in the gearbox replace the kickstart pawl, and detent plunger; if you have high mileage, the bearings, seals and bushes.

If you're lucky you can change the two gears without dismantling the clutch, or removing the gearbox casing.
If you can't get the gears off the shafts in situ you will need to take the clutch off in order to get the mainshaft out. (you need to temporarily put the covers back on so you can get the clutch off and have the clutch puller and holding tools).

Remove the outer and inner gearbox covers, dismantle the outer part of the gearchange mechanism to get to two of the case screws. (for more detailed instructions see my other posting about kickstarter pawl replacement)

Note that the nut on the end of the mainshaft is a LEFT HANDED THREAD.
Do not remove the bolt in the middle of the inner case - it holds the inner kickstart stop and can be left in place. Be aware the kickstart spring will twang off when you remove the domed bearing cover secured by two screws. Lightly tap the end of the mainshaft if it's a bit tight on the inner race to remove the inner cover.

Now you'll see the two gears that need to be replaced at the end of the main and layshafts.

They are supposed to be a press fit on the shafts but this is not always the case. They might just slide off, or be able to remove them aided by heat from a blowtorch.
You can get a 3” 3 leg puller on the mainshaft pinion.
The layshaft will pull out slightly so a 4” puller can be used without fully removing the shaft.

If you are unable to remove then in situ then 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.

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 faced hammer, (carefully, do not damage the end of the shaft - heat helps). Warm the new pinions and lightly tap onto the shafts. Use a big socket as a drift, or place the pinions over a hole and tap the shafts into them if they have been removed.
Reassembly
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 will dislodge the pawl.

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.

Make sure the inner cover faces are clean and use a bit of Wellseal to locate the gasket on the gearbox face.
To get the grease in, take the lid off the tin and place it in a pan of boiling water (or microwave in a non metallic container) to heat up, pour through a small funnel.

Silkolene grease gives a good gearchange and is unlikely to leak out.

[arnaud]

maybe the gearbox of a 350 is different from a 500.. but with a diesel engine, which has far more torque, this gap should give a lesser problem than with a gasoline engine!
maybe you have a too big gear ratio.
My 10hp engine has no trouble getting from 50 to 100km/h in 4th(final\) gear

[Anorak_ian]

If you’re going to fit a close ratio set you will of course lower the 4th gear ratio, no longer will it be 1.1.
So your top speed will be affected, maybe a good idea to raise the gearbox sprocket by a tooth if you haven't already done so.

The bearings that I fit for my own use is quality NSK with rubber seals on them. This is so you can use oil instead of grease; reports from Enfield owners say there is a world of difference.
I would not recommend the cheaper un-named black sealed bearings, also I would use a quality seal not the Enfield seal, side by side you can see the difference.
Remember to use bearing or thread lock on those bearing seats and lay shaft bush seat, I have rebuilt loads of these boxes and a common damage is spinning bearings in the alloy case. If bits get in to the bearing race it can jam up the bearings and you can say good buy the gearbox case. In my view another good reason to use sealed bearings.

If you use the 2002 onwards sprocket nut, you can fit an oil seal to it and keep oil off your main shaft.

Having a big engine I have gone the other route, instead of close ratio I have gone for a wide ratio gear set and geared my primary and final drives accordingly.
This will make the gap between 3rd and 4th even further apart, but I'm sure it will manage. Hopes...lol

[Sphere]

Where are you supposed to obtain 3rd party parts that are above the factory quality of Enfield? Especially seals?

[Anorak_ian]

A good bearing stokest will do them, as they are really set up for industry supplies.
Eriks are the best that I have found; also there is a BSL group outlet that sell them.

I don't want to knock Enfield as people do seem to be a bit sensitive about them, but the Indian seals and bearings are not as good as a good European equivalent. Sure you will pay more for the good quality, but they will do their job better.

[Diesel Dave]

If you’re going to fit a close ratio set you will of course lower the 4th gear ratio, no longer will it be 1.1.
So your top speed will be affected, maybe a good idea to raise the gearbox sprocket by a tooth if you haven't already done so.

Not quite right I'm afraid, top will still be 1:1 and 1,2,3 will be higher.

All brit gearboxes used to work the same way by locking the input and output shafts together for top gear, effectively bypassing the gears, that way you need a lot less machining.

Dave

[oldbmw]

Not quite right I'm afraid, top will still be 1:1 and 1,2,3 will be higher.

All brit gearboxes used to work the same way by locking the input and output shafts together for top gear, effectively bypassing the gears, that way you need a lot less machining.

Dave

Also it will save power because it is not transferred through the gears but along the input shaft.

[Sphere]

Hitchcock Part number 200150
Description CLOSE RATIO GEAR SET (2 gears)
Price £ 150.00 NOT INCLUDING POSTAGE, PACKING or VAT

[John]

maybe the gearbox of a 350 is different from a 500.. but with a diesel engine, which has far more torque, this gap should give a lesser problem than with a gasoline engine!
maybe you have a too big gear ratio.
My 10hp engine has no trouble getting from 50 to 100km/h in 4th(final\) gear

Hi Arnaud. Actually, when it comes to non turbo diesels, they develop far less torque than an equivalent petrol engine. For example, the IB40 462 cc Hatz diesel develops peak torque of 19.4 ft/lbs. The 350 petrol Enfield develops peak torque of 19.7. At 3600 rpm, the Hatz has dropped to 15.6 ft/lbs, while the petrol sustains its 19. this means that at 3600, the diesel develops 10.7 bhp, while the 350 petrol is making 13 bhp. The 406-418 cc chinese Yanmar clones develop 16.7 - 17 ft/lbs peak torque, falling away to 12.85 ft/lbs @ 3600. The impression of great torque from diesel singles largely comes from the inertia of their very heavy flywheels when first letting out the clutch after a gearchange. (By the way, the 350 box is identical to the 500. Only the gearbox final drive sprocket is changed from 16t to 17t)
It always puzzles me that we give our diesels very tall gear ratios through our sprocket choices, that we wouldn't consider for the petrol versions. Despite the fact that the 500 petrol develops 11 ft/lbs more than the 462 cc Hatz, & 14 ft/lbs more than the china clones! - Then we remark at how sluggish they are! If we accepted a more realistic top speed for our meagre 9 - 10 hp, & geared our bikes with the same 16t gearbox sprocket as the 350, (52 mph @ 3600) we might be surprised at how sprightly they can be.

[arnaud]

Hmm i've set up my enfield gearbox with an 18 teeth sprocket, and have no problems you describe with the 418 diesel.
I'ts important offcourse, to keep it revving!
I can imagine the kit will safe the big-end bearing more, because it suffers a lot when struggling form 3rd to 4th..(especially because oil pressure is low at lower rev's with these industrial engines)
But for that mony you can buy 2 complete gearboxes.. i think it will do