2 stroke big end failing

[Crasherfromwayback]

I have heard comments that powervalve gets all gooed up with too much oil in mix. But have not seen this myself.

Not with such clean buring oils we have now in my experience.

[SS90]

I have no experience with this model of KTM, but I have seen plenty of aftermarket rod manufacturers in the last 10 years move production to "cheaper" nations, resulting in lower quality everything.

I have never used hot rod since Steve Ward had one (with about 20 minutes racing) act like a sythe through the cases, destroying cases, cylinder and pretty much everything else.

Experience with two stroke engines suggests to me that low hours such as you have, that the problem is with either the pin hardening, or the bearing (or both)
Pictures would be ideal.

I have seen far too many manufacturers produce faulty pins (and offer nothing for your hassle other than another (faulty) pin.)

What do the shims look like?

This will give a clue.

[DEATH_INC.]

Yeah roller bearing cranks don't actually like being revved super hard despite what peeps think about two strokes! And I always run my smokers at 32:1 regardless of the oil being used. Never lost a big end in many years/bikes.

Funny eh, the smokers really don't rev that hard, they just sound like it....
I'll admit to being jumpy about running such low oil-fuel mixes ( I grew up, like crasher, when 25:1 was considered thin!), but a long time ago someone convinced me to do it in my last mx bike ('85KTM), running either 50:1 bel-ray or 60:1 silkolene and with a bit of rejetting it really made a huge difference to both power and response. Never had any reliability/wear issues either, and everything was always plenty oily enough when I pulled it down to check things. Ran a grey pipe even! I wouldn't hesitate now...

[Conquiztador]

I have no experience with this model of KTM, but I have seen plenty of aftermarket rod manufacturers in the last 10 years move production to "cheaper" nations, resulting in lower quality everything.

I have never used hot rod since Steve Ward had one (with about 20 minutes racing) act like a sythe through the cases, destroying cases, cylinder and pretty much everything else.

Experience with two stroke engines suggests to me that low hours such as you have, that the problem is with either the pin hardening, or the bearing (or both)
Pictures would be ideal.

I have seen far too many manufacturers produce faulty pins (and offer nothing for your hassle other than another (faulty) pin.)

What do the shims look like?

This will give a clue.

Cheers. Yep, I am also allergic to the quality coming from "cheaper" country manufacturers. Will provide pictures when I split the cases and get the crank out.

[Conquiztador]

Funny eh, the smokers really don't rev that hard, they just sound like it....
I'll admit to being jumpy about running such low oil-fuel mixes ( I grew up, like crasher, when 25:1 was considered thin!), but a long time ago someone convinced me to do it in my last mx bike ('85KTM), running either 50:1 bel-ray or 60:1 silkolene and with a bit of rejetting it really made a huge difference to both power and response. Never had any reliability/wear issues either, and everything was always plenty oily enough when I pulled it down to check things. Ran a grey pipe even! I wouldn't hesitate now...

And that is one of the considerations here. Using less oil in the mix will give better performance and response. But will we risk failure as a result? A fine balance act me recons.

[DEATH_INC.]

And that is one of the considerations here. Using less oil in the mix will give better performance and response. But will we risk failure as a result? A fine balance act me recons.

Yep, that's smokers for ya. Most of the better oil manufacturers will tell you what mixtures they recommend, they know their stuff, they do a hell of a lot of r&d before they sell the stuff. As a side note...some of the outboards run 100:1

[Conquiztador]

Wrote an email to Mark Patterson yesterday and got the reply today:


hi pete,there have been some crank issues over the years with these motors,the 2013 85sx has a different crank with a smaller crankpin that rotates at a slower speed.i have checked with australia and this complete crank can be retrofitted to your engine(that would be my recommendation).our 85sx up here we run 118-120 main jet,needle one clip up from middle(same as yours) air screw 1.5 turn out 40:1 fuel mix,regards >
Mark Patterson >
Co-Director/Suspension


So looks like my settings are fine. Now have changed that order to a 2013 crank and conrod assembly and let's hope that it is the solution!!

[Crasherfromwayback]

2013 85sx has a different crankwith a smaller crankpin that rotates at a slower speed.]

So was kinda over revving in a round about way.

[SMOKEU]

As a side note...some of the outboards run 100:1

Apparently that's only recommended by the engine manufacturers because it's an easy way to get past the emissions regulations without redesigning the whole engine or adding EFI.

[Conquiztador]

So was kinda over revving in a round about way.

Yep. And there is apperently some more minor changes ( "Extra shrouding on the crank webs" ) to boost performance also.

So with the new crank/conrod combination I should have a 2009 KTM 85cc that has a crank that will last the 50h before I rebuild it, and also have some added performane compared to other ones from before 2013. So all good!

And as mentioned, my setup is what the KTM shop is using when setting up their bikes, so I feel confident that I will have this sussed. Even the 40:1 mix seems to be right!

[Crasherfromwayback]

Yep. And there is apperently some more minor changes ( "Extra shrouding on the crank webs" ) to boost performance also.

So with the new crank/conrod combination I should have a 2009 KTM 85cc that has a crank that will last the 50h before I rebuild it, and also have some added performane compared to other ones from before 2013. So all good!

And as mentioned, my setup is what the KTM shop is using when setting up their bikes, so I feel confident that I will have this sussed. Even the 40:1 mix seems to be right!

Way to go! Roost on!!!