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HomeAircraftHelicopterBergen R/C Helicopters › Engine vibration following a crash!
11-02-2004 11:07 AM  13 years agoPost 1
ecranage

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West Yorkshire UK

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I have just rebuilt my gasser after a crash that was caused by a battery failure, it hit quite hard on the carb side.

I seem to have deleloped an engine vibration that wasn't there before the crash. The vibes are getting through to the gyro and shaking the tail servo.

Has anyone come across this before?

Is it possible that something in the engine was broken on impact?

Please help me if you can.

Cheers,
Evan

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11-02-2004 11:48 AM  13 years agoPost 2
Malorie

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Paw squared, MI

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During the rebuild, did you dial-indicate the fan?

It is very likely that the crank was knocked out of alignment in the crash.

Malorie

Life's a journey, NOT a destination.

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11-02-2004 12:34 PM  13 years agoPost 3
ecranage

rrApprentice

West Yorkshire UK

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Thanks Mal,

No I didn't, I haven't got the kit to do that. I have got the engine out now, so I will get it checked.

Is it normal for this to happen?

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11-02-2004 01:03 PM  13 years agoPost 4
Chris Bergen

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cassopolis, MI USA

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It kind of depends on the severity of the crash.

You say you crashed carb side down. Did you suck anything into the engine?

Chris D. Bergen

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11-02-2004 01:15 PM  13 years agoPost 5
ecranage

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West Yorkshire UK

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Chris,

I use a K&N air filter, which although it got squashed, it stayed in place so it is unlikely that anything got sucked in.

Mal,

when you say the crank is knocked out of alignment, do you mean the crank maybe bent?

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11-02-2004 10:42 PM  13 years agoPost 6
Chris Bergen

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cassopolis, MI USA

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The crank doesn't necessarily get bent, but twisted out of alignment. This is also why you don't want to hold the flywheel while tightening the fan bolt.

If you dial indicate the fan hub and it is out more than .002, remove it and check the crankshaft on the tapered area where the fan hub sits. If it is out more than .002, then we need to straighten the crank.

Another thing to consider is that the needles may have been inadvertantly turned in the crash or reassembly. Check 'em, just to be sure.

Chris D. Bergen

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11-03-2004 09:58 AM  13 years agoPost 7
ecranage

rrApprentice

West Yorkshire UK

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Chris,

Thanks for your reply, can you tell me if the crank in the 231 engine is the same as the old 23?

Evan

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11-03-2004 10:55 AM  13 years agoPost 8
daveye

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North Carolina

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i dont think it would be a vibration from the motor unless you see the fuel foaming. If it was the engine or fan that was out you would have a high frequency vibration. It sounds more like something else.

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11-03-2004 01:57 PM  13 years agoPost 9
Chris Bergen

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cassopolis, MI USA

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The G23, G231, and G26 all use the same crank. It's the RC engines that have different cranks. I apologize for the error, I was thinking of a mod that we tried using an RC engine cylinder and piston with a puh case.

daveye is right though, make sure you check all the obvious stuff as well. Head axle, main shaft, start shaft, Check the head block itself for being tweaked, frame alignment, engine alignment. Check the delrin bushings on the fan hub for uneven wear.

Tail rotor input and output shaft, front xmsn shaft as well as delrin coupler running true.

Sometimes a crash will "tweak" something that does not become obvious right away.

Chris D. Bergen

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11-03-2004 05:43 PM  13 years agoPost 10
ecranage

rrApprentice

West Yorkshire UK

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I had the engine over to Multicom today and we put it on the dial-indicater.

The fan is running correct to 0.001in, the only thing I haven't checked yet is the clutch shaft.

It is definatley not any further down the system than that as the vibes are evident before the clutch engages.

It could be the clutch unit its self but I haven't taken that out yet. The next step is the put the engine back in without the clutch and see what the gyro thinks to that!

Evan

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11-04-2004 01:43 AM  13 years agoPost 11
Chris Bergen

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cassopolis, MI USA

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Now this is something new to add to the mix. The engine will have vibes at an idle, but smooth up at normal RPM.

I was not aware you were concerned with the vibes at idle .

Did you try it in a hover?

Be careful with running it without the clutch installed. You run the risk of overspeeding the engine.

Chris D. Bergen

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11-05-2004 05:56 PM  13 years agoPost 12
iflybyu77

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Fort Wayne, IN

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the clutch?
Could the clutch have been worn unevenly perhaps? Did the engine continue to run upon impact?

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11-05-2004 07:51 PM  13 years agoPost 13
ecranage

rrApprentice

West Yorkshire UK

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I replaced the clutch today, but it didn't make any difference

Chris,
It's not the vibes at idle that concern me, it's just that they don't go away when the revs increase.
The fact that there were non before the crash is what concerns me.

It's driving me crazy as I can't find anything wrong. There is nothing bent, lose or broken!

The main trouble is that the vibes are affecting the gyro which is making the tail kick so bad that the whole thing looks like it would explode if I attempted to take off!

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11-06-2004 02:24 AM  13 years agoPost 14
daveye

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North Carolina

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that vibration must be comming from off the main shaft or head somewhere and not around the engine or clutch. The vibration there would be much higher frequency. Perhaps your tail kicking is caused from not grounding your bearing block to the tail boom??

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11-06-2004 09:11 AM  13 years agoPost 15
ecranage

rrApprentice

West Yorkshire UK

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It can't be coming from the main shaft as it is there before the clutch engages.
Which bearing block are you saying to ground?

It is a high frequency vibration and is causing the fuel to foam

Evan

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11-06-2004 01:20 PM  13 years agoPost 16
JuanRodriguez

rrProfessor

The Villages, Florida

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Evan,
Since you found nothing bent, broken or loose and the dial indicating is good, I would focus on engine tuning as someone else already suggested (ChrisB ??)

An out of tune engine can certainly cause you "vibe" problems which will more often than not be picked up by the gyro and thus effect the tail.....

Good luck.... keep us posted...

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11-07-2004 01:00 PM  13 years agoPost 17
Malorie

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Paw squared, MI

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Check for a bent headblock.

The easiest way to check it is to lay a straightedge across the bottom of the head perpendicular to the split. If the bottoms of both sides of the split are not even, then your head is bent and should be replaced. A trained eye can also be used to spot this by eyeballing perpendicular to the split.

This is an easy thing to miss on a rebuild and can cause a lot of tail chasing (figuratively and literally).

Best of luck,
Malorie

Life's a journey, NOT a destination.

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