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My dad has a 1979 panther 500cc fan and it's never been messed with and only 650 miles on it he bought it in '79. He had no problems with it up until last year the farthest piston from the fan melted and blew. So he bought new wiseco pistons, rings and pins. heads and cylinders are still good yet. and so we did all that and got a few miles outa it when the same thing happened again. the farthest piston started to melt. it melts from center of piston to exhuast port the spark plug on it was damn hot, the thing is the other cylinder no problems at all runs normal. I gave him some ideas about what it could be, but i was wondering if anyone knows of this problem and has a good idea of to solve it? thanks
 

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At first guess I'd say a bad intake boot that is allowing that cylinder to run very lean. Or could be a carb problem. How did (and how long, the second time) the sled run, before it melted?


Maxwell
 

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Discussion Starter #3
both cylinders run off the same carb with the aluminum intake manifold feeding both cylinders. I can't quite remember how long new piston lasted i'm guessin around 1-2 running time non stop. it could be the carb maybe the fan is keepin the one cylinder cool enough to run normal. well I was guessin the ignition timing might of turn a little making the one fire improper. i know for years it wouldn't idel but given the fact that the piston was replaced and didn't take too long melt it must be something just recent to go wrong.
 

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This seems to be a recurring theme with this engine and single carb setup. I can remember about 15 years ago my dad had a '79 pantera, same engine and carb, and it melted itself twice, exactly how you describe. Never could figure out what the culprit was so he just sold it, knowing it would do it again. Also, another guy was on here about a month or two ago with an '80 pantera with the exact same problem. He was talking about converting to a dual carb setup to jet correctly for each cylinder to try to prevent meltdown (try a search in the archives). Also, you might want to look into getting a new carb or inspecting yours very thoroghly as there might be a crack in one of the components allowing too much air to get in without you knowing it. I know this doesnt help much, but i just thought i would share an experience or two.
 

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Discussion Starter #5
LOL anything would help and yeah i kinda wonder if that year panther was know for that problem. my dad won't sled it i would't neither cause it is in mint shape and ya hardly sled old sleds that look new.
 

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When you rebuilt it, did you check the crank houseing for any leakage? Or maybe even the intake manifold. I have seen many a pistons melt down and people throw a new set in them just to have it happen again all because they didn't go through the lower end and rebuild or at least look for leakage. Check out all components for cracks or leakage. You may have a bad main seal. or a hair line crack in the intake manifold. Making that one side run lean. Or the whole thing run lean and the fan is keeping the one cool enough. Just my 2 cents.
 

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Discussion Starter #7
Nope i know there was no crank case leakage but i am gonna take a look at manifold and carb.
 

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I had a 72 scorpion when I was younger that use to do the same thing. And my solution was to sell it. I narrowed it down to two things. The crank seal or the carb. Maybe both. I was running a different carb on the thing for over a year and all was fine. Then one day poof. Rebuilt it and after a few rides poof again. Bye bye! Since your still stock on the carb I would lead toward the crank.
 

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You must have a Air leak somewhere. Base Gasket, Carb boot.

Thats the only way a single carbed engine could have a problem on one side but not the other.

I got a bad air leak on my 340 project motor. So i just put the whole thing away till next summer.
 
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