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HomeRC & PowerAircraftHelicopterEngines Plugs Mufflers Fuel › bearings and needles question
09-19-2013 04:41 AM  5 years agoPost 1
Rafael23cc

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Junction City, KS

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Need your help.

I've got an OS91HZ and and an OS91SZ-H. Both recently received a new set of bearings from Boca Bearings and to be on the safe side, I decided to set the needles at the factory setting to treat the engines right. Main reason I re-set the needles was because the bearings were of the sealed kind, if I remember correctly they had the rubber sides. (it could have been the metal sides, i don't remember)

1. What effect, if any, would sealed bearings have on these engines? Would it make the tuning of the engine difficult?

2. The SZ-H has a Cline modified carb with a Cline regulator attached. This engine will run with the needles at the factory setting slobbering rich with the glow plug attached. As soon as I remove the glow driver the engine dies at about midstick. I have chased the mid-range needle to about one turn from closed and about 2.5 turns from closed to no noticeable effect. I have tweaked the high speed needle a bit with no noticeable effect either. I changed the glow plug and no difference either.

3. The HZ will not run at all at factory needle settings. After a while the engine floods. I have messed with the low speed needle and get no results, but I have messed with this one lees than the SZ because the hex coupler stripped the last time I tried. I have not tried to change the glow plug on this one yet.

Give me some pointers please. I'm getting really frustrated. These are my two 90 birds that I fly every weekend. My 50s don't see that much air-time since I got these guys.

Thanks in advance
Rafael

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09-19-2013 05:03 AM  5 years agoPost 2
Rafael23cc

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Junction City, KS

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I forgot to that both engines run off crankcase pressure but the HZ does not have a regulator, just the stock carb. The SZ has a Cline carb and regulator.

Rafael

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09-19-2013 06:03 AM  5 years agoPost 3
TMoore

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Cookeville, TN

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Just to be clear are the bearings shielded or sealed? The rear should be open on both sides and the front should be open on one side only.

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09-19-2013 07:15 PM  5 years agoPost 4
Rafael23cc

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Junction City, KS

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To be completely honest, I don't remember if they had the rubber or metal sides. I remember being somewhat comforted when I intalled them that they were not completely sealed, just shielded. So they most have had the metal sides.

I was thinking about getting them out and removing the covers very carefully. May have to do that. Hopefully I can complete the job before Saturday.

Rafael

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09-19-2013 08:04 PM  5 years agoPost 5
darren heaver

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rochester, kent, england.

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These engines can be a pain but we all enjoy it, or we would switch to electric :-)

Good luck

" one day I will learn to fly till then I will just hover"

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09-19-2013 08:18 PM  5 years agoPost 6
Heli 770

rrProfessor

USA.

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If you know the Boca Bearing part no. you could just look them up to find out what the bearings came with.

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09-19-2013 10:13 PM  5 years agoPost 7
TMoore

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Cookeville, TN

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Rafael,

Please verify the situation with the bearings and then I can help you with the Cline and the HZ.

TM

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09-19-2013 10:52 PM  5 years agoPost 8
Rafael23cc

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Junction City, KS

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Ok, I guess I'm confusing myself here. I went back a few months in my email and found the receipt from Boca Bearings. I bought a 90 set and a 50 Set. So the problem is not bearings with both of them. So let's recap.

1. OS91SZ-H Cline Carb and regulator. Crankase pressure These Boca Bearings and an Muscle Pipe (can't recall the number). Acts like it's flooding all the time. I did not remove the shielding of the main bearing.

2. OS91HZ. Stock Carb, Crankase pressure, Muscle Pipe. This engine I had in the parts drawer and replaced a worn YS engine that I could not find parts for. (Maybe I need to look harder). This enigne is also flooding, but now that I rememberd that I did not change the bearings on this one, may be easier to diagnose. First thing I will do is to take off the crankcase pressure and run muffler pressure. Then figure out the rest.
The rear bearings should have no seals as the fuel mixture will not travel through the crankcase, the front bearing should have a seal on the fan side only.
I know the fuel mixture travels thru the inside of the crankshaft towards the backplate and then up the sides of the case between the liner and the case until it reaches the ports. Some of the mixture is diverted (when the ports are closed), thru the bearings for lubrication. Are you trying to say that shielded bearings will not provide sufficient lubrication to the crankshaft?

Rafael

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09-19-2013 11:26 PM  5 years agoPost 9
ticedoff8

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Morgan Hill, CA. USA

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It does not matter if the main bearing is shielded or not.

There is a port on the "snout" of the crankshaft under the carburetor mount,
The fuel / air mixture enters the center of crankshaft and flows down the center of the crankshaft to the rear chamber and exits into the rear chamber.
Not the outside of the crankshaft. If it traveled down the outside of the crankshaft, then a sleeve on the main bearing would be a problem.
But, it doesn't.

The channels on the sides of the crankcase and the ports cut in the piston sleeve allow the fuel / air mixture up into the combustion chamber.

The shield on the bearing reduces the drag of the oil / fuel that accumulates inside and the bearing turn / roll instead of skid on the races.
The shield blocks most of the oil / fuel from reaching the bearing and the bearing is easier to turn.
But, it still receives enough oil / fuel to get the job done.

To get the full advantage of the shielded bearing, you need to install the main bearing with the shield facing the backplate of the motor. If you put it in the other way, it will perform as as well as a stock, unshielded bearing.

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09-19-2013 11:34 PM  5 years agoPost 10
ticedoff8

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Morgan Hill, CA. USA

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On the 91HZ - which carb is it using?
Is the one with the regulator built in?

On the 91SZ-H - its not a bearing issue.

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09-19-2013 11:59 PM  5 years agoPost 11
TMoore

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Cookeville, TN

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If the HZ is running on suction the reason it is flooding is due to CC pressure, switch to muffler pressure on this one and that will fix it.

On the SZ with Cline, check the one way valve in the pressure line going to the tank and suck on it with it submerged in some water to see if you can draw water through it. Blowing through the line on the engine side won't tell you much.

Then set the Mid on the Cline to 1-1.5 turns, 2.5 turns on the high and then make sure once the engine starts that when you release the pressure tap on the tank that you hear/feel air come from the tank. If the tank won't hold pressure this can be problematic too. If the engine won't run at mid stick and turns off rich when you get there chances are the engine is flooding due to the one way valve not working correctly.

If the Cline is the problem it can be easily rebuilt with a new valve.

TM

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09-20-2013 04:11 PM  5 years agoPost 12
bbaxter

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Central Illinois

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Almost always, "factory" settings are very rough starting points and are usually quite rich. You would never fly with "factory" settings. They only give you a place from which you will adjust the carburetor as required by your engine, fuel system, and flying style.

If your engine is too rich with the "factory" settings, then lean it to the point where it's running properly.

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09-20-2013 06:07 PM  5 years agoPost 13
Rafael23cc

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Junction City, KS

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Thanks all for your input. It is right in line with what I knew. Just needed a little reinforcement.

Update:

Since I bought 2 sets of bearings, one 50 and one 90, I decided to take the 50 out and make sure that it is functioning correctly. It did, at least on my driveway and hitting idle up to get the rpms higher than just hovering. So I am almost certain that bearings is not the issue.

On the HZ. Took off the crankcase pressure and put in muffler pressure. Again, hovering and idle up in my driveway seemed ok. Will test out this weekend. I think I have another Cline Regulator somehwere in my parts drawer that may consider installing here and run CC pressure later. that may be a good project for when it gets a little cold.

I did not have time last night to deal with the SZ. Thanks TMoore for the suggestions on the "factory" settings for a Cline carb. I was using the OS "factory" settings and that is what may be wrong. I will check the one-way valve and the Cline diaphragm when I get home tonight.

Rafael

Keep your feet on the ground, but your eyes on the sky.
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09-23-2013 10:07 PM  5 years agoPost 14
Rafael23cc

rrKey Veteran

Junction City, KS

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TMooore:

Update on the SZ:
Thanks for your "factory" settings. that helped a lot. Got the engine running again. Still needs a bit of needle tweaking for max power, but it is running consistently now.

The other engines are running great.

thanks to all
Rafael

Keep your feet on the ground, but your eyes on the sky.
Team Heliproz.com

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