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Old 07-28-2012, 10:22 AM   #1
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Making the Onan generator quieter?

I sure wish the generator was quieter. My Honda gas powered unit is half this loud with the same load. I am considering going to my local muffler shop and seeing if the guys there can come up with anything, problem is I doubt they have anything small enough. Any suggestions on where to get a quieter low restriction muffler small enough for a gen set? I'm not concerned about the warranty, but I don't want to hurt performance.
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Old 07-28-2012, 10:50 AM   #2
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I sure wish the generator was quieter. My Honda gas powered unit is half this loud with the same load. I am considering going to my local muffler shop and seeing if the guys there can come up with anything, problem is I doubt they have anything small enough. Any suggestions on where to get a quieter low restriction muffler small enough for a gen set? I'm not concerned about the warranty, but I don't want to hurt performance.
The noise comes from the "hot" exhaust.

Expanding hot gas, makes noise.

You can quiet that down by increasing the length of the exhaust pipe, which cools the gas down, which in turn, decreases the noise.

Andy 13.4
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Old 07-28-2012, 11:23 AM   #3
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I work at a shop that repairs & installs gens on boats, we use a great sound barrier foam insulation. Low profile 1", flexible, but not cheap, and heavy for it's size. Full sheet (32"x54") $86.40.
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Old 07-28-2012, 12:19 PM   #4
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Used to be able to buy a bolton silencer for the onan. Go to the sprinter forum and use the search function. This was a few years ago. Onan used to be very picky on warranty claims so be careful. Also those devices that hook onto the exhaust and route it to the top of the van also act as a silencer as well as getting the exhaust fumes away from your or your neighbors windows. Jimg
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Old 07-28-2012, 12:44 PM   #5
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Check out gen-turi, also onan sellsan exhaust resonator that helps. jim
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Old 07-28-2012, 03:30 PM   #6
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I check at autozone for cheapest auto muffler and installed by cutting onan exhaust pipe a few inches, added an expansion tube, then the muffler with a greater diameter than the onan, worked fine. If you have room, it was worth it. Did this on SOB, my AS onan is quiet, and we are now usually in CG that have electric.
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Old 07-29-2012, 06:41 AM   #7
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I work at a shop that repairs & installs gens on boats, we use a great sound barrier foam insulation. Low profile 1", flexible, but not cheap, and heavy for it's size. Full sheet (32"x54") $86.40.
Heavy for its size because much of the sound barrier foam used for boat engine compartments is foam-covered lead sheets. My office has a subscription to Professional Boatbuilder magazine, which is how I know. I've never used the stuff personally.
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Old 07-29-2012, 07:52 AM   #8
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On our last trip, mine started make a racket like a sheet metal vibration. Turned out the inner exhaust clamp that AS used to attach the heat shield had both nuts missing which allowed the heat shield to rattle when the gen was running.

Doubt that's your problem but something for others w/ some miles on theirs to be aware of.
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Old 07-31-2012, 06:24 PM   #9
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Thanks for all the input! I think I'm going to try adding an additional muffler in-line with what is already there. There is a nice section of straight pipe where it runs laterally over to the drivers side where there should be room to swedge up to a 2" pipe, fit a low restriction 2" muffler and swedge back down to the stock diameter and use the existing hanger and side exit pipe.
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Old 07-31-2012, 06:59 PM   #10
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Originally Posted by zigzagguzzi View Post
Used to be able to buy a bolton silencer for the onan. Go to the sprinter forum and use the search function. This was a few years ago. Onan used to be very picky on warranty claims so be careful. Also those devices that hook onto the exhaust and route it to the top of the van also act as a silencer as well as getting the exhaust fumes away from your or your neighbors windows. Jimg
A friend of ours uses such a device on his SOB MH. Parked next to him, we hear very little of his generator, and smell none of it. His is removable and comes apart for storage.

Great idea.
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Old 08-10-2012, 12:42 AM   #11
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Very interesting. I am just starting to look into this as I start to restore my 1986 345 MH. It still has the Onan 7000 which is rated at 72 decibels installed, at least 10 higher than the Yamaha someone mentioned a while ago that people consider quiet.

I bought but never used the genturi, I think it was, chimney you mentioned. Does anyone khow much if cuts down on the noise? I know my generator starts up pretty stinky so I'll want go use it if around others. But is it comparable in effect as a muffler to some of the solutions mentioned here? How much quieter do these extensions your talking about make your generators?

I'd rather not replace this unit, it seems pretty powerful and now that it's tuned up it should come in pretty handy.
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Old 08-10-2012, 01:44 AM   #12
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Hi, it was quite a few years [decades] back, but we used to put Volkswagon [Bug] exhaust tips [one] on the Onan exhaust pipe. Not all of the noise is from the exhaust; Air cooled engines make a lot more noise than liquid cooled engines. My latest Onan was a Marquis 7000 and the muffler was mounted inside of the encased generator housing. It was much quiter than my old NH 6.5 generator.
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Old 08-10-2012, 06:45 AM   #13
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It still has the Onan 7000 which is rated at 72 decibels installed, at least 10 higher than the Yamaha someone mentioned a while ago that people consider quiet.
Rated at 72 decibels does not mean that you endure 72 decibels. The fact that it's mounted in an enclosure in or under your motorhome makes a difference, compared to one sitting out on the grass.

Also, that 72dB is an average over every octave of the human hearing range. A generator rated at 62dB will be higher than that in some octaves, but lower in others, and not necessarily the same octaves as with your 72dB generator. Different people are more sensitive to different octaves, so a 62dB generator might SEEM louder to you than your 72dB model, if it's peak frequency is in the range you're most sensitive to.

Here's a standard of comparison for you… Can you hold a normal conversation when the generator is running, without raising your voice or leaning closer to the person you're talking to? If so, the noise level you experience is actually less than 60 dB. Typical conversation at arm's length is 60dB, so if you don't have to raise your voice or talk into the other person's ear, your generator should then be quiet enough for anybody.
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Old 08-10-2012, 04:25 PM   #14
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Cool. Another great answer, Protagonist, thanks. I will test it with a nearby conversation.
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