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A Main Hobbies . Boca Bearings . Modefo's RC Helicopters

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Engines Plugs Mufflers Fuel > third time I've killed OS32SX-H rear bearing in under three gallons...
 
 
ZZ3Astro
Senior Heliman
Location: Panama City, Fl

A quick history:

Raptor 30 with OS32SX-H running Cool Power 30

Yes I know how to align the engine during install, how to keep the needles right and have the opinions of several other pilots that I stay on the rich side of perfect with my needles. I don't run an outrageous headspeed either.

May thru June 2001 - On third gallon through new engine, noticed the engine had less and less power, funny oscillation and ran very hot as if lean, even with super rich needles. Finally pulled engine apart to find it trashed with a bad rear bearing. In October, I sent the engine back and it was repaired (crank/liner/piston/bearings) .

First run was late November - flew it several times a week and burned three gallons by Jan 1. Noticed the oscillation again, drop in power and the funny noise started up shortly. Removed rear plate, rear bearing gone once again.

I immediately ordered a brand new engine thinking this one was just a bad one. I also replaced the fan hub, clutch (the bad bearing kills the clutch pretty quick anyway), started with another new batch of fuel and replaced all of the fuel lines, etc. I even switched to FG blades from wood to take a load off the engine. I spent 45 mins making sure the engine installed without binding, that the clutch was perfectly centered etc. I just started my third gallon of fuel on it and the oscillation is back. On my last flight I could hear the squealing rear bearing begging for mercy once again.

I also owned another OS32 with which I never had a problem with the bearings. The biggest difference with it was I ran mostly CP15 through it, but being a newbie at that time the engine saw plenty of lean runs, etc and still never failed. This newest engine (third I've owned) failed in exactly the same manner as the previous one.

I have narrowed it down to something from the following:

OS32's are garbage
Raptor 30's kill OS32's for some reason
I am doing something stupid I don't know about
Or, I should have used Losi's break-in sand!!

Steve
03-28-2002 Over year old.
HOMEPAGE  
 
 
S.Peterson
Heliman
Location: Sun Prairie, WI

Just a thought. Make sure your engine mount does not touch your engine anywhere but on the mounting lugs. If the little rib down the bottom of the engine hits the bottom of the mount, and then you torque down the mounting screws, it distorts the engine case and will lead to premature bearing failure. Also make sure the top of the mount is perfectly flat and the engine sits flush on it without the screws.

Stu
03-28-2002 Over year old.
 
 
Zxyxx
Senior Heliman
Location: Anaheim

There's definetely nothing wrong with the OS 32. It is the best running, most reliable 30-size engine you can buy. I've owned several of these and never had a problem. I also run 30% CP.
03-28-2002 Over year old.
 
 
mfendley
Senior Heliman
Location: Saint Marys, GA

Try changing the motor mount. You may have gotten one that was machined just a little off. Besides, the mounts are cheap

Mike
03-28-2002 Over year old.
 
 
Darkstar
Senior Heliman
Location: USA

Overtightening

Are you over-tightening the fan assembly to the engine? How did you "lock" the engine when installing the fan?

If you use a piston lock tool and overtighten the fan, this can damage the bearings and seals.

Tim.
03-28-2002 Over year old.
 
 
Steve Campbell
Elite Veteran
Location: Baton Rouge, LA

The OS 32 SX is probably the most widely-used engine in it's class today. Thousands of modelers use this fine little engine with no grief whatsoever.

Having said that, it is obvious yours has a problem. And two with the exact same problem would seem to point at the machine. Could the motor mount possibly be warped, etc., and putting stress on the rear of the crankcase?

Oops; I see that has already been covered by someone else.

I remember hearing about a fellow who had an OS 46 FX-H that was eating rear bearings; he eventually tracked it down to the rear bearing seat being out of round, which was "pinching" the rear bearing, with predictable results. These crankcases are cast aluminum, with some final machining to bring them into specification.

Sounds like you're doing everything right in regards to setting up and operating the engine. Tough call...

Steve

P.S.: I've heard of piston-locking tools damaging the piston, con rod, and wrist pin. But bearings? How? And what seals?
03-28-2002 Over year old.
 
 
Darkstar
Senior Heliman
Location: USA

Steve,

Overtightening the fan assembly can stress the bearings and seals by actually pulling the crankshaft up too far and loading the bearings. There are oil seals on each end of the crank as well that can be damaged.

Tim.
03-28-2002 Over year old.
 
 
Steve Campbell
Elite Veteran
Location: Baton Rouge, LA

Okay, I see now what you're saying. But you can do that regardless of what method is used to immobilize the crank (for tightening down the crank nut).

I thought you were saying that the tool itself would cause this- and that picture just wouldn't focus...

BTW, the delrin fixture that OS makes is far and away the best method for immobilizing the crank, IMO. Other methods put stress on parts; this gadget supports the con rod almost it's entire length, and is nearly stress-free.

Steve
03-28-2002 Over year old.
 
 
Steve Campbell
Elite Veteran
Location: Baton Rouge, LA

I don't recall ever seeing any "seals" either, the few times I've changed engine bearings. Seeing as those big, high speed bearings rely on oil in the fuel for lubrication, seals would sort of defeat that function.

Dunno, maybe Boca makes sealed engine bearings...

I got my crank tool from Tom Unger a few years back. The Evil Empire does have quite a few obscure OS parts, but unless you know the 10 or so digit OS number, you'll never find some of them on the web catalog. I needed that prop drive-washer puller necessary to get the prop washer off the few OS engines that have tapered cranks; in this case, a 12 year old .46 SF plank engine. I searched every which way, with no joy, until I lucked out and saw it in an equally-old flyer that came with my 61 SFN; ya know, the one that shows engines & accessories?

I typed in that long OS number, and there it was, big as day...

Steve
03-28-2002 Over year old.
 
 
Safe_Cracker
Key Veteran
Location: Chicago, IL

Seals??Hmmm nottttt....

Seals you say?Ok, show me....How long does your bearings last?I can see one seal on the outside of the outter bearing to keep oil residue from leaking on your model, but not as a stock item.Actually in an inverted installation in most of the early birds, that oil residue would lubricate the clutch bearing.Anyways, bearings+seals=NO ENGINE!!
03-29-2002 Over year old.
 
 
Darkstar
Senior Heliman
Location: USA

The seal I'm referring to is the shield on the front bearing on the outside of the engine...not a separate seal, and on the front bearing only. Not the rear bearing. My mistake.

But overtightening the fan assembly can certainly cause damage to the bearing and shield by overloading it. Many times a leak will develop as well, while not in itself a problem, it may be a symptom of overtightening.

Tim.
03-29-2002 Over year old.
 
 
jrice45516
Heliman
Location: SoCal

Dude, send that engine into O.S. Repair Service with a sincerely polite, clear, grammatically correct, no-attitude letter explaining the engine history and problem. They will take care of you.

FWIW, the OS32 crankcase clears the stock mount by a good 3/16in.

Dances With Woofs
03-29-2002 Over year old.
 
 
ZZ3Astro
Senior Heliman
Location: Panama City, Fl

Good point on over-tightening the bolt and fan hub. On my last engine, I felt this might be a source of the problem as I really cranked the fan and nut down pretty good. This time I used more loc-tite than usual and screwed the fan on just to snug.. I lock the crank with a toothbrush handle in the carb opening, but like I said I didn't really put the fan on super tight with this new engine. Next I held the fan on cranked the nut against the hub tightly. I wanted to make sure the hub was not putting any real pressure on the bearings.

I will check the motor mount but since I paid such close attention to the alignment in this case, I believe I would have noticed any problem in this area.

Steve
03-29-2002 Over year old.
HOMEPAGE  
 
 
baass
Heliman
Location: Cooper City, Fla.

Your obviously over-torquing the crank. Are u using 3/8 drive tools? My guess is that 100-125 in lbs. is all that is required. You could easily put well over 200 in. lbs. with a 1/4 drive rachet. I worked in a jet engine repair shop for a number of years. Standard torques for a 1/4-28 were 85 in. lbs and 5/16 were 125/150 in.lbs. Not much! Take it easy and your problems will go away.
03-30-2002 Over year old.
 
 
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Engines Plugs Mufflers Fuel > third time I've killed OS32SX-H rear bearing in under three gallons...
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