GAK

Wondering if someone can help me with my YS 120F.

It runs fine, but one of the valve adusters is nearly bottomed out. Also, after 4 flights or so, I find I need to reset the valve clearance. Anyone have any ideas. I thought it was a short pushrod, but replaced it and no change.

Thanks in advance.

peso

I had this trouble when I run my YS on fuel with castor oil. After I switched to fuel with synthetic oil the problem disappeared

GAK

Thanks. That's a good point. I think I was using Castor. Wonder why that would cause the problem?

peso

Well I thought it was due to carbon build up on the valves. Anyway try another oil before you look for mechanical errors.
Generally castor oil more than 2 % should be avoided in fourstroke engines. Use a good synthetic oil instead. I have an YS 120 engine that is 10 years old now and it still runs as it was new. A very reliable engine if set up correctly.

w8ye

My Feedback: (16)

I agree that the carbon under the valves could be a problem but this will only be on the exhaust side. If a valve is being held off it's seat, it will look lower cmpared with the other one when at top dead center on the compression stroke.

Also you should look at the offending push rod.

If your push rod is even a slight amount bent. It will bend even more as you use it. Valve float from running the engine too fast will further bend a slightly kinked pushrod. It will cause problems with even a good push rod.

Pull out the push rod and roll it on a nice flat smooth table. A slight bend and the rod will flip when it rolls. You will have a difficult time trying to straighten it. Maybe in a small lathe with a dial indicator. Anything less and it will just bend again. I would suggest a new push rod in case you find it is bent.

Good luck,

Jim

GAK

Also, a good idea. I'll pull the pushrod and check. As you face the engine from the front it is the right tappet that has the adjustment nearly bottomed out. I have several pushrods, so I'll replace if necessary.

I am using an APC 16 x 8 prop. It has been a while since I ran it, but thinking it was turning around 8500. Wouldn't think this would be an overspeed situation.

This is good stuff thanks.

Dave Shadel

Good advise. Could also be that the pushrod was not heat treated properly and is getting shorter as it runs, we've seen this before. Also look to see that the rocker arm shaft is tight in the head.