Home » Public Forums » GMCnet » ONAN Head Experience
| ONAN Head Experience [message #254788] |
Tue, 08 July 2014 23:52  |
captjack
Messages: 271
Registered: February 2010
Location: Sebastopol, California
Karma: 1
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Senior Member |
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I installed a Pertronix electronic ignition for which I fabricated the mounting. I also decided to de-carbonize the heads. They deserved it!
I retightened the head bolts using a torque wrench to the proper settings. Some time later I noticed what I thought was an exhaust leak which showed up when the ONAN was powering two generators. I finally decided to track it down and found that the head bolts were now loose, some capable of being tightened almost by hand. I really don't understand why, since I was also reusing the old head gasket. But retightening them solved the problem and the generator is now relatively quiet again.
So, head bolts should be tightened after a few hours of operation if the heads are removed.
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
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| Re: ONAN Head Experience [message #254790 is a reply to message #254788] |
Wed, 09 July 2014 00:58  |
jim kanomata
Messages: 257
Registered: March 2007
Location: fremont,ca
Karma: 12
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Senior Member |
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Reusing a head gasket is not too great as it has no life left.
The studs in the head is in an aluminum body and can spin the stud.
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] ONAN Head Experience [message #254813 is a reply to message #254790] |
Wed, 09 July 2014 08:17 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Although I agree with Jim on new gaskets where ever as possible it is common practice to spray the onan head gaskets with aluminum silver paint on both sides and reuse one time. Did you use the paint?
JR Wright
78 Buskirk Stretch
75 Avion
Michigan
On Jul 9, 2014, at 1:58 AM, jim kanomata wrote:
> Reusing a head gasket is not too great as it has no life left.
> The studs in the head is in an aluminum body and can spin the stud.
> --
> Applied/GMC, Fremont, CA
> 1-800-752-7502
> jimk@appliedgmc.com
> www.appliedgmc.com
> _______________________________________________
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: ONAN Head Experience [message #254827 is a reply to message #254788] |
Wed, 09 July 2014 09:41 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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Senior Member |
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This takes me back to the first engine I ever fixed. The family lawn mower would run a little while and stop. Briggs and Stratton flat head four stroke. I had heard that you needed to decarbonize. I didn't have any tools except a monkey wrench, screwdriver, pliers. Only two size bolts on this one, but some were very hard to get to with that wrench. It was the style that came with Model T Fords, if I have noticed correctly. So, took off the head, scraped off the carbon which wasn't really thick, put it back on laboriously, tightened the head bolts. Just wanted to see it fire once, since I had been messing with the holy of holies, internal engine parts. I was about 13 years old. Memory dims, but I might have had a box end wrench for those head bolts, but I remember familiarity with sockets and better tools in a later time frame. Could have borrowed them. I do remember the bolt heads countersunk in the fins, so it must have been difficult. I remember it took hours.
That engine ran another 20 years. Only problem was that I didn't know what I had done to repair it. I now know the head was loose, it heated up, started to lose compression, quit running. The family thought I was a wizard, and I didn't disabuse them of that notion. Lots of head scratching back in those days, just like now. A snow blower later in my life did the same, it was a Sears/Tecumseh, same cure, only didn't have to take the head off. Just tightened the bolts. Needless to say, I didn't even know what a torque wrench was the first time.
Thanks for the ride down memory lane.
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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| Re: [GMCnet] ONAN Head Experience [message #254832 is a reply to message #254827] |
Wed, 09 July 2014 10:24 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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Can run the Onan on propane. That will de-cArbon it
Erf
FREE WIFI @ Mickey D
On Jul 9, 2014, at 7:41 AM, Carey Bryan wrote:
> This takes me back to the first engine I ever fixed. The family lawn mower would run a little while and stop. Briggs and Stratton flat head four
> stroke. I had heard that you needed to decarbonize. I didn't have any tools except a monkey wrench, screwdriver, pliers. Only two size bolts on
> this one, but some were very hard to get to with that wrench. It was the style that came with Model T Fords, if I have noticed correctly. So, took
> off the head, scraped off the carbon which wasn't really thick, put it back on laboriously, tightened the head bolts. Just wanted to see it fire
> once, since I had been messing with the holy of holies, internal engine parts. I was about 13 years old. Memory dims, but I might have had a box end
> wrench for those head bolts, but I remember familiarity with sockets and better tools in a later time frame. Could have borrowed them. I do remember
> the bolt heads countersunk in the fins, so it must have been difficult. I remember it took hours.
>
> That engine ran another 20 years. Only problem was that I didn't know what I had done to repair it. I now know the head was loose, it heated up,
> started to lose compression, quit running. The family thought I was a wizard, and I didn't disabuse them of that notion. Lots of head scratching
> back in those days, just like now. A snow blower later in my life did the same, it was a Sears/Tecumseh, same cure, only didn't have to take the head
> off. Just tightened the bolts. Needless to say, I didn't even know what a torque wrench was the first time.
>
> Thanks for the ride down memory lane.
>
> Carey
> --
> Carey from Ennis, Texas
> 78 Royale, 500 Cadillac, Rance Baxter EFI.
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| Re: [GMCnet] ONAN Head Experience [message #254834 is a reply to message #254832] |
Wed, 09 July 2014 10:31 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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Senior Member |
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I used anti seize on the head gaskets as suggested here. Many hours since and no leaks/Onan runs strong. Might check the torque now however ;)
Todd Sullivan
Sully
77 royale
Seattle
> On Jul 9, 2014, at 8:24 AM, "Mr.erf" wrote:
>
> Can run the Onan on propane. That will de-cArbon it
> Erf
>
> FREE WIFI @ Mickey D
>
>
>
>
>
>> On Jul 9, 2014, at 7:41 AM, Carey Bryan wrote:
>>
>> This takes me back to the first engine I ever fixed. The family lawn mower would run a little while and stop. Briggs and Stratton flat head four
>> stroke. I had heard that you needed to decarbonize. I didn't have any tools except a monkey wrench, screwdriver, pliers. Only two size bolts on
>> this one, but some were very hard to get to with that wrench. It was the style that came with Model T Fords, if I have noticed correctly. So, took
>> off the head, scraped off the carbon which wasn't really thick, put it back on laboriously, tightened the head bolts. Just wanted to see it fire
>> once, since I had been messing with the holy of holies, internal engine parts. I was about 13 years old. Memory dims, but I might have had a box end
>> wrench for those head bolts, but I remember familiarity with sockets and better tools in a later time frame. Could have borrowed them. I do remember
>> the bolt heads countersunk in the fins, so it must have been difficult. I remember it took hours.
>>
>> That engine ran another 20 years. Only problem was that I didn't know what I had done to repair it. I now know the head was loose, it heated up,
>> started to lose compression, quit running. The family thought I was a wizard, and I didn't disabuse them of that notion. Lots of head scratching
>> back in those days, just like now. A snow blower later in my life did the same, it was a Sears/Tecumseh, same cure, only didn't have to take the head
>> off. Just tightened the bolts. Needless to say, I didn't even know what a torque wrench was the first time.
>>
>> Thanks for the ride down memory lane.
>>
>> Carey
>> --
>> Carey from Ennis, Texas
>> 78 Royale, 500 Cadillac, Rance Baxter EFI.
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: ONAN Head Experience [message #254835 is a reply to message #254788] |
Wed, 09 July 2014 10:55 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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captjack wrote on Wed, 09 July 2014 00:52I installed a Pertronix electronic ignition for which I fabricated the mounting. I also decided to de-carbonize the heads. They deserved it!
I retightened the head bolts using a torque wrench to the proper settings. Some time later I noticed what I thought was an exhaust leak which showed up when the ONAN was powering two generators. I finally decided to track it down and found that the head bolts were now loose, some capable of being tightened almost by hand. I really don't understand why, since I was also reusing the old head gasket. But retightening them solved the problem and the generator is now relatively quiet again.
So, head bolts should be tightened after a few hours of operation if the heads are removed.
Jack,
I know well what everybody has been told forever, but stop for a moment read what the guy that was McCord's Aftermarket, Heavy Duty and Racing Gaskets engineer has to say about this.
Reusing head gaskets is not the problem, and in actual fact, I would sometimes advise a client to do it (much to one bosses dismay). This is only a one beer story, but for that price I will relate it in detail at Chippawa Falls.
The problem was that most likely something had gotten into the internal threads that gave you a false tension/torque. The problem with all gaskets is creep. This is compression under load and it is the reason that any gasketed assembly benefits from re-torquing (re-tensioning) the fasteners. If you are reassembling all the same parts, the gasket has already done its creeping. This means it will seal even better the second time because now that gasket knows how to fit where it needs to be.
Well, I have to go out and get the coach into the barn so I can find out why my BF (4.0 Onan) has decided to get weird. I'm sure it is something simple, but I have to find it.
Question?: How do you get an Onan to power two generators??
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] ONAN Head Experience [message #254841 is a reply to message #254835] |
Wed, 09 July 2014 11:29 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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I hate to say, R.T.F.M., but, the Onan manual says to torque the heads in
sequence pictured, in three steps. First, at 50% of final value, Second, at
75% of final value, and finally at final value. Refer to the Friggin'
Manual for the Recommended final value. It is how I do it on Onan engines,
and for that matter, on every engine that I torque the cylinder heads on. I
NEVER, EVER, trust my memory for the recommended value either. JWID.
Jim Hupy
Salem, Or.
78 GMC ROYALE 403
On Jul 9, 2014 8:55 AM, "Matt Colie" wrote:
> captjack wrote on Wed, 09 July 2014 00:52
>> I installed a Pertronix electronic ignition for which I fabricated the
> mounting. I also decided to de-carbonize the heads. They deserved it!
>>
>> I retightened the head bolts using a torque wrench to the proper
> settings. Some time later I noticed what I thought was an exhaust leak
> which
>> showed up when the ONAN was powering two generators. I finally decided
> to track it down and found that the head bolts were now loose, some capable
>> of being tightened almost by hand. I really don't understand why, since
> I was also reusing the old head gasket. But retightening them solved the
>> problem and the generator is now relatively quiet again.
>>
>> So, head bolts should be tightened after a few hours of operation if the
> heads are removed.
>
> Jack,
>
> I know well what everybody has been told forever, but stop for a moment
> read what the guy that was McCord's Aftermarket, Heavy Duty and Racing
> Gaskets
> engineer has to say about this.
>
> Reusing head gaskets is not the problem, and in actual fact, I would
> sometimes advise a client to do it (much to one bosses dismay). This is
> only a
> one beer story, but for that price I will relate it in detail at Chippawa
> Falls.
>
> The problem was that most likely something had gotten into the internal
> threads that gave you a false tension/torque. The problem with all gaskets
> is
> creep. This is compression under load and it is the reason that any
> gasketed assembly benefits from re-torquing (re-tensioning) the fasteners.
> If
> you are reassembling all the same parts, the gasket has already done its
> creeping. This means it will seal even better the second time because now
> that gasket knows how to fit where it needs to be.
>
> Well, I have to go out and get the coach into the barn so I can find out
> why my BF (4.0 Onan) has decided to get weird. I'm sure it is something
> simple, but I have to find it.
>
> Question?: How do you get an Onan to power two generators??
>
> Matt
>
> --
> Matt & Mary Colie - Members GMCMI, GMCES
> '73 Glacier 23 With 4 Rear Brakes that pull as they should
> SE Michigan - Twixt A2 and Detroit
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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