What causes this type of piston and cyl damage? - ArcticChat.com - Arctic Cat Forum
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post #1 of 15 Old 02-25-2016, 09:56 AM Thread Starter
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What causes this type of piston and cyl damage?

My 2003 ZR900 broke the piston and wore the exhaust port on the mag cylinder. This is to the point where the ring goes out when it is in the port and back in at the top and bottom. I am guessing the ring finally caught the exaust valve. The PTO side piston is also worn enough that I could rattle the piston in the bore with my fingers. This happened about 300 miles after replacing the cracked intake boots and the crank seals. The motor was running better than ever and it wasn't till I pushed it hard that it made a blip sound and lost power. I managed to ride it home about a half mile on 1 cyl. Looking at photos of piston failures I dont see one that matches. I am going to assume that it ran lean for quite some time and once it was together the top was next to fail. I have new jugs, pistons and gaskets on the way. Another thing I found strange was after selaing the motor back up, I had 135 and 138lb compression, and after the mag side dropped, the PTO side was 150 lb.

If its not that I ran it lean for along time, I am hoping someone can chime in about the root cause.

Thanks in advance!


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post #2 of 15 Old 02-25-2016, 11:00 AM
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Is this the original motor?
How many miles?
What's the rest of the piston look like (piston skirts other ring lands?)

You may also have junk (piston/ring pieces) down in your crankcase. How far are you planning on tearing the motor down?

If the engine is all original with mileage over 5-6000 it might just be metal fatigue.
When the piston/skirts wear and create too large a piston - cylinder wall clearance they slap around a lot and start breaking things.

These large bore 2 strokes are very hard on pistons - the old triples pistons last a lot longer due to the smaller diameter.
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post #3 of 15 Old 02-25-2016, 11:10 AM
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Snagged a ring is my guess. Probs spun and caught it on the port

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post #4 of 15 Old 02-25-2016, 08:20 PM
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Picture shows NO SIGNS of valve contact (only a spot on valve being "apparently" from piece of chunked piston)...

Very little actual piston wash, instead, more "washing" going on right at transfer port bridge areas of piston dome... When this shows, usually from bridge building heat and making carbon (from unburnt incoming mixture due to low compression) recede... Chances are jetting was kind of lean prior to failure, but, the unburnt sooting afterwards masked this..

However, I have to agree with poster who mention piston skirt fatigue.. With the way these Cat twins of 650cc and larger displacement shook, I'd have to say piston had danced around for a while and weakened top of dome right above ring land...
Add slight detonation from leaner mixtures and usually the top of ring land suffers on these bigger bore twins (right out of 1992 performance manual referring to the 650-700cc machines of back then)... These 800/900cc engines were no different....

I'm suspecting the leaner fuel mixture didn't cause major damage overall due to massive BLOWBY that I'm sure will show once pics of complete piston skirts are shown....

Pull complete engine apart and clean good, inspect for cracks in crank cases just in case... Have the crank checked by reputable source for run-out (trueness.. .002" is max allowable), and don't use rtv sealers, get a tube of Three-Bond 1204 case sealant for reassembly (use new crank seals also)

Who, me?! Don't listen to me.... (I don't know anything, evidently...)

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0637-186: '99 Sno-Pro APV superseded valve inserts update kit p/n...
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post #5 of 15 Old 02-26-2016, 07:44 AM
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Quote:
Originally Posted by C-note View Post
Picture shows NO SIGNS of valve contact (only a spot on valve being "apparently" from piece of chunked piston)...

Very little actual piston wash, instead, more "washing" going on right at transfer port bridge areas of piston dome... When this shows, usually from bridge building heat and making carbon (from unburnt incoming mixture due to low compression) recede... Chances are jetting was kind of lean prior to failure, but, the unburnt sooting afterwards masked this..

However, I have to agree with poster who mention piston skirt fatigue.. With the way these Cat twins of 650cc and larger displacement shook, I'd have to say piston had danced around for a while and weakened top of dome right above ring land...
Add slight detonation from leaner mixtures and usually the top of ring land suffers on these bigger bore twins (right out of 1992 performance manual referring to the 650-700cc machines of back then)... These 800/900cc engines were no different....

I'm suspecting the leaner fuel mixture didn't cause major damage overall due to massive BLOWBY that I'm sure will show once pics of complete piston skirts are shown....

Pull complete engine apart and clean good, inspect for cracks in crank cases just in case... Have the crank checked by reputable source for run-out (trueness.. .002" is max allowable), and don't use rtv sealers, get a tube of Three-Bond 1204 case sealant for reassembly (use new crank seals also)
Went to ThreeBond web site and they don't list 1204? Are what you're suggesting a different part number?
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post #6 of 15 Old 02-26-2016, 08:01 AM
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I have used LocTite Anaerobic sealer as well as Threebond. The Anaerobic sealer is just about the only thing you use on Outboard motors. I just did a rebuild on a sled that did nearly the exact same thing. You would be surprised, there was nicks and dings all over in the crankcase on that cylinder that I had to clean up, and the little fragments had chewed up the crank seal on that side. Don't be afraid of the job, its really not all that bad.
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post #7 of 15 Old 02-27-2016, 10:20 AM
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It does look like something physical happened, IE not a lean burn down or something along that lines. Very possible you either had a bad piston, (did you not just put them in??), or a ring rotated and got caught on the port. I presume you are replacing that cylnder now also, so if both cyl and piston are being replaced, and you have no air leaks thru the seals (are you sure??), then I would have to gander that the problem, should be solved....and happy sledding is in your near future.........should mother nature say so.
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post #8 of 15 Old 02-27-2016, 03:43 PM
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Quote:
Originally Posted by twinrats View Post
Went to ThreeBond web site and they don't list 1204? Are what you're suggesting a different part number?
I gotta be honest and say that I'm not 100% certain anymore.. They've changed the number (and contents) so many times to comply with federal regulations, that I've lost track of which number it was last known as...

Who, me?! Don't listen to me.... (I don't know anything, evidently...)

Quote:
If it's cnote approved it will work good
Quote:
Originally Posted by DonoBBD View Post
That is freeking sick man........
Don
0637-185: '99 Sno-Pro APV (guide and button) update kit p/n...
0637-186: '99 Sno-Pro APV superseded valve inserts update kit p/n...
https://www.arcticchat.com/forum/z-z...tml?highlight=

http://www.randakksblog.com/more-on-...fear-the-corn/

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post #9 of 15 Old 02-27-2016, 03:52 PM
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Quote:
Originally Posted by UBHSTRY View Post
Very possible you either had a bad piston, (did you not just put them in??), or a ring rotated and got caught on the port.
He replaced cracked intake boots and the crank seals...

A rotated ring end that winds up snagging in exhaust port will do a lot more damage than what the pic shows, especially in such a large bore with such a wide exhaust port width.. Heck, it'd remove pretty much the front 1/4 radius of dome, (not just a patch as small as that shown in picture...), plus, the ring end would be shown (all mangled and bent)

Who, me?! Don't listen to me.... (I don't know anything, evidently...)

Quote:
If it's cnote approved it will work good
Quote:
Originally Posted by DonoBBD View Post
That is freeking sick man........
Don
0637-185: '99 Sno-Pro APV (guide and button) update kit p/n...
0637-186: '99 Sno-Pro APV superseded valve inserts update kit p/n...
https://www.arcticchat.com/forum/z-z...tml?highlight=

http://www.randakksblog.com/more-on-...fear-the-corn/

"Arctic Chat is not affiliated with Arctic Cat Inc. in any way, shape or form. We are an enthusiast site run by fans."

(Are you experiencing issues with your local dealer? Feel free to call Cat Consumer Complaint @ 218-681-8558)
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post #10 of 15 Old 02-28-2016, 03:15 PM
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Kinda looks too lean, but maybe seized due to overheating. Do you have picture of sides and bottom of piston? That may help. Was coolant level low? Does the tip of power valve show signs of contact? {shiny spots}

Andrew
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