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Rotax 912 Torque Spec Error

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Dennis.Kirby(at)kirtland.
Guest

Posted: Thu Oct 04, 2007 7:15 am Post subject: Rotax 912 Torque Spec Error

Fellow 912 Drivers -



I discovered an error in the official Rotax manuals that specify the

torque value for the lock-nuts that secure the exhaust system.  These

are the copper M8 lock-nuts - two at each exhaust port.



The Rotax 912 Installation Manual (sec 10.1) clearly states that these

nuts should be torqued to 177 inch-pounds.  While doing maintenance

today, I was reinstalling the exhaust system on my 912ul, and tightened

these lock-nuts to the specified value.  



Afterward, I noticed that the two studs were distorted - they were no

longer pointed straight out of the cylinder head, but skewed a bit from

being overtightened.



I called Lockwood, and the tech guy there looked up the torque value

from the Rotax 912 Illustrated Parts Manual.  The number listed there

was 105 ft-lb.  I had WAY overtightened those nuts!  Looks like I'll be

ordering a pair of new exhaust studs.  Fortunately, this was a cheap

lesson for me - they cost only $3.50 each.  But it mad me mad that, in

my attempt to do the right thing, the Rotax manual provided wrong

information.



So the lessons here worth passing on to you all are: 1) The torque value

for the exhaust system nuts listed in the Installation Manual is WRONG,

and 2) Refer to the Illustrated Parts Manual for all torques for your

Rotax engine.



I hope this helps someone avoid the mistake I made.  Happy flying ...



Dennis Kirby

Mark-III Classic, 912ul, in

Cedar Crest, NM

jenelson1(at)hotmail.com
Guest

Posted: Thu Oct 04, 2007 7:45 am Post subject: Rotax 912 Torque Spec Error

177 inch pounds is only 14.74 Ft-lbs  was it listed in the book as In-lbs or Ft-lbs?

  

 Do not archive



 	  Quote: 	
		   Subject: Rotax 912 Torque Spec Error 

 Date: Thu, 4 Oct 2007 09:07:48 -0600

 From: Dennis.Kirby(at)kirtland.af.mil

 To: kolb-list(at)matronics.com

 

 --> Kolb-List message posted by: "Kirby Dennis Contr MDA/AL" <Dennis.Kirby(at)kirtland.af.mil>

 

 

 

 

 Fellow 912 Drivers -

 

 I discovered an error in the official Rotax manuals that specify the

 torque value for the lock-nuts that secure the exhaust system. These

 are the copper M8 lock-nuts - two at each exhaust port.

 

 The Rotax 912 Installation Manual (sec 10.1) clearly states that these

 nuts should be torqued to 177 inch-pounds. While doing maintenance

 today, I was reinstalling the exhaust system on my 912ul, and tightened

 these lock-nuts to the specified value. 

 

 Afterward, I noticed that the two studs were distorted - they were no

 longer pointed straight out of the cylinder head, but skewed a bit from

 being overtightened.

 

 I called Lockwood, and the tech guy there looked up the torque value

 from the Rotax 912 Illustrated Parts Manual. The number listed there

 was 105 ft-lb. I had WAY overtightened those nuts! Looks like I'll be

 ordering a pair of new exhaust studs. Fortunately, this was a cheap

 lesson for me - they cost only $3.50 each. But it mad me mad that, in

 my attempt to do the right thing, the Rotax manual provided wrong

 information.

 

 So the lessons here worth passing on to you all are: 1) The torque value

 for the exhaust system nuts listed in the Installation Manual is WRONG,

 and 2) Refer to the Illustrated Parts Manual for all torques for your

 Rotax engine.

 

 I hope this helps someone avoid the mistake I made. Happy flying ...

 

 Dennis Kirby

 Mark-III Classic, 912ul, in

 Cedar C-===================================

 

 

 


	


Climb to the top of the charts!  Play Star Shuffle:  the word scramble challenge with star power. Play Now!  [quote][b]

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Thu Oct 04, 2007 11:53 am Post subject: Re: Rotax 912 Torque Spec Error

177 inch pounds is way to much torque for a bolt that size....  The fact that it goes into aluminum make it worse      Lucky its just a bent stud rather than it being stripped out of the cylinder head.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

jindoguy(at)gmail.com
Guest

Posted: Thu Oct 04, 2007 7:06 pm Post subject: Rotax 912 Torque Spec Error

Dennis, Second biggest thing stressed by Eric, was always check that you have the latest version of the manual. R.O.A.N. sent out a notice in late July that all 912 installation manuals had been superceded.



"Rotax has announced the REPLACEMENT of the following 912 Series Installation manuals: 



- Installation Manual Rotax 912 A, Edition 0, Rev 2

- Installation Manual Rotax 912 F, Edition 0, Rev 3

- Installation Manual Rotax 912 S, Edition 0, Rev 2

- Installation Manual Rotax 912 UL, Edition 2, Rev 2 



These manuals ARE NO LONGER VALID and have been REPLACED by:



- Installation Manual Rotax 912 Series, May 01/2007, Edition 1, Rev0. (Rotax Part No. 898642)"



I downloaded the new installation manual and it gives the same spec as the old one, 12 to 20 Nm (106-177in lb) and both refer to SI-05-97, the relevant part, I believe is: 



"It should be noted that this is maximum torque value, and in all cases flange nuts

should never be torqued such that the exhaust flange makes contact with the cylinder

head. If necessary a lesser torque value may be used down to a minimum value of 

12 Nm (110 in.lb.) Maintenance personnel should always insure that the exhaust

flange nuts are tightened to the maximum torque possible, not exceeding 20 Nm (180

in.lb.), while still respecting the need for clearance between the flange and the 

cylinder head."



Hope this helps.



Rick





 



On 10/4/07, Jeff Nelson <jenelson1(at)hotmail.com  (jenelson1(at)hotmail.com)> wrote:[quote]     177 inch pounds is only 14.74 Ft-lbs  was it listed in the book as In-lbs or Ft-lbs?

  

 Do not archive



 	  Quote: 	
		   Subject: Rotax 912 Torque Spec Error 

 Date: Thu, 4 Oct 2007 09:07:48 -0600

 From:  Dennis.Kirby(at)kirtland.af.mil (Dennis.Kirby(at)kirtland.af.mil)

 To: kolb-list(at)matronics.com (kolb-list(at)matronics.com) 

 

 --> Kolb-List message posted by: "Kirby Dennis Contr MDA/AL" <Dennis.Kirby(at)kirtland.af.mil  (Dennis.Kirby(at)kirtland.af.mil)>

 

 

 

 

 Fellow 912 Drivers -

 

 I discovered an error in the official Rotax manuals that specify the

 torque value for the lock-nuts that secure the exhaust system. These 

 are the copper M8 lock-nuts - two at each exhaust port.

 

 The Rotax 912 Installation Manual (sec 10.1) clearly states that these

 nuts should be torqued to 177 inch-pounds. While doing maintenance 

 today, I was reinstalling the exhaust system on my 912ul, and tightened

 these lock-nuts to the specified value. 

 

 Afterward, I noticed that the two studs were distorted - they were no

 longer pointed straight out of the cylinder head, but skewed a bit from 

 being overtightened.

 

 I called Lockwood, and the tech guy there looked up the torque value

 from the Rotax 912 Illustrated Parts Manual. The number listed there

 was 105 ft-lb. I had WAY overtightened those nuts! Looks like I'll be 

 ordering a pair of new exhaust studs. Fortunately, this was a cheap

 lesson for me - they cost only $3.50 each. But it mad me mad that, in

 my attempt to do the right thing, the Rotax manual provided wrong 

 information.

 

 So the lessons here worth passing on to you all are: 1) The torque value

 for the exhaust system nuts listed in the Installation Manual is WRONG,

 and 2) Refer to the Illustrated Parts Manual for all torques for your 

 Rotax engine.

 

 I hope this helps someone avoid the mistake I made. Happy flying ...

 

 Dennis Kirby

 Mark-III Classic, 912ul, in


	


 	  Quote: 	
		   Cedar C-=================================== 

 

 

 


	




Climb to the top of the charts!  Play Star Shuffle:  the word scramble challenge with star power.  Play Now!  [quote][b]  http://www.matronics.com/Navigator?Kolb-List http://forums.matronics.com 

when you live at the airport.  [quote][b]

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Thu Oct 04, 2007 9:26 pm Post subject: Re: Rotax 912 Torque Spec Error

These things can happen, but I would encourage everyone to download the most current manuals on line and sign up for automatic notification of manual changes through ROAN. The torque values of a number of nuts and bolts were changed a while back in a manual revision. 

There is a new Heavy maint. and Installation manual out. 



There is a new SB out as of today.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

slyck(at)frontiernet.net
Guest

Posted: Fri Oct 05, 2007 5:44 am Post subject: Rotax 912 Torque Spec Error

While we are on the torque value topic,  the Warp Drive spec for  

those little 1/4" hub bolts

(4 per blade on the HP) is 120 in lbs.   Three years ago, while  

assembling mine, one of those

"genyoowine" aircraft nuts stripped out while attaining that value.

-Made me feel a little creepy as you might understand.  OK, maybe  

that was a defective

nut but still that is a lot of stress for such a small diameter.  - 

teensy threads too.

I now use 110 in lbs and retorque after either a good ground runup or  

a short test hop.

BB

MKIIIX040

Joined: 31 Mar 2006
Posts: 123
Location: Millinocket, Maine

Posted: Fri Oct 05, 2007 6:42 am Post subject: Rotax 912 Torque Spec Error

Hey Bob,  I noticed that if I loosened the 6 main prop bolts on Warps HPL

hub it

put tremendous presure on the smaller inside bolts.

  Maybe I should be replacing mine, although I doubt anything would happen

even if all those smaller blade bolts fell out.

Vic

_________________
MKIIIX040
912UL

jindoguy(at)gmail.com
Guest

Posted: Fri Oct 05, 2007 6:51 am Post subject: Rotax 912 Torque Spec Error

Bob, Interesting, the 8mm bolts on my Powerfin are torqued to 175 in.lb. into the steel prop flange and into the aluminum body of the prop hub per the instructions that come with the prop.



 Rick



On 10/5/07, robert bean <slyck(at)frontiernet.net (slyck(at)frontiernet.net)> wrote: [quote]--> Kolb-List message posted by: robert bean <slyck(at)frontiernet.net  (slyck(at)frontiernet.net)>



While we are on the torque value topic,  the Warp Drive spec for

those little 1/4" hub bolts

(4 per blade on the HP) is 120 in lbs.   Three years ago, while

assembling mine, one of those

"genyoowine" aircraft nuts stripped out while attaining that value. 

-Made me feel a little creepy as you might understand.  OK, maybe

that was a defective

nut but still that is a lot of stress for such a small diameter.  -

teensy threads too.

I now use 110 in lbs and retorque after either a good ground runup or 

when you live at the airport.  [quote][b]

neilsenrm(at)comcast.net
Guest

Posted: Fri Oct 05, 2007 8:09 am Post subject: Rotax 912 Torque Spec Error

Robert

  

 The friction pressure of a prop bolted against prop hub is the primary way that torque is transfered to the prop. If you reduce the recommended torque on the bolts the prop bolts could break in shear and the prop might come off. I had a wood prop on a Weedhopper that would shrink and expand depending on the weather. One day it got loose and sheared to prop bolts clean off. Later I was told that wood props need to be retorqued with each change of season or sooner.

  

 Richard Girard is right about the 8mm bolts on the Powerfin. I use some long grade 5, 5/16 bolts that have a higher torque rating than the recommended 175 in lb or 20 nm but I torque to the prop makers recomendation. I asked Stuart about using the bolts higher rating once and got my ass chewed just for asking.

  

 Rick Neilsen

 Redrive VW powered MKIIIC

  

 [quote]-------------- Original message -------------- 

From: "Richard Girard" <jindoguy(at)gmail.com> 

Bob, Interesting, the 8mm bolts on my Powerfin are torqued to 175 in.lb. into the steel prop flange and into the aluminum body of the prop hub per the instructions that come with the prop.



Rick



 On 10/5/07, robert bean <slyck(at)frontiernet.net (slyck(at)frontiernet.net)> wrote:   	  Quote: 	
		  --> Kolb-List message posted by: robert bean <slyck(at)frontiernet.net  (slyck(at)frontiernet.net)>



While we are on the torque value topic,  the Warp Drive spec for

those little 1/4" hub bolts

(4 per blade on the HP) is 120 in lbs.   Three years ago, while

assembling mine, one of those

"genyoowine" aircraft nuts stripped out while attaining that value. 

-Made me feel a little creepy as you might understand.  OK, maybe

that was a defective

nut but still that is a lot of stress for such a small diameter.  -

teensy threads too.

I now use 110 in lbs and retorque after either a good ground runup or 

when you live at the airport.  	  Quote: 	
		  

	
	


[b]

MKIIIX040

Joined: 31 Mar 2006
Posts: 123
Location: Millinocket, Maine

Posted: Fri Oct 05, 2007 9:01 am Post subject: Rotax 912 Torque Spec Error

Robert isn't talking about the main prop  bolts.

  

 Vic do not archive

   [quote][b]

_________________
MKIIIX040
912UL

Steve Boetto

Joined: 11 Jan 2006
Posts: 364

Posted: Fri Oct 05, 2007 9:51 am Post subject: Rotax 912 Torque Spec Error

In a message dated 10/5/2007 12:10:47 P.M. Eastern Standard Time,  neilsenrm(at)comcast.net writes:

  	  Quote: 	
		  The    friction pressure of a prop bolted against prop hub is the primary way that    torque is transfered to the prop. If you reduce the recommended torque on    the bolts the prop bolts could break in shear 	


 

 Rick,

 You are right about the friction, but I believe what fails the bolts is  fatigue from the bolts slightly bending.

 Never had any trouble with my Sensenich 64x79 here in Fla where we have big  changes in temp and humidity. I did however check the torque monthly. After the  first year it seemed to stabilize.

  

 Steve

Firefly 007/Floats

do not  archive



See what's t="_blank">Make AOL Your Homepage.

  [quote][b]

jindoguy(at)gmail.com
Guest

Posted: Fri Oct 05, 2007 1:49 pm Post subject: Rotax 912 Torque Spec Error

Steve, I think you and Rick N. are both right, just looking at it from different ways. The prop gets loose as the wood shrinks and the torque pulses of the engine then rock the prop back and forth against the loosened bolts. Eventually, the prop bolts fail in shear. 



Rick



On 10/5/07, N27SB(at)aol.com (N27SB(at)aol.com) <N27SB(at)aol.com (N27SB(at)aol.com)> wrote:[quote]       In a message dated 10/5/2007 12:10:47 P.M. Eastern Standard Time,  neilsenrm(at)comcast.net (neilsenrm(at)comcast.net) writes:

  	  Quote: 	
		  The    friction pressure of a prop bolted against prop hub is the primary way that    torque is transfered to the prop. If you reduce the recommended torque on    the bolts the prop bolts could break in shear 	


 

 Rick,

 You are right about the friction, but I believe what fails the bolts is  fatigue from the bolts slightly bending.

 Never had any trouble with my Sensenich 64x79 here in Fla where we have big  changes in temp and humidity. I did however check the torque monthly. After the  first year it seemed to stabilize.

  

 Steve

Firefly 007/Floats

do not  archive



 See what's t="_blank">Make AOL Your Homepage.

  [quote][b]  http://www.matronics.com/Navigator?Kolb-List http://forums.matronics.com 

when you live at the airport.  [quote][b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Fri Oct 05, 2007 4:14 pm Post subject: Rotax 912 Torque Spec Error

Rick G:

  

 Works a little different if your system uses drive lugs,  like the Warp Drive.

  

 I very seldom break a prop bolt. One or two since I  started flying 912 series engines some time ago.

  

 Question:  Would failure in shear and bending be the  same?  Seems to me shearing off 6 prop bolts would be tough to do with a  wooden prop.  Bend them enough cycles and they will fail.

  

 john h

 mkIII

 [quote]The    prop gets loose as the wood shrinks and the torque pulses of the engine then    rock the prop back and forth against the loosened bolts. Eventually, the prop    bolts fail in shear. 



Rick

[b]

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jindoguy(at)gmail.com
Guest

Posted: Fri Oct 05, 2007 7:46 pm Post subject: Rotax 912 Torque Spec Error

John, Go to Canard Aviators at yahoo groups and read Marc Zeitlin's story. Lyc O-360's have drive lugs and 3/8" bolts to hold on the prop. Look at the pictures of what the prop did to the wing and winglet when it departed. It's a chicken and egg question when you find yourself with a prop one moment and without one the next. 



Rick



On 10/5/07, John Hauck <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)> wrote:[quote]        Rick G:

  

 Works a little different if your system uses drive lugs,  like the Warp Drive.

  

 I very seldom break a prop bolt. One or two since I  started flying 912 series engines some time ago.

  

 Question:  Would failure in shear and bending be the  same?  Seems to me shearing off 6 prop bolts would be tough to do with a  wooden prop.  Bend them enough cycles and they will fail.

  

 john h

 mkIII

  	  Quote: 	
		  The    prop gets loose as the wood shrinks and the torque pulses of the engine then    rock the prop back and forth against the loosened bolts. Eventually, the prop    bolts fail in shear. 



Rick

	
   [quote][b]  http://www.matronics.com/Navigator?Kolb-List http://forums.matronics.com 

when you live at the airport.  [quote][b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Fri Oct 05, 2007 8:13 pm Post subject: Rotax 912 Torque Spec Error

Rick G:

  

 Thank goodness we have no encountered prop seperation  problems with 912 series engines, that I am aware of.

  

 Does an 0-360 have any kind of torsional vibration  dampening, other than the prop?

  

 john h

 mkIII

  

  

 [quote]    

  Lyc O-360's have drive lugs    and 3/8" bolts to hold on the prop. next. 



Rick

 [b]

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jindoguy(at)gmail.com
Guest

Posted: Fri Oct 05, 2007 9:07 pm Post subject: Rotax 912 Torque Spec Error

No, theres a flywheel to carry a ring gear for the starter and that adds very little since it's aluminum. Rotax has the benefit of 40 years of engineering science to make their little jewel work. I didn't really appreciate what their engineers had accomplished until I tool Eric's class. Lyc is stuck making adaptations to the technologies of the 1930's. Like the Rotax, it's a real testiment to the engineering technology of its day. 



Rick



On 10/5/07, John Hauck <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)> wrote:[quote]        Rick G:

  

 Thank goodness we have no encountered prop seperation  problems with 912 series engines, that I am aware of.

  

 Does an 0-360 have any kind of torsional vibration  dampening, other than the prop?

  

 john h

 mkIII

  

  

  	  Quote: 	
		      

  Lyc O-360's have drive lugs    and 3/8" bolts to hold on the prop. next. 



Rick

 	
   [quote][b]  http://www.matronics.com/Navigator?Kolb-List http://forums.matronics.com 

when you live at the airport.  [quote][b]

ceengland(at)bellsouth.ne
Guest

Posted: Sat Oct 06, 2007 5:32 pm Post subject: Rotax 912 Torque Spec Error

John Hauck wrote:

 	  Quote: 	
		   Rick G:

  

 Thank goodness we have no encountered prop seperation problems with 912 

 series engines, that I am aware of.

  

 Does an 0-360 have any kind of torsional vibration dampening, other than 

 the prop?

  

 john h

 mkIII



<Insert looong howl of laughter here.>
	




No. It is, after all, a certified engine with all the shortcomings that 

implies.



I hope y'all don't mind input from a non-Kolb flier.



I'm building an RV-7. Because of how rough Lyc's typically are, I 

debated for a couple of years about using an alternative engine before 

giving in to the time saving factor of doing a standard Lyc 

installation. Any 4 cyl 4-stoke engine has strong torque reversals 

between each power pulse. The only hint of damping in a Lyc is on *some* 

of the -360's, that have a 'G' in the suffix letters. Even those don't 

have anything between the crank & the prop; they have little pivoting 

weights attached to the counterweights on the crank.



The idea that friction between the back of a wood prop & the metal prop 

flange keeps the prop from moving is common among pilots of larger 

planes, too, but it just doesn't pass a sanity check in all but the very 

lowest power situations. In every 'normal' a/c prop installation I'm 

aware of, the drive lugs are what transfer the rotational energy from 

the prop flange to the prop. (That's why they are called 'drive lugs'  )



All the bolts do is keep the prop from 'rocking' in and out of the plane 

of the flange. If the prop bolts get loose, motion of the a/c, torque 

pulses & reversals will cause the prop to 'rock' on the flange, 

wallowing out the close-tolerance holes where the drive lugs fit. Now 

the prop is both rocking, bending the bolts (as John mentioned earlier) 

and getting it's lug-holes hammered out bigger and bigger by each pulse. 

Things feed on themselves & the bolts soon fail.



Want evidence that it ain't friction that keeps blades stable? Ask IVO 

about their props for 4 cyl Lycs (if they have started selling them 

again). There are no drive lugs in an IVO hub, and the bolt holes in the 

blades are way over-sized for the bolt diameter. I've flown 2 different 

IVO's on a 160 hp O-320. Both had blade movement. The installation 

requirements were to place 'witness tape' (1st copper, then stainless 

adhesive backed tape) across the gap between blades and check the tape 

*before and after every flight*. The tapes broke on every flight. Note 

that the 1st prop I tried had the original hub that IVO sold for Lycs, 

with smooth surfaces on the hub plates facing the blade roots. The 2nd 

had deeply knurled surfaces, to bite into the blade roots. The 2nd just 

chewed up the top layer of glass/resin on the blade root. Both props 

were installed to IVO's instructions, using a torque wrench. Eventually, 

IVO quit selling props to Lyc owners because they couldn't solve the 

problem. (Drive lugs would have stabilized the blades.)



Charlie

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat Oct 06, 2007 5:52 pm Post subject: Rotax 912 Torque Spec Error

> were installed to IVO's instructions, using a torque wrench. Eventually,

 	  Quote: 	
		   IVO quit selling props to Lyc owners because they couldn't solve the 

 problem. (Drive lugs would have stabilized the blades.)



 Charlie


	




Charlie:



Probably stabalize the blades long enough for the drive lugs to eat the IVO 

hub.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jindoguy(at)gmail.com
Guest

Posted: Sat Oct 06, 2007 6:03 pm Post subject: Rotax 912 Torque Spec Error

Charlie, I almost mentioned the Ivo Lycoming mismatch, but I have only the experience of others to go by.

Ivo has added drive lug counterbores to the hubs of their bigger props, at least the one that came with my trike had them. I sent it back after reading the installation instructions.  

The instructions were, and I only wish I were making this up:

Torque to spec, run engine for one minute. Torque to spec, run engine two minutes. Torque to spec, run engine four minutes. Torque to spec, and so on, and so on. I added it all up and it came to over eight hours before you could do anything like a normal flight. Then read the tape and retorque every two hours, replacing the tape after each new torque job. Sheesh. 

As I told the owner of the trike co., "How am I supposed to explain to a customer that installation is going to cost as much as the prop, not to mention the cost of sleeping pills should I ever turn one over to a customer."  

I just do not like the idea of prop blades that are held into the hub by bolts alone, although I have to admit, as a life long machinist, I was fascinated by the 60 degree flat knurling on each side of the hub plates. A real testimony to what can be done with CNC machines. 

But when it comes to props, I like the robust blades of the Warp and the light weight of the Powerfin. Now if I could just have both qualities in the same prop. Oh, well, a happy life is knowing where to set your standards and where to compromise. 



RIck



On 10/6/07, Charlie England <ceengland(at)bellsouth.net (ceengland(at)bellsouth.net)> wrote:[quote] --> Kolb-List message posted by: Charlie England <ceengland(at)bellsouth.net (ceengland(at)bellsouth.net)>



John Hauck wrote:

 	  Quote: 	
		   Rick G:



 Thank goodness we have no encountered prop seperation problems with 912 

 series engines, that I am aware of.



 Does an 0-360 have any kind of torsional vibration dampening, other than

 the prop?



 john h

 mkIII



<Insert looong howl of laughter here.> 
	




No. It is, after all, a certified engine with all the shortcomings that

implies.



I hope y'all don't mind input from a non-Kolb flier.



I'm building an RV-7. Because of how rough Lyc's typically are, I 

debated for a couple of years about using an alternative engine before

giving in to the time saving factor of doing a standard Lyc

installation. Any 4 cyl 4-stoke engine has strong torque reversals

between each power pulse. The only hint of damping in a Lyc is on *some* 

of the -360's, that have a 'G' in the suffix letters. Even those don't

have anything between the crank & the prop; they have little pivoting

weights attached to the counterweights on the crank. 



The idea that friction between the back of a wood prop & the metal prop

flange keeps the prop from moving is common among pilots of larger

planes, too, but it just doesn't pass a sanity check in all but the very 

lowest power situations. In every 'normal' a/c prop installation I'm

aware of, the drive lugs are what transfer the rotational energy from

the prop flange to the prop. (That's why they are called 'drive lugs'  ) 



All the bolts do is keep the prop from 'rocking' in and out of the plane

of the flange. If the prop bolts get loose, motion of the a/c, torque

pulses & reversals will cause the prop to 'rock' on the flange, 

wallowing out the close-tolerance holes where the drive lugs fit. Now

the prop is both rocking, bending the bolts (as John mentioned earlier)

and getting it's lug-holes hammered out bigger and bigger by each pulse. 

Things feed on themselves & the bolts soon fail.



Want evidence that it ain't friction that keeps blades stable? Ask IVO

about their props for 4 cyl Lycs (if they have started selling them

again). There are no drive lugs in an IVO hub, and the bolt holes in the 

blades are way over-sized for the bolt diameter. I've flown 2 different

IVO's on a 160 hp O-320. Both had blade movement. The installation

requirements were to place 'witness tape' (1st copper, then stainless 

adhesive backed tape) across the gap between blades and check the tape

*before and after every flight*. The tapes broke on every flight. Note

that the 1st prop I tried had the original hub that IVO sold for Lycs, 

with smooth surfaces on the hub plates facing the blade roots. The 2nd

had deeply knurled surfaces, to bite into the blade roots. The 2nd just

chewed up the top layer of glass/resin on the blade root. Both props 

were installed to IVO's instructions, using a torque wrench. Eventually,

IVO quit selling props to Lyc owners because they couldn't solve the

problem. (Drive lugs would have stabilized the blades.)



 

when you live at the airport.  [quote][b]

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