Thursday, August 11, 2011

Quieting the Onan Generator

In my search to quiet  down the Onan 2500 Microlite propane generator, I decided to install an Onan Resonator (Part# 155-2449) which was recommended by couple of members

To start, first determine the placement of the resonator. You could either install it at the end of the generator exhaust pipe or somewhere in the middle section of the pipe. If you decide to install it towards the end of the exhaust, you may need a bigger u-bolt pipe clamp to accommodate the bigger resonator body. For cleaner/ stock look I opted for the later.

I removed the generator exhaust pipe by unbolting it from the internal muffler flange, then removing the 2-rubber hangers that holds the exhaust pipe. The exhaust is not a simple straight pipe rather it has 2 opposing 135 or so degree bend towards both ends.

Using a marker, I made a straight line along the middle section of the exhaust where the resonator will be installed, doing this made sure that the geometry and shape of the exhaust will remain same after installation of the resonator. Same straight line was made along the resonator body, this line should be in-line with the line made on the exhaust pipe once installed.

Using a metal cut-off saw, I cut out about 10-inches long (double check resonator length, from collar to collar) section of generator exhaust pipe. I fitted the resonator, made sure it was properly aligned and then held it in place using tube clamps on each end. I then took  the whole exhaust pipe assembly  to a local welding shop and have the Onan resonator welded in place. The welding cost $10 and took less than 5 mins. I then painted the whole exhaust with heat resistant paint, or you can just paint the welds to keep them from rusting. If welding is not an option, a U-bolt clamp like this (U-Bolt Exhaust Clamp) maybe used to connect the resonator into the exhaust pipe.

Onan Resonator Specs.

Generator exhaust (with resonator installed) painted with heat resistant paint

I also fabricated a new exhaust pipe hanger, the hanger that came with it was made from hard rubber. When generator is running, exhaust vibrations is being transferred to the RT's body through the old hanger. I purchased an Exhaust Rubber Mount from local auto parts store. The rubber was really designed for automotive exhaust, so it was kinda thick. Using a hack saw, and periodically spraying it with WD-40 for lubrication, I spliced the rubber exhaust mount in half. The metal brackets were fabricated from a metal sheet. See pictures below.

Click on pictures to enlarge.

Exhaust rubber mount spliced in two

New metal brackets

Rubber mount with mounting screws

Side by side comparison of the new and old hanger. Disregard the new hanger upper bracket placement, I ended up mounting the brackets (upper & lower) on the same side of the rubber. I kept the old one as a spare.

Onan resonator installed with new exhaust hanger.

From another angle. The resonator really makes a difference, I highly recommend installing one. The new hanger is a lot better than the stock one.

I found a YouTube video testing an onan resonator, you be the judge.


  1. The correct way to test the resignator's effectiveness is with a dB tester before and after.


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