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300 Cylinder damage

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Curious to see what you guys think caused this. The bike ran great I was just going to re-ring it to get it ready for next season when I found this. The previous owner did a top-end before I bought it; I put 3 races on it and a few trail rides. Sorry for the somewhat blurry pictures the camera had trouble focusing.

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The rings look fine, just wondering when this could have happened. I figure I will need a new piston and re-plate. Any advice on where to go for either?

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impossible to diagnose pics, but: does it line up with the ring gap? gouged into the plating? alum deposited on the nicasil? ring locating pin intact and not sticking out past the piston? was it the correct piston for the motor? good luck

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impossible to diagnose pics, but: does it line up with the ring gap? gouged into the plating? alum deposited on the nicasil? ring locating pin intact and not sticking out past the piston? was it the correct piston for the motor? good luck

The gouge lines up with the upper ring gap. The ring pins are both intact and not sticking out. The 2 rings show no abnormal wear near the pins. It makes me wonder if the damage was caused before this piston kit was put in.

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The ring gap looks to line up with the center of the rear bust port, both ring gaps should travel between the port windows on each side. Why I question the piston being correct. Any sign of the end of the rings marking the chamfer on the port window?

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The ring gap looks to line up with the center of the rear bust port, both ring gaps should travel between the port windows on each side. Why I question the piston being correct. Any sign of the end of the rings marking the chamfer on the port window?

The ring gaps line up with the rear intake port; the top ring gap lines up directly with the gouge in the cylinder, the lower ring gap is about 3 degrees off the upper ring gap.

From what I understand you are saying is the ring gaps should be off-set on both the left and right side of the rear intake port, between the side ports? That would place them a great distance apart from what I have here. The chamfer on the rear port does show markings from the upper ring gap. From the pictures you can see the wear mark by the rear port, this gouge is deeper then the line up the cylinder. The gouge also is present below the rear port, it is not as visible in the pictures. The picture of the piston is showing the ring gaps with blow by, they are not offset by much at all.

So I assume it is possible the piston is incorrect? I was planning to order a new piston and get a re-plate, I just do not want a repeat in the future. Where are the ring gaps typically located on a 2006 KTM 300? I searched the part number I found on top of the piston with no results at all.

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Ok the piston is a Wiseco part # 858M07200 for KTM 300 EXC/MXC 04-07, XC/XCW 06-09. So it is the correct piston I guess.

Edited by MotoX178

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Guessing they put the pins in the wrong location, seen all kinds of goof stuff from that company. PM one of their reps who posts on this site. They should give you a new piston.

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Like High said, the ring end gaps should never travel in the ports. Consider US Chrome, Millenium technology, or PowerSeal for replate service. PowerSeal offers vertex pistons (KTM OEM) which is what is recommended by most due to long service and reliability

I had poor luck the only time I used a Weisco piston in a Maico...no more Weisco for me

Cheers

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foreign matter in cylinder ie a hunk of something.

I don't think so, the gouge is in perfect line with the top ring gap. The width of the gouge matches the ring gap and the gouge stops right at TDC for the ring. I would expect to see marks on the piston or else where if some material was caught in there, but it could be possible.

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Maybe it happen to the guy you bought it from and he just threw it back together and sold it. Thats never happen before. Never liked a Wiseco in KTM very noisy piston rattle use a Vertex or Athenia anything but a Wiseco.

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I've run nothing but Weisco's in my KTMs for 15 years, never a single issue. there is nothing wrong with their pistons.

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I've run nothing but Weisco's in my KTMs for 15 years, never a single issue. there is nothing wrong with their pistons.

I rode one ride with a Wiseco and took it out. Put a stock one back in no rattle. Maybe I'm just fussy.

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Any forged piston is set up loose compaired to a stock cast piston.

It's cheaper for a factory to make cast in bulk and oppsite for an aftermarket. They forge it close and machine it out.

The forged one expands more with heat but is stronger. I run them from Wiseco, never had an issue.

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I read through the thread and unfortunately there isn't much I can tell without seeing a better photo of the piston/locating pins, or without having the piston to analyze. I will check the specs on the knock pin locations.

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the ring pin located dead center of the boost port is perfectly normal - and actually a better design IMHO, especially for making best power possible.

I usually see that type of damage when it is overheated some...or say it's cold outside and your putsing and then get on real hard - the piston expands much faster than the cylinder.

Also - ring gap could have been too tight - and ends fretted together..

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Is it physically damaged? Or just visually marked? That's common too - aka a light hone takes it right out...

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