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Dtrain

Help w A-C 720 Onan muffler

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Dtrain
I am overhauling an Onan CCKB in a 720. It has 1300 hours on it and has standard pistons. It has burned exhaust valves and the top of the pistons have some burning. I am replacing both along with new rings. My mechanic says the mufflers are to blame for the burning as they are too restrictive. The PO did not replace the original muffler but instead installed some can type mufflers and (ouch) chopped the sides of the hood and ran them straight out to the sides. I have two questions: 1- where can I get a replacement OEM type muffler and brackets at the most reasonable price (it exits on left front); or 2- what type of can mufflers would give proper flow of exhaust gases so I do not have burned valves etc. again? If you can give me sources for both solutions, I would appreciate it very much. Thanks. Dave

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Ronald Hribar
I do not have answer for you. But in another post on mufflers they seeem to indicate the lack of back pressure causes exhaust vale burning.

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iweld
I'm sure you have checked out O.E.M.s. I think they are upwards of $180.00. I know this seems extremly high priced but, they are well made with good materials. I know I couldn't build one for that price at shop rate. Of course Nelson muffler is mass producing them and they shouldn't cost that much, but they charge what the market will bear.

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Dtrain
Thank you for your input everyone. Another knowlegeable member emailed me and suggested looking for a poor seal or crack in the manifold which is allowing an excessively high O2 level and excessive heat. I imagine that would result in the same problems as too lean a fuel mixture.

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MPH
Kinda question it being the can mufflers fault, depending on what kind they are I suppose, because an Onan engine I have off a ditcdh witch had a pair of cans on it about the same as the ones many of us have on our Briggs with the exception they exhaut out the side instead of the end. I have one of them on my Landlord as this Onan is rustted solid. To bad about the hood hack job.

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