| [GMCnet] 4k Onan Timing [message #232283] |
Thu, 05 December 2013 10:34  |
gcbgold
Messages: 60
Registered: August 2012
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I thought I read in a manual somewhere that a 4k's timing should be set at 25 degrees BTDC instead of 21 degrees so it would be the same as a 6k. Does anyone know where to find this info?
Gary Bovee
Red Bluff, CA
1978 GMC Royale
Free "Idiot's Internet Guide for Finding GMC MotorHome Information"
www.gmcidiotsguide.com
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| Re: [GMCnet] 4k Onan Timing [message #232291 is a reply to message #232283] |
Thu, 05 December 2013 11:22  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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If you have a standard push rod style ignition, time the Onan to the mark on the flywheel.
You can get by advancing it if you have the more stable Pertronix modification.
The problem with the push rod type ignition is the timing jumps all over the place due the the poor mechanical points design. The later Onan electronic points design was no better because the system still bounces all over the place due to the push rod design. You stand a chance of causing detonation and burning a hole in a piston if advanced too far.
Onan changed the timing spec several times, reducing the advance spec each time due to field reports of detonation problems.
The timing mark location and spec will vary depending on the age of the flywheel or the manual you are reading.
You are pretty safe with the 20-22 BTDC number.
I had a retired Onan engineer tell me that the 1800 rpm Onan engine would run at 30 BTDC with a stable ignition like the Pertronix. I have the Pertronix so I set mine to 26 to play it safe.
Is a little better fuel economy at 30 BTDC worth the chance of destroying an engine? Also engines start better at a retarded setting.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] 4k Onan Timing [message #232322 is a reply to message #232291] |
Thu, 05 December 2013 15:56 |
gcbgold
Messages: 60
Registered: August 2012
Karma: -1
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Thanks Ken.
Gary Bovee
Red Bluff, CA
1978 GMC Royale
Free "Idiot's Internet Guide for Finding GMC MotorHome Information"
www.gmcidiotsguide.com
> On Dec 5, 2013, at 9:22 AM, Ken Burton <n9cv@comcast.net> wrote:
>
>
>
> If you have a standard push rod style ignition, time the Onan to the mark on the flywheel.
>
> You can get by advancing it if you have the more stable Pertronix modification.
>
> The problem with the push rod type ignition is the timing jumps all over the place due the the poor mechanical points design. The later Onan electronic points design was no better because the system still bounces all over the place due to the push rod design. You stand a chance of causing detonation and burning a hole in a piston if advanced too far.
>
> Onan changed the timing spec several times, reducing the advance spec each time due to field reports of detonation problems.
>
> The timing mark location and spec will vary depending on the age of the flywheel or the manual you are reading.
>
> You are pretty safe with the 20-22 BTDC number.
>
> I had a retired Onan engineer tell me that the 1800 rpm Onan engine would run at 30 BTDC with a stable ignition like the Pertronix. I have the Pertronix so I set mine to 26 to play it safe.
>
> Is a little better fuel economy at 30 BTDC worth the chance of destroying an engine? Also engines start better at a retarded setting.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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