| Re: [GMCnet] Onan Repair [message #167552] |
Wed, 25 April 2012 15:13  |
Richard Brown
Messages: 281
Registered: May 2009
Karma: 1
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One thing I can say about the screw with the magnet is that it seems like it would allow the sensor to be farther away from the flywheel minimizing the risk of one of the fins hitting it. It might also allow more cooling air to go around it keeping it cooler & less disruptive of air flow. I do have to wonder if it would be heavy enough to cause an imbalance in the flywheel. It may be possible to drill & tap a second hole 180° away & install an allen bead screw that weighs the same as a counterweight. Perhaps food for thought. I like the idea of a threaded hole with thread locker over epoxy anyway. Mechanical retention over chemical seems more secure to me.Ease of accurate adjustment is a bonus.
Richard & Carol Brown
1974 Eleganza SE
"DILLIGAF"
Lindale, Tx. 75771
903-881-0192
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Richard & Carol Brown
1974 Eleganza SE
1174 Hickory Hills Dr.
Murchison, TX. 75778
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| Re: [GMCnet] Onan Repair [message #167576 is a reply to message #167552] |
Wed, 25 April 2012 20:57  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Be careful when selecting that "screw with a magnet". The Pertronix Hall
Effect sensor is magnetic polarity sensitive. Frankly, I wouldn't bother
-- just be sure to check clearance before cranking the Onan. With a recess
milled (a carbide bit in a Dremel) in the flywheel, there's very little
danger of JBWeld letting the magnet get away.
Speaking of which, I today watched my engine man drill and tap two holes
into a racing Vortec valve seat. He then screwed in cast iron plugs,
coated with JD Weld. After weakening the protruding screws with a hack saw
blade, he broke them with a hammer, then machined them back to the valve
seat's configuration. Seems there's a hot spot at the center two exhaust
valves of early Vortec engines (which have the best intake ports); they
very often crack across the valve seat. Dependent upon the length of the
crack, they either install a seat insert or, for the longer ones, do the
stop-drilling and plugging above. Very common and dependable fix, he says.
The plugs looked like ordinary square-headed set screws but he showed me
that they're soft iron -- he also has similar ones of aluminum for those
heads.
Just some of the new things I learned today. :-)
Ken H.
On Wed, Apr 25, 2012 at 4:13 PM, Richard Brown
<wings77sporty@sbcglobal.net>wrote:
> One thing I can say about the screw with the magnet is that it seems like
> it would allow the sensor to be farther away from the flywheel minimizing
> the risk of one of the fins hitting it...
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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 Repair [message #167642 is a reply to message #167576] |
Thu, 26 April 2012 18:11 |
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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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G'day,
I would like to add a bit to Ken's note below.
"-- just be sure to check clearance before cranking the Onan."
CHECK THE CLEARANCE BETWEEN THE PICKUP AND THE FAN BLADES ONE BY ONE!
I've already confessed to being a dummy and not doing so which resulted in
having to install a SECOND pickup!
Regards,
Rob M.
-----Original Message-----
From: Ken Henderson
Be careful when selecting that "screw with a magnet". The Pertronix Hall
Effect sensor is magnetic polarity sensitive. Frankly, I wouldn't bother
-- just be sure to check clearance before cranking the Onan. With a recess
milled (a carbide bit in a Dremel) in the flywheel, there's very little
danger of JBWeld letting the magnet get away.
Speaking of which, I today watched my engine man drill and tap two holes
into a racing Vortec valve seat. He then screwed in cast iron plugs,
coated with JD Weld. After weakening the protruding screws with a hack saw
blade, he broke them with a hammer, then machined them back to the valve
seat's configuration. Seems there's a hot spot at the center two exhaust
valves of early Vortec engines (which have the best intake ports); they
very often crack across the valve seat. Dependent upon the length of the
crack, they either install a seat insert or, for the longer ones, do the
stop-drilling and plugging above. Very common and dependable fix, he says.
The plugs looked like ordinary square-headed set screws but he showed me
that they're soft iron -- he also has similar ones of aluminum for those
heads.
Just some of the new things I learned today. :-)
Ken H.
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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 Repair [message #167653 is a reply to message #167642] |
Thu, 26 April 2012 19:53 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Senior Member |
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It seems to me that it's a good idea to find out where the high spot is. Then, maybe you can put the magnet there, if there's an easy place to mount the Pertronix unit where the timing hits 25 degrees.
Could I be that lucky?
I'm not lucky enough to be at Casa de Fruita :~(
Larry Davick
Fremont, California
The Mystery Machine
'76 (ish) Palm Beach
----- Original Message -----
From: "Rob Mueller" <robmueller@iinet.net.au>
To: gmclist@temp.gmcnet.org
Sent: Thursday, April 26, 2012 4:11:12 PM
Subject: Re: [GMCnet] Onan Repair
G'day,
I would like to add a bit to Ken's note below.
"-- just be sure to check clearance before cranking the Onan."
CHECK THE CLEARANCE BETWEEN THE PICKUP AND THE FAN BLADES ONE BY ONE!
I've already confessed to being a dummy and not doing so which resulted in
having to install a SECOND pickup!
Regards,
Rob M.
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] Onan Repair [message #167674 is a reply to message #167642] |
Thu, 26 April 2012 21:17 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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Senior Member |
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| Robert Mueller wrote on Thu, 26 April 2012 16:11 |
G'day,
I would like to add a bit to Ken's note below.
"-- just be sure to check clearance before cranking the Onan."
CHECK THE CLEARANCE BETWEEN THE PICKUP AND THE FAN BLADES ONE BY ONE!
I've already confessed to being a dummy and not doing so which resulted in
having to install a SECOND pickup!
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Remembering you telling us about your experience, I didn't file much of a recess when installing my magnet. That way I ensured that it ended up higher than any of the other fins.
I still had to install a SECOND pickup, but mine was due to shorting the negative lead to the positive post on the starter when routing the wires for a clean installation.
I do not need to repeat other people's mistakes.... I can make plenty on my own! 
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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