Over the past few months I have been working on alternative ignition design=
s for our Onan generators. During my tenure as a GMC owner I have suffered =
the failure of two Pertronix 1181 modules mounted in the blower housing scr=
oll - one due to a fatigue failure of the module=E2=80=99s aluminum mountin=
g tab due to wind buffeting - and the other due to a flywheel strike where =
the flywheel magnet somehow impacted the module=E2=80=99s face for at least=
several revolutions. These two events occurred with super-rigid mounting a=
rrangements that I made myself - I was NOT using the C-channel mounting kit=
commonly found in the GMC community. Photo albums of these two: http:=
//www.jcmco.com/gallery/Pertronix http://www.jcmco.com/gallery/Pertronix =
and http://www.jcmco.com/gallery/PertronixModII So I decided to experiment with something different=
=E2=80=A6I mounted the module on the outside of the generator=E2=80=99s bel=
lhousing and have it being triggered by a magnet embedded in an aluminum to=
newheel: http://www.jcmco.com/gallery/Pertronix-ModIII This produced very good results - nea=
rly identical to when the module is mounted inside the blower scroll and tr=
iggered by a flywheel magnet. However, during testing I made the observatio=
n that the ignition coil was running very hot and was uncomfortable to touc=
h even after very short amounts of runtime. I determined that the Pertronix=
1181 module that people have recommended for our Onans was keeping the coi=
l energized for about 355 degrees of rotation of the crankshaft - and only =
dropped its output for a few milliseconds as the magnet went by the module =
at which time the spark plugs fired. This is contrasted with the 140 degree=
s per revolution which the OEM breaker points used as a coil dwell time. In=
other words, the Pertronix 1181 causes current to flow in the coil primary=
for almost three times as long as the original Onan design. No wonder the =
coil is getting so hot=E2=80=A6 once the magnetic field builds up in the co=
re of the coil the remaining current flow produces nothing but heat. I wrot=
e to Pertronix tech support for advice and they confirmed that the 1181 is =
not the right module for this application. Their words: "You really sh=
ould be using what we call a latching Ignitor module. This module takes two=
magnets to trigger the unit. One to turn it "ON" then one to turn it "OFF"=
to fire. This allows you to control the charge time of the coil. We use th=
is module on all our applications that have less then 4 cylinders. This is =
so we don't overheat the coil and don't over heat the Ignitor module. =
=E2=80=A6 The part number I would recommend to modify would be part number:=
1121=E2=80=9D At that point I bought an 1121 and modified my mount an=
d magnet wheel for it: http://www.jcmco.com/gallery/PertronixModIV =09 The 1121 module has been in s=
ervice on my Onan for 20 hours of runtime so far and has worked flawlessly.=
Just as with the 1181 module, the 1121 produces repeatable and precise spa=
rk timing but - unlike the 1181 - the 1121 produces no appreciable heating =
of the ignition coil. Having worked 35 years in an electronics career I kno=
w quite well that heat is the enemy of all electronic devices so I=E2=80=
=99m happy to have my coil running at nearly ambient temperature rather tha=
n around 140 degrees as when it was being fired by the 1181. =E2=80=
=94Jim Jim Miller 1977 Eleganza 1977 Royale Hamilton, OH =
s for our Onan generators. During my tenure as a GMC owner I have suffered =
the failure of two Pertronix 1181 modules mounted in the blower housing scr=
oll - one due to a fatigue failure of the module=E2=80=99s aluminum mountin=
g tab due to wind buffeting - and the other due to a flywheel strike where =
the flywheel magnet somehow impacted the module=E2=80=99s face for at least=
several revolutions. These two events occurred with super-rigid mounting a=
rrangements that I made myself - I was NOT using the C-channel mounting kit=
commonly found in the GMC community. Photo albums of these two: http:=
//www.jcmco.com/gallery/Pertronix http://www.jcmco.com/gallery/Pertronix =
and http://www.jcmco.com/gallery/PertronixModII So I decided to experiment with something different=
=E2=80=A6I mounted the module on the outside of the generator=E2=80=99s bel=
lhousing and have it being triggered by a magnet embedded in an aluminum to=
newheel: http://www.jcmco.com/gallery/Pertronix-ModIII This produced very good results - nea=
rly identical to when the module is mounted inside the blower scroll and tr=
iggered by a flywheel magnet. However, during testing I made the observatio=
n that the ignition coil was running very hot and was uncomfortable to touc=
h even after very short amounts of runtime. I determined that the Pertronix=
1181 module that people have recommended for our Onans was keeping the coi=
l energized for about 355 degrees of rotation of the crankshaft - and only =
dropped its output for a few milliseconds as the magnet went by the module =
at which time the spark plugs fired. This is contrasted with the 140 degree=
s per revolution which the OEM breaker points used as a coil dwell time. In=
other words, the Pertronix 1181 causes current to flow in the coil primary=
for almost three times as long as the original Onan design. No wonder the =
coil is getting so hot=E2=80=A6 once the magnetic field builds up in the co=
re of the coil the remaining current flow produces nothing but heat. I wrot=
e to Pertronix tech support for advice and they confirmed that the 1181 is =
not the right module for this application. Their words: "You really sh=
ould be using what we call a latching Ignitor module. This module takes two=
magnets to trigger the unit. One to turn it "ON" then one to turn it "OFF"=
to fire. This allows you to control the charge time of the coil. We use th=
is module on all our applications that have less then 4 cylinders. This is =
so we don't overheat the coil and don't over heat the Ignitor module. =
=E2=80=A6 The part number I would recommend to modify would be part number:=
1121=E2=80=9D At that point I bought an 1121 and modified my mount an=
d magnet wheel for it: http://www.jcmco.com/gallery/PertronixModIV =09 The 1121 module has been in s=
ervice on my Onan for 20 hours of runtime so far and has worked flawlessly.=
Just as with the 1181 module, the 1121 produces repeatable and precise spa=
rk timing but - unlike the 1181 - the 1121 produces no appreciable heating =
of the ignition coil. Having worked 35 years in an electronics career I kno=
w quite well that heat is the enemy of all electronic devices so I=E2=80=
=99m happy to have my coil running at nearly ambient temperature rather tha=
n around 140 degrees as when it was being fired by the 1181. =E2=80=
=94Jim Jim Miller 1977 Eleganza 1977 Royale Hamilton, OH =
