GMCforum: GMCnet » [GMCnet] Timing the Onan

Home » Public Forums » GMCnet » [GMCnet] Timing the Onan - Ken B.

Show: Today's Messages :: Polls :: Message Navigator

[GMCnet] Timing the Onan - Ken B. [message #83387]

Thu, 06 May 2010 19:15

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

G�day Ken,

You noted that you timed your (and Dan�s) Onan to 27� BTC; could you explain
how you did it.

According to the Maintenance Manual if the line on the back side of the
cooling fan is in the center of the window on a 6KW Onan it is 20�.

I checked the install pictures on Ken H's album and noted the line was set
in the center of the window indicating the Onan was timed at 20� BTC.

How do you pick up the additional 7�?

Regards,
Rob Mueller
Sydney, Australia
AUS '75�Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426

_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

Report message to a moderator

Re: [GMCnet] Timing the Onan - Ken B. [message #83393 is a reply to message #83387]

Thu, 06 May 2010 20:05

jimk

Messages: 6734
Registered: July 2006
Location: Belmont, CA

Karma: 9

Senior Member

by moving the pick up module posit the rotation.
I can achieve the same on the kit we have also.

On Thu, May 6, 2010 at 5:15 PM, Rob Mueller <robmueller@iinet.net.au> wrote:
> G’day Ken,
>
> You noted that you timed your (and Dan’s) Onan to 27° BTC; could you explain
> how you did it.
>
> According to the Maintenance Manual if the line on the back side of the
> cooling fan is in the center of the window on a 6KW Onan it is 20°.
>
> I checked the install pictures on Ken H's album and noted the line was set
> in the center of the window indicating the Onan was timed at 20° BTC.
>
> How do you pick up the additional 7°?
>
> Regards,
> Rob Mueller
> Sydney, Australia
> AUS '75 Avion-The Blue Streak TZE365V100428
> USA '75 Avion-Double Trouble TZE365V100426
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>

--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502

Report message to a moderator

Re: [GMCnet] Timing the Onan - Ken B. [message #83394 is a reply to message #83393]

Thu, 06 May 2010 20:21

WD0AFQ

Messages: 7111
Registered: November 2004
Location: Dexter, Mo.

Karma: 207

Senior Member

Rob,
We marked the flywheel on the outsde so we could see where we were moving the timing as we moved the module.
I tell you, this is a slick mod. The Onan ran real good before but it is really smooth now. I carried that unit in a drawer for 3 years. Really, if you study Ken's album, nothing to it, for those who are wondering how hard this is. On a scale of 1-10, I would put it at a 4, only becasue we had to make a bracket.
Dan

3 In Stainless Exhaust Headers One Ton All Discs/Reaction Arm 355 FD/Quad Bag/Alum Radiator Manny Tran/New eng. Holley EFI/10 Tire Air Monitoring System Solarized Coach/Upgraded Windows Satelite TV/On Demand Hot Water/3Way Refer

Report message to a moderator

Re: [GMCnet] Timing the Onan - Ken B. [message #83396 is a reply to message #83393]

Thu, 06 May 2010 20:23

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Jim,

My question was not well written I should have asked:

1) Where does the line on the fan move to in the window with the timing set
at 27� BTC?

2) Do you have to make a new line on the fan?

Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426

-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Jim Kanomata
Sent: Friday, 7 May 2010 11:06 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Timing the Onan - Ken B.

by moving the pick up module posit the rotation.
I can achieve the same on the kit we have also.

--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

Report message to a moderator

Re: [GMCnet] Timing the Onan - Ken B. [message #83414 is a reply to message #83396]

Thu, 06 May 2010 21:50

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

Many people crank on the points adjustment screw until the generator runs smoothly or runs to their satisfaction. They think they are changing the only the dwell or the point gap. They are indeed doing that but they are also changing the timing. Dan's (with the points running it) was already set quite a bit advanced. So we left it that way when installing the Pertronix unit.

We turned the flywheel over and found the timing mark in the little window. Then we stuck a piece of white double faced tape on the outside of the flywheel at that same point so we could more easily see the mark in the bright sunlight. After that it is simple math to figure out how far around the circumference of the flywheel to go to accomplish one, or two, or three, or more degrees advance from that marked base point. You can also just measure the circumference and divide it by 360 to accomplish the same thing.

If you want to be more scientific / accurate about it, you need to determine which flywheel timing mark you have. I believe, If I remember correctly, they made a 24, a 22, and a 20 degree marked flywheel in the years that engine was used in GMC installed generators. I believe mine was marked at 24 degrees. The value was stamped right in the flywheel on mine. Onan also used that same engine in other things. We have a gasoline Onan powered welder at the airport that uses that same engine. I believe it was marked at 25 BTDC.

I was introduced to a retired Onan engineer around the time that I did mine. This was 5 or 6 years ago. I mentioned to him what we had done with the Pertronix unit. He told me Onan looked at Electronic ignition in the 70's but never got away from the mechanical push rod type of trigger which was what was really needed to be replaced resolve the varying advance problem.

He told me that our Onan would run perfectly at 30 degrees advance at 1800 RPM under full load as long as the timing was stable and not bouncing all over the place. He further stated that they initially retarded the advance due to the poor mechanics of the point push rod system. After a few Onans came back under warranty with detonation damage, they reduced the advance spec. by 2 degrees. That still did not completely resolve the problem and a few more came back with detonation damage, so they reduced it a couple more degrees. They kept doing this until no more damaged returns were received. I think he said over several years they settled on 20 BTDC. It was a band-aid fix rather than a real fix of the mechanical push rod points system problem.

With all of that information, to be safe I decided to settle on some advance figure of less than 30 degrees for mine with the Pertronix installed.

Keep in mind that the Onan is a fixed advance system. It does not retard for starting or for high loads so going too far advanced can cause difficult cranking for starting and detonation for high load applications.

On air cooled airplane engine we have a similar system at similar RPMs but we also have retard for starting. Even with that system the advance is only set for 25 BTDC for all running conditions.

With all of this information I suggest that the maximum you want to go is probably around 27 degrees BTDC.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

Report message to a moderator

Re: [GMCnet] Timing the Onan - Ken B. [message #83416 is a reply to message #83414]

Thu, 06 May 2010 22:00

jimk

Messages: 6734
Registered: July 2006
Location: Belmont, CA

Karma: 9

Senior Member

Rob,
What Ken did seems like a easy way to plot out a location for
additional degrees.
I would want know that the reference mark is valid.
Pre ignition is hard to detect as your not around to hear it .

On Thu, May 6, 2010 at 7:50 PM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> Many people crank on the points adjustment screw until the generator runs smoothly or runs to their satisfaction. They think they are changing the only the dwell or the point gap. They are indeed doing that but they are also changing the timing. Dan's (with the points running it) was already set quite a bit advanced. So we left it that way when installing the Pertronix unit.
>
> We turned the flywheel over and found the timing mark in the little window. Then we stuck a piece of white double faced tape on the outside of the flywheel at that same point so we could more easily see the mark in the bright sunlight. After that it is simple math to figure out how far around the circumference of the flywheel to go to accomplish one, or two, or three, or more degrees advance from that marked base point. You can also just measure the circumference and divide it by 360 to accomplish the same thing.
>
> If you want to be more scientific / accurate about it, you need to determine which flywheel timing mark you have. I believe, If I remember correctly, they made a 24, a 22, and a 20 degree marked flywheel in the years that engine was used in GMC installed generators. I believe mine was marked at 24 degrees. The value was stamped right in the flywheel on mine. Onan also used that same engine in other things. We have a gasoline Onan powered welder at the airport that uses that same engine. I believe it was marked at 25 BTDC.
>
> I was introduced to a retired Onan engineer around the time that I did mine. This was 5 or 6 years ago. I mentioned to him what we had done with the Pertronix unit. He told me Onan looked at Electronic ignition in the 70's but never got away from the mechanical push rod type of trigger which was what was really needed to be replaced resolve the varying advance problem.
>
> He told me that our Onan would run perfectly at 30 degrees advance at 1800 RPM under full load as long as the timing was stable and not bouncing all over the place. He further stated that they initially retarded the advance due to the poor mechanics of the point push rod system. After a few Onans came back under warranty with detonation damage, they reduced the advance spec. by 2 degrees. That still did not completely resolve the problem and a few more came back with detonation damage, so they reduced it a couple more degrees. They kept doing this until no more damaged returns were received. I think he said over several years they settled on 20 BTDC. It was a band-aid fix rather than a real fix of the mechanical push rod points system problem.
>
> With all of that information, to be safe I decided to settle on some advance figure of less than 30 degrees for mine with the Pertronix installed.
>
> Keep in mind that the Onan is a fixed advance system. It does not retard for starting or for high loads so going too far advanced can cause difficult cranking for starting and detonation for high load applications.
>
> On air cooled airplane engine we have a similar system at similar RPMs but we also have retard for starting. Even with that system the advance is only set for 25 BTDC for all running conditions.
>
> With all of this information I suggest that the maximum you want to go is probably around 27 degrees BTDC.
>
>
>
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>

--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502

Report message to a moderator

Re: [GMCnet] Timing the Onan - Ken B. [message #83420 is a reply to message #83414]

Thu, 06 May 2010 22:19

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Ken,

Thanks! Now it all makes sense!

Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426

-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Ken Burton
Sent: Friday, 7 May 2010 12:50 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Timing the Onan - Ken B.

Many people crank on the points adjustment screw until the generator runs
smoothly or runs to their satisfaction. They think they are changing the
only the dwell or the point gap. They are indeed doing that but they are
also changing the timing. Dan's (with the points running it) was already
set quite a bit advanced. So we left it that way when installing the
Pertronix unit.

We turned the flywheel over and found the timing mark in the little window.
Then we stuck a piece of white double faced tape on the outside of the
flywheel at that same point so we could more easily see the mark in the
bright sunlight. After that it is simple math to figure out how far around
the circumference of the flywheel to go to accomplish one, or two, or three,
or more degrees advance from that marked base point. You can also just
measure the circumference and divide it by 360 to accomplish the same thing.

If you want to be more scientific / accurate about it, you need to determine
which flywheel timing mark you have. I believe, If I remember correctly,
they made a 24, a 22, and a 20 degree marked flywheel in the years that
engine was used in GMC installed generators. I believe mine was marked at
24 degrees. The value was stamped right in the flywheel on mine. Onan
also used that same engine in other things. We have a gasoline Onan powered
welder at the airport that uses that same engine. I believe it was marked
at 25 BTDC.

I was introduced to a retired Onan engineer around the time that I did mine.
This was 5 or 6 years ago. I mentioned to him what we had done with the
Pertronix unit. He told me Onan looked at Electronic ignition in the 70's
but never got away from the mechanical push rod type of trigger which was
what was really needed to be replaced resolve the varying advance problem.

He told me that our Onan would run perfectly at 30 degrees advance at 1800
RPM under full load as long as the timing was stable and not bouncing all
over the place. He further stated that they initially retarded the advance
due to the poor mechanics of the point push rod system. After a few Onans
came back under warranty with detonation damage, they reduced the advance
spec. by 2 degrees. That still did not completely resolve the problem and a
few more came back with detonation damage, so they reduced it a couple more
degrees. They kept doing this until no more damaged returns were received.
I think he said over several years they settled on 20 BTDC. It was a
band-aid fix rather than a real fix of the mechanical push rod points system
problem.

With all of that information, to be safe I decided to settle on some advance
figure of less than 30 degrees for mine with the Pertronix installed.

Keep in mind that the Onan is a fixed advance system. It does not retard for
starting or for high loads so going too far advanced can cause difficult
cranking for starting and detonation for high load applications.

On air cooled airplane engine we have a similar system at similar RPMs but
we also have retard for starting. Even with that system the advance is only
set for 25 BTDC for all running conditions.

With all of this information I suggest that the maximum you want to go is
probably around 27 degrees BTDC.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

Report message to a moderator

Re: [GMCnet] Timing the Onan - Ken B. [message #83432 is a reply to message #83387]

Fri, 07 May 2010 02:44

jtblank

Messages: 237
Registered: June 2007
Location: Tulare, CA

Karma: 1

Senior Member

The most obvious and probably easiest way to find any timing would to divide 360 by the number of teeth on the flywheel starter ring. That number would be the number of degrees per tooth, then from either the TDC mark or 20 deg mark you can count teeth to mark your 27 or 30 reference and mark the backside of flywheel with liquid paper (the white shows up great and applies easy) so that it shows through the little window. I don't remember how many teeth on ring so the hardest thing to this is to count the teeth without going cross-eyed.

HTH

John Blankenship '76 Palm Beach Tulare, CA

Report message to a moderator

Re: [GMCnet] Timing the Onan - Ken B. [message #83472 is a reply to message #83432]

Fri, 07 May 2010 11:25

Duce Apocalypse

Messages: 824
Registered: May 2009
Location: Los angeles

Karma: 0

Senior Member

jtblank wrote on Fri, 07 May 2010 02:44

Well thats what im gonna do, so im basicall gonna mark one tooth and keep counting and pray my phone doesnt ring lol

actually another way to set the timing is just take the shroud off which you have to do to install the pertronix anyway, and use the timing mark on the flywheel against the gear cover timing marks to set timing. I think they are in BTDC if they are in ATDC then thats totally useless for that.

73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA

[Updated on: Fri, 07 May 2010 11:27]

Report message to a moderator

Previous Topic:	Jim and Marlys Coach Pictures
Next Topic:	Re: [GMCnet] Arriving at a fair price for coach and, enhancements

Goto Forum:

-=] Back to Top [=-

Current Time: Fri Sep 27 07:23:00 CDT 2024

Total time taken to generate the page: 0.01465 seconds