KR> Detonation as crank failure cause?

[Mark Jones]

No one has mentioned anything about detonation of the engine as a factor in 
crank failure. Detonation causes undue stresses on a crank by creating a hammer 
like force generated from the piston through the rods to the crank. This 
hammer-like shock wave being imposed on the crank causes severe overloading. 
Detonation can destroy an engine very quickly. How many of the crank failure 
engines actually were subjected to detonation. The only one who has confessed 
to having detonation was Mark Langford and his was a brief period on departure 
per his post of June 10th. Just something else to think about.

Mark Jones (N886MJ) 
Wales, WI 
Visit my web site: http://mywebpage.netscape.com/n886mj 
Email: flyk...@wi.rr.com 

KR> Detonation as crank failure cause?

[Jeff Scott]

Detonation can certainly cause some bearing damage, but it would have to be 
quite severe and continuous to break a crank.  I've torn down an engine 
subjected to severe and constant detonation (mistimed ignition timing due to a 
slipped harmonic balancer in a boat).  It looked like someone had worked over 
the tops of the pistons with a ball peen hammer.  The rod bearing damage was 
minimal, any damage to the mains was undecernable, and the crankshaft journals 
were all still within specs, although no longer perfectly round.  Had it 
continued to run as it was, it would have pounded out the rod bearings and 
damaged the crank by flattening or otherwise trashing the rod journals first.

Perhaps it's time to take into account the gyroscopic loads imposed by the 
spinning prop.  The prop makes a great gyroscope out in front of the plane.  
Any change in direction is resisted by the gyroscopic effect of the prop and 
that load is transmitted as a bending moment to the prop hub.  In the Corvair, 
there is only one small bearing in the front of the case taking that load.  
That bearing get's used like a fulcrum with second main countering the 
gyroscopic load from the prop.  That works pretty well when you transmit that 
load through a solid shaft like aircraft engines and even the VW to some 
degree.  However, in a Corvair, you are transmitting that load through the 
front two rod throws.  The 90 degree break across the throw right next to the 
bearing journal indicates to me that the crank was being flexed with that type 
of load just as if you had bent it back and forth until it broke.  The further 
you move the prop out from that bearing, the more it magnifies that load.  That 
doesn't mean that the Corvair is a bad or dangerous engine.  Only that you have 
to be mindful of it's design limitations and place the prop as close to the 
front bearing as possible to keep the gyroscopic loads transmitted to the 
crankshaft to a minimum.  Also perfectly tracked and balanced, as well as light 
weight props would be in order.

Ok, here's the disclaimer.  I am a mechanic, not an engineer, so take my 
analysis with a grain of salt.  It is also not my intention to throw rocks at 
anyone's plane or engine choice.  My interest here lies strictly in the safety 
of my friends.

-Jeff Scott



-- "Mark Jones"  wrote:
No one has mentioned anything about detonation of the engine as a factor in 
crank failure. Detonation causes undue stresses on a crank by creating a hammer 
like force generated from the piston through the rods to the crank. This 
hammer-like shock wave being imposed on the crank causes severe overloading. 
Detonation can destroy an engine very quickly. How many of the crank failure 
engines actually were subjected to detonation. The only one who has confessed 
to having detonation was Mark Langford and his was a brief period on departure 
per his post of June 10th. Just something else to think about.

Mark Jones (N886MJ) 
Wales, WI 
Visit my web site: http://mywebpage.netscape.com/n886mj 
Email: flyk...@wi.rr.com 

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KR> Detonation as crank failure cause?

[Martindale Family]

Hi Jeff

The actual gyroscopic load total doesn't alter because the prop
mass/diameter/speed doesn't change with distance. However, changing its arm
(extension) would alter its distribution along the crank with the bearing
acting as a pivot and could well move it into the same journal as one where
harmonics are focussed as well. The total moments either side of the pivot
must equal zero.

John

The Martindale Family
29 Jane Circuit
Toormina NSW 2452
Australia

ph:  61 2 66 584767
email: johnja...@optusnet.com.au



- Original Message - 
From: "Jeff Scott" <jscott.pi...@juno.com>
To: <kr...@mylist.net>
Sent: Wednesday, June 22, 2005 12:54 AM
Subject: Re: KR> Detonation as crank failure cause?


>
> Detonation can certainly cause some bearing damage, but it would have to
be quite severe and continuous to break a crank.  I've torn down an engine
subjected to severe and constant detonation (mistimed ignition timing due to
a slipped harmonic balancer in a boat).  It looked like someone had worked
over the tops of the pistons with a ball peen hammer.  The rod bearing
damage was minimal, any damage to the mains was undecernable, and the
crankshaft journals were all still within specs, although no longer
perfectly round.  Had it continued to run as it was, it would have pounded
out the rod bearings and damaged the crank by flattening or otherwise
trashing the rod journals first.
>
> Perhaps it's time to take into account the gyroscopic loads imposed by the
spinning prop.  The prop makes a great gyroscope out in front of the plane.
Any change in direction is resisted by the gyroscopic effect of the prop and
that load is transmitted as a bending moment to the prop hub.  In the
Corvair, there is only one small bearing in the front of the case taking
that load.  That bearing get's used like a fulcrum with second main
countering the gyroscopic load from the prop.  That works pretty well when
you transmit that load through a solid shaft like aircraft engines and even
the VW to some degree.  However, in a Corvair, you are transmitting that
load through the front two rod throws.  The 90 degree break across the throw
right next to the bearing journal indicates to me that the crank was being
flexed with that type of load just as if you had bent it back and forth
until it broke.  The further you move the prop out from that bearing, the
more it magnifies that load.  That doesn't mean that the Corvair is a bad or
dangerous engine.  Only that you have to be mindful of it's design
limitations and place the prop as close to the front bearing as possible to
keep the gyroscopic loads transmitted to the crankshaft to a minimum.  Also
perfectly tracked and balanced, as well as light weight props would be in
order.
>
> Ok, here's the disclaimer.  I am a mechanic, not an engineer, so take my
analysis with a grain of salt.  It is also not my intention to throw rocks
at anyone's plane or engine choice.  My interest here lies strictly in the
safety of my friends.
>
> -Jeff Scott
>
>
>
> -- "Mark Jones" <mjo...@muellersales.com> wrote:
> No one has mentioned anything about detonation of the engine as a factor
in crank failure. Detonation causes undue stresses on a crank by creating a
hammer like force generated from the piston through the rods to the crank.
This hammer-like shock wave being imposed on the crank causes severe
overloading. Detonation can destroy an engine very quickly. How many of the
crank failure engines actually were subjected to detonation. The only one
who has confessed to having detonation was Mark Langford and his was a brief
period on departure per his post of June 10th. Just something else to think
about.
>
> Mark Jones (N886MJ)
> Wales, WI
> Visit my web site: http://mywebpage.netscape.com/n886mj
> Email: flyk...@wi.rr.com
>
> ___
> Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp
> to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net
> please see other KRnet info at http://www.krnet.org/info.html
>
>
> ___
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KR> Detonation as crank failure cause?

[Al Friesen]

Where is the thrust bearing in a Corvair engine? Al
- Original Message - 
From: "Jeff Scott" <jscott.pi...@juno.com>
To: <kr...@mylist.net>
Sent: Tuesday, June 21, 2005 6:54 AM
Subject: Re: KR> Detonation as crank failure cause?

KR> Detonation as crank failure cause?

[Martindale Family]

Nearest the balancer ie, at the back of the engine and not near the prop.

John

The Martindale Family
29 Jane Circuit
Toormina NSW 2452
Australia

ph:  61 2 66 584767
email: johnja...@optusnet.com.au
- Original Message - 
From: "Al Friesen" <nesei...@telus.net>
To: "KRnet" <kr...@mylist.net>
Sent: Thursday, June 23, 2005 7:03 AM
Subject: Re: KR> Detonation as crank failure cause?


> Where is the thrust bearing in a Corvair engine? Al
> - Original Message - 
> From: "Jeff Scott" <jscott.pi...@juno.com>
> To: <kr...@mylist.net>
> Sent: Tuesday, June 21, 2005 6:54 AM
> Subject: Re: KR> Detonation as crank failure cause?
> 
> 
> 
> ___
> Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp
> to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net
> please see other KRnet info at http://www.krnet.org/info.html