OS 91 FS SURPASS
 

I recently bought a used OS 91 FS SURPASS. I fired it up, adjusted the needle for a ritch setting,took off and found the engine was too ritch so I landed turned it in about 1/8 turn and took off again. Flew about 15 min. the engine was perfect did some spins, loops, rolls stall turns and 4 touch and go,s I lowered the idel 2 clicks and landed. As i approached the engine was at low idel and quit just before landing. I felt I had just brought the idel too low. A few minutes later after refueling I found the engine had no compression. I pulled the valve cover and found the intake valve spring completely collapsed. My question is, How do i get the valve spring retainer off? HELP....
Thanks, Jim

RE: OS 91 FS SURPASS
 

When you say collapsed you mean the spring broke, it should be no problem just remove the two half reteiners, by pressing down on it, you need to remove the head to hold the valve from the chamber side. Not a big deal.

RE: OS 91 FS SURPASS
 

Your prop was too small too.

RE: OS 91 FS SURPASS
 

I've seen lots of valve springs break, both intake and exhaust. I've never heard anyone attribute it to the wrong prop size before; that's a new one on me. But I could rationalize it, thinking about over revving?

What prop were you running?

RE: OS 91 FS SURPASS
 

Thanks Mister Biplane that worked Now to find a set of springs, Tower no longer lists engine on their parts list. Cowboy the prop is a Graupner 13.5X8 wide blade 15% nitro running at 9000 rpm. If thats too small or overrevving its time to go back to 2 strokes.
Thanks for the help guys,btw the spring was broken in three pieces. Jim

RE: OS 91 FS SURPASS
 

bipeflr,

Go here: [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCW93&P=Z]Valve Springs[/link]


Tom

RE: OS 91 FS SURPASS
 

Nope, that's not under propping / over revving.

I've seen the spring broken in multiple pieces too. Not uncommon in my experience with these engines, they just break for some reason.

RE: OS 91 FS SURPASS
 

Thanks for the link Tom with your help I will have it running soon. Jim

RE: OS 91 FS SURPASS
 

If you are planning to remove the valve springs and keepers, do it inside a large size zip-loc bag, so when the parts go "flyin", you can find them.

RE: OS 91 FS SURPASS
 

Thought I'd mention that because my 120 sucked a valve because the prop was too small...was running a 14X7 instead of a 15X7 both 3-blade.