Vee Two Sprag Clutch Upgrade

Sprag clutches for Ducati bevel drive motorcycles have long been a thorn in the side of owners of these fine machines.

There were four different generations of Ducati bevel drive engines: Round-case (with points ignition), early Square-case (with stator plate ignition), later Square-case (with Bosch ignition), and the plain bearing 1000cc Mille engines which also used the Bosch ignition.

Late 900 GTS, Darmah, and S2 models all ran square-case engines with an ignition system made by Bosch and Vee Two’s kit is designed specifically for those engines.

There are a number of reasons these original equipment sprag clutches were unreliable, especially as the bikes got older. First up, the original sprag one way bearing was a VW part and really struggled to do the job, especially as ignition wiring inside the engine degraded over time and altered the ignition timing, or if the battery was a bit down on power.

This would often cause the engine to back fire, and put excessive strain on the bearing pawls, causing them the flip backwards and the bearing to fail.

Often owners would blame the bearing, thinking it was the cause of the problem, where the answer really lay in what caused the bearing to fail.

You can fit our upgrade sprag clutch kit but if you haven’t changed the original ignition to a modern system like the German made Sachse for example, then you are only reacting to the broken starting system, not treating the cause.

Removal Time

Replacing the sprag bearing with Vee Two’s upgrade kit can be done at home as long as you take your time, have some mechanical knowledge and a decent half inch drive rattle gun.

You will need to remove the gear lever, rear exhaust header pipe, starter chain and the clutch cover to get access to the clutch and sprag clutch parts. You can unplug the ignition wiring where it attaches to the main loom or simply hang the clutch cover to the side if you don’t wish to unplug the wiring. Having said that, where the wiring comes out of the clutch cover is often a leak point for engine oil, so it’s a good chance to unpick the ignition wires from the plug/harness and fit a Vee Two billet gland nut and seal to fix that problem. 

For the object of this exercise we are assuming you have an original Bosch ignition and rotor on your engine.

Now use the rattle gun to remove the nut holding the ignition rotor, primary gear and starter clutch on. Once that is off you can remove the ignition rotor. Take care not to lose the ignition rotor key.

You will now need to remove the clutch pressure plate and both the steel and fibre clutch plates themselves. Use a rattle gun to undo the clutch hub nut and this will allow the hub and clutch basket to come off. Don’t lose the washer that sits behind the clutch basket. This then allows you to to be able to remove the flywheel and starter gear.

Besides being held on by the crank nut, there is also a taper on the crankshaft which assists in the job of holding the flywheel and primary gear in place.

The “hold” of the taper needs to be broken and we do this by using a copper or brass drift and a good hammer. Place the drift on the flywheel and hit with some force in a circular motion around the flywheel and in most cases this will release the flywheel etc from the crankshaft.

There is a special Ducati puller that grips behind the primary gear but that is unlikely to be in your armoury of tools. You will also need to pull the starter idler gear out of the crankcase. It cannot come out until you remove the flywheel etc as this stops it from being able to be removed from the engine.

You should see a spacer on the crankshaft after you remove the flywheel. This remains on the crank as it’s where the needle roller bearing sits and the starter gear slides over.

Preparing for installation

You will notice the original flywheel is much larger than the Vee Two unit. People can get confused here, thinking something is missing. It is not.

There are three distinct parts to the Vee Two, and indeed the original set up. There is the flywheel, the sprag bearing and the starter gear. The sprag bearing sits inside the Vee Two flywheel, and the “male” section of the starter gear slides inside the sprag bearing.

As you don’t use your original flywheel, you need to remove your original primary gear from that part. You get access to these screws by simply pulling the starter gear and sprag bearing away from the flywheel and primary gear.

You must use heat to remove these Allen headed screws. They are a special part and you cannot buy them from Ducati anymore. They will most likely have some sort of thread locker on these screws and the heat will help break this down. If you don’t do this you may damage the factory screws and you don’t want to do that

Once you are ready to attach the original primary gear to Vee Two’s smaller and lighter flywheel you need to make sure everything is clean and free of oil, then use medium thread locker on the flywheel screws.

On Vee Two’s starter gear you will see arrows laser etched into the surface, which shows the direction the sprag bearing must freewheel for it to work correctly. Slip the sprag bearing inside the flywheel and then put the starter gear male boss inside the sprag bearing. Check to make sure the starter gear freewheels in the right direction.

Installation

This really is a reversal on the removal process. Make sure the clutch mainshaft is thoroughly clean and devoid of oil. Install the clutch basket and hub. Vee Two doesn’t recommend using alloy tab washers on the mainshaft when fitting the mainshaft nut. We use mid strength thread locker to hold the nut in place and torque it to factory settings. You can do this with a torque wrench and clutch holding tool or with a rattle gun set to the desired torque.

Install the steel and fibre plates and then the pressure plate and screws.

We have produced a video showing this process and the setting up of the clutch : View it in the links below

Moving on to the sprag clutch, flywheel, ignition rotor etc. Make sure the needle roller bearing is in good condition, clean and lubricated with e few drops of engine oil. Place it over the crankshaft spacer and then slide the entire starter clutch, flywheel, and primary gear arrangement over the needle roller bearing on the crankshaft.

Place the ignition rotor key in its place and slide the ignition rotor over the crank shaft and key.

Once again, we don’t use an alloy washer on the crankshaft. Ewe use mid strength thread locker to hold the crankshaft nut on, again using the rattle gun to torque the nut to spec.

Because Vee Two’s flywheel is much smaller you can slip the idler gear for the starter back into place.

Now fit the clutch cover, then the starter motor chain, starter cover, exhaust etc and the job is done.

We have also produced a two part video on this entire process which you can watch in the links below.

Watch the second part of the installation series