Place yah bets! Whadda yah think caused this!??

[fabr]

When a 2 smoke is running it's very best is when it will happen  too! They LIKE being lean-for a bit anyway.

[Nutz4sand]

That is definately not a det. killed piston...
When they 1st started adding alcohol to all the gas We had alot of those, not burnt all the way thru but a bad spot on the exhaust side, running down to the ring...causing the drop in power...a couple of factors come into play here, the fuel is most likely the cause...when they add the alcohol, it takes 1.4X the fuel to keep the stroker happy, thus making it a tad lean on top...Not all 2 smoke oils are compatible with "oxygenated fuels"...In some cases I've seen this shit is up to 40% alcohol...It runs great at the lower rpms and throttle area's...But on top when things tend to get lean it leans way out and you get a melted edge,
Coulda just been a fluke... When was the last time the motor was gone thru ?

I could not tell you when this motor was gone thru last Spec. I got it used with little history. It LOOKS like I may be the first inside it. I think its the stock piston. Its a cast unit for sure.

Problem is my other machine (Scrambler 400) which started to loose a crank bearing (Polaris 400cc two smokes are famous for loosing the flywheel side bearing. Its due to how they HAVE to be put together it hurts the single bearing there. It gets stressed being pushed as the cases are assembled. Even freezing the bearing and heating the case (The clutch side has TWO bearings thank goodness)) That machine is doing the same thing to its piston. I can JUST see it starting to work the piston when I peek in the exhaust. I plan to pop the head back off and clean it up (when) if I can cure this problem. But I completely went thru that motor not that long ago.

Your talking about the alcohol content is something I have questioned before and told its not an issue. But apparently it is.

But I think Spec nailed my issue and what I suspected. I will be seeking much larger jets and or a better fuel source.

I am wondering if the fuel in my area is not extra cheesy. I buy 91 or 92 octane for my toys (93 when its at the station I am at) but My Honda Pilot tossed a couple pistons the same way. It was way built with way too high compression (170 to 200 PLUS PSI depending on which head and jug I ran. Long story. I got the parts reworked to 165 PSI max.) and I thought it was that high compression that screwed those pistons. I did better on $$$$ race gas but again I thought it was to much compression for the motor. As others told me it was not the gas I am getting today.   

I actually was starting to think that the oils I used were not liking the gas and breaking down even.  I tried a different brand that was alcohol compatible and it was a "little" better. But not much. 

So anyone know of a fuel company that still makes "normal" GAS. Not alcohgas?
Thanx for all the input! Bill 

[Admin]

I run yamalube, are you premixing or oil injecting?

[Nutz4sand]

Both machines are oil injected. The Scrambler runs Yamalube injection oil.

I forgot what the guy I got the Trailblazer from ran but I emailed him. Its a nice light green color but that does not tell me much about it.   

[artie on edge]

Nutz, these guys have NO idea what they are talking about. The issue is immediately obvious and Im surprised some of these guys have missed it. It is nothing to do with detonating or lean runs etc.

Mate Im amazed. I thought you would have picked it up easily. Im a bit disapointed in you over this......

[artie on edge]

oops, almost forgot...

Your oil ring is missing.......

[fabr]

Artie,are you SURE that YOU aren't missing a ring or 2? LOL!!!!!

[SPEC]

I think atie's been smokin'
OUTA THE BILLY BONG


 

[b.c.bugger]

take it from someone who has melted more pistons than Wiseco, you are running lean. Alcohol in your fuel can make you run leaner/hotter, try looking for unoxygenated fuel, and consider the possibility you have a bad crank seal/carb boot. Also keep in mind that 2 strokes usually run the leanest/hottest in the upper midrange of the throttle, not necessarily W.O.T. Main jets will only do so much in the midrange so try adjusting your needles higher

[fabr]

+1

[trojan]

I think atie's been smokin'
OUTA THE BILLY BONG

3:24

[artie on edge]

Artie,are you SURE that YOU aren't missing a ring or 2? LOL!!!!!

That might explain one or two things that have been puzzling my therapist.....  :-[

With regards to the above video clip... dont worry if it means jack shxt to you guys...definatley Aussie humour... still cracks me up..... you have to know the place names for it to 'do it' for ya....

[tone]

hi

running lean could be bad fuel or exhaust leak near cylinder
just my 2 cents

cheers

[Nutz4sand]

hi

running lean could be bad fuel or exhaust leak near cylinder
just my 2 cents

cheers

I may just be misunderstanding but what are you meaning by an exhaust leak near cylinder causing it to be lean?

 

[fabr]

It can suck fresh air into the cylinder on the downstroke and cause a lean condition due to the extra free oxygen in the fresh air compared to exhaust gas.  On a four stroke using an O2 sensor it is IMPERATIVE that there be no exhaust leaks since a wideband O2 sensor is sensitive enough to "see" the extra O2 and will erroneously indicate the AF ratio. An engine ,2 stroke or four, will also "see" that extra O2 and run lean.