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HomeAircraftHelicopterEngines Plugs Mufflers Fuel › New piston,ring & liner in OS 91HZ
01-03-2014 01:23 AM  4 years agoPost 1
ttaylor63

rrApprentice

Floresville,Tx

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Replacing liner, piston & ring on a OS 91HZ. Do i need to scuff up the new cylinder with emery paper before assembly to help the ring seat or not.

Also what is the starting needle setting for a 61B carburetor...

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01-03-2014 04:04 AM  4 years agoPost 2
TMoore

rrMaster

Cookeville, TN

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No, it is ready to use. Use a little oil on the cylinder when you insert it into the case. When you get it together I would put a few drops of oil in the cylinder and rotate the crank through several times and then wipe out the debris with a clean lint free paper towel before you finish the assembly.

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01-03-2014 03:05 PM  4 years agoPost 3
Richardmid1

rrProfessor

Leeds, England

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When replacing only the piston ring, should you swirl some emery paper round the liner as the original honing marks will be worn smooth?

60% of the time, it works every time!

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01-03-2014 03:13 PM  4 years agoPost 4
TMoore

rrMaster

Cookeville, TN

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That will not hurt a bit. You have to remember that on an OS they use Nikasil as a coating and it is very hard.

TM

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01-03-2014 03:23 PM  4 years agoPost 5
ttaylor63

rrApprentice

Floresville,Tx

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Ok thanx alot. Also replacing the bearings as well. On the rear bearing does the open end go towards the front or back or does it really matter. I didnt pay attention which way the old bearing was facing when i removed it...

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01-03-2014 03:25 PM  4 years agoPost 6
Richardmid1

rrProfessor

Leeds, England

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Rear bearing should be open at both ends.

60% of the time, it works every time!

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01-03-2014 03:26 PM  4 years agoPost 7
Richardmid1

rrProfessor

Leeds, England

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Thanks tm!

Will it just take longer to bed in if you don't?

60% of the time, it works every time!

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01-03-2014 03:27 PM  4 years agoPost 8
TMoore

rrMaster

Cookeville, TN

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If the bearing retainer is steel I typically place the closed end toward the inside of the case. On a plastic retainer it really doesn't matter since oil will flow either way.

Richard, since the cast iron ring is many times softer than the Nikasil it won't take long to seat to the liner. That's why these engines will break in in a short period of time. It is also a good reason to keep an extra ring or two on hand.

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01-03-2014 03:55 PM  4 years agoPost 9
Grimracer

rrVeteran

Eau Claire WI

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Found this for ya..

Carburetor Settings-
High Speed Needle: Two turns open from fully closed
Medium Speed Needle: One turn open from fully closed
Idle Mixture Control: At basic position when engine leaves factory

Michael J Zaborowski

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01-03-2014 04:38 PM  4 years agoPost 10
Richardmid1

rrProfessor

Leeds, England

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Thanks tm.

I thought the rear bearing needed to be open to allow oil to get to the front bearing?

60% of the time, it works every time!

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01-03-2014 08:13 PM  4 years agoPost 11
ttaylor63

rrApprentice

Floresville,Tx

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I bought this 700 used with an OS 91HZ. I hovered it in my backyard & seemed like motor was running a little lean at 2 turns out on both needles. Then all sudden it just died. When i got up to it was smoking & very hot. Then it wouldn't re start & compression seemed low. So i tore it apart & the piston was scared up some on the exhaust side & the piston ring was stuck to piston. Previous owner stated only had approx 3 gallons thru motor. Also the rear bearing was rough. So i'am replacing the piston, liner, ring & bearings. I may just start 3 turns out on the high needle & 2 on the low and go from there.
I also own a OS 91 HZ-R as well & think says to start at 2 1/2 turns out on high needle. I'am running Byron 30% heli fuel... I knew better than to buy used....Oh well lesson learned..

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01-03-2014 10:28 PM  4 years agoPost 12
TMoore

rrMaster

Cookeville, TN

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A 91 on suction should run on those settings with 30%. Sounds like there was a fuel delivery problem causing the engine to go lean. I would look carefully at all of the usual suspects like tank plumbing, fuel filter and carb cleanliness. The carbs are very easy to work on.

The R runs more consistently but not necessarily stronger. I have both here and if you don't mind running a header tank or putting up with a couple of minutes of lean out the suction version is fine.

Better to start really rich and work your way up from there. Since you are replacing all the parts you detailed, start the break in from scratch as if it were new.

TM

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01-04-2014 12:58 AM  4 years agoPost 13
ttaylor63

rrApprentice

Floresville,Tx

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It does have a header tank...It was smoking really good so i didn't think it was running lean... Guess will look over it all..

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01-04-2014 01:19 AM  4 years agoPost 14
TMoore

rrMaster

Cookeville, TN

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Remember that most 30% fuel will have 23% oil so you can be lean and still smoking a lot.

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01-08-2014 03:34 AM  4 years agoPost 15
ttaylor63

rrApprentice

Floresville,Tx

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Well broke the damn brand new piston ring trying to get the cylinder over it inside motor. I replaced all bearings. Got the connecting rod over the crankshaft. Then tried to gently slide & twist the liner over the piston ring & it wouldn't slide over. Took piston back out & the darn ring was broken in 3 pieces.So now i have to get another $22.00 ring. I'am damn near tempted to send this sucker to service center... I watched a video on how to get the cylinder over the piston ring but it didn't go well...So now back to waiting on another ring...

Anyone have any input on an easier way to get together..

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01-08-2014 04:31 AM  4 years agoPost 16
TMoore

rrMaster

Cookeville, TN

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Use a little oil on the assy when you start and begin with the cylinder at a slight angle with your finger pushing the piston up from below.

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01-13-2014 04:57 AM  4 years agoPost 17
Dr.Ben

rrMaster

Richmond, VA, USA

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DO NOT twist the liner once it's down in contact with the piston and ring. Twist the sleeve into the correct orientation before you get it all the way down.The ring broke when you turned the sleeve such that the ring gap hung up in one of the sleeve's ports. As noted a little oil helps things get started a lot. You can also stick your pinkie up into the underside of the piston to rock it into place into base of the sleeve. Advance the piston up into the sleeve. Do not try to force the sleeve down onto the piston.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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01-13-2014 05:54 PM  4 years agoPost 18
BONO1

rrApprentice

AR

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ring
Be sure the ring gap is over the retaining pin inside the ring groove. I usually mark this with a fine tip marker on top of the piston to ensure the end gap is in place before starting the sleeve over the piston. Take your time and don't force anything and as mentioned before twisting is a no-no. Good luck.

Sam

blow smoke

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