View Full Version : Triumph 5 into 4 Gearbox conversion

09-03-2009, 11:57 AM
Be the envy of your friends by shoving an extra gear into your 650 Trumpet.

Things you'll need:

A Triumph workshop manual
Tools (esp. an angle grinder and a large round file suitable for Aluminum)
A complete 5 speed cluster with all the associated selector forks, camplate, sleeve-gear bearing, selector quadrant, gearchange quadrant, and final drive sprocket, nut and lockwasher
TONS of patience.
I also recommend Wes White's 650 Triumph engine Rebuild dvd. You can get this at http://lowbrowcustoms.com/ or http://www.fouracescycle.com/. It's a great reference and he goes into detail on teardown and reassembly of the stock gearbox.

Step one - Mr. Gorbachev, tear down this gearbox!


This is a 1950 4-speed gearbox. Aint she purdy? I bet some stuffy bike restorer would love to get his well manicured mitts on this. Well tough titties, Sir Reginald Snottybottom! We're going to stuff her full of five speed goodness.

I'm not going to explain how to unbolt everything in fine detail because pretty much every workshop manual and reference covers this.

NOTE: All off this can be applied to 4-speed unit and pre-unit motors alike.


Cover removed


The inner cover


The inner cover removed and the gears exposed

09-03-2009, 11:58 AM

The 4-speed cluster minus the sleeve-gear. (keep your shirt on, we're getting to that) You'll be throwing this on the Chop Cult classified section


If you look inside the gearbox cluster. You can see the sleeve gear and the bearing for the lay shaft. (heh heh I said "lay shaft")


Flip that bad boy over. See the black seal that covers the sleeve-gear bearing? Work out some aggression on it and rip that fucker off. (don't worry, you're going to be putting a brand spankin' new one back on during re-assembly)

09-03-2009, 12:07 PM

Once you pull the seal off you'll see the bearing. First remove the clip. You can warm the gearbox up with a torch. (I SAID WARM - NOT INCINERATE). A large socket the size of the bearing can be used to drift out the bearing.


Bringin' the heat.

Step Two - Gettin' down to business. Awww yeaaah, son!


This is a comparison of the 4-speed and 5-speed cases. You can see the hole in the 4-speed case for the sleeve-gear is too small for the 5-speed sleeve-gear.

You can also see the 5-speed case uses needle roller bearings while the bearings in the 4-speed are brass. Heat up the 4-speed case and remove the brass bearing. You'll be replacing the brass bearings (there's one in the inner cover as well) with late-model needle roller bearings.


The 5 speed sleeve-gear. I'm pointing to the edge that makes contact with the bearing. The hole in the 4 speed gearbox needs to be opened up so that this edge fits and the gear spins smoothly

09-03-2009, 12:14 PM
Step Three - Open up and say ahhhhh 5-speed!


Mark the gearbox. This is the material you'll be removing so the sleeve-gear can pass through. Time to bust out those tools and grind/file away some aluminum! Are you with me?! Woohooo!!!!!!!


This is a comparison of the 4-speed and 5-speed lay shafts.

09-03-2009, 12:30 PM
A case for better bearings....or better bearings in your case. Whichever the case may be.

As I mentioned before, you're going to replace the brass bearings with needle roller bearings.

Compare the 4 speed and 5 speed shafts:


4 speed


5 speed

Fortunately, Triumph didn't change things around that much and the outer diameter of both bearings is the same. So the new needle roller bearing (a stock 5-speed part) fits right into the older case.

09-03-2009, 3:28 PM
Hey Mike, very nice writeup and pics, thanks for taking the time to do it!

09-04-2009, 12:27 PM
well done. How is that whole project coming along anyway?

09-05-2009, 3:18 AM
More info from OZ bike 1961? I think