At this point I would recommend pulling the cylinder off. It is not that difficult to do, check the ring, if it is even a bit stiff in the piston you will not get enough compression to run. Alos check the cylinder. one score and you will not get any pop.

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Ok

After pulling the head off I found on each side of the piston the alum is scored ( the scoring is directly across from each other) and the ring is covered with alum. There is no damage in the cylinder and the damage in not in front on any port. Not sure what happen. Is this the type of damage that can happen if a engine is left running upside down for over a min?

running upside down won't hurt anything.... 2-strokes can run in any orientation for any length of time. That looks like maybe and over-heating issue, or even a lean oil issue. Time for a head kit!!

Not sure it was over heated - the temp outside was only 40F and when the engine stop I could touch it without issue. As for too lean, during the checking my L needle was 1.75 turns out and the H need was 1.5 turns out. That is a 1/2 a turn on the rich side compaired to the factory setting. The only mod to the engine is the Jet Pro v2 pipe.

Are these engine like Nitro were you can damage them if they are run too cool?

A fuel lean condition and an oil lean condition are 2 different things... the oil has nothing to do with the needle setting in what I am talking about. What oil ratio were you using? 25:1, 50:1??

I really don't know... I have never burned up one of these engines before, several Nitro's, but no gassers. I am just offering possibilities that come to mind, a stab in the dark if you will, and I want to know how it happened to for my own knowledge.

Hi merchjo, It sounds like what Acs_guitars said, "an oil lean condition & What oil ratio were you using? 25:1, 32:1, 50:1?" Here is a helpfull tool Gas Oil Mixture Ratio Calculator. [link=http://www.csgnetwork.com/oilfuelcalc.html]Csgnetwork[/link]. Just put in the # of US Gallons and the
Gas/Oil Mixture Ratio, then click Calculate.

I am running 25:1 (5 ounces to 1 gallon of 93 fuel)

I am just worried I did something wrong and I would hate to burn up another engine.

I throw this out, when upside down the fuel pickup was probably not totally in fuel, is it possible the engine could still run and lean out by fuel starvation? The engine was just idling when we flip the truck over.

Hi merchjo, Chance's are it did not lean out when it fliped. The pick up line in the tank is flexable & will hang down in the fuel. If it was trying to lean out by fuel starvation, the RPM would have ran on the real high side. PS 5.12 oz of oil to 1 gal. =25:1.

Thanks Scooter and all the other guys. I am just going to replace the motor with a new one and will rebuild this one in my spare time. Since I have the HPI Baja and the FG a spare engine is always a good thing. The damage is weird and looks like the piston was not perfectly straight in the cylinder so I guess it was possible it was built that way. I have the tools on order to remove the flywheel and such so I can pull the crank and check everything out prior to rebuilding it. I have also switched my oil to Klotz Super Techniplate Oil that is recommended by davesmotors.com (people I ordered my new engine from).

Joe

just wondering what kind of head your engine has, billit or with full top shroud?(sp). The reason I'm asking is that I've heard that the billits don't cool the cylinder as evenly as the full shroud does. I ran the billit before upping the motor to a 30.5cc and went through 3 top ends in a summer, the cylinder was scored badly but not the piston. It could have been dirt or not cooling properly but they were all scored in the same place.( Note: I was running at 40:1 but now I'm running 32:1 in the new engine)

Stock engine (full top shroud)

i seized a zen engine a few months back on the exhaust port after a couple of tanks from new,crap when it happens but theres a good variety of cylinder kits available for little money

that may actually be cold seizure, It is not from lean condition and definatly has nothing to do with oil.

That is also what a extreme heat will do, motors that have most of the fan blades removed will seize in that fashion.

i was running it through a boggy/muddy field and went through a massive pool of water next thing it just stoped dead - prob went from hot to cold to quick,removing the cylinder was the worse bit as it was stuck solid

Hey radio

If you look at our pictures, the damage is in the same place. I have about 2 gallons of fuel through my engine.

damage looks identical in both pics,i put mine down to running through cold water - but i remember reading that zen had a batch of engines or problems with alot of 230/260 seizing around the exhaust ports,i contacted zen as i thought it shouldnt of seized so easily but they wernt intrested

Well I am replacing the engine with a bb28x - CY29RC 3.5 HP Engine w/ Inner Clutch. I figure I try a CY engine and see if they are any better.

[:'(]

CY if anything is not as good as ZEN... definitely not better, at best the same. After all it is a copy of the ZEN design.

Well my zen only lasted 2 gallons of gas so its not that great either. My Baja has a CY and I have no problems with it.

My Zen has had about 10-15 gallons (atleast) thru it and the cylinder still looked new when I sent it to O'neill for a little work. There are always a few bad lemons from any company..... Zenoah is not know for engines that blow easily. This is either the result of a lemon that mad it out or operator error. In either case, mistakes happen and things don't always work like they are supposed to.

Well its not like I tossed the motor. I will rebuild it using zen parts, maybe go to a 30cc. I just wanted my truck up and running until I decide what I wanted to do.

I started it today and the engine ran very smooth and was very responsive. Tomorrow I take it out and finish heat cycling it and then really open it up.

hmmpf.... so you rolled over a good few times, ran about 300 ft and it died. now it wont start. replace your gas and fuel return lines. they may look ok, but im willing to bet you ll find a crack or hole in the line allowing it to suck air in. if you push the primer bulb repeatedly, does it empty out or does it continue to move gas from the tank to the carb and back to the tank via the return line? the return line should push the excess gas back into the tank and you should hear it when pushing the primer bulb. if you can not circulate the fuel by pushing the primer bulb, then your lines may be shot. new fuel lines should help here. when you do this look for a gas leak, check your clunk in the gas tank too.

how many gallons you got thru the motor? i doubt your engine is toasted UNLESS while rolling over a seal opened up, or you got a crack somewhere in the cylinder or case... again i doubt this but it is possible with a long violent rollover.

also check your gas cap that it is not plugged. if the vent hole is plugged, then your engine will be starved for fuel.

im leaning toward a fuel delivery problem.
Timmahh

Timmahh

Look at the picture at the top of this page...Piston is toast.