Wombat Rear Axle

[Bill2001]

I am assembling the Wombat rear axle after checking bearings, seals, brakes and whatever. Bearings, etc, felt OK and I replaced the iffy inner grease seals (35x22x8, double lip) 'cause I didn't want to risk the new brake shoes.

Here is the problem I ran into: when the rear wheel is inserted into the swingarm forks, and the axle nut is tightened down just enough to hold the wheel and axle in the swingarm, there is about 0.140" of "play" between the wheel_bearings--spacers--chain_adjusters and the inside of the swingarm forks. The PO had a washer in the axle stack-- this washer is about 0.09" thick, and still leaves some 0,05" that will be taken up once the axle nut is tightened. This is not really a large amount for that axle nut, but I'm used to my BMW where everything goes together withe near-zero clearance and the axle nut torque goers to bearing preload (long story behind that involving sidecars).

I don't see any specs on that axle stack dimension, or the swingarm fork dimensions, etc, so I don't know if that pre-axle nut tightening play of 0.14-0.09" is normal or not. Or anything to worry about. I can get washers or machine bushings and put them in the stack to give whatever play I want.

What are your thoughts?

--Bill

[hodakamax]

Bill, I think you are alright as long as everything turns freely when torqued down. There is some clearance so the assembly will be easy to install. Where is the extra washer?

Max

[racerclam]

also ball bearings should NOT be pre loaded only tapered roller bearings.

Rich

[ossa95d]

The most important spacer is the one between the inner bearing races. This is the one that will determine there is no side load on the bearings. The rest of the spacers on the axle stack should be organized in a way that ensures proper chain alignment with both sprockets. I don't think a little over 1/8 inch clearance is an issue once everything is torqued.

[Bill2001]

Thanks for the feedback.

The extra spacer was between the left (sprocket-side) "short" spacer and the chain adjuster. The bearings feel "good" and making up temporary to fit just the axle to the bearing stack, when the axle nut is just snugged, I feel no undue play in the bearing, and when the axle nut is tightened (guessing 15-20-ish ft lbs) there is no drag or preload. I think that the bearing stack is set "perfectly". As I said, I'm used to old-old school tapered rollers, and the preload on them has to be just-so. My concern over need to torque the axle too much to get that play between the swingarm forks and the bearings is that if you have too much torque load on the bearing inner spacers they can compress and create unwanted bearing preload. I'm not accustomed to UJM's and I'm on the picky-picky side of my learning curve.

Just to double-check, I'm going to see how much torque it takes to get the swingarm forks to give -zero- clearance with the bearing stack. I've not seen a spec on the axle torque on the Hodaka, but my "TLAR" sense suggests to me that 20-25 ft-lbs should be about right for the value. You want it tight enough to keep the axle from shifting, but not over tight and trash the wheel bearings.

Once I get the rear wheel snugged up I'll tie the back end down, lift the front wheel and tinker with the front wheel and brakes.

--Bill

[ossa95d]

Bill,
Just to reiterate, the inner races of the two wheel bearings are clamped solidly between the inside spacer between the bearings and the spacers outside of the two bearings. It clamps only the inner races holding them firmly and can be torqued to 100 ft-lbs or more without putting any side load on the bearings because it is a positively solid stack. That's why I stated earlier that the inner spacer is the most important one for keeping the bearings free from side loading.

[---]

I haven't yet seen a Hodaka swing arm that assembled with zero clearance before tightening. Quite the opposite. There is a ton of clearance, like a quarter inch more or less. Not until the assembly is tightened can you verify the parts are all in the right spot and the sprockets line up. Far as I know there are no washers between the arms on the wheel side, only on the outside under the nut. But do check sprocket alignment once snugged down, and that the wheel turns freely.

[Bullfrog]

Bill(2001),
I'd just like to reiterate what "Pop" just posted. So long as the proper spacers are on the axle and between the wheel bearings, etc., you simply can't do this, "too much torque load on the bearing inner spacers they can compress and create unwanted bearing preload". These ball bearing inner races are not at all like the tapered bearing inner races you are used to. While I don't necessarily recommend it, I've seen rear axle nuts tightened by placing a Full Bore (vintage) riding boot on the end of the axle nut wrench and pushing with the leg to full bore grunt tightness. OK, I suppose it is POSSIBLE to over-torque to the point of crushing the spacer between the wheel bearings . . . and that would indeed be bad and cause problems. But I've never seen it happen - not even with the full leg, hard grunt tightening.

By comparison, the slightly wide swing arm will "flex in" to the wheel "stack" relatively easily. Once things come in full contact, the torque value will rise. Note that it is semi-difficult to get a precise measurement with the wheel installed in the swing arm - but my chrome tank Wombat/Combat Wombat appears to have 7 and 7/8" between the inside faces of the swing arm plates when the axle nut is tight. The slightly wide "un-constrained" positioning of the swing arm plates allows for easy insertion of the wheel assembly. Slightly narrow would be a PITA. (Pain in the a_ _)

Stock situation would not have any washers in the stack between the swing arm plates. Only one washer is needed - the thick one under the axle nut.

Ed
PS: Please translate "UJM" and "TLAR"

[Bill2001]

Thank you again.

Sometimes when I get into my "picky-picky" mode I will overthink about details, especially in the middle of a project like this one. It helps to thwack me o'er the head with a 2x4. Go ahead. I'm thick-skinned but not hard-headed.

UJM = Universal Japanese Machine. A generic catch-all for Japanese motorcycles.
TLAR = "That Looks About Right" Similar to One, Two or Three Grunts on a wrench as a measure of torque.

--Bill

[Bullfrog]

Being nearly purely "Hodaka-centric", I'm not quite sure how I feel about UJM to describe my beloved Hodies. But TLAR? I've got to write that down!

Ed

[viclioce]

Wow. I wish I had that much clearance on my Road Toad! I find it hard to get everything lined up its so tight. I actually have to beg the spacer on the right side of the wheel to go in the space. Maybe I need to put a jack in there and open it up enough to give me 1/8-1/4" clearance??? ; / Victor

[Bill2001]

I'm not quite sure how I feel about UJM to describe...

I've never looked at it as derogatory-- Especially since the Japanese are the dominant producer of motorcycles and Japanese motorcycles have design philosophies in common. The Americans, British, Germans, Italians and Spanish have their own character, but since they are small(er) players in the big picture, they don't need a catch-all name like the Japanese motorcycles do.

--Bill

[---]

Wow. I wish I had that much clearance on my Road Toad! I find it hard to get everything lined up its so tight. I actually have to beg the spacer on the right side of the wheel to go in the space. Maybe I need to put a jack in there and open it up enough to give me 1/8-1/4" clearance??? ; / Victor

Maybe yours hasn't been ridden as hard, beaten as much, or jumped as far as some of the others around. No, I would not deliberately bend the arms apart. I just find that most of them have a bit of spring in the opening. Always thought of it as manufacturing tolerance.

[Bill2001]

My "FWIW" thought would be after checking the wheel bearings, cush drive, the whole "axle stack", take the righthand (longer) outer wheel spacer, chuck it ion a lathe and shorten it 3/16" to 1/4". The replacement part is still available and if it's not, a new spacer could be turned in a few minutes.

On mine, I left the extra washer out (truth is, it wasn't even a washer-- it was a sawn-off half of a wheel adjuster) when I assembled it this afternoon. No drama-- everything clicked into place. Job tonight is to finish the electrics so I can clean all the electrical stuff off that side of the lift. Next job is to jack up the front wheel and check the front end.

--Bill

[---]

Spacer lengths perform a function in that they locate the wheel assembly behind the frame and engine. I wouldn't change spacers unless the sprockets don't align, and then, anything I took from one side I would put on the other.

[Bill2001]

Let me tag another one of my esoteric inquiries onto this thread.

Got the front wheel off today, and the FRONT grease seal doesn't even fit snuggly in the bore. Odd seal, the only one I've ever seen without a metal shell-- it's just a lipped rubber ring. No markings on the seal, but I measure 32x16x5 in size. No luck looking it up online, but there was a hint that this seal size is used on a Kawasaki, so my measurement is OK.

I'm off to town to hunt up a new seal. Does anyone have a confirmation on the size or an x-reference?

Happily, although the seal was not sealing well, there was no grease slobber on the NEW brake shoes, so I'm glad I checked.

[---]

Lots of seals don't have a metal shell. Just depends on the application.

[Bill2001]

No luck today. Went into town and checked with all two of the Industrial Supply Houses and NAPA and no one had that odd-size grease seal, so I'll have an order ready for SH first thing in the morning. I could probably get it at Motion Ind, but I can't justify a 90-mile round trip into the city.

--Bill




PS-- One "apparently more available" seal is 16x32x7 (7mm instead of 5mm thick). The seal bores in the hub are 5mm deep, and there is no extra space between the brake backing plate or the speedo drive to allow use of the thicker seal. The size is 16x32x5. Period. During the web search for that seal I did see references to "Kawasaki", so I'll ferret that out for a specific. Not that I have anything against the SH seals, it's that seals, bearings and sparkplugs are "service items" and I like to have local alternative sources.

While I'm waiting for the parts to show up from SH, I'll clean, inspect and properly grease the steering head bearings and see about removing and replacing the fork oil drain M4 screws that have snaggled phillips head slots. Hope I don't end up needing to drill them out. I love old bikes.

--b

[Bill2001]

'Fore I forget-- that extra impromptu washer was there because the just contacts the chainguard. Moving the tire over 0.050" to the right by adding a washer on the left keeps if from rubbing. No big deal.

--Bill

[---]

It most likely also puts your two sprockets out of line although not by much. Hodaka made bikes back when a 3.50 was a big tire for a 125. Plus the Wombat came with a trials tire not a knobby. These days the smallest metric that comes close is a 100, which is something over 4 inches wide depending on tread type and brand. It isn't possible to stuff such a large tire into the swingarm and keep the chain guard unless you move the wheel back farther away from the engine to a point where the swing arm is already wider. The alternative to shifting the wheel over to the right is to find a tire that fits, or remove the chain guard. While it is hard on chain, I raced for two seasons in the mid west back in the 70's with no chain guard, and my bike still doesn't have one. On a street bike it is no big deal. On a trail bike it isn't a problem either unless you ride in mud regularly. On a race bike it is up to you.

Depends on what you are wanting to build. There are still one or two tires in standard sizes available that will fit the original plan without moving the wheel around. Or, if the slight shift doesn't badly misalign the chain on the sprockets, go with what you have. A misaligned chain will wear quicker, and is more prone to derailing.

It is also possible to shift the rim slightly to the right with relation to the hub by retuning the spokes.

[Bill2001]

The tire is a 4.00x18 so that explains it. On the BMW the rear tire size can't be increased much for the same reason-- there simply is not enough space around the tire. For the newer low-profile tires BMW offers a thicker "top hat spacer" to move the hub over. And, as-designed, BMW has appreciably more offset between the front and rear wheels so it may not be a critical problem. I checked the sprocket alignment and it is still good, so I'll keep watch in this. I'll look at the chainguard and see if there is a way to increase the tire clearance. And, of course, consider going back to the standard tire size once these wear out.

There are several options.

--Bill

[---]

Moving the tire rearward isn't all that hard. It also changes handling for the better, yielding a bit more axle travel. You will notice that the swing arm gets wider as you go back. An inch and a half can make a lot of difference. Mine is moved rearward almost three inches and it never handled like this when I was racing cross country in the 70's. I also have room for a 100/100 knobby which is a bunch of tire for a 125 Hodaka. Beats the old 3.50/18 Nitto I raced on. But with that tire I still can't really stuff a chain guard into the mix. If a chain guard is mandatory for you, look for one of the 3.00 or 3.50 tires still out there.

In truth, a 94 Wombat can't really make use of a wide tire. I would rather have a narrow tire that I can power around than a wide tire I can't even spin on grass.

[Bill2001]

I just got the bike as a restoration and these one-size-up tires came on it. They are good enough to get riding this Summer.

--Bill

[viclioce]

My Ace has a 300 knobbie on it right now. Everything lines up but the chain guard is a no go. The tire rubs hard on the chain guard. I was only able to put it on for the first pictures. When it goes back to trials/enduro tires I will be able to put the guard back on.

I also can't run an upper guard on my Model 03 frame. I suspect it may be because of running a Model 94 bottom end in this frame. I think the motor is a bit narrower than the stock Model 03 motor. But I did get the lower guard on. And I'm only running trials on it.

I'm setting up the Road Toad with upper & lower guards and traditional tire's & hoping that since everything is stock that it will all work together. ; D Victor

[hodakamax]

Ok, time for me to stir things up (for fun) and bring out opinions. Why are we talking about wanting to spin tires. This is not a subject we would be discussing about automobiles nor should we be wanting to lose traction on a motorcycle. Wider tires have several advantages in that they spread out the footprint preventing you from sinking into the medium and losing energy. Wider tires can have more biting edges along with bigger spaces to clear mud. Weenie tires do none of the above. Disadvantages on larger tires are obvious in that clearance problems arise along with extra horsepower needs. The terrain is the big factor as are the elements. A slippery terrain needs more sharp edges and less power. It seems too general of a statement that tires are too big for the motor. A big factor is that you really do need a chain guard in muddy conditions and chain dangers are decreased also. If you are serious about going around the course faster you will need both power and traction. It's all not as easy as it sounds and we haven't even discussed gearing. You may be unable to spin the tire (if that's what you want) because you are geared to high. Slipping tires=lost energy.

How's that?

Maxie

One last shot--My model 94 requires a large rear tire.