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HomeAircraftHelicopterEngines Plugs Mufflers Fuel › os 91 hz service
02-03-2013 10:54 PM  5 years agoPost 1
pitfall

rrApprentice

england

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HI Guy's

looking to change the bearing on my os 91hz engine. this will be my 1st go at it, so any advise will be grateful, any tools i need, also how do you if the con rod is the right way round

cheers

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02-03-2013 11:21 PM  5 years agoPost 2
dchekas

rrKey Veteran

Farmington, CT

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No real tools needed, other than a proper crank shaft locking tool to loosen the fan nut.

Remove the carburetor and carburetor neck pieces, pull the head off, pull the sleeve out, slide the connecting rod off the crank shaft and pull the piston out. Tap the crank shaft on a piece of wood and it should pop out.

You'll be left with the bare engine crank case, and the rear/front bearings.

Heat your oven to 350°F, let it sit for ~15 minutes. In the meanwhile, install the new rear bearing on your crank shaft and put it in the freezer.

After 15 min, quickly pull the engine out, and hit the engine on a piece of wood. The rear bearing will fall right out. Quickly pull the crank shaft out of the freezer with the rear bearing install on it, and drop it down into the engine crank case. Pull on the crank shaft and make sure the rear bearing is fully seated. Let it sit and cool.

Reassembly is the reverse. You can tell the connecting rod orientation by looking the piston ring groove. The little roll pin in the groove should face away from the exhaust port. Which ever conrod orientation gets it the furtherst away from the exhaust port is correct.

Make sure when you go to assemble the sleeve back into the crank case that the gap in the ring is lined up with that roll pin, or you'll break your piston ring.

Team Align, Team Futaba, Team Byron Fuels, Team Thunder Power

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02-05-2013 01:04 PM  5 years agoPost 3
daytimer

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Joliet, IL.

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I'm in the middle of doing this on my 55hz engine. First time for me too.
Instead of the oven, I used a heat gun for a couple minutes. Then whack it on a piece of wood and the bearing will pop right out. the front bearing I had to use a stick from the inside to pop it out the front after I heated the engine.
That's where I'm at right now. I don't have it back together yet Gotta figure out how to clean it up real good.

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02-19-2013 06:54 AM  5 years agoPost 4
Dave's Raptor

rrApprentice

Kennett, Mo USA

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If you have not heard of the Magnum Center Glide bearing replacement here is the link for the post. https://rc.runryder.com/t701109p1/
If you decide to send it to Buzz and have this system installed, you will never have to worry about replacing the bearing anymore. The cost is not bad compared to replacing the bad bearings yourself.

Dave

Team HeliDirect, Team Synergy U.S.A.

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02-25-2013 09:20 PM  5 years agoPost 5
CoronaL

rrKey Veteran

Winnebago IL

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many videos on the internet and youtube. I think Curtis has one up on rebuilding a 91HZ, you can look for it .

easy enough, just a bit intimidating until you realize it's not

Randy!!! I am the liquor

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05-10-2013 03:10 AM  5 years agoPost 6
feudallordcult

rrNovice

Singapore

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I actually took half day off to replace the bearings when it actually took less than two hours. Mr Youngblood's youtube vid is an absolute gem.

I hv a query though, would changing the crankcase improve compression hence performance? I m asking cos after every flight, the backplate would be leaking and since its a pretty old engine, I thought of changing, amongst others, a new crankcase. Anyone with advice? Thank you in advance.

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05-10-2013 01:10 PM  5 years agoPost 7
CoronaL

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Winnebago IL

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unless it's cracked I wouldn't change the case. Maybe the O ring on the backplate is leaking.
Make sure head bolts are torqued correctly as well.

Randy!!! I am the liquor

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05-12-2013 02:41 PM  5 years agoPost 8
feudallordcult

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Singapore

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Thank you.
Grateful for the advice. Appreciate it.

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