TDR Project. Bottom End Strip Down

A couple of weeks ago I completed the very simple task of removing the top end of the engine and after sourcing a clutch/flywheel holder and a flywheel puller I could carry on with the bottom end strip down.  By the way, the engine was working perfectly before I stripped the bike down, the reason for the engine strip down is to have the engine cases vapour blasted and painted.

The first item to be removed is the clutch basket, clutch plates and primary drive gear.

The first few steps were very straightforward but I knew that the next steps would be somewhat more difficult after reading various internet forum posts on the subject.  To remove the clutch boss you have to first flatten the retaining washer which locks the 30mm nut (centre of the clutch boss) in place.  You have to then hold the clutch boss in place whilst attempting to loosen the centre nut.  I made the mistake of not clamping onto the outside of the clutch boss but tried to lock it off using the threaded pillars inside the clutch boss.  I hadn’t thought this through and snapped off one of the pillars.  (Bottom left pillar in the picture below).

Using the clutch tool (photo later on in this blog post) on the outside of the clutch basket was much more successful but the 30mm centre nut still required some serious torque to loosen it.

Thanks to rubberfingers at the fantastic TDR250 Forum I now have a replacement clutch boss.  Thanks again Andy!

The next step is to remove the primary drive gear and the clutch housing.  The Yamaha service manual recommends jamming the 2 gears with a folded rag to allow you to loosen the nut holding the primary drive gear.  My first attempt at this used an old pillow case but this was too thin and simply passed  straight between the gear teeth.

My second attempt was with an old towel, but this time the gear teeth simply cut through the towel material.

So in the search for something tough yet thin enough to jam the gears I spotted an old boiler suit which is made of a denim-like material.  This worked and the gears were jammed sufficiently to allow me to loosen the primary drive gear.  This also required significant torque to loosen.

It took me a while to figure out how to get the rag back out of the jammed gears until I figured out that I needed to nip up the primary drive gear nut just enough to turn the assembly in the opposite direction used to jam the rag originally.

To remove the primary drive gear nut I slotted a socket set extension bar through the piston rods to lock them in place.  I’m not entirely sure that this is the recommended method but as the nut was not torqued up it seemed to work well.

The next stage was to remove the gear shift shaft.  The end opposite to the actual foot lever is shown below.

I had already removed the gear lever so the shift shaft could be pushed through from that side.  To get clear access to it I first had to remove the sprocket cover.  As I could sit down in comfort when removing the sprocket cover I also took off the flywheel cover.

The shift shaft could now be knocked thorough (using a rubber mallet) the bottom end of the engine.  I think the fact that it was very cold did not make it any easier to knock it through.

I should point out that the shift shaft did not require an unreasonable level of force to get it moving out but after my previous experiences I took it very steadily.

Now it was back to the flywheel side to remove the flywheel and stator.  Without the prescribed holding tool (Yambits link) I am not sure quite how you can remove the flywheel as it will spin when you try to loosen the centre nut.

Once you have removed the centre nut you then have to use another specialised tool.  A flywheel puller (Yambits link).  You start by screwing in the larger (outer) part of the tool into the flywheel and then screwing in the smaller centre piece which pulls the flywheel away from the stator.

Now the stator and associated cable can be removed.

The crankcase was now almost ready to split open.  The final pieces to be removed were the carburetor joints and intake reeds.

The crankcase could now be separated.  There are a series of numbered fasteners on the top and bottom of the crankcase which (like the head) should be loosened by a 1/4 turn in turn (starting with the lowest number first).  When splitting the crankcase you should start with the lower (higher numbered) fasteners first.

With a little gentle percussive persuasion the crankcase then split into its upper and lower halves which in turn exposed the gearbox and crank shaft.

The gearbox could then simply be lifted out of the bottom half of the crankcase and a couple of retaining rings required lifting out of the case.

Once a retaining washer was removed the gear selector arms could be slid off the mounting bar and the selector cam could be lifted out of the case.

Finally, the crankcase could be lifted out of the case and that was it.  The engine has now been stripped down.

All that remains is to de-grease and clean up the cases ready for vapour blasting and possibly painting.  While the cases are away being vapour blasted I shall measure all of the components for their service limits and order replacement parts where necessary.