2013 ktm 450 sxf piston questions

[raleigh111]

Time for rebuild, 2 piston sizes listed from ktm but my cylinder has a number 3 on it? It is a dedicated snow bike that is ridden at elevation so was thinking of going high compression piston, what are options. Any big bore experience out there?

 

[M5-]

You have a few options. Ideally you will need to measure the cylinder. How many hours on it? If it's still in round then you may be able to get away with a light hone and a stock piston but it will likely end up on the outer limit of the ring gap spec after the hone. There isn't much Nikasil to work with. The guy I use for honing wont even touch my cylinder until he has my new piston in hand which allows me to go stock. He also does Nikasil plating so he re-plates the cylinder then hones it to the spec of the new piston. Its perfect. That's the best method. All of my KTM big bores blew up. Each time the con rod bearings eventually failed. I'm sure everyone will chime in and say it's the best thing since sliced bread, each to their own. I now go the cams and porting route if I even bother at all. As far as I'm concerned stock rocks.

M5

 

[raleigh111]

You have a few options. Ideally you will need to measure the cylinder. How many hours on it? If it's still in round then you may be able to get away with a light hone and a stock piston but it will likely end up on the outer limit of the ring gap spec after the hone. There isn't much Nikasil to work with. The guy I use for honing wont even touch my cylinder until he has my new piston in hand which allows me to go stock. He also does Nikasil plating so he re-plates the cylinder then hones it to the spec of the new piston. Its perfect. That's the best method. All of my KTM big bores blew up. Each time the con rod bearings eventually failed. I'm sure everyone will chime in and say it's the best thing since sliced bread, each to their own. I now go the cams and porting route if I even bother at all. As far as I'm concerned stock rocks.

M5

M5 Thanks much appreciate your response. I am heading over this am to buddy house who is machinist so he has all the right tools to measure bore. I see vertex has 3 pistons a b c in 12.6 13.2 and 13.5 compression. I only ride above 6000 ft really so don’t see how 13.5 could hurt me at all or effect dependability on good pump gas..just not sure on forg vs cast ? Anyway I kinda go along the lines of thinking on these Nic cylinders the Indy dan way. Wait and see how it measures before I do anything with that. You have any experience with Ecu on these 13-15 bikes? Good or bad. Thanks for sharing your big bore experience! Hours on bike are over 100 for sure. Can you share the guy you use to do your plating if you are happy with him?
Robert Z

 

[eric82930]

I would do high compression for sure. if you are rebuilding anyway It's free horsepower with no down side at high elevation.
Forged pistons swell more than cast so they have to be smaller when they are cold. (They fit very loose like a cr250) But the mfg process makes the metal stronger and less prone to cracks.
I always thought cast would be better in the snow because of the chance of wild coolant temp fluctuations but in practice forged pistons have worked just fine for me for many many builds.
No on the big bore. Do cams porting and ecu on the dyno. between 13 and 21 the factory gained almost 5hp

 

[raleigh111]

Bore is 3.7415 and 3.741 old piston (worn some was 3.737 . Going to order high compression forged piston from vertex 3.7389 13.5-1 unless someone has better idea? Who to reccomend for Ecu ? Anything left in the head and cams? Not sure I want to spend thousands for 4-5 Hp??

 

[CB_Rob]

Raleigh,
I'm looking at the 450 SFX older bikes, do you consider 2013 to ve a good year to build in?
When shopping around for KTM s how far back can i go and get a good builder base?