Those with a sharp eye will see that this is not the YDS5 engine, but actually my TD1B engine (same as YDS3, with the clutch on the crankshaft).

Now we start with the engine. For most of the old single cylinder and twin cylinder engines a vertical split crankcase is used, whereby the crankshaft has to be installed from the drive side with a special puller.

 

 

It is very easy to make a wooden base with a few holes in it so that you can let one side of the crankcase rest firmly on the base as is shown here.

 

 

With these vertically split crankcases it is always necessary to heaten them up in order to install the bearings. When the bearings are too loose because of wear, you can use Loctite 603. After inserting the bearings you can push the oilseals in with your thumbs (use a little LM grease).

 

Replace, if possible, all bearings and oilseals. It can take a while to find them all, but that is nothing compared to the missery when you later-on find out that just that one bearing that you did not renew was bad after all.

Fitting the 2 crankcase halves together I always do with socketbolts. It is easier to torque them (11-12 Nm) and you do not see them anyway. For the crankcasecovers you can use the nice original PH3 screws. I always use Loctite 574 for this operation, it is perfect and also removes easily. I use it also very thin on the sidecover gaskets as they are normally also quite worn on these old bikes.

 

 

Before finally tightening up the crankcase it is wise to check that the gearbox functions properly. As is show non the picture, you can slide the shifterforks and see that they engage properly with each other. Same goes for the clutch, check its operation by just temporarily mounting the clutch lever on a handlebar and you do know for sure that you can fit the clutchcover.

 

 

Very important now is too install the gearchangeselector plate correctly and adjust it properly. After assembling move the selector arm and while changing gears up (rotating the selector anti-clockwise!) make sure that the shifterpawls just rest on the curved point of the pawl plate and not further. Any further and the gearbox might jam solid! In the Yamaha manual is mentioned 1 mm clearance, but this is incorrect.

You can see on this picture that the upper pawl is just (safe) on the plate. That is the way to adjust the setting bolts.

 

In rest the plate looks like this, (gearbox in neutral)

Okay, the bottompart is now more or less complete and now we continue with pistons and cylinders. I always smear a little grease on both sides of the basegaskets. Take the pistons and fit the pistonpinclip on the inside of each piston (left piston r.h., right piston l.h.). Mount the pistonrings with some oil and fit each piston with their respective pin and bearing (some oil). Insert the outside pistonpinclips. When this has been done you can slip the cylinder over each piston. Just pull the piston in its top dead center, with one hand hold the piston and compress the pistonrings and the cylinder will slide over the piston easily. Really easy …..!

 

Now better have a coffee first before you turn the engine over !!!

For the cylinderhead I also use a little grease for the coppergasket (or o-ring). Fit thecylinderhead and tighten the bolts cross-wise. When it is a 2 cylinderhead (or more) always start with a cross in the center, then make the cross bigger to the outside. 8 mm bolt sneed about 22-24 Nm, the 6 mm bolts 10-12 Nm.

The engine is ready now for fitting into the frame: