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Discussion Starter #1
Hi All,

In early December, I bought a half disassembled 1972 panther 303 from it's original owner. It seemed to have been sitting since the early 90's until the previous owner got it running a few days before I bought it. It ran ok, not great, and was pretty hard starting (10-15 pulls). Somewhere on here I read that dropping some ATF down the spark plug hole and letting it soak can remove some carbon buildups. I put about 3 oz down each side of the rotor. It definitely did something as it started pretty consistently in about 4 pulls. After that, I checked the timing and it was pretty far advanced. It's nearly spot on now, and the machine starts consistently on the first or second pull. Not bad considering how long it sat outside. I got the track back under it about two weeks ago, and it's performed well so far, aside from one problem.

It runs fantastic for about 15 to 20 minutes, then it becomes hesitant to idle. It stays running as long as you keep the rpms up but eventually if you let off at all, it dies. Pulling it over reveals no spark. Pull the recoil off, clean the points, put it back together, and it fires right up and runs as good as before.

So I know the chances are this engine needs crankshaft seals, which I plan to do over the summer. However snow is not always consistent year to year, and I don't want to tear down the engine now and have it back together just in time for warm weather. Also it seems surprising that the seals can be bad enough to foul the points in 20 minutes but the engine can run and idle mostly fine (rpms wander a little bit at idle but it shows no signs of stalling out until I've ridden it a little ways).

The only other cause I can think of is that the engine is just so dirty that crap is somehow getting on the points from the fan housing. The sled definitely spent a lot of time under a pine tree and I'm sure the 3 oz of ATF I spilt on the cooling fins isn't helping either. I cleaned up behind the recoil as best I could, and I'm thinking of trying to clean the fan housing better. I've tried a few things but I'm not sure what's the correct process to clean the corroded aluminum. Does anyone have a good way of cleaning the fan housing?

Also could there be any other obvious cause that I'm missing? This is my first engine with the points under the flywheel so I'm far from knowledgeable about these ignition systems.

Thanks in advance!
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Nice sled. i can say after rebuilding quite a few of these motors that it is likely the crank seals. at idle it wouldn't spit as much fuel mix past the seal to foul the points, but as you run it and load the engine it sprays mixture past the seals onto the points, the pto side seal is right there below the points. its actually pretty easy to change the seals and you dont have to split the case halves off the rotor housing to do them. they are standard shaft seals available from lots of places. there are good instructions in the manual for this motor on how to disassemble it.
the ATF trick is a good one and dose help free rotor seals up and blow carbon out of the motor.
 

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Discussion Starter #3
Thanks for the reply!
I took another look through the manuals that I've found for the engine. I have a copy of the Sachs service manual, parts manual, and the 72/73 Cat service manual. A lot of forum posts I've read say that the seals are different on the PTO side and the recoil side, but the Sachs manual seems to list both under the same part number and dimensions [Part number 2730 006 100, seal 30 x 42 x 7]. Does that sound correct to you?
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they are both 30x42x7mm standard shaft seals. you need a couple o-rings that go under each of the seal holders. one is 70mm ID x 75mm -OD 2.5mm cross section, the other is 50mm ID x55mm OD- 2.0mm cross section. also real cheap i got on amazon
 

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these are actually really easy motors to work on, takes a little practice to get all the internal seals and their springs back in just right if you were to take the whole thing apart ( witch you do not have to just replace seals ) but not hard at all.
 

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Discussion Starter #6
Just placed an order. Hopefully I'll be back in business in a week or two!
Depending on how well it runs, I might open it up in the summer and give it a proper decarbonizing and replace rotor seals as needed. I originally bought this thing mostly because it was cheap, unique and in decent shape, but I've really fallen in love with the character of the engine. It has the perfect amount of power for my yard and is an absolute blast to ride. I'm in central MA and snow can be hit or miss year to year, so I just want to get as much riding as possible in before the white stuff disappears.
 

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i hear ya on these motors. I had one many years ago and it was a blast in the woods here in south eastern Vermont, not far from you. then about 4 years ago i picked up a 71 303 panther that had a shot chassis and now i have three 303 sleds all ported out and about 2 or 3 spare motors and parts.
they are great motors and only one have i found the seals were actually really bad. some close to out of spec but most are ok.
 

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Discussion Starter #8
The seals and one set of the O-rings are in. I'm still waiting on the other set, but I should be able to try and swap the seals this coming weekend. Since the snow is disappearing fast, I moved the sled closer to the garage today. That quick ride reminded me to try and figure out how to get the clutch off. Looking around on the internet I've seen a couple of generic tricks, and a couple horror stories, so I was wondering what actually is the safest way to remove this clutch?

It's the original Salsbury 780 and it works great. It seems parts for this clutch are hard to find so I'm a bit worried about the possibility of breaking while trying to remove it.
 

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i can help. i need to go measure the treads on my spare 780 and ill get back to ya. you can make your own puller easy fro ma bolt and a short rod of steel
 

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so you can make your own puller from a 9/16"-18 bolt and a 3/8" solid rod. if you get a bolt that is 1-1/2" long youd need a 2-3/4"-3" ( i think- may need to adjust this so you have at least a half inch of thread into the clutch ) long solid steel rod.
remove the clutch bolt and slide the solid rod in ( try to see that it bottoms inside the threaded hole-3/8" should fit in the hole and not mess the threads on the crank, as a precaution you could also grind the dia- a little to be sure it sits nice in the crank and ) and then thread the 9/16"-18 bolt into the clutch and holding the clutch tighten the bolt till it pops the clutch off. on the 303 you can use a large wrench or something on the counter weight if need be to hold the clutch from turning.
 

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best to pull the clutch while its in the sled. you will have to take the motor out of course to get to the mag side seal. to remove the flywheel nut you can use a flat bar with two holes that line up with the m6 recoil bolt holes and anotehr hole with a bolt to stick into the hole on the outer part of the flywheel to holt it in place to break the nut free. then use a typical steering wheel puller and two m8 bolts to pull the thing off the crank. thats it. the rest is easy.
 

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Discussion Starter #13
Well, in an unfortunate turn of events, I only just received my last O ring yesterday. Just in time for all the snow to be gone. Judging by the various stamps and addresses on the packaging, this thing has been in transit for nearly 3 months.

Oh well. I'll be gone on vacation almost until April, so I ended up moving the sled back to the barn today. What was interesting, is that I started running it on the Rotella oil since I put a good fuel tank back in it, and it actually was able to run for a few hours between each cleaning of the points on the thicker premix. I probably put a good 30-40 miles on it just around my yard, and aside from stalling out once it got hot, it performed well and was reasonably reliable considering it still needs the seals.

I'll be sure to post some pictures of the process once I have the chance to do it. These things are fun little machines.
 

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Too bad about the o-rings taking so long and the snow melting away. I just finished a more radically ported 303 engine with a big carb and hot clutching and there is not enough snow to test it.
 

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It's been a little while. I hope everyone is safe and healthy! My backyard flooded sooner than it usually does, so the sled was trapped in it's trailer until now, but since it's now dry I'm planning on taking care of this project this week. I realized I had 2 more questions so before I start I figured I should ask.

I assume I should wet the seals and or rings before putting them in. Would the same Rotella oil be good for this or should I use something else? Also should I do anything special to 'break in' the seals when I start it the first time, or should I just start tuning it?

Also, Motorman, you seem to really understand tuning these engines. Is there anything I should know about tuning a stationary sled? The past few times I've messed with the carb I was able to ride a lap of the yard to test it, but without snow I was thinking of just jacking the back up like I did when I aligned the track. I just don't want it to overheat or do some other easily preventable thing I'm not thinking about.

Thanks!
 

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I would wet the seals with whatever oil you use in the gas, rotella is fine. no break in for seals needed. as far as tuning the carb set the jets to stock, i think its 3/4 turn out for the Low needle and 1 1/2 for the high, on the stand warm it up a bit and turn the low needle in slightly till the idle increases, then turn it out form there ~1/8 -1/4 turn. the high needle will vary where it is ideal with air temp and humidity. you can run it full throttle on the stand if your sure it secure and adjust the H needle for highest speed and clean revving from idle. sometimes you need to open the L a little to get a clean throttle pull off from idle. you will get your best H side tuning from running it under load around the yard, you may find it gets better power and pull as you lean the H closer to 1 turn out. you wont over heat it

just my 2 cents
 

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I managed to get the engine out today. Your clutch puller worked perfect. The bolt on the counterweight put up a decent fight but it came off with a little heat. I still haven't removed the counterweight itself. I had to stop for the night because I think I need to go get an impact socket for the flywheel nut. I made the bracket to hold the flywheel in place, but bolt that held the flywheel was bending faster than the nut was moving. I've had decent luck with the impact so far with things like this, but that nut is really on there solid so we'll see.

Also thanks for the tuning info. I was messing with it all the time in the winter, but it never on a stand. This machine was a first introduction to snowmobiling for a lot of my friends, so I'd adjust it to idle better for them, then change it back to run good but not idle when it was just me riding. I'll probably tune it as best I can on the stand, then stick it in the barn for the summer and drain the fuel out of the tank . Save the fine tuning for when the white stuff returns next year.

Once I'm done I'll post some pics of how the process went.
 

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sounds like your on track. tap a wedge or large screwdriver in the gap on the flyweight and it should come off easy. i made the same kind of tool to hold the flywheel, make sure the flat bar is screwed down all the way to the fan housing so your m6 bolts dont bend, to break that big nut free i use a good sized ratchet , hold it in place at the ratchet on the nut and carefully give the end of it a good hit with a large ball peen hammer. otherwise an impact wrench should do it.
 

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Mission success!
I didn't get the chance to put it back in the sled yet. I'd like to maybe clean the engine up a bit first, and I'm also going to throw a coat of high-temp paint on the original muffler which is somehow in decent shape. I never realized how solid it was until I had it off.

Getting the seals themselves out was a bit of a trick. I did not expect them to have a metal outer edge, so it took me some time to figure what I was even aiming for because it was so covered in sludge. I did the mag side first, which took me a few hours because a few things needed some mild hear cycling. The other side took about ten minutes. I skimmed the service manual and it suggested heating the plate thing to make the seal come out easier. That certainly helped.

I found it interesting that it feels like there's been a noticeable increase in compression with the new seals. I can't wait to see how it runs. What also surprised me was just how much dirt was behind the fan shroud. I knew it spent some time under a tree but there was a solid 8 ounces of dirt at the bottom. I'm sure that wasn't helping cooling.

Image 1 - clutch puller
Image 2 - new seal/old seal
Image 3 - mage side shaft/bearing
Image 4 - Finished and re-assembled
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wow , great job, i like the engine cradle. you should be good to go now. these are such fun engines to work but the sound and torque is the most enjoyable part. it will defiantly run better now with good seals
 
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