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Onan Generator Compartment Problems [message #205883]

Thu, 25 April 2013 18:50

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

How does the air flow through a 4kw Onan in a 23' GMC?

How far back from the door is the power drawer supposed to sit to allow enough air through the grill?

Where does the air come in and where does it go out?

In this picture, you can see that the only hole, other than the grill in the door, is the bottom of the compartment. The power drawer mostly covers the hole. Doesn't look very conducive to cooling.

http://www.gmcmhphotos.com/photos/data/6268/4K_Onan_Compartment.JPG

http://www.gmcmhphotos.com/photos/data/6268/4K_Onan_Compartment.JPG

I am working on putting the Onan back in the gen compartment, and I don't have the OEM frame bracket. When I get a bracket that will bolt in, I need to position the drawer on it and then mark/drill the holes. I want to make sure the airflow is at least as good as original.

And while I have your attention, what did they make the original enclosure out of? All I have between the living space and the gen compartment of the Sequoia is 1/2" plywood.

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Re: Onan Generator Compartment Problems [message #205897 is a reply to message #205883]

Thu, 25 April 2013 20:26

C Boyd

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Registered: April 2006

Karma: 18

Senior Member

Maybe this will help.
http://www.gmcmhphotos.com/photos/g6270-4k-onan-bracket.html

A Hamilto wrote on Thu, 25 April 2013 19:50

How does the air flow through a 4kw Onan in a 23' GMC?

How far back from the door is the power drawer supposed to sit to allow enough air through the grill?

Where does the air come in and where does it go out?

In this picture, you can see that the only hole, other than the grill in the door, is the bottom of the compartment. The power drawer mostly covers the hole. Doesn't look very conducive to cooling.

http://www.gmcmhphotos.com/photos/data/6268/4K_Onan_Compartment.JPG

http://www.gmcmhphotos.com/photos/data/6268/4K_Onan_Compartment.JPG

I am working on putting the Onan back in the gen compartment, and I don't have the OEM frame bracket. When I get a bracket that will bolt in, I need to position the drawer on it and then mark/drill the holes. I want to make sure the airflow is at least as good as original.

And while I have your attention, what did they make the original enclosure out of? All I have between the living space and the gen compartment of the Sequoia is 1/2" plywood.

C. Boyd
76 Crestmont
East Tennessee

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Re: Onan Generator Compartment Problems [message #205903 is a reply to message #205897]

Thu, 25 April 2013 20:40

A Hamilto

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Registered: April 2011

Karma: 39

Senior Member

C Boyd wrote on Thu, 25 April 2013 20:26

Maybe this will help.
http://www.gmcmhphotos.com/photos/g6270-4k-onan-bracket.html

Chuck,

Kerry Pinkerton shortened the 6kw bracket from his art deco car hauler (parts unit), but it is not like OEM for a 23' model. I found out after I got it home that it won't work without more modification. I thought I could do it myself, but without a vice, bandsaw, oxy-acetylene set, holesaw, arc welder, sheet metal break, and scrap steel, it is too big a job for me. With your photos and measurements, I will get it (or one) to work, but even when I do, I am wondering about airflow. And also wondering what the compartment was constructed from originally. A PO removed the Onan and reconfigured the compartment as storage, and the only thing between the gen compartment and the living space is half inch untreated plywood. That doesn't seem right to me. Should be sheet metal, shouldn't it?

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Re: Onan Generator Compartment Problems [message #205921 is a reply to message #205903]

Thu, 25 April 2013 21:47

John Sharpe

Messages: 489
Registered: February 2006
Location: Texas

Karma: 1

Senior Member

Quote:

...How does the air flow through a 4kw Onan in a 23' GMC?....

Air flow of an Onan in a GMC is out the bottom of the front edge of the powerdrawer. Air is drawn across the engine and blown out the bottom. That way vapors are blown away from and not into the compartment where they could find there way inside the coach.

A lot of cooling air enters the compartment from underneath at the back of the power drawer. That's why a great deal of dust collects in that area.

John Sharpe
Humble,TX
'78 Eleganza TBI
'89 Spectrum 2000 MPI V-10
'40 Ford Panel Delivery TPI
johnasharpe@gmail.com

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Re: Onan Generator Compartment Problems [message #205922 is a reply to message #205921]

Thu, 25 April 2013 21:55

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

John Sharpe wrote on Thu, 25 April 2013 21:47

Quote:

...How does the air flow through a 4kw Onan in a 23' GMC?....

Air flow of an Onan in a GMC is out the bottom of the front edge of the powerdrawer. Air is drawn across the engine and blown out the bottom. That way vapors are blown away from and not into the compartment where they could find there way inside the coach.

A lot of cooling air enters the compartment from underneath at the back of the power drawer. That's why a great deal of dust collects in that area.

So the louver on the door doesn't really serve any purpose?

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Re: Onan Generator Compartment Problems [message #205961 is a reply to message #205922]

Fri, 26 April 2013 07:48

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

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A Hamilto wrote on Thu, 25 April 2013 22:55

John Sharpe wrote on Thu, 25 April 2013 21:47

Quote:

...How does the air flow through a 4kw Onan in a 23' GMC?....

Air flow of an Onan in a GMC is out the bottom of the front edge of the powerdrawer. Air is drawn across the engine and blown out the bottom. That way vapors are blown away from and not into the compartment where they could find there way inside the coach.

A lot of cooling air enters the compartment from underneath at the back of the power drawer. That's why a great deal of dust collects in that area.

So the louver on the door doesn't really serve any purpose?

I can't tell you about any 26', but I can tell you about a '73 23' where it is functional.

When the Onan is running, the compartment is at a negative pressure, as air is drawn out by the flywheel fan and dischraged under the coach. The cooling air is drawn in through the door grill and the gap at the door's lower edge. That air flows back (coach right) in the compartment where it is available to cool the electric end. The the flywheel fan draws that air over the cylinder heads and jugs and as stated above blows it out under the coach. There is no bottom opening to allow air into the machinery space. The original enclosure is all plywood inside and SMC to the outside with a metal heat shield under the plywood in the area of the machine's footprint.

A number (six that I know of) 6KW in 26s have had the field damaged by small gravel that ends up in the generator bell casting. I am not all sure how this material gets there. I have noticed that many machines in 26s are quite dirty and I have never seen this in my coach. There may be some different air path with those.

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: Onan Generator Compartment Problems [message #205963 is a reply to message #205961]

Fri, 26 April 2013 08:00

tphipps

Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL

Karma: 9

Senior Member

I lined my gen compartment with flameproof material, designed for firewall installation. Got a great deal at Bontrager's while at International. Used adhesive spray to install. Had to add strapping and screws to top, adhesive would not hold. Drops noise and heat level.
Tom, MS II

2012 Phoenix Cruiser model 2552 KA4CSG

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Re: [GMCnet] Onan Generator Compartment Problems [message #205970 is a reply to message #205961]

Fri, 26 April 2013 08:51

Jim Miller

Messages: 501
Registered: March 2008

Karma: 10

Senior Member

On Apr 26, 2013, at 8:48 AM, Matt Colie wrote:

> A number (six that I know of) 6KW in 26s have had the field damaged by small gravel that ends up in the generator bell casting. I am not all sure how this material gets there. I have noticed that many machines in 26s are quite dirty and I have never seen this in my coach. There may be some different air path with those.

The air path in a 6kW is in through the generator bell housing (via the plastic snap-in grilles), across the heads and then into the center of the flywheel which then exhausts the hot air out the bottom. The sealing ring around the oil filter is critical since the air is "sucked" through the machine rather than "blown" as would be done on a typical air-cooled engine. If the sealing ring is not in place the pressure differential across the system is decreased which gives you less airflow across the heads.

Small gravels do indeed ruin a lot of fields - the Onan on my Eleganza was damaged in that way - I found several pebbles inside the rear of the bell housing and had multiple breaks in the lower pole winding. I've seen debris in others as well.

--Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH

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Jim Miller 1977 Eleganza II 1977 Royale Hamilton, OH

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Re: Onan Generator Compartment Problems [message #205986 is a reply to message #205961]

Fri, 26 April 2013 10:44

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

Matt Colie wrote on Fri, 26 April 2013 07:48

I can't tell you about any 26', but I can tell you about a '73 23' where it is functional.

When the Onan is running, the compartment is at a negative pressure, as air is drawn out by the flywheel fan and dischraged under the coach. The cooling air is drawn in through the door grill and the gap at the door's lower edge. That air flows back (coach right) in the compartment where it is available to cool the electric end. The the flywheel fan draws that air over the cylinder heads and jugs and as stated above blows it out under the coach. There is no bottom opening to allow air into the machinery space. The original enclosure is all plywood inside and SMC to the outside with a metal heat shield under the plywood in the area of the machine's footprint.

A number (six that I know of) 6KW in 26s have had the field damaged by small gravel that ends up in the generator bell casting. I am not all sure how this material gets there. I have noticed that many machines in 26s are quite dirty and I have never seen this in my coach. There may be some different air path with those.

Matt

That seems reasonable, given the gunk at the bottom right of the compartment near the louver. I will have to cobble together some heat shielding, or a metal enclosure to replace the fireproofing that was removed with the Onan.

How far back from the door does the power drawer sit when the door is closed? Looks like I need to leave room for air to come in and get past the front panel of the Onan.

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Re: Onan Generator Compartment Problems [message #206135 is a reply to message #205986]

Sat, 27 April 2013 14:21

Dennis S

Messages: 3046
Registered: November 2005

Karma: 2

Senior Member

A,

Here is a photo album showing some of the dimensions of the Onan compartment on my 73, 23ft, with 4KW.

http://www.gmcmhphotos.com/photos/g6363-onan-4kw-compartment.html

Mine is gaucho seating style. The original compartment is made of plywood and the access to the battery is from inside under the front gaucho pad. The opening is simply a cut out in the plywood with no provision for sealing to prevent entry of exhaust fumes. There is sheet metal about the Onan and down the back side -- and then the compartment was covered with foam insulation that had a perforated black vinyl facing glued and stapled in place. This same foam insulation was used above the drop down ceiling in the hallway and in some areas around the rear windows.

Dennis

Dennis S
73 Painted Desert 230
Memphis TN Metro

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Re: Onan Generator Compartment Problems [message #206145 is a reply to message #206135]

Sat, 27 April 2013 16:42

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

Dennis S wrote on Sat, 27 April 2013 14:21

A,

Here is a photo album showing some of the dimensions of the Onan compartment on my 73, 23ft, with 4KW.

http://www.gmcmhphotos.com/photos/g6363-onan-4kw-compartment.html

Mine is gaucho seating style. The original compartment is made of plywood and the access to the battery is from inside under the front gaucho pad. The opening is simply a cut out in the plywood with no provision for sealing to prevent entry of exhaust fumes. There is sheet metal about the Onan and down the back side -- and then the compartment was covered with foam insulation that had a perforated black vinyl facing glued and stapled in place. This same foam insulation was used above the drop down ceiling in the hallway and in some areas around the rear windows.

Dennis

Dennis,

Thanks for the photos. I PM'd you one final question. My 73 CanyonLands has gaucho seating and the battery compartment for the generator is the same - no sealing. I don't know if the generator compartment is the same size or not, but the CanyonLands has a Kohler 4kw, so I can't take power drawer measurements from it.

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Re: Onan Generator Compartment Problems [message #206202 is a reply to message #205883]

Sun, 28 April 2013 09:06

habbyguy

Messages: 896
Registered: May 2012
Location: Mesa, AZ

Karma: 3

Senior Member

My PO installed a couple NACA ducts in the rear generator compartment in my Royale.

http://www.habcycles.com/GMC3.jpg

The generator has been replaced with a modern Onan Emerald Plus 6500 watt unit, but I can happily report I've been able to run the generator while driving in temperatures WELL over 100 degrees for hours, including stop and go traffic and long stopovers without any (apparent) heat issues.

Might help, might be a placebo, but the whole package is working.

Mark Hickey Mesa, AZ 1978 Royale Center Kitchen

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Re: Onan Generator Compartment Problems [message #206274 is a reply to message #206145]

Sun, 28 April 2013 21:49

Dennis S

Messages: 3046
Registered: November 2005

Karma: 2

Senior Member

A,

Posted more photos of my Onan 4KW drawer.
If you refer to page 28-48 -- do you have all but the bracket 44?

Dennis

http://www.gmcmhphotos.com/photos/g6363-onan-4kw-compartment.html

A Hamilto wrote on Sat, 27 April 2013 16:42

Dennis S wrote on Sat, 27 April 2013 14:21

A,

Here is a photo album showing some of the dimensions of the Onan compartment on my 73, 23ft, with 4KW.

http://www.gmcmhphotos.com/photos/g6363-onan-4kw-compartment.html

Mine is gaucho seating style. The original compartment is made of plywood and the access to the battery is from inside under the front gaucho pad. The opening is simply a cut out in the plywood with no provision for sealing to prevent entry of exhaust fumes. There is sheet metal about the Onan and down the back side -- and then the compartment was covered with foam insulation that had a perforated black vinyl facing glued and stapled in place. This same foam insulation was used above the drop down ceiling in the hallway and in some areas around the rear windows.

Dennis

Dennis,

Thanks for the photos. I PM'd you one final question. My 73 CanyonLands has gaucho seating and the battery compartment for the generator is the same - no sealing. I don't know if the generator compartment is the same size or not, but the CanyonLands has a Kohler 4kw, so I can't take power drawer measurements from it.

Dennis S
73 Painted Desert 230
Memphis TN Metro

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Re: Onan Generator Compartment Problems [message #206283 is a reply to message #206274]

Sun, 28 April 2013 22:37

A Hamilto

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Registered: April 2011

Karma: 39

Senior Member

Dennis S wrote on Sun, 28 April 2013 21:49

A,

Posted more photos of my Onan 4KW drawer.
If you refer to page 28-48 -- do you have all but the bracket 44?

Dennis

Which manual?

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Re: Onan Generator Compartment Problems [message #206320 is a reply to message #206283]

Mon, 29 April 2013 08:20

Dennis S

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Registered: November 2005

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Senior Member

[quote title=A Hamilto wrote on Sun, 28 April 2013 22:37][quote

If you refer to page 28-48 -- do you have all but the bracket 44?

Dennis[/quote]Which manual?[/quote]

The bracket shown as 44 on page 28-48 of the Parts Manual 78z.
Here is a link to the pdf -- it is page 358 of the pdf.

http://bdub.net/manuals/parts/GMCMH-Parts.pdf

Dennis

Dennis S
73 Painted Desert 230
Memphis TN Metro

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Re: Onan Generator Compartment Problems [message #206337 is a reply to message #206320]

Mon, 29 April 2013 11:25

A Hamilto

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Registered: April 2011

Karma: 39

Senior Member

Dennis S wrote on Mon, 29 April 2013 08:20

A Hamilto wrote on Sun, 28 April 2013 22:37

Quote:

If you refer to page 28-48 -- do you have all but the bracket 44?

Dennis

Which manual?

The bracket shown as 44 on page 28-48 of the Parts Manual 78z.
Here is a link to the pdf -- it is page 358 of the pdf.

http://bdub.net/manuals/parts/GMCMH-Parts.pdf

Dennis

I had the MM, OM, Assembly manual, and others, just never downloaded the parts manual.

Yes. The bracket numbered 44 on page 28-48 of the Parts Book (78Z) is the part that I am missing and trying to get fabricated.

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Re: Onan Generator Compartment Problems [message #206346 is a reply to message #206337]

Mon, 29 April 2013 12:57

Dennis S

Messages: 3046
Registered: November 2005

Karma: 2

Senior Member

Looking at the bracket, I wonder if it could be made from two lengths of 1 1/2 inch square tubing welded to a heavy channel.
Drill oversize holes in the tubing from below to allow access to install nuts.

Dennis

A Hamilto wrote on Mon, 29 April 2013 11:25

Dennis S wrote on Mon, 29 April 2013 08:20

A Hamilto wrote on Sun, 28 April 2013 22:37

Quote:

If you refer to page 28-48 -- do you have all but the bracket 44?

Dennis

Which manual?

The bracket shown as 44 on page 28-48 of the Parts Manual 78z.
Here is a link to the pdf -- it is page 358 of the pdf.

http://bdub.net/manuals/parts/GMCMH-Parts.pdf

Dennis

I had the MM, OM, Assembly manual, and others, just never downloaded the parts manual.

Yes. The bracket numbered 44 on page 28-48 of the Parts Book (78Z) is the part that I am missing and trying to get fabricated.

Dennis S
73 Painted Desert 230
Memphis TN Metro

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Re: Onan Generator Compartment Problems [message #206361 is a reply to message #206346]

Mon, 29 April 2013 18:07

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

Dennis S wrote on Mon, 29 April 2013 12:57

Looking at the bracket, I wonder if it could be made from two lengths of 1 1/2 inch square tubing welded to a heavy channel.
Drill oversize holes in the tubing from below to allow access to install nuts.

Dennis

Almost certainly. That would be even better than OEM. I don't have a convenient source of steel, or a way to bore the large holes, or welder, or any welding ability.

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Re: Onan Generator Compartment Problems [message #206365 is a reply to message #206361]

Mon, 29 April 2013 19:00

Don A

Messages: 895
Registered: October 2008
Location: Dallas, TX

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<<<convenient source of steel, or a way to bore the large holes>>>

Home Depot and Lowes sell steel. Maybe unistrut from the elec conduit area would work as it is a U channel, open on bottom?

Don Adams Dallas, TX
'76 26' Glenbrook, '90 Sidekick
rebuilt by R Archer, powered by J Bounds, Koba
[IMG]http://www.gmcmhphotos.com/photos/data/6109/G2.jpg[/IMG]

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Re: Onan Generator Compartment Problems [message #206368 is a reply to message #206365]

Mon, 29 April 2013 19:31

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

Don A wrote on Mon, 29 April 2013 19:00

<<<convenient source of steel, or a way to bore the large holes>>>

Home Depot and Lowes sell steel. Maybe unistrut from the elec conduit area would work as it is a U channel, open on bottom?

Thought about that. That is still a fallback plan, but I still needed the measurements to get the power drawer at the right height and the right depth in the compartment for airflow.

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