Yamaha YA-1 Resurrection

[Yamanatic]

Wow, only 1 Year since the YA-1 got dragged out of the corner! Going back to last year's comments, I did sign up to get one of the 'Soft Parts Kits' offered through Communications Plaza Yamaha Japan, and amazingly was one of the first 5 (they only produced 5 additional kits) requests, but when they contacted me to make the deal, the first question was my location; so much for that - the bike and owner had to be in Japan and Japan only, no where else, period =(. Oh well, I tried.

Since the RD350 project is finally done, I restarted the YA-1 resto in earnest, and have reduced the entire bike to a parts-book quality exploded diagram. I saved the wheels for last, knowing the spokes would be a nightmare; most everything has to be reused since just about everything is unique to the bike and there is no 'superseded,' to it. Also a true historical restoration favors marginal original to pristine replacement - getting the bike apart without destructive removals is crucial.

The front wheel took 2 full days to nurse apart, and today is day three on the rear with 12 spokes left. Thought I'd pass along a little insight on how to remove badly rusted stuck spokes; someday in the distant future there is a good chance a 2SW member may face the same challenge restoring a 70 year old RD or something.

First thing was to mop the business end of the spokes down with Liquid Wrench (actually PB-Blaster) a half a dozen times over a week or two to free things up. A good wheel stand and a bar stool helps. Buy a couple of the best full nipple-width spoke wrenches you can; a short one and a long one if possible. Add good tunes and a pinch of Indica PRN(as needed)! 





Verify that the nipple squares have not been brutalized first, then give it a try. If the nipple doesn't move at all, the nipple has corroded to the rim; I have a small brass hammer to firmly tap the nipple from both sides a few times, and if really stuck give the screwdriver end of the nipple light angular hits with a fine drift - just stay away from the end of the spoke area. 

The tricky part now is to not torsion-break the spoke; at this point it doesn't matter which way it breaks loose; hearing that 'pop' is music to the ear. I start with about a 20-degree twist back and forth, and stop at 30-degrees. More penetrating oil, and sometimes hitting the end of the spoke wrench holding tension will do it; worst case a little heat sometimes help.

I find that 45-degrees is about the limit of twist before the spoke breaks. If and when it finally comes loose, even just tiny bit, start working the nipple back and forth further and further until the threads free up - it might only take a few back and forths or 20 times, but it will loosen; this step saves fighting the nipple all the way off.

The last 12 spokes have been successfully removed - all the spokes and nipples are salvageable; all 72 came loose!

Warren

[Yamanatic]

OK, Enough with the spokes - must be time for some fun stuff; motor work! Solving Nipponese motor puzzles is better than a night at the movies. There is nothing on the intricacies of YA-1's assembly beyond history and color, but, they are very close to an exact copy of the '49 to '57 DKW RT125, probably the most duplicated motor ever - the BSA Bantam, Russian Minsk, Polish Sokol and SHL, Harley Hummer, and of course, the Yamaha YA-1. Lots of DKW vids and the only obvious difference inside the cases is the shifter mechanism design.

First, the gearbox. The 4-speed transmission is a marvel of simplicity; the mainshaft carries the clutch on one end, and the drive sprocket on the other. The countershaft is more an idler shaft that handles the gear reductions. The shift mechanism is a bit of a mousetrap but well made, similar to the mechanism used in YDS motors but fully contained inside the cases. Luckily everything inside was in excellent++ condition including the bearings and bushings.

The gear and roller bearing sitting in the crankcase goes on the drive end of the main-shaft, then the drive sprocket mounts on the splines. Can't see the gears very well so it was moved aside for pics. That arrangement mounts to the left case prior to assembly. A couple of the lipped seals (especially the drive sprocket shaft) ended up being obsolete, but eBay pulled through - a European seller had one and only one, and it should be here by next week.   

No Phillips-head screws in the entire motor; all Cheese-head with straight slots. Star washers go under all the case screws. The cases are Yamabonded together with no gasket.

[Yamanatic]

Speaking of Crankshafts...

After hitting the International market to source the rather unique engine oil seals (India and China), I'm finally down to installing the crank and closing the cases. Going by both the parts book and the way the motor came apart, there are 0.012" thick, bearing-OD diameter flat shim-washers that go between the outer flywheels and the mains. With the washers installed, they basically turn the mains into partially sealed bearings (they fit the bearing faces flush - see pics).

The only oil supply to the bearings would be through the feed holes at the base of the transfers. Yamaha could have intended the washers act as oil retainers, but it wouldn't seem enough oil would pool there in the first place. Given that Yamaha didn't continue using the full-coverage washers on future 2T cranks, I decided to take 6mm off the washer radiuses, thereby exposing the races.
Note: The removed bearings were nasty dirty but functional.

Even though this engine is a direct copy of an RT-125 DKW, Yamaha's fingerprints are all over it, and some of the evolution/development of future engines is apparent. One thing noticed was the un-characteristically minimal crankcase volume; besides the 8mm's between flywheels, there is only 0.013" clearance on either side of the crank and 0.10" difference radially - almost like they didn't want the crankcase to contribute to charge volume. IMO, the mains need as much exposure to circulating pre-mix as possible given the space.

Here are the 'before' pics:
<img src="https://i.imgur.com/jRB922M.jpg" title="source: imgur.com" />
<img src="https://i.imgur.com/3f4lGw5.jpg" title="source: imgur.com" />

Considering the bike will only see a few hundred miles (maybe), the purist in me says leave everything 100% stock and original as possible - I digress...

Warren

[m in sc]

that's interesting. the triples would oil in the sane way with 'slingers' and def held in the sludge. it also made premixing on the h1s kind of a no go w out modding the crank

[Yamanatic]

Bottom end is done! The crank with new OTC main bearings and seals went together fine, with the drive side seal sandwiched between two main bearings (the outer oiled by the gearbox, and the inner by premix), and only one timing side bearing with the seal mounted in a carrier much like a YDS/TD. The bottom-end is all done and the cases are Yambonded shut. The gearbox was originally shimmed a little too tight - the synchro clearance in neutral  was 0.002" at the C-shaft gear, so was relieved of a few shims. Shifts like butter now!

Interesting that there are no Phillips Head screws anywhere on the motor or chassis; all engine screws were Cheese Head. Even though the DKW RT125 they copied almost exactly used a center-case gasket. The actual engine case is slightly (maybe 5%) larger than the DKW; a DKW qasket set was obtained and the base and head were exact matches - the center case and clutch cover gaskets were too small. All tolerances and fitments were very tight; reminded me of the British.  

The clutch was a problem; the fibers welded themselves to the steels over the last 60 years, and was stuck into a big chunk. The disks had to be pried apart, leaving much fiber bonded to the steel faces. There were no equivalent fiber plates available, but luckily the fibers (48 cork inserts) were replaceable, like many British bike clutches from the 50's and older. Fortunately working in a British shop back in the 60's gave OJT to re-corking clutches. 

To recork, the friction disks were thoroughly cleaned and wire brushed, and a sheet of 4mm thick (0.3mm thicker than the originals measured) cork was obtained to cut the inserts from. The inserts should be 1mm oversize/OD all around since there is no adhesive - tolerance fit. Make a metal template on a stick to use as a pattern , then cut the pads (48) out with a utility knife. Cut the pads slightly larger than the template to allow for sanding the edges smooth and true; a flat sheet of 150-grit sandpaper taped to a board works well - match them to the template.

The inserts were then softened up for pushing into the holes by soaking them for about 20 minutes in near-boiling water (a shallow bowl in the microwave), 8 at  a time.  A bit of panache is needed, but after mastering the technique, they go in pretty fast. Bare fingers worked best (for me). Finally, sand the entire face or each side using the board and a metal disk to insure a full contact patch and solid engagement; when saturated with oil, cork glazes instead of wearing in.

Once complete, the corks must be sanded flat to insure maximum contact - same 150 grit flat sandpaper with the disk held true with a flat piece of wood; both sides. Sand until all faces make contact.

Warren 

[m in sc]

   wow that is interesting! i never would have known any of that. 

[Simmons1]

What a great skill to have in our world of throw away everything.

[mnein]

Jeez. Truly a labor of love.

[JKV45]

Great work in bringing this one back from the dead!

Impressive improvising!

[Bryan H]

Great work Warren. Looking forward to seeing it finished    I see Yamaha were offering the rubber parts again recently 

[AAAltered]

Damn Warren.  Fantastic.

[SoCal250]

Impressive Warren! Never seen clutch friction plates getting rebuilt. That's some nice work! That engine will be better than new.

[Yamanatic]

Thanks for all the encouraging replies! Luckily there were no real stoppers, just lots of challenges.

I did submit a request for one of the Rubbers Kits, but was rejected even though it was one of the first received. According to the response, they made 5 kits but will only sell them to verified Japan resident owners. They were very nice about it though...

I failed to attach the picture of the tool to cut the clutch inserts to the correct shape so here it is.

Warren

[Kawtriplefreak]

Very Very Cool!!!

[RDnuTZ]

Awesome! I wish I had the patience for restorations to this degree.