Indy Project Snowmobile - Rolling the Chaincase

Nov. 01, 2005 By ORC STAFF

Rolling the Chaincase

Cost: Under $100 (US), not including any tools you may need to rent/buy
Risks: HUGE! If you mis-drill the tunnel, you can scrap the sled
Benefits: Improved track attack angle, more efficient drive train, clearance for large tunnel cooler
Tools Required: Everything in your toolbox and then some - right-angle drill makes it much easier
Parts Required: Roll templates, sharp hole-cutting bits, lots and lots of rivets
Mechanical Skill Required: Advanced

This was the single biggest sub-project that I have ever done on a snowmobile. I decided to roll the case to give myself more clearance in the front of the tunnel in order to use a single, large tunnel cooler to reduce weight. As it turns out, for trail riding that single cooler is not adequate, so I had to scrap that plan. By the time I realized that, I had the sled apart, so I decided to go ahead with the roll in order to get the other, admittedly smaller benefits. Which are a lower center of gravity and a more efficient drive train. I did not measure the CG of the sled before the roll but I can probably get my hands on a stock Indy 500 pretty easily. I suspect that the difference will be only barely measurable. Still, it's worth a couple of mental horsepower. The tangible benefit is the improved rolling efficiency. With the roll completed and the sled reassembled, I can now roll the track with one hand when the rear of the sled is suspended off the ground. Those are the reason that the '98 XCs came stock with rolled chaincases. So, if it's good enough to the latest generation of trail-pounders, it's good enough for my sled.

You have to pretty much dismantle your snowmobile to do this job. The rear suspension, track, driveshaft, jackshaft, driven clutch and chaincase all have to be removed. It's much easier to work on the sled if the hood is off also and on the Indy wedgie chassis, you have to remove the nosecone to get the hood off - well, I've seen guys get the hood off without removing the nosecone, but you have to bend it out of the way and my nosecone has had several patches applied to it that make it somewhat less flexible.

After the hood is off, if you chose to remove it (highly recommended), take out the rear suspension and the driveshaft following the instructions I gave in the section on replacing the track. From there start by removing the drive belt and pulling off the driven clutch. If you haven't serviced your driven for a while, this would be a good time to do so. Remove the jackshaft next by removing the 3 bolts from the clutch-side bearing retainer, then remove the top sprocket from the chaincase. You'll have to remove the airbox and the oil bottle to get the jackshaft out of the sled (I *told* you you have to dismantle the sled, didn't I? :), but first you have to get the chaincase-end of the jackshaft out of the chaincase bearing. It's a very tight fit and the way I got it out (I had to remove it twice . . . don't ask, it's a long story) was to put a "sacrifice" bolt in the jackshaft and pound on that to push the shaft out of the bearing. That bolt will get really beat up, so don't use the one that was holding the sprocket in place unless you plan on replacing it anyway.

Once the jackshaft it out, remove the 3 bolts holding the chaincase in place and pull it out. You'll have to drain the engine coolant and remove at least the hoses to the chaincase-side running board cooler. I say "at least", because you might try leaving the others on and working around them. I don't know if you can or not, since mine were out anyway, since I was hoping to take them off permanently to save weight.

The reason you have to pull the hoses off the chaincase- side cooler is that you are going to have to move it back about 2 inches. It is a very tight fit and you'll have to cut some of the footwell away to get the hoses reconnected. A side note: I'm planning on upgrading to the '99 tunnel coolers and will be removing the side coolers once again this summer. IMO, it is a much more "sano" solution that is probably a little lighter overall because it requires less cooling hose. More on that the next installment of this article. But you might want to take a long look at doing that while you have the sled dismantled. It'll make the roll easier. I recommend waiting until the chaincase is ready to install before relocating the cooler, it will be much easier to determine the exact location at that time. For now, just remove the hoses, drill out the rivets and remove the cooler.

You're through dismantling at this point, now you need to mount the templates. To do that, you'll have to remove a number of rivets - it's easy to figure out which ones to remove. I used a drill to drill them out until I got smart (pretty far along in the process, unfortunately) and began using a dremmel to grind off the heads.

Once you have those out, you can mount the clutch-side template. Let's talk for a moment about the "templates."

SLP quit selling them, I'm not sure why, it's a great little mod IMO, but there are other companies out west who still sell them. When I first heard about the templates in the kit, I thought they were just that - templates that you used to locate the new drive/jackshaft holes that then got tossed aside. But in this case, they might be better termed "tunnel strengtheners and shaft locators" since they stay on the sled. Templates is shorter, so let's stick with that for now.

Anyway, rivet the clutch-side template in place using steel rivets. A hand-pulled rivet tool is going to have a tough time with steel rivets of this size, if you have or can rent or borrow an air-powered riveter, you'll be much happier. I used a good quality hand-riveter and was able to do the job. It's a good grip strengthener.

To mount the chaincase side template, you'll have to cut a hole in the bellypan. Maybe this is a good spot to discuss the philosophy of this mod for a second. There's no instructions with the templates, at least none with the ones I "bought" - I got mine from a friend who had rolled his chaincase and made me a copy of his templates. When he offered to do that for me, thinking that they were just plastic or paper templates, I thanked him and forgot about it. Now that I have done the mod, I realize the work that it took to fabricate those "templates", so I am not about to grouse about a lack of printed instructions! But again, now that I've done the mod, I don't think I would have wanted explicit, written instructions. I figured out where to cut the bellypan on my own and did a good job and I reaped a tremendous amount of satisfaction from a job well-done. It works, it looks good and I did it myself.

Enough editorializing, back to the mod. You'll need the rolled chaincase protector that SLP sells, it's $40 or so and is absolutely essential. Not only does it protect the bottom of the case, which will now protrude through the bottom of the bellypan, it gives the mod a professional look and it makes it easier to determine the size of the hole to cut in the pan. You'll also have to cut some aluminum, but that's OK because it gives you a more solid mounting point for the case protector.

Once you have determined the location for the pan cutout and made the cut, remove the necessary rivets from the chaincase-side of the tunnel and rivet in the template. You're almost to the home stretch at this point, take a deep breath, steady yourself and get your drill ready - we're ready for the most critical part of the project, drilling the new shaft holes.

A couple of things before you do this. First, DON'T SCREW UP! Let me repeat that: DON'T SCREW UP! If you do, you've got big problems. Be careful, be accurate, take your time. Second tip is that a right-angle drill will allow you to drill the holes without removing the bellypan. I rented a very good drill and it made this part so much easier, it was worth twice what I paid to rent the drill for a morning. And use sharp hole cutters, you'll be glad you did. I had a good drill and new hole cutters and it went very smooth and quick.

You'll have to drill 4 shaft holes and a number of smaller holes for mounting the chaincase and bearing retainers. The bottom chaincase mounting hole will be in the chaincase protector you mounted above. You'll want to square all these holes so that you can use the stock carriage bolts, although you might have to buy slightly longer bolts to hold the chain- case on depending on how thick your templates are. When squaring the holes, pay special attention to the holes in the bearing retainers - they must match!

The size of the shaft holes on the clutch side is easy to determine - they should be the same size as the stock holes, since the bearing retainers must fit the same way. The chaincase side is a bit more difficult to determine, since the fit of the chaincase changes. The top hole should be as small as possible, since it will not be sealed and will permit snow to enter the engine compartment from the tunnel, which will soak the brake rotor, a very bad thing. So, keep the hole as small as you can. The bottom hole must be large enough for the chaincase "tail" to fit all the way through but not too large as to allow snow in. If you want, you can drill pilot holes for the shaft holes and drill the large holes from inside the tunnel. I had to do that on one hole because of clearance problems with the drill I had rented.

After the holes are drilled, it will take about an hour to square off the smaller holes. Once that is done, you can fit the chaincase in place temporarily to relocate the chaincase-side running board cooler. You will have to move it back about 2 inches, it's a very tight fit and there's not a lot of options here. I used the existing stock hole as a pattern for the new one, again, there aren't many optional sizes or shapes other than what Polaris used. Drill the holes for the new rivets and remount the cooler. As I said above, you will have to cut away a portion of the footwell to get the hoses back down to the cooler. I also added a liquid-cooled brake kit, so I had to cut the inside edge of the footwell away.

Once the cooler is back in place, you can start to reassemble the sled. Start with the jackshaft. You're not done improvising though - the templates in effect widened the bulkhead and as a result, the way the shafts mount have changed. You may need to install a spacer behind the shoulder of the jackshaft where it seats into the chaincase bearing. I did not need to shim here, since I was installing a new brake rotor and hub, I was able to compensate for the new jackshaft location by grinding a bit off the in-board side of the new hub. Keep in mind that the upper sprocket will now not seat fully on the splines of the jackshaft. That's just the way it goes, there's not much you can do, but it has not caused a problem for me or for anyone else that I've talked to who has done this mod.

Once you have the jackshaft installed in the chaincase, you will need to install the clutch-side bearing. But hold off on that for a minute until you get the driveshaft back in, you'll need to adjust the chaincase to align both shafts in the tunnel correctly. When you are ready to reinstall the bearings, the procedure is to slide the clutch-side bearing and bearing retainer back on and bolt it in place. Then adjust and tighten the fafnir collar. When you reinstall the driven clutch (not yet though), you'll need some extra spacers and perhaps a longer clutch bolt, since the length of the jackshaft available to mount the clutch on has decreased. My templates were made from 1/16 inch aluminum, so the offset was pretty large.

Now you can reinstall the driveshaft, it will need a spacer behind it's sholder also on the chaincase side. It's important to get the spacer the right thickness so that the drivers sit in the proper location in the tunnel, otherwise your track will run offset in the tunnel. When you put the bottom sprocket on the first time, you can leave the chain off, since you'll more than likely have to remove both sprockets again anyway to get the spacing behind them right anyway.

Once you have both shafts reinstalled into the chaincase and have the chaincase bolted securely in place, observe the clutch-side ends and their location in the bearing holes - they should be perfectly centered. If they are not, you'll have to shim the chaincase in one or more locations to make that happen. If you have drilled the holes correctly as marked on the templates, both shafts will either be perfectly aligned or off by the same distance in the same direction. If they are not, you have screwed the pooch and it's time to call the local sled salvage yard to see what they'll give you for 400 pounds of scrap. Well, OK, it's not that bad, but it sure would have all worked better if you had listened to my advice about how to drill the holes. *grin* It's too late to do anything about it now except put in a new bulkhead or to adjust the chaincase as well as possible, bolt the shafts in and live with it.

If they are off-center by approximately the same distance in the same directions, loosen the chaincase mounting bolts and determine where to put a spacer and how much of a spacer to use. Put it in, bolt the chaincase back down and check the alignment again. It make take a couple of iterations, but if everything is right, you should be able to get the shafts perfectly aligned. If you do, you'll be rewarded with a freer running drivetrain and snappier performance as a result.

Now you can bolt in the bearings, bearing retainers and fafnir lock collars. Oh, don't forget the track before putting the driveshaft in. Not that I know anyone who has ever done that. *grin*

Next, you'll more than likely have to remove both chain sprockets to adjust their relative heights with spacers. Use a straight-edge to determine which gear is too high or low and add or remove spacers to get them to the same level. Once you have them spaced properly, put the sprockets and chain back on as a single unit. A little tricky if your chain is close to tight - I tried 18/39 gears with a 64-pitch chain and it was maddeningly close to fitting, but I couldn't make it go on, so I dropped back to 18/37 and there was enough slack that getting the gears on was easy, but not so much that I could put the gears on first and slip the chain in place afterwards.

I adjusted the chain tension while I had the cover off, it was much easier to do and feel confident about. When I can't see the chain, I always worry that I've gotten it too tight.

Now you can put the chaincase cover back on and put the gear oil in. You're almost finished!

Next you'll need to fabricate a small sheild to cover the hoses on the clutch side from the driven. The hoses will be really close to the driven, so I made a small sheild out of some of the scraps of aluminum I had left over from the cutouts I made and riveted it in place. Before reinstalling the driven clutch, you'll need to hammer back the footwell slightly to give yourself room to remove the belt. Doesn't take much, so go easy or you'll move it too far and make it too small for your boot to fit in.

Reinstall the driven clutch and the drive belt, reinstall the suspension and adjust the track tension and you're ready to ride! Newsletter
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