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

[Adnoh]

I'am going with seals. Check your balancer oil levle. seal betweeen cylinders. To late for air test. 92 cot on an 87 oct motor will heat things up via burn rate. Still going with seals thu.

[Adnoh]

Forgot to ask what plug was that. right one listed for stock or one step hot leaving to much heat in cylinder with to high of octane.

[Nutz4sand]

I'am going with seals. Check your balancer oil levle. seal betweeen cylinders. To late for air test. 92 cot on an 87 oct motor will heat things up via burn rate. Still going with seals thu.

Oil level in balancer is fine. Its only a one popper (single cylinder so no seals between cylinders) I also did a positive and negative air pressure test on the motor before I pulled it apart (See my very first post) and will do another before I try to fire it up. (I always do on a two smokes.) 

Explain why you think 92 octane will burn hotter than 87? (The only arguement I have ever heard on this is higher octane burns slower and  due to this its still burning more as it leaves the cylinder. I question this as this is a bascally stock motor with moderate revs. Higher octane burns fine in racing engines turing MUCH faster speeds so I am somewhat questioning  THAT explanation to me.)  But I would like to hear your thoughts on this.


Champion 8902 is the plug. 


As also noted the other machine I have (Polaris scrambler 400 (Same motor) With a NGKbr8es plug. NEW seals throughout. Fresh rebuild. Started to do the same thing. The only thing the motors had in common was the fuel being used.

[SPEC]

Crank seaks would make it way lean at idle and it would have a lean bog anytime on the throttle...it went south running hard and pulling...It most likely was fuel or just it's time...Nutz try the NGK equivilant plug...IMO they are a truer plug in terms of consistancy than the champions

[Nutz4sand]

Thats the funny part Spec. The 2wd trailblazer had this champion plug. The Scrambler had a NGK in it. Both machines still did bit of the same noise at top end. The trailblazer just happened to have it affect it during a hard hill climb. Thus the piston damage.

I am pulling the jug off the Scrambler to check it as well.

[Nutz4sand]

The Scrambler still has greta compression as I never was on it hard once it started to make the noise.

Both machines have the same motor but each motor is at different levels of mods.

I jsut find it funny that both seemed fine. Then one day they both started to detonate on the top end some.

The only common thing was fuel. Thats why I suspected it. I think I got a batch of crummy gas to be honest.

[thedoctor]

I don't know if it applies in this case. I read that on a 2 stroke running alcohol you should not let off the throttle suddenly, it cuts off the cooling effect of the alcohol. I know the gas pumps here say there is   at least 10% alcohol in the gas. I know alcohol adds octane. I wonder if they are just adding alcohol to get  the 93 actane. Also, on a sprint car,it will melt the piston if it goes lean at all. I think alcohol in the gas is the problem. Tim

[Nutz4sand]

Aside from $$$ pure race gas I need to find a gas  station that simply sells gas that is still gas and just gas.

[Admin]

Aside from $$$ pure race gas I need to find a gas  station that simply sells gas that is still gas and just gas.

Good luck on that...

[thedoctor]

One trick the six day riders used to use when they ran wide open for a long time was to hit the kill button with the throttle open. Fuel flowed to cool engine without ignition. Tim

[b.c.bugger]

nutz, you are right race gas will not run hotter in your motor it will actually run cooler. It's a common misconception that race gas is more volatile...actually the opposite is true it burns slower than lower octane fuel which is why you need it in higher compression motors.....less chance of predetonation. You can try running a splash of race in with your regular fuel to boost the octane a bit but I think that would be a band-aid, not really fixing your problem.
You may have got a bad batch of fuel but I still think you have a lean condition probably caused by a bad crank seal. I would spend the extra few hours and change your seals while you have the motor apart, cheap insurance.
The only place I know of up here in Canada to get non oxygenated non alcohol 92 octane at the pump is esso marked marine gas. It's all I run in my sleds. If I'm going on a trip I bring enough so I don't run out. Maybe you can get it in your area? Make sure you look for the marked 92, the clear 91 has alc in it

[Adnoh]

I guess I didn't win. Oh well just a guess. So the higher octane fule burn slower and this has no effect on the engne. I sure thought it would run hotter due to the slower burn and eginte the squish band gases that are used to cool the edge of the piston. I looked at it like retard in timming. If the squish gases are burned up the squish is ineffective. The trapped gases mixing with the egnited gase mix and help keep heat off of edge of crown as the exhaust gas dumpes into exhaust port. If the compressed mix in the squish is gone the edge of the piston on the exhaust side will melt away by lack of cooling. Why this does not happen on the intake side is because the intake ports open and cool that edge off and the intake charge is being pulled across the crown into the exhaust port for stuffing and building up on its compressen stroke once the intake and exhaust ports close.  If the timing is changed and the ignition is late via burn rate the piston is to far down on the power stroke relesing the squish gases and mixing with the combustion chamber gases and making the squish ineffective. Brief but asking, wrong?

Plus is useing high octane on a low compressin motor good. I say no. I bet the four stroke guys who burn up those valves dont thnk so either. Using v-2 corrected you can use high cranking pressure to a point with a low CR and get away with pump gas.

[Nutz4sand]

Yah I had some squish issues on my Honda Pilot thanx to that doofus who used to work at PCP. Dunno if he still does.
Needs to be banned from touching anything more than a plastic push car.

Polarises are NOTORIOUS for HUGE squish bands.
If you ever pop a stock Polaris two smoke apart the squish band is FRIGGING beyond huge compared to what most think they should be.

Yet most fo them run like this for years without a burp.

 

[SPEC]

Ya,
The PO's squish band is a touchy animal too...Mill off too much and it's just a boat anchor...1st couple I did ended badly...AHHH How I miss hi-school and no internet to edjimacate me

[fabr]

Lots of good info been put up here.