After much bickering I can have them made at $239.99 in the OEM 89mm bore. I will proceed with this asap.
390 engine connecting rod
- Thread starter kostean
- Start date
@Superpacman13. Super good to hear!
Are there any other specific spec changes considered now with the piston design besides the single ring setup, eg higher compression ratio achieved? Just wondering that to know if these pistons could be used in combination with slim head gaskets or even then with high lift cams (though no plans to have one).
Also about making of these, will you want to have a repurchase made or will just let to be created and create some stock to sell from?
I am having 8 made initially on my dime, we will see how they do. They are single ring, stock compression ratio and fully boxed unlike the stock piston.
Raising this topics a bit. Superpacman13 can maybe comment on the progress with JE pistons what I at least have already pre-ordered from GreyArea store 
What concerns the rod bolts- I am becoming increasingly worried about the fact that also these could be a potential risk for having a sudden complete engine destructing event to take place. Especially on engines used at the race track and subjected to high rpm most of the time. There seem to be a number of documented cases on 390 engine rod bolt failures and I know at least one case where relatively new engine got destroyed at the track because of a "rod failure" (that was all I heard after).
Superpacman13 as you commented having experience with 2 of these bolt failures alrady- do the bolts themselves seem to be the reason for the failure, or do you suspect some other element causing them to break?
While thinking one way to mitigate the risk of such rod bolt failure would also to replace the conrod with aftermarket one- I am questioning though, would that combo (JE piston, Carillo conrod) would throw the engine out of balance when aftermarket components are probably considerably lighter then OEM ones?
What concerns the rod bolts- I am becoming increasingly worried about the fact that also these could be a potential risk for having a sudden complete engine destructing event to take place. Especially on engines used at the race track and subjected to high rpm most of the time. There seem to be a number of documented cases on 390 engine rod bolt failures and I know at least one case where relatively new engine got destroyed at the track because of a "rod failure" (that was all I heard after).
Superpacman13 as you commented having experience with 2 of these bolt failures alrady- do the bolts themselves seem to be the reason for the failure, or do you suspect some other element causing them to break?
While thinking one way to mitigate the risk of such rod bolt failure would also to replace the conrod with aftermarket one- I am questioning though, would that combo (JE piston, Carillo conrod) would throw the engine out of balance when aftermarket components are probably considerably lighter then OEM ones?
When and if the bolts fail what is left is not enough to be able to determine what caused the failure. Also I would not be concerned about primary balance as the bike already vibrates a fair bit and that's only going to increase which isn't the end of the world. If you wanted to fix it then you could send the entire crank assembly to crank works in AZ to get balanced.
KTMasean
Member
Hi picto,
I'd be interested in a technical drawing of the OEM piston rod if you have this.
Hi,how is the kit going on
All my pistons were JE std and over bore. The plus 3mm works fine, plenty of cylinder wall left. Carrillo rods work well of course. Did several of them.
I wanna buy that,Chad
Fangfactor
Member
I just had a rod on a 2015 model stretch. The small end hole elongated around 5 thou causing excessive piston side wobble. Caught it in time as the engine had a knocking sound at idle which I thought might be the clutch as it seemed to go as the revs increased.
KTM must have known of the issue as they changed the design of the oil gallery above the small end from a long slot on top to just two holes which strengthens that area on the later models
KTM must have known of the issue as they changed the design of the oil gallery above the small end from a long slot on top to just two holes which strengthens that area on the later models
I race a 390 here in Canada. Over the winter we built the motor with the fire ring, new piston, gaskets, valves, etc. Well, it just blew on me. The connecting rod bolts let go! Just as you describe. Every part inside the motor is toast……Raising this topics a bit. Superpacman13 can maybe comment on the progress with JE pistons what I at least have already pre-ordered from GreyArea store
What concerns the rod bolts- I am becoming increasingly worried about the fact that also these could be a potential risk for having a sudden complete engine destructing event to take place. Especially on engines used at the race track and subjected to high rpm most of the time. There seem to be a number of documented cases on 390 engine rod bolt failures and I know at least one case where relatively new engine got destroyed at the track because of a "rod failure" (that was all I heard after).
Superpacman13 as you commented having experience with 2 of these bolt failures alrady- do the bolts themselves seem to be the reason for the failure, or do you suspect some other element causing them to break?
While thinking one way to mitigate the risk of such rod bolt failure would also to replace the conrod with aftermarket one- I am questioning though, would that combo (JE piston, Carillo conrod) would throw the engine out of balance when aftermarket components are probably considerably lighter then OEM ones?
