2017 ktm 250 sx top end re build

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1/4/2018 7:13 AM

Now that it is the off season I am going to be rebuilding by top end. I got roughly 50 hours on the bike now. Right now I am running a 40% mix of 110 and pump. Am I better off sticking with a stock piston? if so which one (the oem parts list show two different options)? Or should I look into a high compression piston or a aftermarket stock like piston?

Thanks in advance

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1/4/2018 7:27 AM
Edited Date/Time: 1/4/2018 7:29 AM

Vertex is the OEM in KTM, thats what i always put back in mine.

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1/4/2018 7:36 AM

navalseabee wrote:

Vertex is the OEM in KTM, thats what i always put back in mine.

X2. I have used Vertex in a couple different 125s, very good piston.

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1/4/2018 7:40 AM

Goulding wrote:

Now that it is the off season I am going to be rebuilding by top end. I got roughly 50 hours on the bike now. Right now I am running a 40% mix of 110 and pump. Am I better off sticking with a stock piston? if so which one (the oem parts list show two different options)? Or should I look into a high compression piston or a aftermarket stock like piston?

Thanks in advance

KTM's come with vertex as the OEM piston, so if you look at the top of the piston, it should say a letter, such as A, B, C, or D. I believe B is the stock sized piston. If the bike is that new, I would just order the same exact piston size, the B.

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1/4/2018 7:45 AM

not familiar with KTMs stock stuff but 99% of the time going with a wiseco, je, or cp forged piston is an upgrade & will allow for more hours on the top end. Get away from cast ones if thats what you have.

Also do they make high comp pistons for 2 strokes? Cant say ive ever seen one...

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2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

1/4/2018 8:41 AM

If you are happy to change pistons at 50 hour intervals then stick with cast. They run a lot quieter and don't require as much of a thorough warm up as a forged piston. Vertex is a solid choice.

You will want to take a squish band measurement before you start playing around with compression. Getting the head or base of barrel cut is the best way of increasing compression. Alternatively you can purchase different thickness base gaskets from Athena. This is a cheap and easy way to experiment with different squish measurements.

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@russ_69

1/4/2018 9:53 AM
Edited Date/Time: 1/4/2018 9:56 AM

I used a vertex in my 15 xc300 when I did the top end, I had 100 hrs on it & was still running great. Measure your base gasket in a few spots,Ktm uses different base gasket thicknesses to achieve the proper measurements for piston to head clearance, What Ktm Calls " X" distance. If your happy with the way the bike runs, put Oem parts back in. Slavens racing makes wrist pin clips that are much easier to install compared to the stock vertex clips, the vertex clips are thick & tricky to install compared to most clips. I have no problems with wiseco Pistons, have used them in many of my bikes, but when I see a piston that has 100 hrs on it that was still within specs, I"m thinking its a good product.

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1/4/2018 1:46 PM

A vertex piston is what KTM uses. Also, there will be a I or II on the top of the piston (intake side usually) it's to tell you what size it is. The manual has spec at what the clearance tolerance should be. If your are good with your air filter and minimum scoring in the cylinder with 50hrs you should be able to stay with the size that came out, but measuring is always the best option It's also a double ring design, some guys put a single ring piston in and they definitely don't last as long. If you go stock your local dealer can get a complete top end kit, including gaskets, piston, o-rings basically everything you need to do the top end correctly. Sandman768 and RussB are both right, check your "x" height before installing. The gasket kit in the top end kit comes with different size base gasket so you can pair them up and and measure to get the correct height. If you want some more hit and you haven't touched your power valve adjustment screw try doing that before going into a hi-comp piston. Easier and quicker to turn a screw or change a little spring... Hope this helps!

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1/5/2018 2:57 AM

I would also say go with no lower than the .5mm base gasket and no higher than .6 the Ktm gasket kit comes with a bunch of gaskets. When you take your cylinder off and if it’s still stock there will be two base gaskets stacked on top of each other. I’ve always been a little frustrated by Ktm replacement parts as there is no references on any packaging that they send. Also a little grease on the bottom of the right side pv cover gasket will help it slide in place without tearing, either way you will fight that gasket. And don’t forget some paper towel in the hole when you re attach the clip for the pv linkage arm because if you drop it you’ll be taking the inner cutch cover off the fish it out, ask me how I know haha

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2/1/2018 4:41 PM

What does my piston tell you guys? Does it look like it’s running rich? Also where should I see the mark as to what piston I need?

Photo

Photo

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2/1/2018 6:13 PM

Piston burn looks good. The spark plug on the other hand says really rich. Do you ride moto or mostly woods?

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2018 KTM 250sx
Instagram CamaroAJ

2/2/2018 2:38 AM

AJ565 wrote:

Piston burn looks good. The spark plug on the other hand says really rich. Do you ride moto or mostly woods?

Moto but my last few rides of the year was woods.

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2/2/2018 11:39 AM

Also if the piston skirts look to be in good shape whats everyone's opinion on just re ringing?

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2/2/2018 11:49 AM

Goulding wrote:

Also if the piston skirts look to be in good shape whats everyone's opinion on just re ringing?

I never put only new rings on. Always a complete top end. I dont like the idea of it. Not saying you cant or anything, because tons of people do it. I like the peace of mind of having fresh shit.

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2/2/2018 1:14 PM

Goulding wrote:

Also if the piston skirts look to be in good shape whats everyone's opinion on just re ringing?

kb228 wrote:

I never put only new rings on. Always a complete top end. I dont like the idea of it. Not saying you cant or anything, because tons of people do it. I like the peace of mind of having fresh shit.

I can understand that mindset, if I have the money, I also just say screw it and do a complete top end kit instead of just piston ring, unless the piston is perfect and only has a few hours and not much wear at all. However if the bike has 50 hours of ride time, I'm guessing that also means 50 hours on that piston? If that's the case, there's no way I'd be putting just a piston ring on it and that's it.. Buying the whole kit is literally just like buying insurance for your motor. Just put in an entire kit.

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2/2/2018 10:27 PM

I'd do a complete top end rebuild with 50 hours on it. I've never re-ringed a piston. I like having the insurance of fresh product especially when it comes to the motor.

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2/2/2018 11:29 PM

Definitely change the piston if it has 50 hours on it. I do rings at 20-25 hours and pistons at 40-50 hours

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2/3/2018 8:36 AM

You need to be able to mic your piston and compare the bottom of the piston skirt to the top above the ring groove blah, blah, blah, to see how much taper you have in the piston. I don't have the tools or the skills and if i did, I wouldn't skip replacing the piston unless the wear was close to zero.

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The older I get, the faster I was.

2/4/2018 4:43 AM

All right every one thanks. Going to do a new piston. What’s every ones opinion on pro x Pistons?

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