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Engines Plugs Mufflers Fuel > OS 37SX-H worn carb barrel (again)
 
 
pgoelzSenior Heliman - Location: Rochester MI -
Anyone else seen this? This engine has had MAYBE 20 flights on it since new last year!



I thought the mixture problems I was having were due to my inability to diagnose and tune. Turns out the carb barrel was moving abnormally in the hover area.

It almost looks like the barrel heat treating was defective. I've Emailed OS. Let's see what they say.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
05-11-2008 01:27 AM
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pgoelz
Senior Heliman
Location: Rochester MI

UPDATE:

OS wants me to send the carb to them. I thought the rotor (barell) was an expensive part but I just found out it is all of $16 so for now I have ordered a replacement and will simply eat the cost. Perhaps I'll send the defective rotor to them and ask for a warranty replacement so they can have a look at it, but it isn't worth sending the whole carb and waiting for the parts to come back.

The carb body is scored inside by the ridges on the rotor but with a little polishing is probably reusable since there is a lot of surface area and the area is wetted by the fuel and lubricant.

Still curious why it happened and whether anyone else has seen this. Even if the rotor is not obviously stuck, the wear is obvious if you disconnect the throttle linkage and move the throttle by hand while applying a bit of in/out pressure on the rotor. This totally explains my wa-wahs during transition from FFF to hover.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
05-12-2008 07:37 PM
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payne1967
Veteran
Location: warwick uk

it looks like the screw was fitted incorrectly at some point and forced into the barrel
have you taken the carb apart before? or anyone taken the carb apart? has the barrel been stiff to turn from new?
that isn't wear it's incorrect assemble
05-12-2008 11:36 PM
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pgoelz
Senior Heliman
Location: Rochester MI

Interesting take on it.

No, the carb was never disassembled until last weekend. The engine was purchased new in July of 2007. At that time, the throttle rotor was not stiff. In fact, as of last weekend it was still responding OK to the throttle servo.... I just noticed the servo seemed to be straining so I disconnected the linkage and checked it. That is when I noticed the stiffness and the abnormal movement in and out.

I am not sure I can accept that the screw and/or incorrect assembly caused that gouge in the side of the groove. To do that, the screw would have had to be forced into the groove while the rotor was firmly prevented from rotating. That is not easy to do at mid throttle. And there would have been material pushed into the groove. There is none. There is a tiny bit of wear apparent on the end of the screw (barely visible in the photo) but nowhere near what is seen on the rotor. However, the screw is steel and I think the rotor is aluminum with some sort of coating/anodization.

Not readily apparent from the photo is the fact that the gouge is 99% on one side of the groove. If this isn't an assembly issue, then it is probably vibration. But I can't imagine vibration that would be so unidirectional unless there was a force pushing on the rotor to bias it. And there isn't. I checked.... this carb doesn't have a return spring.

The plan is to replace the rotor and screw and also add a second throttle linkage to convert it to a push/pull setup. That might relieve any excess vibration. Beyond that, I'm not sure what else to do.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
05-13-2008 05:05 PM
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pgoelz
Senior Heliman
Location: Rochester MI

Well, OS just Emailed me to tell me they are sending a new carb. Nice service. Unfortunately, I still don't have an explanation of why it happened. But this way, I'll have a new carb AND a replacement rotor so if it happens again I'll at least have a spare while I try to figure it out.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
05-13-2008 07:39 PM
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philthewrench
Senior Heliman
Location: Westchester Co. NY

I had the same thing happen to mine last summer.

I noticed the slop when I was pulling the engine. I was gonna pull the carb apart to give it a good cleaning and change all the fuel lines because I coundn't get it to run right at in a hover. My carb barrel was identical. I thought I somehow left the screw loose or something the last time I had it apart. I ended up taking the dremel to the slot and making it deeper and then taking some material off the boss the screw is in until it felt good again.

That was I guess 3 or 4 gallons ago. I just checked it now and I didn't notice any slop. I think I'll pull it apart a bit later and see. I haven't flow it in a while but the last time I did I don't recall any problems.

Phil

... and now my impression of a lawn dart .......
05-14-2008 02:58 AM
 
 
pgoelz
Senior Heliman
Location: Rochester MI

Uh oh. I was thinking maybe mine was simply a fluke. Now that we have another example, I think this needs a bit more attention.

I looked over my setup carefully. First of all, the gouge is 99% on the side that you can see in the photo. But there is a small amount of gouging on the opposite side of the groove. The two sides of the gouge look to be aligned with the slot.... ie., at an angle to the rotor body. The servo has a bit of gear slop... nothing abnormal. The linkage is loose but near zero slop at the servo abd loose with a bit of slop at the throttle arm. That could allow for some movement in response to vibration. Other than that, everything else looks very normal.

If this was a vibration issue, wouldn't the gouges be symetrical on both sides of the groove? Vibration isn't usually unidirectional, is it? In any event, I find it very hard to imagine any vibration that would be capable of causing that kind of rapid wear in a properly designed carburetor.

So it's back to wondering if there is something wrong with the surface finish (hardening?), assuming the rotor is aluminum. I have not tried scratching it to see if I can tell if it is aluminum or steel. The surface finish looks to me to be anodized aluminum.....

FWIW, I run a fairly low head speed (and therefore engine speed) since I am just sport flying..... about 1600 - 1700 tops. I am not into 3D or violent aerobatics and with this engine I have confined my flying to mostly hovering and slow and fast FF.

EDIT:

After I posted this a thought occurred to me.....

Phil, you said you deepend the slot and lowered the screw. That has to mean the end of the screw is nowhere near as fully engaged in the slot in the area of the gouge as it is elsewhere.... yet you say it has not worn again to the point of being able to feel it. It would be VERY interesting to see if there was any additional wear in the bottom of the deepened slot. If it is not wearing further, then maybe this was a pre-existing condition from the factory?

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
05-14-2008 02:32 PM
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philthewrench
Senior Heliman
Location: Westchester Co. NY




Looks like it hasn't gotten to much worse. I checked for play lateral slop and it felt pretty good even though it looks really bad. I have the very tip of the screw riding all the way down against the bottom of the slot where it is not so deformed.

It looked much more like yours before I beat it up with the dremel but it still works ok. I flew it this morning cause I was thinking about it and wondering how bad it really was. But it seemed alright.

I had assumed that I had just done something stupid reassembling it one day but never really figured what that might have been.

Well I think I'm gonna go order a replacement now .

Phil

... and now my impression of a lawn dart .......
05-15-2008 03:30 AM
 
 
pgoelz
Senior Heliman
Location: Rochester MI

When you took the Dremel to it, could you determine if it is aluminum or steel? If it is steel, then I think it is a LOT less likely this is vibration wear, since the end of the screw would show similar wear.

EDIT:

After handling the rotor again, I think it is obvious that it is aluminum..... it doesn't weigh anywhere near enough for steel.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
05-15-2008 11:45 AM
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pgoelz
Senior Heliman
Location: Rochester MI

OK, to partially close the loop.... I got the replacement rotor today, installed it and a new clutch (the old one was dragging a bit) and test flew it. It ran like a totally different engine. The mixture was easy to set, it idled great, and the mixture was nearly constant from start to finish. So I am thinking the gouge may have been there from the beginning. I don't recall it ever ran this well.

On a side note, the new clutch is great too. I have always had clutch issues... they either break or drag. The last one was fine until I spooled up the first time. As I advanced the throttle, it was loose and then suddenly grabbed. Upon returning to idle, I discovered it now grabbed at idle. When I replaced it this time I wrapped two turns of electrical tape around it and discovered that it was a nice snug fit, so the liner wasn't worn. But the replacement clutch is nice and loose, grabs at an appropriate engine RPM and seems smoother overall. My guess is that there is something funky about Raptor 30 clutches and their heat treatment and the living hinge fatigues...... sometimes to the point of cracking and breaking.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
05-15-2008 11:59 PM
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Jasper7
Key Veteran
Location: Birmingham , UK

Had it on two barrells now

One no as bad as the other.

Jasper 7
T-Rex 600N
Sceadu EVO 50
Lisa, the kids & a Morgage
05-24-2008 08:54 PM
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pgoelz
Senior Heliman
Location: Rochester MI

Uh oh. I'll have to remove mine in another several tanks and see if there is ANY sign of wear. There was none when I installed the replacement.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
05-25-2008 01:56 AM
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JuanRodriguez
Elite Veteran
Location: Rochester, New York

Quote 
My guess is that there is something funky about Raptor 30 clutches and their heat treatment and the living hinge fatigues...... sometimes to the point of cracking and breaking.

Paul,

Regarding your "side note", this has been a well known and well documented problem with the Raptor clutches from day 1..... The problem being too much clearance between the clutch and the liner. Too much excess flexing, as you suggested, and the shoe breaks off eventually. Many of us make our own clutch liners and then machine them on the lathe to give about 6 thou per side (12-14 total) clearance between the two.....

Another "trick" for those who rather not get into the machining aspect is the electrical tape method which in theory, gives the approximate same result......
06-05-2008 08:08 PM
 
 
marked23
Key Veteran
Location: Lynnwood, WA

In Paul's original picture the divot appears to be pretty clean... not like it would look if it was a wear pattern.

Phil's picture looks like a wear pattern.

When you mill a slot like this, the machine would likely come in with a drill and plunge a hole to clear some room before a milling bit would come in and cut the slot. What it looks like in Paul's picture is that the drill missed its mark. So that looks like a manufacturing mistake.

-Mark
06-05-2008 08:36 PM
 
 
pgoelz
Senior Heliman
Location: Rochester MI

But but but..... if you look closely you can see that the edges of the worn area are bare metal. There is a finish on the rest of the rotor. That tells me that the worn area happened after the surface finish was applied. But yes, it did strike me as odd that it looked THAT clean and precise.

Re: my clutch.... the funny thing about my old clutch was that the shoes were NOT broken. Not even cracked. Just sprung out enough to contact the clutch liner at anything above a very low idle. The new one is much better, with no change to the liner. I wonder if the metal is a bit better tempered?

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
06-05-2008 11:23 PM
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jester4
Veteran
Location: Brampton, Ontario (Flyin' outta Mississauga)

Quote 
When you mill a slot like this, the machine would likely come in with a drill and plunge a hole to clear some room before a milling bit would come in and cut

A center cutting end mill will drill and mill in 1 pass. I'm 99.99% sure they didn't use a drill first then mill, especially in aluminum. Just thought I'd point that out

NO SOUP FOR YOU!!
06-06-2008 01:26 PM
 
 
pgoelz
Senior Heliman
Location: Rochester MI

OK, a followup....

I just disassembled the carb from the TT36 that the OS37 that started this thread replaced. The TT36 had hundreds of flights on it and I was curious to see how the carb rotor was holding up. What I found was that the TT36 carb rotor is totally pristine / like new. No wear at all after hundreds of flights in the same heli.

But there was one major difference between the two rotors..... the TT36 rotor is STEEL, not aluminum. I suspect THAT is the major contributer to premature rotor wear.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
06-09-2008 09:27 PM
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pgoelz
Senior Heliman
Location: Rochester MI

UPDATE:

I dropped the engine today to diagnose a grabby clutch (it is a Raptor, after all) and discovered the replacement OS .3SZ-H carb rotor is wearing exactly like the first one. This is after maybe 15 flights. This is ridiculous! I have written to Great Planes (OS service) and advised them of the situation. But unless they have a good answer, I am done with this piece of junk. I have put the TT .36PRO back in the Raptor and I'll put up with the rich midrange if I have to.... at least the carb doesn't wear out after 15 flights.

Let's see what Great Planes has to say.

FWIW, the .37SZ-H carb does NOT have a spring like many other carbs do. Perhaps a spring would prevent vibration from causing rotor wear?

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
08-03-2008 02:14 AM
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captb
Senior Heliman
Location: Arizona Desert

May have some excess vibration from the fan/clutch, balance and check runout. captb

If it's gonna happen it'll happen up there!
08-03-2008 04:36 AM
 
 
pgoelz
Senior Heliman
Location: Rochester MI

If the problem is vibration then the OS design is FAR more susceptible than the TT design. Absolutely nothing has changed..... same fan, clutch, etc. All I did was swap out the TT 36PRO for the OS 37SZ-H. And suddenly the carb rotor started failing.

In the end, of course I agree.... this is obviously a vibration issue. My point is that the aluminum rotor in the OS 37SZ-H is not adequate for the vibration normally found in a heli engine. The TT 36PRO rotor (as well as the rotors in every other engine I have owned since 1970) is pristine after 7 years. The rotor in the OS 37SZ-H has failed twice with an average lifetime of MAYBE 15 flights. THAT is a design flaw. And it does not seem to be confined to the 37SZ-H or to OS, for that matter. Check out the "stuck rotor" threads.... some of the TT Redline rotor seem to have the same problem.

Paul

Paul Goelz
Rochester MI USA
http://www.pgoelz.com
08-03-2008 12:53 PM
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