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Old 06-20-2024, 05:16 AM   #1
MattHelm21
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Generator exhaust leak

Hi. I'm one of those people who tries to fix things themselves to the point I obsess over it until I get the job done right(OCD?). Unfortunately that is going to make for a bit of a long post here. If you know me from other posts, you are probably aware that I use my gas generator(Onan EVAP 5500) exclusively at NASCAR races while camping. It runs 24/7 and I use a Genturi with 18 inch extension to run the exhaust above the roofline.

Several years ago now, we had a CO alert inside the trailer. We opened some windows and turned on an exhaust fan to bring fresh air in and chalked it up to the generator, wind currents, or proximity to other campers running generators. This has occurred off and on, always at night, only running the generator which we only do perhaps one to three times a year. We continued to beleive it was random. The only other times the generator runs is when I am outside and exericising it monthly. During this time, I replaced my CO detectors with WiFi enabled models in both the master bedroom and livingroom. These have PPM displays and alerting capabilities via a phone app.

Fast forward to the North Wilksboro race this year and our first night running the generator. Before bed, the CO detector triggered on 30 PPM. I vented the inside and readings returned to 0. Closed up during the day with airconditioners runnin and readings were 0 ppm CO. I made a note to check things when I get home.

Getting started on the troubleshoot, I first purchased one of these Portable Carbon Monoxide detector. I used it to detect CO and expected to find it around the Genturi and possible leaking in around a slide seal. What I was surprised to discover is that more CO was being exhausted from the bottom of the generator itself in the stream of cooling air which the generator expells around the exhaust. I used engine fogger to confirm this and could see exhaust leaking from around the flange between the muffler and the exhaust pipe. This CO was triggering readings of over 100 PPM under the RV and higher in the cooling exhaust compartment of the generator.

Ok. That describes the problem, and discovery. Now the things I've tried to fix it. I have tried resealing everything with exhaust putty after removing, and cleaning up the surfaces of the flanges. I waited the 24 hours for full curiing only to find the same leak. This time, I was able to see that the leak was coming from the part of the exhaust pipe's flange facing rearwards on the RV as evidenced by soot deposits. I removed the exhaust, cleaned up all the putty(removed or ground off), smoothed the flange surfaces, ordered a new gasket from Onan/Cummins(I had previously used the old one), put it all back together only to still have the leak as evendenced by the CO streaming from behind the exhaust pipe under the flange. I've now dissassembled the exhaust one more time. I'm going to contact Onan/Cummins to see what they think going with two gaskets. During all this time, I did find that service work I had a shop perform which required removing part of the coroplast directly behind the generator from the cross rail in the same location left gaps or bows between the cross frame rail allowing access to the underbelly for gasses to intrude. Several of these bows between the mounting screws had been filled with spray foam but several had not. I filled the ones which had not myself but still am not satified with leaving CO and exhaust exiting in this location.

I'm beginning to think a machine shop will have to resurface the flanges but while the bottom/pipe end will be easy to remote and transport to one, I can see no way to get the top flange out without removing the generator from the RV in order to remove the top cover to get at the muffler.

I'd love to hear if anyone has a similar issue and what your resolution was.

Thanks in advance.
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Old 06-20-2024, 06:08 AM   #2
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Could the flange or manifold possibly have a crack in it? Just throwing that out there.
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Old 06-20-2024, 08:40 AM   #3
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Originally Posted by flybouy View Post
Could the flange or manifold possibly have a crack in it? Just throwing that out there.
I don't think so. I've taken pictures of everything that I can reach. Here is a picture of the upper surface of the lower flange. I painted it white and sanded it to see if there were low spots. I think the gasket would take care of what you can see.
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Old 06-20-2024, 03:37 PM   #4
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Iíve never liked the design of Onan generatorís intake of cooling air being next to the discharge of hot air. This canít be good for an air cooled engine. On the past campers Iíve had with Onan generators, Iíve had our sheet metal shop build a right angle elbow which directs the hot discharge towards the driverís side. As part of that, the exhaust pipe flange was clocked to be keep exhaust pipe contained in the elbow/duct so that both the coolant air and engine exhaust are expelled 3Ē past the trailerís side. This eliminated the regurgitation of intake and discharge air and in retrospect helped eject exhaust gases away from the trailer along with slip stream of heated air of cooling system. Any leak of exhaust from manifold would have been mingled with flow of cooling air.
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Old 06-20-2024, 03:49 PM   #5
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That looks pretty rough to me, but I don't have it in my hands to feel it. Unfortunately, it's tough to judge not knowing what the mating surface looks like. How did you sand that flange? I've had greater success myself by afixing sandpaper to a solid surface (steel workbench or welding table works great) then hold the flange flat against it and move it back & forth in a straight line.

This has been my experience, YMMV.
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Old 06-20-2024, 05:18 PM   #6
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Quote:
Originally Posted by flybouy View Post
That looks pretty rough to me, but I don't have it in my hands to feel it. Unfortunately, it's tough to judge not knowing what the mating surface looks like. How did you sand that flange? I've had greater success myself by affixing sandpaper to a solid surface (steel workbench or welding table works great) then hold the flange flat against it and move it back & forth in a straight line.

This has been my experience, YMMV.
I used a heavy automotive sanding block with 320 grit paper and never allowed the block to go past the edge of the flange. Unfortunately, I can't do the same with the mating surface without taking the generator out of the RV. I did use my Dremel tool to take all the surface rust you can see in this picture off before trying to mate them again. The one thing I can't find is exactly what to torque the bolts to. The installation and parts manuals don't make any recommendation about torque except where spark plugs are concerned.
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Old 06-20-2024, 05:50 PM   #7
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Here's a pretty good bolt chart for torque ratings, https://www.portlandbolt.com/technic...-torque-chart/
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Old 06-21-2024, 05:10 AM   #8
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Originally Posted by flybouy View Post
Here's a pretty good bolt chart for torque ratings, https://www.portlandbolt.com/technic...-torque-chart/
Thanks for that. It doesn't specifically mention the bolt being used. I'm attaching a picture of the bolt head. The code F593C seems to indicate a Stainless Steel bolt Cold Worked or CW1. The head is 13mm and to me it seems to be coarse thread. I hunted around and the closest I could find for torque specs was 12 to 20 ft-lbs. This seems quote low to me. Another thought I had is the flange bolts are mounted east west which if the exhaust pipe vibrates up and down might open the side of the flange joint not covered by a bolt. I was thinking of turning the flange 90 degrees to orient the bolts north south. I'm not sure why a two bolt flange is used to mount up to a 4 bolt flange here.
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Old 06-22-2024, 04:47 AM   #9
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While I can’t help with the leak, I can tell you from an engineering point to not exceed the 20 ft-lbs.
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Old 06-22-2024, 07:10 AM   #10
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Quote:
Originally Posted by MattHelm21 View Post
Hi. I'm one of those people who tries to fix things themselves to the point I obsess over it until I get the job done right(OCD?). Unfortunately that is going to make for a bit of a long post here. If you know me from other posts, you are probably aware that I use my gas generator(Onan EVAP 5500) exclusively at NASCAR races while camping. It runs 24/7 and I use a Genturi with 18 inch extension to run the exhaust above the roofline.

Several years ago now, we had a CO alert inside the trailer. We opened some windows and turned on an exhaust fan to bring fresh air in and chalked it up to the generator, wind currents, or proximity to other campers running generators. This has occurred off and on, always at night, only running the generator which we only do perhaps one to three times a year. We continued to beleive it was random. The only other times the generator runs is when I am outside and exericising it monthly. During this time, I replaced my CO detectors with WiFi enabled models in both the master bedroom and livingroom. These have PPM displays and alerting capabilities via a phone app.

Fast forward to the North Wilksboro race this year and our first night running the generator. Before bed, the CO detector triggered on 30 PPM. I vented the inside and readings returned to 0. Closed up during the day with airconditioners runnin and readings were 0 ppm CO. I made a note to check things when I get home.

Getting started on the troubleshoot, I first purchased one of these Portable Carbon Monoxide detector. I used it to detect CO and expected to find it around the Genturi and possible leaking in around a slide seal. What I was surprised to discover is that more CO was being exhausted from the bottom of the generator itself in the stream of cooling air which the generator expells around the exhaust. I used engine fogger to confirm this and could see exhaust leaking from around the flange between the muffler and the exhaust pipe. This CO was triggering readings of over 100 PPM under the RV and higher in the cooling exhaust compartment of the generator.

Ok. That describes the problem, and discovery. Now the things I've tried to fix it. I have tried resealing everything with exhaust putty after removing, and cleaning up the surfaces of the flanges. I waited the 24 hours for full curiing only to find the same leak. This time, I was able to see that the leak was coming from the part of the exhaust pipe's flange facing rearwards on the RV as evidenced by soot deposits. I removed the exhaust, cleaned up all the putty(removed or ground off), smoothed the flange surfaces, ordered a new gasket from Onan/Cummins(I had previously used the old one), put it all back together only to still have the leak as evendenced by the CO streaming from behind the exhaust pipe under the flange. I've now dissassembled the exhaust one more time. I'm going to contact Onan/Cummins to see what they think going with two gaskets. During all this time, I did find that service work I had a shop perform which required removing part of the coroplast directly behind the generator from the cross rail in the same location left gaps or bows between the cross frame rail allowing access to the underbelly for gasses to intrude. Several of these bows between the mounting screws had been filled with spray foam but several had not. I filled the ones which had not myself but still am not satified with leaving CO and exhaust exiting in this location.

I'm beginning to think a machine shop will have to resurface the flanges but while the bottom/pipe end will be easy to remote and transport to one, I can see no way to get the top flange out without removing the generator from the RV in order to remove the top cover to get at the muffler.

I'd love to hear if anyone has a similar issue and what your resolution was.

Thanks in advance.

Could the extension pipe be causing the exhaust gasses to cool too much and the CO is spilling back down on hot days?…instead of floating away from the rv,it is cooler then the outside air and falling down thru gaps around slides etc?
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Old 06-24-2024, 06:57 AM   #11
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Quote:
Originally Posted by jasin1 View Post
Could the extension pipe be causing the exhaust gasses to cool too much and the CO is spilling back down on hot days?Öinstead of floating away from the rv,it is cooler then the outside air and falling down thru gaps around slides etc?
Yes, the condidtion you describe could be a source of CO. So far though we have only been through the issue at night where the outside air has cooled. I've also examined the slide seals around the exhaust area and they are in good shape.
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Old 06-24-2024, 07:09 AM   #12
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Originally Posted by notanlines View Post
While I can’t help with the leak, I can tell you from an engineering point to not exceed the 20 ft-lbs.
Thank you. A couple if bits of good news, I was able to confirm the torque on these bolts should be 11 ft-lbs so rather than mess around with a 3/8 inch torque wrench and trying to dial it back to nearly nothing, I picked up a 1/4" torque wrench which reads in in-lbs and used my final setting as 132. However, I torqued each bolt to 40 in-lbs then 80 in-lbs and finally the 132. I tested and using the CO meter found no CO leaks around that flange any longer.

Now the bad. I do still get a reading of 100 - 150 PPM behind the verticle part of the exhaust pipe running up to the flange but I cannot determine the source only that it is not the pipe itself or the exhaust flange or muffler. Below the belly of the trailer, this disperses out to 30 ppm to 50 ppm and having sealed up what I beleive was the opening allowing these gasses into the underbelly, I'm going adobt the wait and see attitude until our next big generator trip which probably isn't until next spring. I thank everyone for their help.
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