hi,
just wondering how will the engine behave if the piston is fitted facing wrong way?

i know for novas if piston fitted wrong way; it'll hit the crank but for piccos, even if fitted wrong way, it'll not hit the crank at all...

why do you even want to know???? lol

Once the piston has been worn into the sleeve. This creates a very precise fit. If you place the piston in 180 out this precise fit is lost. Remember due to the earth gravitational pull nothing can never be perfectly round. In a nut shell don't do it unless you want to ruin a engine.

It can toutch the crankshaft and it opens the exhaust when the piston is at the upper position.

Just as Roelof said, on most engines the piston will jam or break, because it won't clear the crankshaft. That's the reason why you have one side of the piston cut.

Some picco engines do not have the extended skirt on the bottom of the piston that would hit the crankshaft. (ie Mega ZX-12)

Pictures says something else:
http://www.serpent.com/product/201011/
http://www.serpent.com/image.php?ImageID=1234568798

if the 'wrong way' piston is not hitting the crank at all; can the engine be started at all? just curious...

You are correct. But the skirt is not long enough to hit the crankshaft. I personally have done this after cleaning the engine. The engine will start and the botton of the piston will not hit the crankshaft. The engine just runs like Sh!t. The symptoms are the engine will not hold an idle and the engine would constantly lean out while on the starter box.

oops
so the engine can be started and run; any damages done?

No physical damages were done just by looking at it. But I mentioned earlier when you break-in an engine you are lapping the piston to the sleeve. If you for some reason rotate the piston this precise fitting is lost. You are re-lapping the piston to a already worn cylinder. The only thing I notice is the last time I ran this engine during a qualifier it came off the track at 280 Plus degrees and the idle was thru the roof( this was after I placed the piston back the correct way). I believe the engine is loosing compression once the engine get's up to race temp. I will give it another shoot during my club's test and tune day. If it's does the samething then off to the round file.


Pass you soon...

It will run badly because the cut out in the piston skirt allows the crankcase to be opened to the exhaust at the top of the stroke. This kills your crankcase compression which is what helps fill the cylinder. Also, it's probably going to hurt your compression since it was broke in the other way around.

I think also your glow plugs will burn out faster if I'm not mistaken....

I agree. I have since moved on from this engine. On the first practice day of the season I always use my weakest engine. Because at that time of the year the weather is still nasty 60's and 50's.

I did this once by accident. If you can get it to run it runs like crap and it will spit fuel back through the carb at you.