Getting custom gears ground

Hello fellow motorcycle tech people,

1) Supposing I am insane and want to fabricate my own motorcycle
gearbox for a shaft-driven diesel motorcycle project, where could I get
some custom gears ground?

2) In the quite likely event that having custom gears ground is
prohibitively expensive, and it turns out that I am still insane and
want to make my own gearbox, who makes stock gears for existing lines
of motorcycle transmissions that might send me a catalog with
specifications (or at least pictures of both sides of the gears,
dangit!) so that I can mix-and-match my own gear cluster out of
existing parts?

Any help would be greatly appreciated!

Chuck "No, really, I don't want to just use a BMW tranny" Perkins

 

yes, custom gears are prohibitively expensive.
(yes, you are allowed to be insane and i have a bmw bike with a diesel
engine)
you may want to look at shaft to shaft dimensions of existing trannys.
the gears can be used which are the correct shaft-to-shaft distances.
the old honda hawk had gears we would swap around to give different
intermediate ratios.
the shifting devices may be thought out for using different gears in other
places.
i'm interested in what you are trying to do.
the bmw tranny does need help. i don't like the ratios either.
sammmmm

 

What is the peak RPM your diesel engine turns? Is it "happy" with the
final drive gear ratio?

Is it a situation where low gear is just too damned low for the amount
of available low RPM torque? I would think you'd have to have a whole
new mainshaft made, as first pinion gear is usually a physical part of
the mainshaft...

 

It would be ideal if I could use gears from existing aftermarket parts
supply.

Does anybody know the typical shaft-to-shaft distances of particular
motorcycles? Is there a Big Book O' Gears somewhere?

One of the reasons I'm looking at a custom transmission is because the
engine I want to use (the new Hatz 4w35t... 42 HP! Wohoo!) is a bit
long. If I'm going to sit it in-line and put a standard six-speed after
it the wheels will be too far apart or the shaft will be super stubby,
adversely affecting suspension and all that.

Now the BMW shaft-drive transmissions have three shafts--input,
intermediate, and output. At least the one on my R1200C does. All the
input shaft does (as far as I can tell) is drop the rpms a bit and
transfer power to the intermediate shaft. Oh yeah--it also provides
something to hang the clutch disc off of. The intermediate shaft and
the output shaft have all those fixed, idling, and sliding gears. The
fact that there are three shafts means that the output shaft is far
enough out of line with the input shaft to make room for a rear wheel,
which you're going to need if you actually want to go anywhere...

What I want to do is actively use all three shafts. I want to put what
amounts to a three-speed transmission on the input and intermediate
shafts. There will be no rpm drop from the engine speed, but the engine
speed tops out at about half of what a gas engine does anyway so I
figure I can take advantage of the built-in 2:1 reduction.

I want to put an additional two gears on the output shaft (directly
meshing with the high and low gears of the intermediate shaft) and
select between them. This way I can multiply each of the three gear
ratios by a high ration and a low ratio, giving me six gears.

I'm hoping that this will give me six gears in the same case length of
a four-speed.

Anyway, that's my cunning plan.

Note: If you're paying attention and diagram this out and assume the
same shaft-to-shaft distance for input-to-intermediate as for
intermediate-to-output you'll say "Hey! You've got two gear ratios that
are exactly the same in there!" which is true. You will have two 1:1
paths through the gear cluster, so you subtract one from the total set
of ratios available to you. With four intial gears you get a 7-speed,
with three you get a 5-speed. If you don't actually USE the first gear
on the input shaft of a four speed other than to slide its dogs into
other gears to engage them, you can call it a 6-speed.

Chuck "In theory there is no difference betwee theory and practice..."
Perkins

 

Have you ever dyno'd the bike? I'd like to see the torque curve for it.
Can you post some details?

 

strangely enough, the low speed torque is real good.
the engine is governed at about 3600 which is good for about 63 MPH.
there's power for faster but the rear gears are the 2.91 (or such) and are
the highest offered
in the rears. there is a reductionnin all bmw gearboxes.
there are slightly higher tranny gears available from germany. they're
pricey.
my friend with a similar rig, tried them. they help but are not the final
answer.
i *could* run the governed rpms up but i hate to.
it's a yanmar 3tna72 engine.
sam

 

Yup. Diesel engines are known for their low rpm torque and ability to
pull heavy loads. I though you might have some larger diesel in there,
maybe a 1500 cc or so, but yours is only 879cc...

Diesel engines often run at 1800 or 3600 RPM so they can turn
generators. I looked up the yanmar 3tna72 engine. The Yanmar site
showed a snowblower that used it. 13.02 kw, 17.7 PS @ 2880 RPM, 879cc.
I reckon that it would have about 32 ft/lbs of torque, and if you
multiplied that times 2.91, you should have about 100 pounds of rear
wheel thrust, considering that most rear wheel diameters are close
enought to 1 foot in radius, it makes a foot pound of torque convert to
about a pound of thrust. That's enough thrust to go about 82 mph.

Vaguely related to diesel engines:

Several years ago, I was interested in a small company that wanted to
utilize hundreds of little 1500cc Yanmars to power generators and sell
electricity to the major utilities...

They had a mysterious proprietary technology they called "pulse
charging" and they were going to sell licenses to all the diesel
manufacturing companies to use their technology that improved the fuel
efficiency of diesel engines. They demonstrated the fuel economy of
their "pulse charged" Yanmar engine in an economy run at the California
Speedway, and again in an open highway test. The engine was mounted in
a Geo Metro sedan. It got around 100 mpg, if run continuously at 45
mph...

The company claimed that Asian manufacturers would be interested in
cars that got great economy at lower speeds than drivers on American
highways usually like to drive. Nobody wanted the technology though,
not even Yanmar...

I talked to the engineer that was developing "pulse charging"
technology. I looked into the engine when it was all torn down on the
work bench for modifications and the engineer dropped mysterious hints
that it utilized the same technology that had been used in the
German V-1 Buzz Bombs at the end of WW2...

Little did he know that I had studied up on pulse jets that used reed
valves and pulse jets that didn't use reed valves, and that I
understood the physics of such things as tuned headers...

It turned out in the end that their mysterious "pulse charging" was
nothing more than a tuned 3-into-1 header which wasn't patentable
technology....

They even showed potential stockholders a Yanmar with a 60 KVA aircraft
alternator bolted to it, and they claimed that was going to be the the
basis of a hybrid automobile they were developing. The
power would supposedly be trasmitted back and forth from the crankshaft
of the engine to the wheel of the car through the alternator's quill
shaft...

A quill shaft is about half an inch thick or less, it's like a torsion
bar. It allows an airplane engine to start an alternator turning when
there's already a heavy electrical load on it. If the quill shaft snaps
the alternator won't turn, but nothing major gets broken...

No way in hell would a quill shaft be thick enough to propel even the
smallest car. I told those guys that, first they got a little paranoid
that I was talking in front of potential investors, then they asked
what I did for a living. I said I was retired. They offered me a job.
They would have paid me in their worthless stock. That's how those
crooks paid their consultants and employees...

 

I am intrigued by your project and eager to view any progress reports
I hope you post in the future.

 

i am interested, too.
i built a diesel motorcycle and had the same questions.
we have a few diesel bikes in this area, mines a bmw-yanmar, my friend did a
bmw-briggs(daihatsu)
and another friend's harley clone-perkins. all are 3 cylinder.
i saw at daytona after i had mine, a homebuilt with ddetroit 3-53 and
another
with an aircooled 4 cylinder turbo diesel in a boss hoss frame.
fun!
sammmm