main vintage

Drive Train and Clutches

Hello everyone,

So you did it, you took my advice and bought a new old sled. Unfortunately, you can’t just take it to
the car wash and call it good. The old thing is going to need a complete going over,
using common everyday tools, of course.

While you sit and contemplate the natural beauty of your beast, consider this. The sled pulls itself
over the snow, not push, as some would think.
The idea is that the drive sprocket pulls the track over the top from the back.
That is where we start, at the rear wheels where the first pressure will be felt by the chassis.

You must remove the rear drive wheels from the shaft. Often removal of the rear axel will be required.
No big deal. Just loosen the track right off, remove the bolts and tap loose the wheels.
Most wheels have the bearings inserted in their centre.
A common snap ring set of pliers would help but are not mandatory for this. Pop out the ring and
push the bearing out. All bearings are sized according to inside diameter (ID) and outside
diameter (DO) and width. There will be a number on your bearing and if not, measure the ID, OD,
and width and visit your local bearing supply shop. 20 bucks should take care of it.
Install them using the process above in reverse.
If during the disassembly you feel it is too complicated just make some simple drawings to assist you in
the reassembly.

That done you can leave the track loose, next thing is to check the drive axel.
There are two bearings down there that need inspection. The one in the chain case
runs in oil but its partner has probably not seen oil since the showroom.
In order to continue at this point the exhaust and chain case must come out. Catch the oil as best as
you can and clean the whole case. Solvent works best on chain cases along with a
paintbrush. Put a drip pan under the chassis and you will use surprisingly little solvent
and have a nice clean chain set up. Loosen the chain tension adjuster right off and grasp
the bottom gear and push and pull in an effort to discover bearing wear. If there is no play the chances
are it is OK.
The other dry side is another story. Most bearings sit in a cup of sorts, secured by 3 bolts,
some use a lock collar bearing and others are slip fit.
Look at it closely and you will see how the bearing is held in place. This dry side bearing
should be replaced. Over the years that bearing has been known to cause more grief
than most other bearings on your sled. It must be replaced!

After that, you can begin to tackle the chain case.
There are few principals of physics that apply here. Power must be taken off the drive axel at 90’.
This means that the alignment of the top and bottom gears must be true.
Use a straight edge to check and if they are not then use spacers to align.
Also a chain that is too tight is bad.
To properly adjust, pull on the drive side of the top gear to remove any slack.
Set your tension adjuster to allow you about 10mm chain movement, (tight is bad but loose will slip).
Any gear oil (synthetic), will work fine.
Add just enough for your case. A good sealant will usually seal the case up but occasionally you get a leaker.
Don’t let your chain case run dry!

Track tension is a matter of taste. I like mine loose until it won’t skip. Some guys run
tighter but similar to chain tension, too tight is also bad. Take your belt off and jack up the
rear end of the sled. Tighten both tension adjusters evenly until you get a track that just hangs
off the rails a bit. Turn the secondary clutch by hand, you’re looking for a free moving track
with no tight spots. If you notice a tight spot, investigate and remove the problem or it will all add up
lost horsepower at the end of the day. A sign of a track that is too loose will slap up
against the tunnel when you do your first test run. The first few test runs should be easy
going until you can determine that the track tension is close enough that it won’t skip on the
drive cogs, this could cause track damage.

Secondary clutches are next. Most guys run with just enough tension to give adequate belt grip.
A frozen or limp secondary clutch is just useless. Usually a breakaway force of 3-5 Kg/m is normal.
More will hold your shift back, and less will let your other clutch run amok. Clean up the
ramps and springs and lube the main shaft. Removal may or may not be required, most can be
cleaned right on the sled. Notice that the spring fits in holders both ends. Make sure the spring tabs
are in the holes and the whole deal works in and out smoothly with about a 3+ Kg/M push.

Primary clutch removal will require a clutch puller tool. I usually pop out the engine at this point
and drop it on the bench. Take off the carbs, the pipe and the starter, also unhook any wiring,
(drawings or photos of the original configuration are a good way to get things back to normal if
you are unsure). Now the engine is out and stripped you can take it down to the local dealer and
have the clutch pulled. Most serious backyarders have their own set of various clutch pulling tools
and depending on what your local dealer charges, you may want to join their ranks and pick yourself up
one. They cost roughly 30 bucks for the tool.

Some clutch setups are spring loaded. If you’re not sure just ask your local expert.
There are not a lot of different clutch types and most guys can tell just by looking. Be careful and ask,
read or surf the net if you are unsure. 

What you need to do is to find the worn spots and replace as required. ‘Clutch work‘ requires
basic parts replacement. Clean and lightly lube all the moving stuff and make sure the unit slides
together and apart under spring pressure. Used parts work fine so try the local wreckers.
Replace until you are happy with a nice tight smooth clutch.
Be aware when lubing clutch parts there are areas within the clutch that are designed to roll
against one another, not slide. Do not lube these areas, it will cause the rollers to slide and
wear a flat area on the roller.

Next on the agenda will be the steering and brakes, then on to the engine.
For now you will have lots to do, or at least something to think about.

I must break off and tend to my new long track version of a vintage racer. My theory is that a long
cleated track is better than short. We found this to be the case in 1983 with our Sno-Pro oval sleds.
A lot of the twitchy stuff is smoothed and I don’t think the extra cleats will add an
appreciable drag. We’ll see.

Until next time.
Gord

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