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Discussion Starter · #1 ·
This is the start of a project my brother & I are working on… Code Name: Stubby – short for stubborn Mule.
I bought a “running 2510 that needed a primary clutch” on Ebay… When I got it home, I learned I was along way away from adding a clutch& turning the key. Wait, there wasn’t a key either…..
Lets just say that the motor DOES run, but it did not have a wiring harness or cooling system so I decided to swap the motor & build a play toy for the trails…. (we have another 2510 for yard work)
To start, we are installing an E-start 503 Rotax motor and exhaust… Once we get that down we have plans for the seating area, suspension, and of course wheels…

More pics to come as we move forward…
Kevin
Stubborn2510
 

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Discussion Starter · #2 ·
I have the motor in (test fit) with new mounts... i will post more pics this evening - I need to resize what I have...

K
 

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Hold on to your shorts! The 497cc Rotax has twice the power and three times the rpm of the Kaw engine, but no bottom end, so you will need to use different gearing and a snowmobile primary and secondary clutch. Be real careful to install a steel shield between you and the clutch, I have blown a couple and they really do big explosive damage when the come blowing through the back of the rig. They turn so many more rpm's than the OEM engine that you have to really be careful.
 

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Discussion Starter · #4 ·
RCW, thanks for your reply... My shorts are on tight!!!! I was ready to pass on this project, but my brother is leading the charge....

I do have the primary & secondary from the s-mobile, but the gearing seemed to be 1:1 on the s-mobile gear box so I installed the Primary Rotax clutch to the Kaw secondary directly ;-)

I can understand where the rotax clutch can explode & thanks to you I will contain that ASAP. Take a look at the pics am posting now & tell me what you think... Bomb? I just dont understand (my lack of gear knowledge) why it matters... When you say no bottom end, meaning that I will be using lots of RPMs as in always in a powerband? I am excited about this build, but not so in love that I couldnt stop & sell my goods... I just got the complete motor set-up and havn't even unpacked thecarbs, starter, wiring harness ect...

Thanks for your feedback

K
 

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The Rotax makes its power with lots of rpm's, just like a two stroke motorcycle. The Mule is set up with a gearing system in the transaxle that is designed for the much lower rpm and higher starting torque of the Kaw engine.

The dual carb version of the 497 cc Rotax will make right at 67 horses properly tuned. The OEM mule engine made maybe 19 horsepower at the limited rpm allowed by Kaw on the Mule.

The Bombardier drive system uses two sets of reduction drives. There is a primary chain reduction attached to the secondary countershaft that reduces the rpm significantly before it is transmitted to the drive sprockets, and then the drive sprockets for the track are small diameter which works like small diameter tires on an axle and further reduces available engine rpm to the ground.

I suspect you will find the repowered Mule will have to start only in low range, and then will still top 50 mph.

You will need a strong plate between the engine and the transaxle to stabilize the loading force of the torque converter. If you apply full force of the Rotax engine to just the shaft sticking out of the transaxle without case support between both the engine and transaxle, you will break the transaxle case. The belt torque converters put a huge amount of side thrust on the shafts that hold the primary and secondary clutches and the Kaw case is just not designed to handle that without additional torque plates/struts to support the side thrust.

If you are familiar with snowmobiles, you will know that the two stroke engines they use are very sensitive to altitude and air temperature. Be sure you run the carbs with rich enough jets to avoid burning down a piston. It is a good idea to use a pyrometer and keep the EGT below 1,250 degrees F to avoid melting a piston. Snowmobile pyrometers are cheap and easy to install. Any skidoo dealer will be able to provide you a jetting/altitude/ambient air temperature chart for that engine so you know which pilots and mains to use.
 

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Discussion Starter · #8 ·
interesting... I agree about the bracing - I will take care of that before I hit the ground. I will check with the guy that sold me the 503 & ask about the jets on the carb.
 

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From your response I deduce you are not that experienced with the Rotax snowmobile 2 strokes. The jet numbers are stamped on the jets themselves, so once you obtain the proper jetting chart it will be easy to know which to use. The chart will also state which needle to use and at what groove to set the clip.

There is another item to think about on a snowmobile engine. The carb intakes are made to run in an air box because of what is known as intake reversion. The fuel/air mix blows back out the intake side of the carb when it runs, and the faster you spin the engine the more the fuel and air mix will blow out. It will be necessary to install short tubes and air cleaners to avoid running too lean and raising the combustion temperatures too high and burning out the pistons. I have used K&N direct connect clamp on type air filters with excellent results, just be sure to use K&N oil and not regular oil on the filter media if you go that route.

The 497 cc (marketed as a 503) Rotax engines do not use reed valves like most high performance 2 strokes, but rely on a rotary valve. That valve is not as positive in locking the air fuel charge in the crankcase as are the reed types used by most others, but they also last forever so are excellent as long as the carb intakes are properly managed so the fuel does not just fly away in the atmosphere.

Another thing with the 497 Rotax, warm it up throughly before you mash the throttle. That particular Rotax uses sintered iron cylinder liners and require being warmed up to operating temperature before the pistons will fully expand to match the cylinder bores and to close the tolerances on the rings. Mashing it cold will spit one or more compression rings right out the exhaust port and nearly always ruins the cylinder when the piston clips the remaining chunk of ring in the port.

It is an excellent engine and one of the few that carry FAA certifications for use in aircraft. Just treat it right and you will have a real go getter of a toy.

By the way, you can also turn the carbs over and run that engine upside down with absolutely no problem - should that ever be an option.
 

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Discussion Starter · #10 ·
OK.... After a few test runs, the verdict is in.... The 503 was fast TOO F-A-S-T!!!!! It was fun, but I think all things considered, I should go back to the stock engine.

So I guess its back to ebay to track down a few parts I need... (wiring harness and converter cover). The engine has the plugs, but the entire harness has been removed.... I am sure there is a way to get the engine to run without the full harness - I have no clue on that ;-)

I'll keep you posted... My wheels arrived, I am half done with the camo-clad, and the suspension is just around the corner...

How about a rebuild kit? Do they sell a rebuild kits for the 620?

Thanks
 

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The generic Kawasaki engine you are looking for is a FD620D. They are common in John Deere lawnmowers and a significant number of other commercial power equipment.

The best deal is to find an older John Deere lawnmower with that engine in good shape on Craigslist for cheap and pull the engine. Sometimes these same engines pop up on Ebay, but unless you hear it run or have a guarantee from someone you can trust, you may be worse off than when you started.

I know of no prepackaged rebuild kits, but a Kaw power dealer will have access to short and long blocks, and complete engines. A ready to roll complete new engine will run between $1,350 - $1,700. A brand new engine with radiator and all the electronics from a Kpower distributor like tulsaenginewarehouse will run you $1,800, but will have everything it needs to run without having to scare up an OEM Mule wiring harness.

By the time you fool around trying to rebuild one from parts you will have as much in just the parts and machine work, not counting the mess and your labor getting it disassembled and prepped.
 

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Discussion Starter · #12 ·
...okay, I did check-out the engines but not ready to take that leap just yet. Great source though...!!

This motor has cream-milk colored oil & will actually blow(2ft) the oil out of the motor with the filler cap off, runs at half power, overheats, yet starts without fail & purrs to quite I almost can't hear it idle... I was thinking I would re-ring and check for bent rods ect for around $150 in parts.
 

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From your description of the cream colored oil, I would suspect coolant in the oil. The symptom of compression blowing by enough to cause oil blow-out to the extent you describe can be a blown headgasket, a cracked head, stuck compression rings, or even a cracked cylinder.

I would drain the bad oil and use clean oil, then do a compression test. Also, check your radiator for bubbles when the engine is running and the radiator is clear full to the top and the cap off. If you see a stream of bubbles when it is running, then you are looking at needing to pull the heads and dig in and see what the problem represents.

If there are no bubbles in the coolant and the compression is good, then look for a bad waterpump. If the seal to the engine crankcase goes south they will fill the crankcase with coolant.

The waterpump seal problem could actually be good news. Most often you do not have to tear into the engine to do anything with the cylinders or pistons, even if the rings are stuck and you have low compression, if they have been run with coolant in the oil. Pick up some PBBlaster penetrating oil and use the entire can in both cylinders. Let it set overnight and then spin it over with the sparkplugs out to clear any penetrating oil, then button it up and start it after you have changed the waterpump and installed new coolant and oil.

The rings will work loose about 90% of the time and they will be good to go. If not, then it is time to spend about $300 for new pistons and rings and gaskets if the cylinder walls are good. I have yet to see a bent rod unless someone has sunk the Mule in a lake with the engine running, but I suppose it could happen.
 

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Looks like you have had combustion gases in the water jacket. The carbon trace on the first head in the photos shows blow through all across the 2 to 6 o'clock, and in the 7 to 9 o'clock positions.

With that much blow by I would have both cylinder heads resurfaced, just touched enough to remove all staining and roughness.

What it looks like to me is stretched or loose headbolts, and a loose head caused that broad of a leakage problem. It may not have been retorqued at the first warranty check, or the owner skipped that.

The spark plug for #2 looks real good, so I do not suspect the rings or pistons need any work at all. #1 would be black carbon fouled from low compression. If your bores look good, I would just resurface the heads, clean the block, and install new headgaskets. Very inexpensive.
 

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Discussion Starter · #16 ·
Any reason a FD620 would not be a direct fit for my mule? I found a guy with a tractor with a FD620.... Any reason to think the shaft is different? i'd hate to buy this old tractor only to learn that my primary clutch spline is not the right size ;-)
 

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Discussion Starter · #18 ·
Ouch....! I bought the mower with the FD620 and they are not the same... I have not pulled the engine yet to see the shaft, but I have found a few FD620's online with key-way shafts vs the spline shaft needed for my clutch. The part the I already notice is the casing area around the crank is different - I'll try to upload the pics.
 

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did you read my request?

i was reading your posts an RCW's replies. iwas wondering if you saw mine cause maybe i would be interested in the flywheel off of your mower engine if you arent going to be able to use it. that is if you decide to part it out. i would'nt want to have you do anythong that would make it harder to unload the engine if you can't use it for yourself. i was also wondering what you did with the 503. i was originally thinking of shoe-horning a suzuki 1100 into my mule frame and now after the troubles i've encountered with the 2510/3010 swap i wish i would have just done it.
 

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Discussion Starter · #20 ·
I did see your post... I am on the fence right now about what i am doing. I sold the 503 and now trying to get the 620 back in my 2510. We do have two running 620s, but I am not sure what the parts box is going to look like after I get done....

As far as your venture on the 1100... I'd like to see that!!
 
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