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4rcsimmons(at)comcast.net
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 Posted: Sat Jun 01, 2013 3:23 am Post subject: JabiruEngine-List Digest: 3 Msgs - 05/31/13 |
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I never say much but had to here!
I work for a major auto manufacturer and here, we do use offsets. Our pistons are also barrel shaped with a taper at the area of the ring landings.
Example is if you find the piston drawings, the diameter if the upper ring landing has a judged size determined by the diameter of the area right above the pin boss area as you measure up from the pin boss area up into the ring landings, the piston gets smaller in diameter. All for expansion.
The are also egg shaped some what, again, for expansion. Left to right vs. from to rear. All due to expansion.
A lot of this was done as skirts began to get smaller to reduce friction zones.
A piston is an interesting part when you see how they are really designed.
You auto see how they are really cut from a casting. Pretty cool stuff!
Ours are always clearly marked as to direction and yes, it would make a difference! They are designed that way for many reasons.
- Rich
P. S. no electron B. S. here!
On Jun 1, 2013, at 2:01 AM, JabiruEngine-List Digest Server <jabiruengine-list(at)matronics.com> wrote:
[quote] *
==================================================
Online Versions of Today's List Digest Archive
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Today's complete JabiruEngine-List Digest can also be found in either of the
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HTML Version:
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================================================
EMail Version of Today's List Digest Archive
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----------------------------------------------------------
JabiruEngine-List Digest Archive
---
Total Messages Posted Fri 05/31/13: 3
----------------------------------------------------------
Today's Message Index:
----------------------
1. 06:10 AM - Re: Re: Offset pistons in Brand "L," "C" or "F"? (FLYaDIVE)
2. 08:17 AM - Re: Re: Offset pistons in Brand "L," "C" or "F"? (Rob Turk)
3. 05:57 PM - Re: Re: Offset pistons in Brand "L," "C" or "F"? (Gary Aman)
________________________________ Message 1 _____________________________________
Time: 06:10:39 AM PST US
Subject: Re: Re: Offset pistons in Brand "L," "C" or "F"?
From: FLYaDIVE <flyadive(at)gmail.com>
Marty:
I do not know about Suzuki or Harley - But I do know about Lycoming and
Continental - They DO NOT HAVE ANY PISTON OFFSET.
I know of NO reason to have the wrist pin offset - It just does NOT make
ANY sense at all. There are Front & Rear to some pistons but that is
because of piston dome designs and valve clearances.
Think of it this way: What CENTERS the piston in the center of the
cylinder?
THE RINGS!!!
So, how or why would there be a wrist pin offset?
If there was piston pin offset, then the rings would be offset also - And
that would lead to uneven wear and loss of compression.
Whomever started this Wives Tail should be SHOT with Dumb-Dumbs because it
would match their intellect.. Always REMEMBER B.S. is spread at the speed
of an electron on the internet.
*Barry*
*"Do you know why pilots think they are mechanics? Because they can but
tools at Home Depot."*
On Thu, May 30, 2013 at 9:45 PM, Martin Hone <aerobiz1(at)gmail.com> wrote:
> Hi Frank,
>
> There has been a lot of discussion on the Jabiru engine list on this
> subject. It started when someone couldn't work out which way the pistons
> should be fitted. Most engines have piston pin offset, mainly to reduce
> piston slap at TDC hence noise. Some racing types reverse it to try and
> get a little more torque, while others 'desax' the bore by offsetting the
> barrels/cylinders relative to the centreline of the crank, ie. moving the
> cylinders forward or backwards a few millimetres in the same plane, not
> rotating around the crank as in a v-twin or radial. In a motorcycle
> production racing class I was involved in, a guy got caught cheating by
> doing just this. He moved the entire cylinder bank on a Suzuki 1000cc four
> cylinder engine !
>
> Marty
>
>
> On Fri, May 31, 2013 at 11:31 AM, Frank Roskind <frankroskind(at)hotmail.com>wrote:
>
>> Thanks for your response. I have googled offset piston with lycoming,
>> continental and franklin, but found nothing relevant except a reference to
>> the Franklin automobile having offset piston pins. After your message I
>> also googled the same three with "desaxed" and found nothing relevant. It
>> seems like a great idea, given all the fooling around with exhausts,
>> intakes and ignition, it is kind of odd that I am not reading of anyone who
>> took a shot at offsetting the pistons.
>> Maybe I just found a great retirement occupation.
>> ------------------------------
>> Date: Fri, 31 May 2013 06:58:04 +1000
>> Subject: Re: Offset pistons in Brand "L," "C" or "F"?
>> From: aerobiz1(at)gmail.com
>> To: frankroskind(at)hotmail.com
>>
>> Frank , this has been discussed at length. Many engine types use offset
>> piston pins or 'desaxed' bores. Harleys for example.
>> Try Googling either term.....
>>
>> Marty
>>
>
>
________________________________ Message 2 _____________________________________
Time: 08:17:50 AM PST US
From: Rob Turk <matronics(at)rtist.nl>
Subject: Re: Re: Offset pistons in Brand "L," "C" or "F"?
Barry, before lashing out like this and having people shot for sending
information, perhaps you should read up on Piston slap.
If it were an old wives tail, then no engine manufacturer would bother
to put an orientation in their manual, don't you think?
On 5/31/2013 3:09 PM, FLYaDIVE wrote:
> Marty:
>
> I do not know about Suzuki or Harley - But I do know about Lycoming
> and Continental - They DO NOT HAVE ANY PISTON OFFSET.
> I know of NO reason to have the wrist pin offset - It just does NOT
> make ANY sense at all. There are Front & Rear to some pistons but
> that is because of piston dome designs and valve clearances.
> Think of it this way: What CENTERS the piston in the center of the
> cylinder?
> THE RINGS!!!
> So, how or why would there be a wrist pin offset?
> If there was piston pin offset, then the rings would be offset also -
> And that would lead to uneven wear and loss of compression.
> Whomever started this Wives Tail should be SHOT with Dumb-Dumbs
> because it would match their intellect.. Always REMEMBER B.S. is
> spread at the speed of an electron on the internet.
>
>
> *Barry*
>
> *"Do you know why pilots think they are mechanics? Because they can
> but tools at Home Depot."*
>
>
> On Thu, May 30, 2013 at 9:45 PM, Martin Hone <aerobiz1(at)gmail.com
> <mailto:aerobiz1(at)gmail.com>> wrote:
>
> Hi Frank,
>
> There has been a lot of discussion on the Jabiru engine list on
> this subject. It started when someone couldn't work out which way
> the pistons should be fitted. Most engines have piston pin
> offset, mainly to reduce piston slap at TDC hence noise. Some
> racing types reverse it to try and get a little more torque, while
> others 'desax' the bore by offsetting the barrels/cylinders
> relative to the centreline of the crank, ie. moving the cylinders
> forward or backwards a few millimetres in the same plane, not
> rotating around the crank as in a v-twin or radial. In a
> motorcycle production racing class I was involved in, a guy got
> caught cheating by doing just this. He moved the entire cylinder
> bank on a Suzuki 1000cc four cylinder engine !
>
> Marty
>
>
> On Fri, May 31, 2013 at 11:31 AM, Frank Roskind
> <frankroskind(at)hotmail.com <mailto:frankroskind(at)hotmail.com>> wrote:
>
> Thanks for your response. I have googled offset piston with
> lycoming, continental and franklin, but found nothing relevant
> except a reference to the Franklin automobile having offset
> piston pins. After your message I also googled the same three
> with "desaxed" and found nothing relevant. It seems like a
> great idea, given all the fooling around with exhausts,
> intakes and ignition, it is kind of odd that I am not reading
> of anyone who took a shot at offsetting the pistons.
> Maybe I just found a great retirement occupation.
> ------------------------------------------------------------------------
> Date: Fri, 31 May 2013 06:58:04 +1000
> Subject: Re: Offset pistons in Brand "L," "C" or "F"?
> From: aerobiz1(at)gmail.com <mailto:aerobiz1(at)gmail.com>
> To: frankroskind(at)hotmail.com <mailto:frankroskind(at)hotmail.com>
>
> Frank , this has been discussed at length. Many engine types
> use offset piston pins or 'desaxed' bores. Harleys for example.
> Try Googling either term.....
>
> Marty
>
>
> *
>
>
> *
________________________________ Message 3 _____________________________________
Time: 05:57:31 PM PST US
Subject: Re: Re: Offset pistons in Brand "L," "C" or "F"?
From: Gary Aman <zeprep251(at)aol.com>
http://www.motorcycleproject.com/motorcycle/text/cows-offset.html
You might try this page for some insight into pin off set before you start
calling people names.
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BobHaas
Joined: 22 Mar 2013
Posts: 17
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| Posted: Sat Jun 01, 2013 5:49 am Post subject: JabiruEngine-List Digest: 3 Msgs - 05/31/13 |
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I ran a "full service" Imported auto shop. Real engines always had
orientation marks on the piston, to denote direction of thrust. Big bad
news
if the marks were assembled wrong, that is flywheel end or prop end. "Real
engines" Porsche, Alfa, Mercedes, Coventry, VW, Ranger, ETC.
I concur with Rich, there was a mark some where, inside on the gudgeon
pin boss, or the crown of the piston. Bob Haas, Checkpoint Foreign Car.
Washington DC, before the Beltway.
--
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