This Shop Manual covers the following Bombardier made 1978 snowmobiles. LIST OF ENGINE SECTIONS. Elan et Spirit 250. Elan Deluxe (248), Citation 300(294). ROTAX TWO CYLINDER. Top end and complete overhaul. Single cylinder engines. This manual provides periodic maintenance, tune-up,.

• Rotax Aircraft Engine Manuals

I've been searching around for more information regarding the Rotax 248 and 294 now that I have a couple of Elan twins and haven't come up with many specifics. I'm an engineer by trade so I'm always looking for more information about my engines and finding ways to improve them. Since my search was less than fruitful I got the degree wheel out and started taking some measurements of my own. Then a thought hit me.'

Why don't I share with the class?' So here we are. I'd like others to chime in with their info so we can compile an information thread on these engines for anyone looking to rebuild them, build a tuned pipe, etc. I'll be updating and adding information as I measure/receive it. There is a wealth of info within the members of this board regarding these engines, let's get it all in one place! The willing victim of my unending quest for knowledge is my 74' Elan 250T. This well worn example actually runs pretty good, and appears to have stock port timings (no grinding marks).

Engine ID Tag Type 248 Port Timings: Intake Open - 72.5 o BTDC Close - 72.5 o ATDC Duration - 145 o Transfers Open - 60.5 o BBDC Close - 60.5 o ABDC Duration - 121 o Exhaust Open - 90 o BBDC Close - 90 o ABDC Duration - 180 o Unfortunately I'm taking measurements on an assembled engine. Anyone have a 248 and 294 jug that can measure the port areas? I have searched through the SkiDoo parts manuals to establish a revision history for these engines. Below is a summary and spreadsheet with the part #'s 73-79 years of the 248/(249 73 only) use the same cylinders and heads based on part #s 73-74 294 use the same cylinders and heads based on part #s (no data for after 74) Type 248 1973:. First Year.

Single PTO Bearing Crank & Case (Same case # as Silver Bullet 294). 2 Rectangle Ring Pistons 1974:. Single PTO Bearing Crank & Case. Pistons changed to 1 L-ring, 1 Rect. 1975 on:. Change to Double PTO Bearing Crank & Case (Same # as Elan 300SS & TNT 300 case) Type 249 1973:. Only one year.

Single PTO Bearing Crank & Case. 1 L-ring, 1 Rect. Ring Pistons Type 294 1973:. First Year. Single PTO Bearing Crank & Case. Single L-ring Pistons 1974:. Change to Double PTO Bearing Crank & Case.

Pistons changed to 1 L-ring, 1 Rect. Both Jennings and Blair have written some great stuff for the 2 stroke world. Mechanical autocad 2013 training manual pdf. I too have been pouring through the books lately. That's part of what got me going on this. I think the right tuned pipe could really wake these little engines up. I think you are right.

I don't think the stroke is the same, but you might be able to go from the idea stage to big smile stage faster if you start by chopping up a 377 pipe.might get you close.I am not familiar with the 250 twins, but our 12/3, and elan are both single cylinder and have the straight pipe leading to a canister.probably pretty easy to feel a seat of the pants improvement. Remember, there are Yami 292's out there making 60 plus HP lately. A 5500 is only 56 KJC.

I think you are right. I don't think the stroke is the same, but you might be able to go from the idea stage to big smile stage faster if you start by chopping up a 377 pipe.might get you close.I am not familiar with the 250 twins, but our 12/3, and elan are both single cylinder and have the straight pipe leading to a canister.probably pretty easy to feel a seat of the pants improvement. Remember, there are Yami 292's out there making 60 plus HP lately.

A 5500 is only 56 KJC That's exactly what I'm thinking. Work out the numbers, then get a pipe that is close and modify it, rather than roll the cones from scratch. I have done scratch pipes for motorcycles in the past, and it's very time consuming. I think these engines will be like certain motorcycles I've worked with. My 72' Yamaha R5 is a piston port, 350cc twin. Power is in the mid 30's stock, but they don't have expansion pipes from the factory either. Fitting a set of good pipes is the single best performance modification you can make, and can add roughly 10hp in that application.

Of course, that is a free air 350cc in an application where low end power is less important but still I think it shows the potential of these little Rotax engines. For comparison, here are the port durations for the 72 R5. Intake - 153.5 Transfer - 114 Exhaust - 173 My take on these numbers is that the Yamaha engineers acheived their design goals by using fairly conservative (= short) Exhaust and Transfer timings, and then pushed the power peak up to 7000rpm by extending the inlet duration. This was no doubt at the expense of some low and mid range power, but on a 5 speed street bike that is an acceptable compromise.

This also explains why these engines respond so well to raising the exhaust port slightly and fitting a sharp set of pipes. The exhaust port angle/area is increased to a level appropriate for an 8k rpm engine, the strong negative wave from the pipe helps pull charge up through the transfers, and the intake timing is already setup for the job. The Rotax 248 is setup in the opposite way. The exhuast duration is pretty hot for a 6-6.5k rpm engine, whereas the intake and transfer timings are more low/middle of the range. This setup makes more sense for a sled, since the conservative inlet timing should help that lower end power required to get the track spinning.

I bet raising the intake ports and fitting a set of twin pipes would make these engines scream, if you could get the clutching worked out. All of this is a generalization though without the port angle areas.

I need to find a 248 and 294 jug to create port maps from and get the port areas. Then I can really do the numbers right on the pipe dimensions. Anyone got some damaged cylinders they want to get rid of cheap?

Good stuff, I've measured a Type 249. I'll dig up the #'s Here we go Ex opens @ 93.atdc for 174. dur Trans. Opens @123.

atdc for 114. dur Int.

Opens @74.Btdc for 148. dur Distance from piston face to Ex flange 44.5mm Ex port area @ cyl.

Equiv to dia. 30.96mm Trans areas of bridged are 144sq.mm + 252sq.mm =396sq.mm/side/jug I have ran a few different 'free' programmes from the net & input the info. Into MOTA to print out a cone layout & found the resultant pipe mock-up to appear quite under sized compared to what I envision as 'looking' right from others I've seen in pictures. I haven't built a pipe before so am not sure what to think. I'd like to try a set of pipes too so let us know what you find out steve.

Rotax Aircraft Engine Manuals

Egads, then our numbers should be the same. I've heard using a degree wheel isn't the most accurate method of determining port timings, but I didn't expect that much variation in the numbers. I'll re-check mine. How did you measure your timing numbers?

I remember reading about your findings on the 248 vs. 249 in an earlier thread. Further proof that the right induction/exhaust should make a world of difference. I ran the rough numbers for a tuned pipe using Jennings and Blair's formulae, and came up with the below: Jennings: Tuned length = 50.5 in Blair: Tuned length = 51.25 in These numbers are 1st order approximations using Ex port duration, average Ex temp, and expected engine speed @ maximum power. Based on my prior experience with motorcycles, the tuned length seems like it's in the right ballpark. It also seems significantly longer than the factory Elan tuned pipes, but I don't have one to measure on hand.

51in does seem comparable to what more modern sleds (ie. 377) are running. Egads, then our numbers should be the same. I've heard using a degree wheel isn't the most accurate method of determining port timings, but I didn't expect that much variation in the numbers. I'll re-check mine. How did you measure your timing numbers?

I remember reading about your findings on the 248 vs. 249 in an earlier thread. Further proof that the right induction/exhaust should make a world of difference. I ran the rough numbers for a tuned pipe using Jennings and Blair's formulae, and came up with the below: Jennings: Tuned length = 50.5 in Blair: Tuned length = 51.25 in These numbers are 1st order approximations using Ex port duration, average Ex temp, and expected engine speed @ maximum power. Based on my prior experience with motorcycles, the tuned length seems like it's in the right ballpark. It also seems significantly longer than the factory Elan tuned pipes, but I don't have one to measure on hand.

51in does seem comparable to what more modern sleds (ie. 377) are running. I used a full size degree wheel mounted on the crank with the heads removed. Much easier than doing with the heads on or non removeable head type motors.

The pipe length I got was 1329mm (52 5/16') from piston or 1284.5mm (50 9/16') from flange. What rpms were you using?

I used a 7800 max. The 249 was just a 248 that came with dual tilly's.

And then were mostly changed back to a single. As far as the diffs between bike and sled engines shouldn't make any diff as the centrifical clutch has infinite ratios until full shift out. In theory you should be able to make a 248 scream by porting the crap out of it and a decent set of pipes. But it may take ALOT of fandangling as it's ported for working. I'm good with that!!!!!! I just lack the know-how to figure where to put my ports, the 'hands on' is a piece of cake.

I have another 249 & a 248 (with a bad crank ), down in the shop. I used a full size degree wheel mounted on the crank with the heads removed.

Much easier than doing with the heads on or non removeable head type motors. The pipe length I got was 1329mm (52 5/16') from piston or 1284.5mm (50 9/16') from flange. What rpms were you using? I used a 7800 max.

Steve I used 6500 rpm for my calcs, just an educated guess since I don't have my Tiny Tach in yet. I had a thought on the discrepancy between our timing numbers. The 73' 250T was rated at 16hp. From 74' on the twin 250 was rated for 19hp. My measurements were made on a 74', so the Type 248 may have had a port timing change during it's production run to boost the power from 16 to 19.