OS FS-91 Question
 

Hi Guys ....I was flying my 100-50 bird this am, and on landing approach, the engine quit, just over the threshold. The wind was blowing my hair off, but luckily the old 100/50 suffered no damage. The reason for this post is I am looking for any possible information. The engine is an OS FS-91. When i refueled and went to restart, there was no compression. Removed the valve cover and found the intake valve spring broken. I realize things break, but this is the 2nd time I have had valve springs bust on the FS-91. I have three of these engines, so i have a good batting average for valve spring breakage. Does anyone have any such experiences with this engine, or am I treating it mean somehow?

Bruce

RE: OS FS-91 Question
 

This is often caused by either wide valve clearance gaps or sticky valves.

The exhaust valve sticks more often than the intake

RE: OS FS-91 Question
 

Do you check/adjust the valves? I like to do mine in the spring every year. If you dont, be careful. I've seen the rocker arm cup break on engines that were not maintained.
Edwin

RE: OS FS-91 Question
 

I normally check valve clearance a couple of times a year, but in all honesty, I do not know when this one was last checked. It is my 100/50 bird and normally fly it when i can't stand not flying any longer, and the wind is blowing so hard that you have to tie your hat down and keep a strap on the tx so it does not get ripped out of your hands. The engine had been setting for a while since the last run. I had shot some transmission fluid in the bottom end and rolled her over a few times and then sat in corner. I just received new valve springs yesterday from Tower (ordered sunday evening ... how about that service) I will have a look and see if the valve stems may be carboned up or sticky.

Bruce

RE: OS FS-91 Question
 

Carbon on the valve stems can give you squirley performance. I bought an old os.91fs several years back. Ran it for about a year then set it aside. When I came back to it, it didnt want to idle very well. It had some carbon on it but I didnt think it was that bad. Cleaned it anyway and what didnt come off in the crockpot got ground off with a crown wire brush in a dremil. I removed the valves and clean them up too so it was as clean as you could get. What a difference! Runs like a top and idles lower than my saito's. Dont know if that could have anything to do with your valve springs breaking though, anybody else chime in (W8ye)?
Edwin