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HelicopterEngines Plugs Mufflers Fuel › was my Align 91 shipped with piston in backwards ??
09-03-2009 01:26 AM  8 years agoPost 1
jschenck

rrProfessor

La Vista, NE.

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I broke the piston on my Align 91 last week. Thread here:

http://runryder.com/helicopter/t537183p1

Tonight I installed the replacement piston and took note of a relief that is cut into the piston skirt. It occurred to me that if this relief had been at the rear of the piston it would have prevented the damage. Is it possible that my engine was assembled at the factory with the piston in backwards? The drawings in the manual are not really clear.

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09-03-2009 02:28 AM  8 years agoPost 2
Kevin Dalrymple

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Indianapolis

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The cut out is to clear the crank. (See bottom picture.This side gose toward the crank counter weight.) If it was install backwards you would know it as soon as you spun the motor over by hand. The other thing is if you install the back plate upside down you will break the piston skirt.

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09-03-2009 02:36 AM  8 years agoPost 3
AzHyper

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Peoria, Az.

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If the piston has a pin for locating the ring end gap it would have been in the wrong location. Do you have a way of verifying it from that perspective?

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09-03-2009 06:21 AM  8 years agoPost 4
jschenck

rrProfessor

La Vista, NE.

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I was checking the clearances out after I wrote this post. Rymps has it right, the cut is to clear the crankshaft counterweight. So bottom line, the piston skirt will go into the crank locking tool if you are not careful.

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09-03-2009 06:24 AM  8 years agoPost 5
jschenck

rrProfessor

La Vista, NE.

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If the piston has a pin for locating the ring end gap it would have been in the wrong location. Do you have a way of verifying it from that perspective?
The ring pin is ~ 2:00 position if I remember correctly (12:00 facing the carb as a reference). I didn't know there is a right or wrong location for this pin, as long as the ring gap is over the pin. Is the ring gap supposed to be in a specific location? Makes sense you wouldn't want it going by the exhaust ports or maybe even any of the intake ports.

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09-03-2009 01:17 PM  8 years agoPost 6
BarracudaHockey

rrMaster

Jacksonville FL

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Yep, you don't want the ring gap on a port.

Andy
AMA 77227
http://www.jaxrc.com

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