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Old 01-18-2013, 01:34 PM   #1 (permalink)
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Bad Crank Seal?

Just finished a complete carb clean and rebuild for a customer and put them back on the sled. Adjusted everything (including the choke plungers and the slide heights at WOT) and fired it up. Had some trouble getting the idle speed to set up correctly and then finally dialed it in around 1500.

Thick bog coming up off of idle that I didn't like still there, so I kept poking. In the end, I found that covering the right side carb would kill the motor but covering the left side carb made it run really nice (and the idle would run up to about 3000).

I'm expecting this is a PTO-side crank seal as the carbs boots look ok. But, I can not determine that definitively.

My questions here are as follows:

- How likely is this to be a PTO-side crank seal issue?
- What else could it be?
- What's the recommended course for repair if it IS the crank seal?

It's a '93 Trail Deluxe, so it's a 440 fan-cooled motor.
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Old 01-18-2013, 01:53 PM   #2 (permalink)
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i'm no mechanic what so ever,but if its even possible and not to much work,what about switching carbs and seeing if the issue follows the switch
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Old 01-18-2013, 01:55 PM   #3 (permalink)
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I thought about doing that, but just ran out of time. I didn't obsess over it too much because, as I said, I had just finished a complete clean and rebuild on them.
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Old 01-18-2013, 04:15 PM   #4 (permalink)
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Spray carb cleaner on that crank seal while it's running. If RPM's change, it's the seal. Pop the clutch and replace the seal.
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Old 01-18-2013, 04:32 PM   #5 (permalink)
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Did that. No difference in RPM.

The owner talked to a mechanic at a Polaris dealer and he said bad needle / seat. I don't agree. That would require MORE air to run properly, not LESS (the effect of covering the carb). Also, covering the carb should still cause it to stall.
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Old 01-18-2013, 04:46 PM   #6 (permalink)
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Did you run wire down each and every jet?
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Old 01-18-2013, 04:54 PM   #7 (permalink)
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Yes. That side of the motor is much colder too.
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Old 01-19-2013, 07:08 AM   #8 (permalink)
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If that side is cold, did you check compression on that side? And spark? Just to eliminate the easy stuff. Spray a little 2 stroke mix into the cold side and see if it runs differently.
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Old 01-19-2013, 07:36 AM   #9 (permalink)
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I checked compression, but the motor was warm (so the reading wasn't accurate). Both cylinders read out at about 138 (way too high for that motor, but they were both the same).

The cylinder seems to fire and the motor will run very strong when I restrict air flow to that cylinder by covering the carb. The plugs look about the same after running 30 seconds or so like that.

I have to pick up an in-line spark tester, though, so I can verify that as well.
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Old 01-19-2013, 07:38 AM   #10 (permalink)
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Bad Crank Seal?

Slide Height is the term I was looking for!! Thanks meburdik!! Where does one find such info? I didnt see it on the sticker underneath the hood...


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Old 01-19-2013, 07:56 AM   #11 (permalink)
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Quote:
Originally Posted by ringneckryan View Post
Slide Height is the term I was looking for!! Thanks meburdik!! Where does one find such info? I didnt see it on the sticker underneath the hood...
That's part of syncing carbs... Check the stickies section for info on cleaning and such.
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Old 01-19-2013, 10:07 AM   #12 (permalink)
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Have you checked the piston skirts for damage? A piston with a bad skirt would still give compression but may have issues being able to pull the air/fuel through the crankcase...
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Old 01-19-2013, 04:32 PM   #13 (permalink)
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I haven't yet. It will be a couple of days still before I can get my hands on the sled again... I plan to swap the carbs and check the intake side of the skirts. I'm not sure if I'll be able to get the Y-pipe off to check the exhaust side or not.

I'm also going to do a cold-motor compression test.
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