Splitting the cases:
As already mentioned, I have quite a variety of motors and cases to work my way through. But before jumping in I thought I would list the serial number prefixes and try and identify the models and years they correspond to.
3R5 = 1980 YZ465G with 5speed gearbox
4V4 = 1981 YZ465H with 5-speed gearbox
5X6 = 1982 YZ490J with 4- speed gearbox
23X = 1983 YZ490K with 4-speed gearbox
26A = 1983 IT490K with 5-speed gearbox
1LV = (?) 1985 YZ490N with 4-speed gearbox
xxx = 1986 YZ490S with 5-speed gearbox
The above listing is my best guess at the moment, please correct me if this is in error. You can see that both 4 and 5 speed transmissions were used across all the models. The 465 only used the 5-speed. The YZ490 used a 4-speed gear box from introduction until 1985 with the N model. The 1986 S model went back to a 5-speed. The 1983/84 IT490 also uses a 5-speed although I believe the design and/or gear ratios differ from the 465 5-speed in some way.
Because of this change in the '86 490 back to five-speed, I was optimistic that I could use the 1LV cases with the 465 5-speed gearbox and this turns out to be true. Another interesting point is the change from side port cylinder to center port cylinder that occurrred in the 1984 490. I found that this change had no impact in the case design. My guess is that cases as new as the WR500 also work in the 465's, not bad!
So my plan going forward is to strip two 465 motors. One being a 3R5 and the other being a 4V4. I plan to use a 5-speed gearbox as original. I have a few different case sets to choose from but have decided to go forward with the 1LV cases from the 1985 490. I found some changes involving the clutch arm and venting that swayed me to go in this direction (I will point these out later).
I should mention that I consulted the factory YZ465 and YZ490 manuals extensively while breaking these down. Reading through them both before starting work is well worth the time. Not being in a rush, I took plenty of time and proceeded cautiously. It is not a difficult job but it is easy to break something if not careful.
I will also mention that an air wrench is handy for removing the sprocket nut, flywheel nut, clutch hub nut and the crank gear nut without having the factory holding tools.
I wont go through every detail as that what the manual is for. Instead, I will just try to point out some traps and differences in the model years as that is what I am most interested in.
Ok, so here we go with the 1st set of photos. The engine covers, cylinder and case screws are already removed and the next task is to remove the flywheel.
After removing the flywheel nut with my air wrench, I attempted to use this nice aftermarket puller to get the darn thing off. Although specified as correct for the YZ465, the puller had an internal shoulder that prevented it from threading far enough into the flywheel. The fix was to chuck it in the lathe and hog it out this area. Had I not noticed this I am sure I would have pulled the threads out of the flywheel and had a real mess on my hands.
After threading the modified puller body fully into the flywheel I then tighten the bolt to press the flywheel off the crank taper. It is not too often that they pop off unless you go overboard on the tightening. But I prefer to avoid tightening too much so as not to distort the flywheel. Instead, I give the bolt head a couple of sharp raps with a hammer and usually the sharp impact is enough to break things loose. Make sure you save the key (replace with new) and examine the keyway slot in both the crank and inside the flywheel. Look for galling or other signs of movement or spinning (shifts or bad fit here can affect ignition timing and balance)
Inside of the puller after some machining to add depth
After removing the clutch assembly, kickstarter shaft assembly, and crank gear, this is what one of the 4v4 motors looks like. One thing to point out is the shift drum near the bottom of the case. In this motor, the selector star is removable from the shift drum via a screw (it is already removed here).
In later 465 and 490 motors the selector star is welded to the shift drum and is not removable. The shift drum bearing resides under the selector star and so is not easily replaceable in this version. When I first saw the welded star I actually thought a previous owner had done that. But in fact, that is a factory Yamaha weld! You can see the welded star in the next photo.
In splitting the cases, you may choose to leave the transmission and crank in either case half. However, you must make sure the welded star (if you have one) is correctly positioned if you plan to separate things such that the drum is removed from the right hand case (this detail is also explained in the manual).
You will need another puller to press the crank through the crank bearing during the splitting process. A steering wheel puller can often do the trick. Mine was not large enough so I whipped up a puller out of some scrap steel.
Here is the 1st motor split with transmission and crank in left hand case
And here is the 2nd motor with transmission in right hand case and crank in left hand case.
The 5-speed transmissions
More to come...