YS91AC repair advice needed please. - RCCanada - Canada Radio Controlled Hobby Forum
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Old 08-16-2013, 10:12 AM   #1
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YS91AC repair advice needed please.

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I tore the exhaust out of my YS 91 AC, and it broke the casting away where the muffler screws into the engine. I tried JB Weld, but it can't withstand the heat, turned to liquid and the muffler came out.

Looking at the YS website for parts, it appears that the entire cylinder and head is one piece, so that's what I need to repair this engine.

Had anyone ever done this repair?
Are the valves included with the new cylinder, or do I remove them from the scrapped cylinder and transfer them over?
If I have to transfer them over, I'm not looking forward to figuring out how to remove valve guides, seals...

Does anyone have a cylinder assembly that they want to get rid of, or the whole engine?

Anyone have a better idea? I don't want to put a different engine in the plane, it was quite a bit of work to get this one set up and balanced with the YS, and it is a nice running motor as well.
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Old 08-16-2013, 03:41 PM   #2
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Re: YS91AC repair advice needed please.

Post some pictures.
Do you have all the pieces that broke off?

I have an OS 120 that I acquired that had the muffler exhaust ripped out the same way.

I had a co-worker weld the parts back on and he added a bit of extra aluminum inside the threaded section. Then we had to find a tap that was the same thread as the muffler- that was the hardest part since that thread is very rare. But we managed to get one and tapped it. Now its as good as new.
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Old 08-18-2013, 09:54 AM   #3
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Re: YS91AC repair advice needed please.

The thread on that exhaust pipe is 12 mm and is the same as 1/2" NF. I ran a tap in mine to clean the odd shape of the threads and now the stock muffler fits and my home made pipe. My engine is listed for $180.00 with two mufflers.

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