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HelicopterEngines Plugs Mufflers Fuel › OS91 breaks 3 piston ring locator pins
01-26-2013 09:40 AM  4 years agoPost 1
jdvuyk

rrApprentice

Auckland, NZ

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over the last 3 months my trusty OS91 suddenly started shearing of piston ring locator pins. 3x so far. Each time its a new ring and piston as the pins themselves aren't easily replaceable.

I have pulled engines apart countless times and I know all the rules. I took super special care the last time i did the job. Without a shadow of a doubt the ring was located dead right on the locator and the piston was the right way around.

The question is: What could possibly cause this to repeatedly happen?

700LE Nitro | Atom 500 | 6HV | MCPx | DSX9
Jamie

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01-26-2013 11:02 PM  4 years agoPost 2
Toddc72

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weed,ca-usa

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If your motor has a lot of run time on it? It has too much piston to cylinder wall clearance and will keep breaking them no matter how many times you change pistons and rings. You will need to install a new liner and than your problems will go away. Change the piston, liner and ring assemble

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01-27-2013 03:09 PM  4 years agoPost 3
P Johnston

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Ann Arbor MI

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Your trusty os91 needs a new rod and crank. After a lot of use the crank and rod develope a taper on each other. This causes a twisting motion back and forth with every rev thus hammering your ring locator pin.

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01-27-2013 09:27 PM  4 years agoPost 4
keiser BLADE

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WV USA

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+1 on the new con rod

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01-28-2013 12:00 AM  4 years agoPost 5
Toddc72

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weed,ca-usa

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Yes the rod can do it too. Anything that is making the piston slap in the bore can cause issues on breaking ring locating pins.

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01-28-2013 08:39 AM  4 years agoPost 6
jdvuyk

rrApprentice

Auckland, NZ

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ouch. So basically its poked.
It now needs a new ring, piston (again) and rod. maybe crank. plus the bore isnt perfect now its had a few bad rings up and down it. that's gonna cost a bomb.

Looks like a 105 might be on the shopping list.
mostly
a little

700LE Nitro | Atom 500 | 6HV | MCPx | DSX9
Jamie

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03-20-2013 10:03 PM  4 years agoPost 7
Gary H

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Minnesota USA

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+ 1 on the 105!!

GH

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03-21-2013 03:43 AM  4 years agoPost 8
steve9534

rrKey Veteran

yakima, wa.

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Piston pin

The rod isn't going to make the piston slap. The sleeve is worn and that allows the piston to slap back and forth, eventually knocking the pin loose. steve.

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05-01-2013 12:34 AM  4 years agoPost 9
airdodger

rrElite Veteran

Johnston USA

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The ring locator pin breaking loose did no damage?

Chris

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05-02-2013 09:36 AM  4 years agoPost 10
jdvuyk

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Auckland, NZ

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I wouldn't say no damage but scoring was minimal. Went for 105 in the end. Was over this problem. Will wait until a sleeve comes my way and try again. Thx.

700LE Nitro | Atom 500 | 6HV | MCPx | DSX9
Jamie

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