Alignment of every moving part is critical to how easy the sled will roll, so performance gains can be made by making sure all parts of the sled are properly aligned. Whether you’ve got a brand new sled that you’re looking for top performance out of, a relic you’re restoring, or something in between, these are a few alignments you can examine:
- Drive sprockets to each other
- Drive axle and suspension to tunnel
- Drivewheels to track
- Drive axle to jackshaft
- Drive clutch to driven clutch
This type of work is time consuming. It takes me two full days, or at least 20 hours to complete this type of project. No special tools are required, other than those used in regular sled maintenance, so if you have the time and basic skills, you can likely accomplish the job on your own.
In addition to basic tools, you’ll need a carpenter’s square to align various parts. The complete sled will be torn down, except for engine, which is only removed from the frame. While this isn’t absolutley necessary, it makes life a lot easier!
The hood, seat and gas tank may also be removed, for complete ease of working on the chassis. In the long run, this will likely save you time.
Drive sprocket spacing should correspond with the space between the drive lugs on internal drive tracks. While the sample shown has three separate wheels, yours may only have two, or as many as four. Each wheel has paddlesides, on one or both sides, that fit into the drive lugs in the track. The center of the drive wheel should sit exactly in the center of the space between the track lugs.
On external drive tracks the sprockets should run to the outside of the holes in the track. This type of track works by having the drive wheels actually drive in the holes to turn the track.
The manufacturer provides specs for your particular drive wheel spacings. You will have to ask your local dealer for this information, or purchase a shop manual for your model of sled. Check each measurement as shown in the manual. Remember that your sled is assembled on a production line, so you may occasionally find one that it is 1/16 of an inch or so out. For maximum performance this can be corrected.
The drive sprockets must also be aligned to one another. This is done by using the indexing marks that appear on one of the top edges. The marking is usually a dot or an arrow. This is done to keep the drive lugs or teeth [necessary on internal and external drive tracks] in time with each other. Most drive axles are hexagonal or have six sides, so unless you had either six or twelve teeth they wouldn’t line up with each if one sprocket was out 1/6 of a turn.
It’s rare that you would find a new production sled has a problem in this area. However, if the indexing marks don’t line up, you’ll need to press off the sprockets and press them on correctly. This will require more than basic mechanical equipment.
If you are working with a used sled, or one you are restoring from scratch, you may find that an error has been made with a previous installation, or they are worn out and need to be replaced. Press off the worn drive sprocket and replace with new or used parts.
Also, you should check to make sure the axle is not bent or that the splines for the chain sprocket are not twisted or worn as shown in the picture above. A visual inspection should be sufficient. If you lay the drive axle on a flat surface, rotating to all six sides, it should consistently lay flat. To check for a bent end on the chain sprocket side, measure the distance of the tip to the flat surface on all six sides — it should be the same with each rotation.
Drive Axle and Suspension to Tunnel
The first thing to align is the drive axle to the tunnel. Use the carpenter’s square and position it with the short side touching all of the wheels on the drive axle and the long side down the inside of the tunnel. It should be exactly square. [see photo below]
Manufacturer’s tolerances may allow some leeway, so if you want it exact in your new sled you may have to make some changes. If it’s not square, you will have to slot the mounting holes [see illustration below] in the frame with a file or a die grinder, on the bearing cap side until it is. You will need to move the drive axle forward or backward until it is completely square with the frame.
Once the drive axle is square, mount the rear suspension. To check rear suspension alignment you begin by determining if the sliderails are running at 90 degrees to the drive axle. Measure the distance from the outer edge of the sliderail to the inner edge of the tunnel at both ends of each each side. It should be the same in all measurments. If they are running to one side or the other, you cut off a portion of the suspension mount and shim the opposite side.
In the image above, you can see the drive axle and suspension mounted into the tunnel of the sled.
If you’re working on an older model, you’ll also check for wear at any moving part. A rear suspension that is bent will not be able to be aligned, and must be replaced. Once bent, a rear suspension is weakened, so shouldn’t be straightened and reused without reinforcement.
Many older models of snowmobiles didn’t have grease nipples on major moving parts, so this is an ideal opportunity for you to add some. Without lubrication the old suspensions seized and were frequently damaged.
Drive axle to jackshaft
Begin by loosening the bolts and the bearing locking collar [shown in photo below with a blue line] of the clutch-side jackshaft bearing. Even in brand new bearings you’ll notice that there is some play or movement. You can feel this by wiggling the shaft up and down, and left to right. Find the center of the circle that is created by experimenting with the full range of motion. Using your carpenter’s square, measure to make sure the jackshaft is square with the frame.
If the jackshaft is not square with the frame, you will need to shim the chaincase in the appropriate corner to move the jackshaft into a square position. The mount on the clutch side may require the mounting holes to be slotted if you can’t move the jackshaft far enough. A file or die grinder will be sufficient for this task.
When the adjustments have all been made, and the jackshaft is square, make sure to scribe a mark around the mounting brackets so that if the jackshaft is ever removed, you can line everything up to the correct markings that you have just squared.
Note that if you are working on a restoration, you should check that the jackshaft is not cracked or damaged in any way before proceeding. Also, check the bearings while everything is apart. This is done by confirming the amount of play and if it spins freely, or feels rough when turned.
In the picture below, the jackshaft, chaincase, and drive axle have been removed from the sled. The red lines point to the chain case mounting points, while the blue line points to the jack-shaft bearing and locking collar.
Next, you check the axial play — side to side, or left to right movement — of the drive axle. This may have to be spaced to use manufacturer’s specifications. Shims can be placed between the left housing or the right housing, to keep the axle centered in the track tunnel.
You need to make sure your gears are properly aligned to avoid having your chain run crooked. This can cause lost performance and excessive wear on your moving parts.
To align the gears, you place a straight edge across all four edges of the gears as shown in the picture below. The straight edge should touch all the way along both gears, if they are straight. If not, you will have to add or remove shims from behind one or the other gear, making sure that the chain will not touch either the chain case or cover. The chain must run freely between the chain case and the cover.
Drive clutch to driven clutch
Clutch alignment is accomplished by shimming the secondary clutch and moving the engine. You require the manufacturer’s specification sheet BEFORE you begin making any adjustments.
Begin by opening the secondary clutch and inserting a bar. The clutch will close over the bar, holding it firmly in place. This will allow you to use the bar to measure the specifications for the front and back of the primary clutch as shown below.
If the measurements are not within the range required in the specifications sheet, you need to loosen engine mounts and twist or move the engine ahead or backwards until they are reached. You may add or remove shims from the secondary clutch, to move it left or right only. Make sure that the secondary clutch doesn’t contact the frame when it is completely opened.
Your specifications will also provide you with a correct center-to-center measurement for your clutches, which will be set with the above adjustments. Make sure to recheck this before doing the belt deflection.
Next, you will move to belt deflection. You check this in either of two methods, both illustrated below.
1. Set your square bar on top of the belt, and with a belt deflection tool, which is available at most automotive stores, push down halfway between the clutches. Exerting the pressure indicated in the spec sheet for your sled, the belt should push down the distance listed in the spec sheet.
2. Instead of using a belt deflection tool, you may use a fish scale or spring scale and a ruler. Again, you are looking for the specifications listed for your sled.
If the belt deflection is incorrect you will have to open or close the secondary clutch with the screws [indicated with the red line in the picture under #1 above] on some models. On others, you will have to take apart the secondary clutch and add or remove shims. Add shims to loosen the belt, remove shims to tighten the belt.
In the photo below, you can see that a snowmobile belt has a directional arrow on it. The belt must be installed so that it spins the correct way, or points forward on the top [points towards the sled’s front bumper].
Even belts that do not have an arrow on them should always be installed the same way after they have been used. In order to remember which way it has been installed, I always install a belt so that I can read the writing when standing beside the sled. If installed the opposite way, the writing will be upside down.
Your sled is now aligned and completely reassembled. There are various different videos available from performance shops that you can purchase to watch this done step by step at home. If you are a novice mechanic, I highly recommend you purchase one. Besides, everybody needs a good collection of snowmobile performance videos!
This article originally appeared in SnowRider Online Magazine in January 2002. Copyright David Aksomitis.