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Old 03-11-2008, 01:47 PM   #1 (permalink)
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Piston Damage

Hey guys,

Sorry to post this on a SKi-Doo forum, but the help here is always really great... I just bought a sea doo with a 657cc engine with no compression on one cylinder. I popped the head off, and the mag piston has chips out of the corners, and the dome has been damaged too. Is this a foreign particle for sure? Could something from the crank have come loose and come up and caused this? Or is this something that can happen from bad gas? I'm pretty sure this thing has piston sleeves in it, and they do not look damaged at all. It rotates freely and is not seized at all.

Thanks for any help!
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Old 03-11-2008, 05:42 PM   #2 (permalink)
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How does the spark plug color look?
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Old 03-12-2008, 07:34 AM   #3 (permalink)
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Broken ring cause the problem?
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Old 03-12-2008, 10:17 AM   #4 (permalink)
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Turns out that it was a broken ring. I was going to do a complete teardown anyway, so I will probably find pieces of the ring in the crankcase right?
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Old 03-12-2008, 03:48 PM   #5 (permalink)
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Maybe, sometimes all the pieces go out the exhaust port.
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Old 03-27-2008, 07:03 PM   #6 (permalink)
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Hey everyone. I accidentally broke off a tiny piece of the block on the left intake port here. Two sea doo guys think the engine should be ok. Any opinions? There is nothing getting in the way of any bearings, rods, pistons, rotary valve, etc. Just maybe a bit of a fuel flow issue?
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Old 03-27-2008, 07:25 PM   #7 (permalink)
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I think you hit it right with the fue flow issue, you'll notice it. Can you JB Weld it back on?
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Old 03-27-2008, 07:49 PM   #8 (permalink)
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That's what I thought SEG

Do you think that can be JB welded? I have the pieces but they are very very small. Could they be tig welded or is that just too precise?
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Old 03-27-2008, 09:11 PM   #9 (permalink)
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Quote:
Originally Posted by Goldeneyes
Hey everyone. I accidentally broke off a tiny piece of the block on the left intake port here. Two sea doo guys think the engine should be ok. Any opinions? There is nothing getting in the way of any bearings, rods, pistons, rotary valve, etc. Just maybe a bit of a fuel flow issue?
I say you won't notice a thing- run it. But I have to know how you did that.
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Old 03-27-2008, 10:09 PM   #10 (permalink)
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My concern is that the piece that broke off has a taper on it that looks like it might direct fuel in a specific direction.

SO here it is guys.... I had the head/pistons off so I couldn't put a rope in a cylinder to hold the flywheel. So... My buddy thought that wrapping a big johnson bar in a rag and stuffing it into the open side of the crank might work. Well, indeed this would have worked with a steel block.. not with aluminum!

Yes. I'm an idiot.

If I JB weld this properly, will it hold??
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Old 03-27-2008, 10:23 PM   #11 (permalink)
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Quote:
Originally Posted by Goldeneyes
My concern is that the piece that broke off has a taper on it that looks like it might direct fuel in a specific direction.

SO here it is guys.... I had the head/pistons off so I couldn't put a rope in a cylinder to hold the flywheel. So... My buddy thought that wrapping a big johnson bar in a rag and stuffing it into the open side of the crank might work. Well, indeed this would have worked with a steel block.. not with aluminum!

Yes. I'm an idiot.

If I JB weld this properly, will it hold??
It doesn't matter what "direction' the fuel is directed to at this point in the engine- when the rotary valve opens, atmospheric pressure fills the crankcase with the fuel-air mixture. This fuel-air charge does not have to be directed to any specific place in there, it just has to fill the void created when the piston is going up in the bore. Do not attempt to J-B weld the piece or pieces back on- that's courting disaster, they could break off and damage the engine further. Just put the engine back together as is and you will have no problems, it will run fine (assuming you put it together right). This is NOT a space shuttle.
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Old 03-27-2008, 11:16 PM   #12 (permalink)
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This is NOT a space shuttle
Words of a wise man. I had to laugh as it remind me of my younger days and an old carpenter that said "this ain't no piano were building".
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Old 03-28-2008, 07:11 AM   #13 (permalink)
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Wouldn't you at least smooth out the break a little to help flow?
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Old 03-29-2008, 09:36 AM   #14 (permalink)
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I found a top half off of ebay.. If that falls through I will just smooth it.

Ok what's everyone's opinion on this:

How can I steady this crank enough to get the flywheel and the flywheel nut off? My jugs are off already and I don't want to snap another crank half. I also need to get the PTO off, which is a circular balancer on the take off side of the engine.

Also, I found a wiseco piston kit for $214 including all top end gaskets. Should I go for it? Everything else seems so much more expensive, except the WSM's which I believe are Chinese made and have lots of bad reviews throughout the internet

Thanks for any help!
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Old 03-29-2008, 12:08 PM   #15 (permalink)
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Quote:
Originally Posted by Goldeneyes
I found a top half off of ebay.. If that falls through I will just smooth it.

Ok what's everyone's opinion on this:

How can I steady this crank enough to get the flywheel and the flywheel nut off? My jugs are off already and I don't want to snap another crank half. I also need to get the PTO off, which is a circular balancer on the take off side of the engine.

Also, I found a wiseco piston kit for $214 including all top end gaskets. Should I go for it? Everything else seems so much more expensive, except the WSM's which I believe are Chinese made and have lots of bad reviews throughout the internet

Thanks for any help!
Rotax crankcase halves should not be mixed and matched, they are machined together at the factory as are all snowmobile engine crankcases. You may not get good bearing "crush" when using two case halves from different motors. Also the rotary valve faces may not line up flush when assembled. Use the case you have, it will be fine.
Use an impact wrench to remove the flywheel nut and a harmonic balancer puller to remove the flywheel. DO NOT screw the puller bolts in too far, you will damage the stator.
You will need the splined removal tool and an impact wrench to spin the balancer off the crank as well as a lot heat applied to the balancer to help remove it.
$214 is $5 over actual dealer cost for the Wiseco kit. I can't come close to that price.
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Old 03-29-2008, 06:00 PM   #16 (permalink)
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Agh! I was taking off the flywheel with a puller and didn't have much luck. So, my buddy was looking at the flywheel side as I was spinning the crank (using the rods in my hand) and it looks like the crank is out of round.

Hopefully SBT will still take it. Yowwza.
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Old 03-30-2008, 07:41 AM   #17 (permalink)
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It's getting to the point where a used motor will be more cost effective....
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