| [GMCnet] Onan Flywheel [message #172610] |
Fri, 08 June 2012 16:05  |
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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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After installing the RAGUSA starter bracket I did not heed the manual and simply reinstalled the flywheel bolt with my electric impact wrench.
This is a mistake.
The shaft is tapered and the impact wrench is strong enough that it cracked the hub of the flywheel. I pulled the flywheel off today - a task I’ve become quite good at - and inspected it. I was hoping it was not damaged (to my eyes) so that I might simply reinstall it at the proper torque. That’s not how my luck runs.
<http://www.gmcmhphotos.com/photos/onan-the-barbarian/p44486-onan-flywheel-crack.html>
<http://www.gmcmhphotos.com/photos/onan-the-barbarian/p44485-onan-flywheel-crack.html>
These are sorrowful pictures of my cracked flywheel hub. Fortunately a call to Nick at Applied GMC and a replacement flywheel was had, reinstalled at the proper torque and the Onan runs again. I don’t think it runs as smoothly as it did before, but with all the fiddling I’ve been doing it’s a wonder it runs at all.
I’ve got to install the Pertronix ignition upgrade...
Larry Davick
The Mystery Machine
1976(ish) Palm Beach
Fremont, CA
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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 Flywheel [message #172639 is a reply to message #172610] |
Fri, 08 June 2012 18:10  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Larry,
Glad your mis-step didn't cause more trouble. It's interesting, and should
be noticed by everyone, that Rob's comment about checking at the corners of
the keyway was prophetic. The "stress riser" that's always created at
sharp corners is something we all need to keep in mind all the time. That
same phenomenon is the reason such practices as pipe wrenches on torsion
bars should be avoided.
Everyone really does need to do the Pertronix mod. The improvement is hard
to believe until you've seen it.
Ken H.
On Fri, Jun 8, 2012 at 5:05 PM, Larry Davick wrote:
> After installing the RAGUSA starter bracket I did not heed the manual and
> simply reinstalled the flywheel bolt with my electric impact wrench.
>
> This is a mistake.
>
> The shaft is tapered and the impact wrench is strong enough that it
> cracked the hub of the flywheel. I pulled the flywheel off today - a task
> I’ve become quite good at - and inspected it. I was hoping it was not
> damaged (to my eyes) so that I might simply reinstall it at the proper
> torque. That’s not how my luck runs.
>
> <
> http://www.gmcmhphotos.com/photos/onan-the-barbarian/p44486-onan-flywheel-crack.html
> >
> <
> http://www.gmcmhphotos.com/photos/onan-the-barbarian/p44485-onan-flywheel-crack.html
> >
> ...
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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 Flywheel [message #172660 is a reply to message #172639] |
Fri, 08 June 2012 21:22 |
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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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Ken,
The reason I "knew" about the cracking in the corner of the flywheel keyway
is that is a common failure on Harley clutch baskets that are mounted to the
trans main shaft on a taper. The original basket had a steel sleeve cast
into the aluminum hub that had a wall thickness marginally bigger than the
keyway slot after it was cut. They improved the design by increasing the OD
of the cast in sleeve greatly but it was still a problem as the average HD
mechanic couldn't spell torque wrench let alone know how to use one or
bother to do so! The final fix was to do away with the taper and change to a
splined main shaft.
I agree the Pertronix mod makes a BIG difference in the way that the Onan
runs. However, don't be a dummy like me and mount the pickup so close that
the fan can hit it. IIRC the VW pickup I used stated that the clearance
between the magnet and sensor should be 0.60 in. I made it a "tight" 0.60
in. I wasn't dumb enough not to turn the flywheel by hand to make sure the
magnet and fins cleared the sensor. However I was too dumb to realize the
clearance when turning the flywheel by hand might not be the same as when it
was running. It fired up instantly and ran for a few seconds and then
something hit the sensor and pieces went flying. Fortunately my good buddy
JohnS had bought two of them off eBay and we installed the second. Since all
the holes were drilled I couldn't move it so I decided to remove a tiny bit
from the magnet and then check the clearance between the flywheel and the
sensor fin by fin. If a fin was too close I'd flap wheel a bit of material
off the fin.
When I got done I decided it would be a good idea to have the flywheel
rebalanced and took it to a shop. When John and I reassembled it when I was
there back in March we noticed there were a couple of BIG new holes in the
periphery. When we fired it up it ran damn SMOOTH! At the Shawnee Convention
I asked a couple of people to fire up their Onan's and I compared how
smoothly they ran in comparison to mine I opened the access door and put my
hands on the Onan and they didn't feel as smooth as mine. I know that's a
half-a$$ed test as I probably "wanted" them to run rougher so I could
justify my mistakes and follow on action. ;-)
Regards,
Rob M.
-----Original Message-----
From: Ken Henderson
Larry,
Glad your mis-step didn't cause more trouble. It's interesting, and should
be noticed by everyone, that Rob's comment about checking at the corners of
the keyway was prophetic. The "stress riser" that's always created at
sharp corners is something we all need to keep in mind all the time. That
same phenomenon is the reason such practices as pipe wrenches on torsion
bars should be avoided.
Everyone really does need to do the Pertronix mod. The improvement is hard
to believe until you've seen it.
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 Flywheel [message #172676 is a reply to message #172610] |
Fri, 08 June 2012 23:57 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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That is exactly where mine is cracked. Someone in the past welded it back and it cracked again right through the weld. I have since had it welded correctly and reinstalled it. If I stumble across a replacement that is not cracked, someday I'll replace it. It runs just fine the way it is.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan Flywheel [message #172682 is a reply to message #172676] |
Sat, 09 June 2012 02:06 |
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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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Somehow I knew it would be cracked, but I also knew that Jim K’s shop is only a mile or two away. What kind of shop balances a flywheel? For that matter what kind of shop re-welds cracked flywheels?
The Onan doesn’t seem to run as well now as it did before. Of course it starts every time now, but once started it seems to run rougher.
Larry Davick
The Mystery Machine
1976(ish) Palm Beach
Fremont, CA
On Jun 8, 2012, at 9:57 PM, Ken Burton wrote:
>
>
> That is exactly where mine is cracked. Someone in the past welded it back and it cracked again right through the weld. I have since had it welded correctly and reinstalled it. If I stumble across a replacement that is not cracked, someday I'll replace it. It runs just fine the way it is.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
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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 Flywheel [message #172732 is a reply to message #172694] |
Sat, 09 June 2012 19:07 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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| Robert Mueller wrote on Sat, 09 June 2012 09:23 |
Larry,
The shop I took it to specialize in engine balancing. They had an arbor that
fit the Onan flywheel but not perfectly. The shop owner likes to have no
more than 0.003 run out. The arbor he used had 0.008. He adjusted the depth
and number of new balancing holes to compensate for the run out.
www.gmcmhphotos.com/photos/random-photos/p44490-onan-flywheel-rebalanced.htm
l
Regards,
Rob M.
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this URL should work. The final "L" above wrapped to a new line
http://www.gmcmhphotos.com/photos/random-photos/p44490-onan-flywheel-rebalanced.html
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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