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Male WalkingWounded
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Question About KTM 350 Top End Reply to this Post

My 17 KTM 350 has 163 hours. The fork seals survived for 100 hours. The chain slider, guide and protector made it to 162 hours. The rest of the bike is original other than tires, chain, and sprockets.

My top end is original too. Compression is still good, and it lites off well in cold weather too, but my fear is fatigue of the piston. I want to replace before it makes me step through the bars on a jump, and makes a mess of me and the engine.

I want ot use an O.E. piston, and not sure where to purchase one. I've heard that the piston is not made by KTM, but either Namura, Wiseco, Wossner, ProX, Vertex, JE, Mahle or some other brand.


I'm wondering if the piston made by "company A" for KTM, is the same one that would that "company A" would send to an Mx store for a KTM, or, are they more precise with the ones that go to the plant/factory?
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Monty 14 KTM250SX's 2017 KTM350SX-F #045 - A Lot Of Pit Bikes, And Added Another One
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Male rick61
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Re: Question About KTM 350 Top End Reply to this Post

Buy the piston that comes with the coolest sticker...
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Male WalkingWounded
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Re: Question About KTM 350 Top End Reply to this Post

I am a sticker hound, so that may be plausible.

I don't have a problem with an aftermarket piston, as long as it is as dependable and as durable as what came in my bike.
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Monty 14 KTM250SX's 2017 KTM350SX-F #045 - A Lot Of Pit Bikes, And Added Another One
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Male rick61
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Re: Question About KTM 350 Top End Reply to this Post

Which ever you decide, get a fresh bore.. cant hurt.
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Gatorade,Advil & Cosmic Brownies.

75 360 Pursang
79 YZ 125
79 YZ 250
84 YZ 125
86 YZ 490
81 RM 250
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Male Bigmaico
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Re: Question About KTM 350 Top End Reply to this Post

Monty

If I Remember right your KTM uses a Vertex piston.

But your best bet would be to get a Oem piston, as KTM May have Vertex produce the piston to their own specifications.

.then all you need to do is check the bore to make sure that?s its true & has no ridges in it.
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Male WalkingWounded
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Re: Question About KTM 350 Top End Reply to this Post

Yes, that was my thought, that whoever makes it for KTM, may not make it as precise for the aftermarket vendor world.

I'll call Munn for all the parts just to be sure.
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Monty 14 KTM250SX's 2017 KTM350SX-F #045 - A Lot Of Pit Bikes, And Added Another One
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Male bclick
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Re: Question About KTM 350 Top End Reply to this Post

they make a kit with piston, jug and all gaskets thats under 500 bucks,,,never hurts to clean up valves if you are down to that point,,,i had over 200 hrs on my 14 350 and did a top end but it looked really good ,,never a bad thing to fix it before it breaks,,,
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Male WalkingWounded
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Re: Question About KTM 350 Top End Reply to this Post

Well, at 175 hours I decided to go ahead and do the top end. Although there are others out there with 400+ hours and still all original, I needed to know. I tore it down, and it was new and needed nothing. But of course I'm still going to do the top end anyway while it is apart. I went with all new parts from KTM. Along with the new top end, I also replaced the tensioner too. The cylinder had no wear, and still had the crosshatch honing marks. The piston skirts and ring lands had no wear, and the big rod end side clearance was on the tighter side of the new range clearance. The big end of the rod is exceptionally wide too. My valve clearance was at 3 and 7, but I set them at 4 and 6.

The engine is a European Formula 1 master piece. The piston is forged, very short, and heavier than most. My fear was one of the skirts breaking off, but each skirt has 2 walls/braces from the pin boss area, out to each skirt. The piston has 1 very thin compression ring, and 1 thin, fragile 3 piece oil scraper ring, but apparently it works. There are oilers spraying at cams and the bottom of the piston. There are no lifters/followers like the Japanese bikes. There are half rockers on a shaft with the cam pushing directly on top of the rocker. The valve shims sit directly on top of the retainer. There is no roller bearings in the wrist pin, just a bronze bushing which also had no wear. The wrist pin keepers are the diameter of rebar and stiff. The are shaped like a 'C', but at one end of them there is a 90 degree turn that goes into a hole in the piston clip groove. I suppose it is to keep them from rotating, and keeping the gap at 12 o'clock. At high rpm, and with the gap being at 3 or 9 o'clock, I reckon they could close up and come out. The 90 degree turn also helps hold them in place while installing them too. The cam timing marks are very obvious and visible. Right below the water pump is an allen bolt that is tapered on the end, with a very thick copper washer. Remove the bolt, remove the thick copper washer from the bolt. Look in the hole and slowly rotate the motor until you see a 'V' notch in the gear. Take the allen bolt and run it into the hole until it wedges into the 'V', and that holds the crank on TDC. But just hand tight is enough, don't over tighten it. You can rock the crank back and forth to make sure you are wedged in the 'V' to be sure.

I lite it off this past Wednesday with the new tensioner released and awaiting oil pressure to pump it up. It rattled for a second or two and got quite. Took it to 3 Palms this past weekend, and run it through 3 lower and varying rpm heat cycles, and then on the 4th moto out, I lite it up. It performed well, but really no better than before the rebuild. I will continue to ride/race it in power mode 1 and traction control turned on. The 350 pulls fairly hard, although not the torque of a 450, but what it does do, is accelerate/explode very quickly, and doesn't sign off until about 14.5. I think the reason it explodes so quickly, is the short connecting rod. It breaks over center very fast.

I also installed and new set of Warp 9 wheel assemblies too. @ 175 hours, my wheels were tired, but still functioning. I beat them pretty hard on the Main and GP tracks square edges and pot holes. So far the spokes have not loosened, but will keep an eye on them just like any wheels.

I don't like the color orange that much, and I would not ever own a European car, but I love my durable KTM.
----------------------------------------
There are no easy answers, but there are simple answers.

http://houstonmotocross.com/theforum/viewthread?thread=33552&offset=0

http://houstonmotocross.com/theforum/viewthread?thread=44047

Monty 14 KTM250SX's 2017 KTM350SX-F #045 - A Lot Of Pit Bikes, And Added Another One
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