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HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › OS 91 SZ-H Compression
09-15-2009 03:02 AM  11 years ago
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schucb

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Minnetonka, MN 55345

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OS 91 SZ-H Compression
Has anyone used a compression tester

http://www.centralhobbies.com/Tools/tool1.html

when flying my Raptor 90 recently, it was really bogging under a load. It used to make a lot more power. I am getting good RPM at hover, but it seems to be weak when I punch out. What kind of compression should I have? Is there a way to determine what I should have?

Will bearings effect performance? I checked them less than a gallon ago and they didn't seem bad.

Should I just try new ring, bearings, and glow plug?
Brian
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09-15-2009 03:12 AM  11 years ago
Dr.Ben

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Richmond, VA, USA

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How many gallon on the engine?

Can you show be a GOOD, non blurred pic of the ring in the exhaust port?

If the power has gone away, the ring is a prime suspect. If the bearings are original, do them while you're in there.

Ben Minor
Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA
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09-18-2009 12:07 AM  11 years ago
schucb

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Minnetonka, MN 55345

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Exhaust Port
I ordered a ring for the motor. I also have a set of bearings and will put them in. I attached a picture of the cylinder. I bought the engine used. I supposedly had new bearings and a new ring when I bought it. I have probably ran 4-6 gallons of CY wildcat 30% with 23% oil. I have a carbsmart and have kept the motor at 110C.

I also noticed the glow plug was slightly loose when I pulled it. I would say it was slightly loose. Did I say slightly? I know a loose plug can cause a motor to run lean, but this was still fully threaded in. It also may have a slightly weak element. It was black on the bottom. I am going to try a new glow plug when I get a chance.

Let me know what you think of the ring?

Brian
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09-18-2009 11:16 AM  11 years ago
S Bell

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Nova Scotia Canada

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The ring gap should not ride over the exhaust port. The ring index pin is likely gone or pushed in. You need a new piston and ring, maybe a liner too if it got scratched. That's what it looks like to me anyway.
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09-18-2009 11:28 AM  11 years ago
airdodger

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Johnston USA

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Did you rebuild the engine?Chris
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09-18-2009 02:28 PM  11 years ago
schucb

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Minnetonka, MN 55345

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I have never rebuilt this engine. I bought it used. It had a new piston ring when I bought it.

It has made a lot of power until the last time out.
Brian
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09-18-2009 06:55 PM  11 years ago
airdodger

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Johnston USA

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It was clearly not assembled correct.Chris
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09-19-2009 03:42 AM  11 years ago
Swoop

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Newark, DE USA

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It was clearly not assembled correct.
Is it even possible to get the liner back in, when the ring ends are not straddling the locating pin?

Id say your lucky the ring didn't snag the exhaust port because you would be shopping for a new motor.
Chris
X50, B320, Radix, Spartan
Titan,Kasama,MP5,Radix,JR770
Trex450SE,MavrikkG5,Phoenix35
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09-25-2009 08:23 PM  11 years ago
schucb

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Minnetonka, MN 55345

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It appears my head has a stripped glow plug hole. I put the compression tool in and it tightens, but the compression blows it loose.

I have another head, but it was beat up by a bearing ball. What can I do with this? Or should I find a new head?

Are helicoils available for rc engines?

Brian
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09-25-2009 09:26 PM  11 years ago
ttrip06

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Central Pa

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Yep you can get coils for the glo plug threads, just don't remember the number at the moment.

If look in the back of the AMA mag there is a place that will do it for ya if you don't want to be the tools.
Tim Tripoli

Team Futaba, Rail Blades
Team Crash
ProggressiveRC
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09-26-2009 02:06 AM  11 years ago
airdodger

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Johnston USA

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