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HelicopterEngines Plugs Mufflers Fuel › OS .50 -- Murder or Suicide
04-26-2004 07:53 AM  13 years agoPost 1
pariah

rrVeteran

South Jordan, UT - United States of America

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While setting the main needle on my OS .50, I ran into a problem: I'd already ran about 1.5 gallons of fuel through it (entirely on the bench), so it should be fairly well into the 'broken in' phase.

I (either wisely or foolishly) decided at that point to see how it ran in my heli, and while I was at it, set the radio's 'idle' setting, as well as its 'cutoff' setting. For the entire process, I had removed the main and tail rotor blades; I did leave the flybar paddles on, however. It's also noteworthy that I didn't even get through one half tank before my 'whoops!'

The engine had been running rather rich, and was quite cool after a few minutes of running at 1/2 throttle, so I moved it to full throttle, checked the temp, moved it back down, and then I leaned it out a bit-- being very, very careful throughout the whole process that I didn't get it too lean. I was actually in the process of richening it up (engine was starting to get hot at the backplate) when it appeared to seize. Not only did the engine stop-- when the engine quit, everything stopped instantly -- rotor head, tail rotor grips -- the whole smash. This is from full throttle.

So now I know what it's like if life had a 'pause' button.

The second thought was pretty much along the lines of the first one: The engine was quite hot -- ie at the back-plate of the crankshaft. However, it should be noted that it had not run for very long in this state -- probably 20-30 seconds at most.

While I was waiting for it to cool down enough to comfortably remove it from my machine, I took a close look -- and noticed something.

The screw (and blocks) that hold the carb down? Not there anymore. The carb was in place, but not secured down. (They were on the ground directly beneath the model)

This was my fault, and I realized it instantly: I forgot to put loc-tite on this as for some reason it didn't occur to me that the carb needed some loc-tite to hold it down. I do have no doubt that every other bolt in my heli did have loc-tite. (On my heli, I knew I had to loc-tite everything metal-to-metal; the engine, however, came mostly assembled with loc-tite in every bolt but the carb... so I used threadlocker everywhere but the carb!

As I pulled the engine out, I noticed another thing: one of the bolts that attaches the clutch to the fan had come loose, and had scored (lightly) the top of the clutch bell. Looked more like a screwdriver scratch than anything. Obviously not enough lock-tite on that particular clutch bolt.

I can say that everywhere else, I did use enough threadlocker. After pulling off the backplate, I was greeted with a nasty sight: The connecting rod had broken -- actually, looked like it had shattered where it connects to the crankshaft. The wrist pin looked none the worse for wear, however.


So, I pulled off the head, and worked the cylinder liner and piston out of the engine. There was no debris in the top end of the cylinder, and no rattling in the muffler. Nothing on the cement under the model either... So, I pushed the piston out through the top. No problems. The cylinder lining and piston have no scoring, scratches, or nicks. The first good sign so far.

So it appears that the connecting rod had broken, and the piston had continued to move towards BDC; but the crankshaft spun around and struck what was left of the connecting rod, stopping all movement in an instant-- keeping any of the debris from being sucked into the cylinder and causing damage there.

As previously stated, the cylinder, piston, and crankshaft appear to have absolutely no damage whatsoever; just the connecting rod.

After taking it to my LHS, and attempting to learn exactly what had gone wrong, the explanation I recieved was this:

Because the carb had come loose, it probably was sucking extra air in under the carb, and that leaned the engine out well beyond my intentions. It got hot, and the connecting rod broke. He also told me it would likely be the only thing that needed replacement.

Sounds like that's exactly what had happened. But I'm wondering if I could get a more detailed explanation on what happened.

Did the loose bolt on the clutch contribute to the demise of the connecting rod?

Was this actually a good thing? (meaning that by some coincidence, breaking the connecting rod saved me from breaking something more expensive?)

Either way -- I hope my story might help some dry-roasted nut like myself from making the same mistake(s) I did.

I'd appreciate any comments on just how stupid the mistakes I made were, so long as you help me understand why they were stupid, and just how dangerous they really were. Did I do anything right?

PS: The LHS is currently rebuilding/repairing the engine (connecting rod is $17), and setting up/safety checking my heli while they're at it.

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04-26-2004 10:57 AM  13 years agoPost 2
Al Magaloff

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12,199 Posts- Enough Time Wasted. See Ya!

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I think the connecting rod broke, because you were running with virtually no load , lean, at full throttle. Start your car up, and hold the pedal to the floor in neutral, see how long it lasts. When you get your new motor, forget the bench break-in. Put it in the helicopter and fly it. That is the best break-in.
.

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04-26-2004 11:16 AM  13 years agoPost 3
nivlek

rrProfessor

Norfolk England

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Personally I like to run my heli engines in while fitted in a fixed wing machine, so my opinion differs from that of Al Magaloff in that respect.
However, running the engine flat out with virtually no load is certain to
destroy the engine, so I have to agree with him on that point.

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04-26-2004 01:28 PM  13 years agoPost 4
T.C.

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Nottingham. England.

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Running it like you did with no load, would almost certainly have allowed it to over rev, which is possibly why the con rod has shattered.

Also the bolts that have come out, can also be put down to the engine over revving & high frequency vibrations.

Tony

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04-26-2004 01:29 PM  13 years agoPost 5
T.C.

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Nottingham. England.

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BTW.

I agree with Al on this point.
When you get your new motor, forget the bench break-in. Put it in the helicopter and fly it. That is the best break-in.

Tony

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04-26-2004 01:45 PM  13 years agoPost 6
brian chan

rrApprentice

Hong Kong

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Previously, I run in my Webra 35 in the Raptor with the tail and head blades removed. However, I just run it with high speed for 5 secs and then low speed for 30 secs consecutively.

Now, I won't do that as it is wasting fuel at all. Just fly the heli.
Without loading on the main rotor, the engine can easily over speed causing execusive heat unless you keep it in 4 strokes stage

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04-26-2004 04:30 PM  13 years agoPost 7
2LTime

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Walworth,NY

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I'm surprised your clutch and bell didn't explode at that high of Revs. Put it in the machine and fly!

Jeff

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04-26-2004 05:07 PM  13 years agoPost 8
cdrking

rrElite Veteran

Seattle

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I agree with Al. Stick it in and fly it. I broke my OS 50 in just by putting in the heli and running it a bit rich for a few tanks. Lean it down and fly the piss out of it.

It now has about 25 gallons thru it and everytime I tear it down to inspect it looks great. The reason I pull it apart is because I've running wildcat fuel and want to see how it's holding up.

No problems at all.

Jeff

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04-26-2004 07:16 PM  13 years agoPost 9
pariah

rrVeteran

South Jordan, UT - United States of America

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Thanks for the replies.

I did notice one other thing, but it's not so much related to the engine dying... Maybe doug or someone can give a good answer on this one.

I've noticed in doug's comments about the rear bearing (and web removal mod) picutres that show the damage done to the bearing after enough runtime. I noted the repeating 'bands' that appeared in the pictures.

When I took a close look at my crankshaft (after pulling it apart), it had similar 'bands' where it sits against the rear bearing. These bands were on the counterweight-side of the crankshaft, but not on the wrist-pin/webbing side.

Just wondering if this is 'more of the same' with reguards to the rear bearing and its assosciated problems, and was simply unmentioned in the posts I read.

Again, thanks for the replies.

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04-26-2004 08:23 PM  13 years agoPost 10
AndyH

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Rockledge, FL

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One note: Locktite is softened by heat - so it wouldn't have done you any good had you put it on the carb bolts.

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04-26-2004 10:02 PM  13 years agoPost 11
HeliNerd

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Navarre, FL

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.

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04-27-2004 12:23 AM  13 years agoPost 12
Al Magaloff

rrMaster

12,199 Posts- Enough Time Wasted. See Ya!

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The only place hot enough to melt LockTite is the exhaust side of the motor, not the carb.
.

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04-27-2004 01:03 AM  13 years agoPost 13
jb_turner

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USA

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.

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04-27-2004 01:04 AM  13 years agoPost 14
jb_turner

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USA

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You broke it with an improper break in procedure (no load). Get a new motor and HELP!.

DO NOT USE HEAD LOADERS for break in... use only Blades and HELP.

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04-27-2004 01:10 AM  13 years agoPost 15
Al Magaloff

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12,199 Posts- Enough Time Wasted. See Ya!

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Agree with JB. I've been breaking in motors while flying them, for a while. Never broke one yet. Only wore one out. You break them in as you will use them. My business is automotive/marine engines. We never break a motor in doinkin' around on the test stand, running pig rich. In fact, it's the worst thing you can do to a new motor, be it model or full scale. As always, YMMV.
.
.

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04-27-2004 01:47 AM  13 years agoPost 16
Gary Jenkins

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Nowhere, US

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Fly it to break it in.

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04-27-2004 07:00 PM  13 years agoPost 17
A. Bundy

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Aurora,IL. 30W/SW of Chicago

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Just fly it.Pooch it one tank and go.

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05-01-2004 04:57 PM  13 years agoPost 18
challenger

rrNovice

S.E. Michigan

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I also believe a bench break-in is unecessary

I have built an operated many many models and full size engines, and a bench break in is the last thing that I would do (unless it is a multi cylinder 4 stroke model engine, and even then, its an operational check under a load.
I agree that you simply over rev'd your engine, and all of your other observations may have contributed, but my guess is, the over rev'g did you in.

I simply install my engine, run it rich for for a few tanks, and if its a heli that I'm flying, I'll hover for the first tank or so and progressively lean it with each new tank of fuel.

By the time I get to my 4th tank, the mixture is pretty close to were it will remain, for a few of gallons, and at best it will be about a half turn from its final resting place.

During my couple tanks of hovering, the engine should not be so rich that it will not rev with authroity. It shoud not load up and bog down, but it should have a good amount of smoke and power.

During my hovering excercise I will frequently pop it up into a high hover then slowly settle to a low hover and repeat this for a couple tanks. Then fly it and inspect everything between each flight.

When everything else fails read the instructions

Good Luck
Al

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05-01-2004 05:17 PM  13 years agoPost 19
Colibri

rrKey Veteran

The Netherlands

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PS: The LHS is currently rebuilding/repairing the engine (connecting rod is $17), and setting up/safety checking my heli while they're at it.
If the shop owner didn't warn you not to run your engine without any load at full throttle (I assume you told him what you told us) then I wouldn't let him near my helicopter.

You obviously made an honest mistake but the shop owner should know better.

Tim

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HelicopterEngines Plugs Mufflers Fuel › OS .50 -- Murder or Suicide
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