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Last year I attempted to repair damaged exhaust port threads on my Onan BF engine, detailed in the following thread:

eroded exhaust port threads

The engine runs great! But unfortunately, the exhaust repair didn't last. After the first tractor use, the metal repair compound was showing signs of erosion. By the third use, the exhaust pipe was rattling freely again. It was obvious that I needed to implement plan B: the _PROPER_ repair.

I bought 2 exhaust port adapters from boomer, here on the forums. The adapters were not designed for the Onan BF 16 hp, so I had to do a bit a cutting and grinding to make them fit properly. I had to remove the engine anyway to re-torque the head bolts, so took it to a machine shop and had them drill and tap two 5/16-18 holes around each exhaust port. I was planning on just using bolts and washers. But due to the high heat exposure and relative shallowness of the holes, the machine shop _STRONGLY_ recommended installing studs with loctite. I was sold on the idea.

Cut my own studs from high-temp threaded rod. Installed them with high-temp threadlocker (Loctite 2620, 650 F). Fastened everything down with lock washers and oversized nuts. Still working on the final assembly, but everything feels very solid.

If there's anything I learned from this, it's: just say NO to pipe threads. The guys at the machine shop also commented that pipe threads are a poor choice on an exhaust port.


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