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HomeAircraftHelicopterEngines Plugs Mufflers Fuel › align 91 H rebuild
01-21-2010 03:05 PM  8 years agoPost 1
Duckster

rrApprentice

Brunei

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I just wanted to know if anyone have tried this before and what do u think,

I have a blown piston about 2 week ago, and now am replacing with a new piston, what have just arrive to my door is new os 91 sz piston and new ring, but this piston got is blank flat piston head without any hole unlike the hz version, i have install everthing just right on my engine but i didnt replace the liner since it look fine and unscratch either, and now am running on the 3rd tank and i ve lean it at 3rd from 2 turn to 1.5 turn, the carb is still sweating and it has produce lots of power and i cant really compare the power od SZ to HZ piston, is it ok to lean some more on the 4th tank or just let it on rich side until i finish a gallon of break in.

Trex 600,700 AND 450, GY611, GY401, OS5H, OS91HZ, MGP, HS65HB, Scorpion 2221-8,

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01-21-2010 03:36 PM  8 years agoPost 2
Against Gravity

rrVeteran

Pottstown PA

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HZ piston
You want to run a HZ piston, Not the SZ. Hz piston is 1 of many improvements made to your engine. Sz is designed for the SZ motor.
I think first you will find that the Motor will vibrate more. When they went to the HZ version they lightened the piston to help with balance. The holes are there to help seal the ring. And I think the skirt is cut differently to help with the porting.
Get the right piston for your Motor, it will work much better.

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01-21-2010 04:00 PM  8 years agoPost 3
Duckster

rrApprentice

Brunei

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thanks for the reply AG, i ve install the sz piston on the align 91 h engine, and find that everything seem work properly, ideal speed work fine, i dont find engine vibrate and sound just right.

Anyway what skirt are u refering to am bit confuse, i ve compare both hz and sz piston the only different is the waight by 0.02gm, and the hole on the piston top. All the cut shape and diameter is exactly the same, i ll make a review what i find on this combination after a gallon on breakin.

Some of the flyer in my local flying field change the hz head to the sz wc (blue head) and says the blue head is better, which on the os review said that the HZ black have more better cooling system then the blue can any1 explain the fact of this, what do they said the blue head is bigger and cool better the the small black head is this true or just a rare guess of thought..... Confused

Trex 600,700 AND 450, GY611, GY401, OS5H, OS91HZ, MGP, HS65HB, Scorpion 2221-8,

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01-21-2010 07:48 PM  8 years agoPost 4
CoronaL

rrKey Veteran

Winnebago IL

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the SZ piston will work fine for the HZ. Maybe not optimal, but it won't destroy itself, provided you keep it tuned properly. The balance may be a bit effected, but if you think it's running well and making good power, then leave it and be happy.

I have a friend who taco'd like 3 of his OS 91's this past year. Between them he was able to cobble together a bastard child of a motor with HZ case, liner, crank, carb, and OS SZ piston, rod. I'm not sure which head he's using but I don't think that really matters. His motor runs well.

Kinda nice in some regards that the OS 91's use so many of the same parts. You can upgrade to the HZ stuff as time/$ permits hehe!.

Randy!!! I am the liquor

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