Home » Public Forums » GMCnet » [GMCnet] Onan Timing
| [GMCnet] Onan Timing [message #183767] |
Sun, 09 September 2012 13:31  |
Gary Bovee
Messages: 177
Registered: August 2008
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I have a 6 KW Onan in my 1978 Royale. The Onan manual shows the timing setting at 25 degrees BTC. I have the flywheel off and found two stamped markings. One is stamped 0 and the other is stamped 20. There is no 25 degree mark. My question is why is there a 20 degree mark, but no 25 if that is what I am suppose to be setting the timing to? Ready to install my Pertronix ignition, but confused as to what to use for a timing mark. What have others found or done?
Any info would be much appreciated.
Gary Bovee
1978 Royale by Coachmen
Red Bluff, CA
Idiot's Internet Guide to Finding 1973-1978 GMC Motorhome Information
Alternator & A/C Belt Tensioner Adjustors
http://www.gmcidiotsguide.com
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| Re: [GMCnet] Onan Timing [message #183778 is a reply to message #183767] |
Sun, 09 September 2012 14:46  |
Dennis S
Messages: 3046
Registered: November 2005
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| Gary Bovee wrote on Sun, 09 September 2012 13:31 |
I have a 6 KW Onan in my 1978 Royale. The Onan manual shows the timing setting at 25 degrees BTC. I have the flywheel off and found two stamped markings. One is stamped 0 and the other is stamped 20. There is no 25 degree mark. My question is why is there a 20 degree mark, but no 25 if that is what I am suppose to be setting the timing to? Ready to install my Pertronix ignition, but confused as to what to use for a timing mark. What have others found or done?
Any info would be much appreciated.
Gary Bovee
1978 Royale by Coachmen
Red Bluff, CA
Idiot's Internet Guide to Finding 1973-1978 GMC Motorhome Information
Alternator & A/C Belt Tensioner Adjustors
http://www.gmcidiotsguide.com
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Gary,
The photos Dan G posted of Ken installing a Pertronix has detail on the timing.
http://www.gmcmhphotos.com/photos/eastern-states-spring-10-calhoun-ga/p33344-pertronix-install.html
I think most folks temporarily clamp the pick up unit and run the Onan to be sure they are happy with the timing before permanently attaching. That is what I did -- but my mounting device broke and I am back to using points until I redo.
I also estimated 30 degree advance timing based on the circumference of the fly wheel to decide where to start initially.
Does this help?
Dennis
Dennis S
73 Painted Desert 230
Memphis TN Metro
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| Re: [GMCnet] Onan Timing [message #183779 is a reply to message #183767] |
Sun, 09 September 2012 14:48 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Gary, I believe you have an earlier ONAN engine. On engines fitted with
recoil starters, ONAN used less initial timing advance. On engines that
were intended for electric starters ONLY, they used more advance (23
degrees.) This prevented the engine from kicking back when the hand recoil
starter was used. The wheels are otherwise the same will interchange. If
you are fitting the pertronix module, place the magnet in the 23 degree
position and then locate the pickup so your timing light flashes at the
same advance. Some twiddling is required to get it spot on, before you
permanently attach the module to the sheet metal. Be sure to rotate the
flywheel before you try to start the engine, and check that no flywheel
fins interact with the module. Bad stuff happens if they hit. On another
note, please put together a wireless air system for me. I and Judy will be
traveling past your place next few days. I will call you with exact dates.
Jim Hupy and Judy Countermine
SALEM,OR
78 GMC Royale 403
On Sep 9, 2012 11:31 AM, "Gary Bovee" <gcbgold@digitalpath.net> wrote:
> I have a 6 KW Onan in my 1978 Royale. The Onan manual shows the timing
> setting at 25 degrees BTC. I have the flywheel off and found two stamped
> markings. One is stamped 0 and the other is stamped 20. There is no 25
> degree mark. My question is why is there a 20 degree mark, but no 25 if
> that is what I am suppose to be setting the timing to? Ready to install my
> Pertronix ignition, but confused as to what to use for a timing mark. What
> have others found or done?
>
> Any info would be much appreciated.
>
> Gary Bovee
> 1978 Royale by Coachmen
> Red Bluff, CA
> Idiot's Internet Guide to Finding 1973-1978 GMC Motorhome Information
> Alternator & A/C Belt Tensioner Adjustors
> http://www.gmcidiotsguide.com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Onan Timing [message #183792 is a reply to message #183781] |
Sun, 09 September 2012 18:18 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I made a posting on this several years ago. The first question for you is: Are you using the Onan points system with the push rod? If so then go with the 20 BTDC setting.
If you are using a stable ignition like the Pertronix then 25 to 27 will work just great.
The reason for the difference is with the push rod points system the actual firing time was not stable. Firing time is not stable with that system and the timing jumps around quite a bit. You will easily see this with your timing light.
After Onan had quite a few engines returned for detonation and burning holes in pistons, they changed the spec from 25 to 22 or 23. That did not fix their problem as a few more still came back so they changed it again to 20.
Unfortunately they never changed their documentation.
The retired Onan Engineer I talked to about this said the engine would run all day at 30 IF the firing time was stable. They never managed to get it stable enough with the point / push rod ignition. That is why they retarded the settings.
I have a a very stable Pertronix ignition and I run mine at 27 BTDC. On the back of my flywheel I painted the 20, 25, 27.5, and 30 degree marks. This way I can time mine easily with a timing light.
It will run smoother, slightly cooler, and use less fuel with a more advanced setting.
Onan did offer a retrofit electronic ignition at one time. I have never seen one but I understand that it still used the push rod. IF that is what you have, then you still need the ignition retarded to the 20 degree setting.
HTH
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan Timing [message #183794 is a reply to message #183792] |
Sun, 09 September 2012 18:52 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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I found the Onan electronic ignition system (built by Pertronix for Onan)
on 50% sale at an RV dealer in WA a couple of days before we left for
Alaska in June 2000. I was there looking for a replacement coil for my
failed Onan. After replacing the coil and installing the electronic
ignition, I found it to be a big improvement over the points. But, the
timing DID still bounce +- several degrees.
About 3-4 years later, that ignition failed shortly after Lawrence Gaskins'
first developed our current Pertronix mod. Only after installing that did
I realize why the original timing was so erratic. Lawrence's mod is vastly
superior to the Onan version -- for about 1/2 the cost.
Ken H.
On Sun, Sep 9, 2012 at 7:18 PM, Ken Burton wrote:
> ...
> Onan did offer a retrofit electronic ignition at one time. I have never
> seen one but I understand that it still used the push rod. IF that is what
> you have, then you still need the ignition retarded to the 20 degree
> setting.
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Onan Timing [message #183806 is a reply to message #183794] |
Sun, 09 September 2012 22:14 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Ken Henderson wrote on Sun, 09 September 2012 18:52 |
I found the Onan electronic ignition system (built by Pertronix for Onan)
on 50% sale at an RV dealer in WA a couple of days before we left for
Alaska in June 2000. I was there looking for a replacement coil for my
failed Onan. After replacing the coil and installing the electronic
ignition, I found it to be a big improvement over the points. But, the
timing DID still bounce +- several degrees.
About 3-4 years later, that ignition failed shortly after Lawrence Gaskins'
first developed our current Pertronix mod. Only after installing that did
I realize why the original timing was so erratic. Lawrence's mod is vastly
superior to the Onan version -- for about 1/2 the cost.
Ken H.
On Sun, Sep 9, 2012 at 7:18 PM, Ken Burton wrote:
> ...
> Onan did offer a retrofit electronic ignition at one time. I have never
> seen one but I understand that it still used the push rod. IF that is what
> you have, then you still need the ignition retarded to the 20 degree
> setting.
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Thanks for the info on the Onan electronic ignition. I heard that it still used the push rod and you now have confirmed that.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan Timing [message #183917 is a reply to message #183908] |
Mon, 10 September 2012 20:20 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Gene,
HUH?
If one mark is at 0 degrees and the second mark is at 20 degrees a mark in between them would be at 10 degrees!
Regards,
Rob
-----Original Message-----
From: mr.erfisher
Or you could just make even marks
Between the 2
Gene
On Sep 10, 2012, at 4:56 PM, "Rob Mueller" <robmueller@iinet.net.au> wrote:
> Gary,
>
> 1) Take a 12" steel rule and orient it so that one edge intersects the center of the flywheel (eyeball is fine).
>
> 2) Run that edge through the 0 degree mark and out to the edge of the flywheel and scribe a line.
>
> 3) Repeat the step above at the 20 degree mark.
>
> 4) Bend a steel six inch long / half inch wide steel rule along the circumference of the flywheel and measure the distance between
> those two marks.
>
> 5) Divide that measurement by 4 (that will give you 5 degrees).
>
> 6) Use the six inch steel rule again and press it to the circumference of the flywheel at the 20 degree mark and scribe a mark at
> the measurement you calculated.
>
> 7) You now have a mark at 25 degrees.
>
> 8) Take the steel rule and repeat step 2).
>
> 9) Using a Dremel tool deepen the scribe mark and fill it with white paint.
>
> 10) Reinstall the flywheel torquing the bolt 35 - 40 ft lb.
>
> Regards,
> Rob M.
>
> -----Original Message-----
> From: Gary Bovee
>
> I have a 6 KW Onan in my 1978 Royale. The Onan manual shows the timing setting at 25 degrees BTC. I have the flywheel off and
> found two stamped markings. One is stamped 0 and the other is stamped 20. There is no 25 degree mark. My question is why is
there
> a 20 degree mark, but no 25 if that is what I am suppose to be setting the timing to? Ready to install my Pertronix ignition, but
> confused as to what to use for a timing mark. What have others found or done?
>
> Any info would be much appreciated.
>
> Gary
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Onan Timing [message #183951 is a reply to message #183925] |
Mon, 10 September 2012 23:56 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Matt,
You must have missed the part noting that Gary had the flywheel off! ;-)
Regards,
Rob M.
-----Original Message-----
From: Matt Colie
Not quoted (this time)
Rob,
Why do you work so hard?
Since the invention of the reciprocating engine, people like me have been "trameling" them. Tramel is measure with an arbitrary
standard.
In this case, it means put something in the machine (engine) that blocks the piston from reaching TDC.
Mark that place however you choose.
Reverse the rotation until it hits again.
Mark that place.
Now, with either a flexible tape or dividers, split that and you now have a confirmed TDC.
Measure around the ring gear (or other) to get a circumference and do the math for 25/360.
Make the mark there and you have 100% confidence that it is correct.
This is the way it has been done since Newcomen (the guy that Watt copied to make a better steam engine).
Even tough Onans are a little newer, the principle hasn't changed.
Matt
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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