why is there no sealed chain drive?

If it's possible to encase a shaft and submerge it with oil, why can't the
same be done for chain and sprocket? A totally enclosed chain drive could be
both efficient and maintenance free.

 

I suppose you could but sealing the thing would be a bit tricky. I think
that by the time you get done it would be easier to retrofit a belt drive.

 

Shaft drives are not submerged in oil. They also run *through* the
swingarm. You'd need to run the chain through the swingarm, or have a
single-sided swingarm, neither of which are cheap and easy. (Indeed, I
can't imagine how you could get the chain through the swing-arm pivot and
to the transmission. Shafts use a U-joint.)

And it'd really just be pointless. Just get a freakin' shaft drive or belt
drive. (Larry? Paging Larry!)


Don't you have some laundry or something to do?

 

Harley did this years ago. Chains lasted very well, but maintenance was more
difficult. Most have been stripped and run open now.

 

I was thinking about some sheet metal covers that sealed up tight. Another
real PITA to accomplish.

 

It was been done several times. The Bultaco Metralla, Yamaha 920
Eurosport, Honda Dream are a few examples.

Chain cases add to the work required to fix a flat tire. There are
sealing problems at both ends and tensioning of the chain requires
accordionlike rubber boots so the whole case can move back and forth a
bit.

There would usually be a rubber plug in the lower side of the chain
case so the chain tension could be observed. The rubber parts would
usually be made of natural rubber and they would deteriorate. Riders
would tend to leave the chain case off after about the second flat
tire.

Another thing to think about is whether you really *want* a leaky sheet
metal, rubber-sealed chain case filled with oil next to your rear tire
to drip on it and cause you to crash.

If motorbike engineers really wanted to solve those problems, the chain
case could be a die-cast aluminum part of the swing arm, with
teflon-lined rubber lip seals and neoprene accordion boots.

It would add to the expense of the motorcycle and it would be difficult
to make it look stylish like those abbreviated plastic chain guards
which do almost nothing, but which don't have to do very much anyway,
because anal retentive riders prefer to replace a chain every 8K miles
instead of going through all the mess of lubricating the chain.

 

The Yamaha you mentioned didn't run the chain in an oil bath.

I don't know about the others, but I strongly doubt they did either.

Secondly, lots of bikes, usually small ones (the Yamaha vees were an
exception) ran enclosed chains. You don't really need the oil bath -
with a lubed chain, there's no weather/rain to wash it off, and no dust
and dirt to degrade it.

Thirdly, most enclosed chains were metal cases., in two halves. MZ used
the rubber affairs you mentioned, and Yamaha copied the concept. Rotting
of the rubber components was not a problem with MZs (or Yamahas, AFAIK),
unless you were talking in terms of decades.

Fourthly, they don't necessarily make rear wheel removal difficult at
all. I have just sold a small Honda CD200 which was fitted with a
chaincase. The rear wheel was QD - if you undid the wheel nut and
removed the wheel, the sprocket and carrier stayed in the chaincase,
separately mounted.

In short, you're talking a load of half-assed nonsense.

The main reason why chains aren't fully enclosed is style.

 

It used to be done on early Yamaha XV750s.
Chains lasted for 80,000Kms+ I believe

 

The Older Gentleman wrote:

The same reason front forks don't have protective rubber gaiters anymore!

 

Has been done. THe maintenance was greater than maintaining the chain.

 

It can be done, and probably *is* done on your motorcycle -- there's a
99% chance that your overhead cams are driven by a chain and sprocket
system that is lubricated by oil splash -- but there's a couple of
interesting issues that come into play. The first one is maintaining
chain tension, but that's not a big issue -- just run a single-sided
rear swingarm and have the chain on the other side with its output shaft
on the axis of the swingarm, and your chain will not tension/detension
as the swingarm moves up and down, meaning you can use an automatic
tensioner device like is used with cam chains. But a single-sided
swingarm setup is additional expense and most vendors don't care to do
this. But that's not the important issue. Bulk and drag are the real
issues. Submerging the chain in oil (or, rather, having a limited amount
of oil in the housing that the chain splashes through on its way around
to keep it lubricated) adds a slight amount of drag, and adds a bit of
weight for the chain housing. And because final drive chains on bikes
sold in the United States and Canada are only used on sport bikes, where
squids want the utmost in efficiency, or dirt bikes, where weight and
compactness are at a premium, that additional drag and weight is not
desired by the majority of customers.

In other marketplaces, where motorcycles are used for transportation
rather than as weekend fetish objects, enclosed chains are quite common.
In general they don't bother running the chains in oil, though. The
enclosures are simply to keep dirt and water off the chain in order to
extend its life. For the normal sport bike rider in the United States
who rides maybe 5,000 miles per year (national average), that's not a
big deal. For a delivery driver in Thailand who puts 40,000 miles per
year on his bike, it *is* a big deal -- doubling the life of his chain
means he can most probably make it last for an entire year, rather than
having to replace it 2 or 3 times and cut into his profit margin
accordingly.

- Elron

 

What about cruiser/custom bikes? A lot of those use chain, too. OK,
Harleys use belt, and the big Jap ones seem to use shaft, but I can
think of several that use chain drive.

 

I think a buddy in Arkansas has one on his bike, but I wouldn't swear to it.
Never really looked at it that close when I was over there a few weeks ago.
I've heard several people talk about how long the chains last though.

Les

 

It would not require a single-sided swing arm, but the chain case
ideally should be part of one leg of the swing arm and the swing arm
pivot should be concentric with the countershaft so chain tension stays
the same throughout
the entire arc of movement.

The concentric sprocket business would require the engine to be moved
forward to get it out of the frame, but some designs already have no
lower engine cradle, or a cradle that unbolts.

An alternate design would have have *two* chain cases, and a short
chain would go from the countershaft to another sprocket with internal
bearings spinning on the swingarm pivot bolt and the main drive chain
would go to the rear sprocket.

A belt would be simpler, but who has a belt that can withstand 150 rear
wheel horsepower?

 

Like on a Hesketh.

 

Using oil would require very good seals, and like TOG said,
is not really required. I had one of the Yamaha V-twins
that used an enclosed chain, the 1000cc TR-1. It used
a non-O-ring chain and the enclosure was filled with 1 kg
of bearing grease. All parts of the swing arm and final
drive was conventional, no special design at all.
Suggested replacement interval for the chain was 60 000
km (I replaced mine at 80 000 km and it was visually in
very good shape, hard to say how close to failure due to
metal fatigue) and I would estimate that around four
times in that time it would need adjustment.
Maintenance with the Yamaha system (other than
replacement/adjustment) was zero, nada, none. Removal
of the rear wheel was like on an old BMW with two arm
swing, the sprocket and housing was not disturbed.

My guess is that the enclosed chain system never was
a success because it did not look "cool". And the word
never got around how well it really worked on a bike
intended for touring.
Today, with extremely good O-ring chains, automatic
oilers that actually work and a good selection of shaft
drive bikes, there is very little driving force to
reintroduce the system.

 

Yes, I can see that.

 

Doesn't make them last much longer, just makes it hard to check for wear so
people think everything's fine when really the chain and sprocket were
bagged out many miles ago.

 

Oh yes, it does.

 

Many years ago I briefly owned a Hungarian Pannonia which did in
fact have an enclosed chain (dry, no oil bath) and a front sprocket
that was concentric with the swingarm pivot. One piece frame cradle,
engine lifted up and out as I remember it.

Details are hazy now, but as I recall, it also had some unusual
kind of adjustment mechanism for chain tension, interchangeable
front and rear wheels and a set of rubber bushes in the wheel
which engaged with pegs on the sprocket.

Thinking back, I'm guessing that the sprocket ran in its own
bearings and separated from the wheel, remaining in position if
you had to change a tire.

Slightly weird by U.S. standards but built along the lines of
Jawa, CZ, Ural etc. Google "pannonia motorcycle" if you're
curious.