Tired OS FS-90
 

Hello all,

Checking out a box of goodies I bought from a long time flyer who got out of the hobby and have an OS FS-90 and 70. Easily 15 years old, probably closer to twenty by the dates in the original boxes he kept. Anyway, when I checked out the 90 it seems to turn very freely with little hint of compression. Not sure if it is poorly seating valves or ring (engine guru I am not). Never dabbled with four strokes so am wondering if anyone has advice as to where to start deciding if it is salvagable and the cost benefit of such an endeavor.

Never crashed. Clean and little residue build up. He seems to have taken very good care of his equipment.

Ran a search and was most happy to find several posts from the PIPE, Bill Baxter and others discussing these older power plants. Just looking for how to evaluate and my next possible steps.

Thanks to all.

RE: Tired OS FS-90
 

Squirt some oil into the cylinder through the glow plug hole. Get
it on top of the piston, and onto the ring....try not to get oil on the
valves. Put the plug back in, and turn it over by hand. If the compression
makes a dramatic return, it needs rings. If it doesn't....it needs a valve job
....as the compression is leaking out the valves.

I would check the valve adjustments....oil it up real good, and run them
before I condemed them to the engine rebuilders. You said they looked
clean and well cared for....give them a chance. ;)

Dave.

RE: Tired OS FS-90
 

If this engine has been sitting around for awhile, the lifters might be stuck. My OS 240FT sat for about 2 years and the lifters were stuck on it. I oiled them with light oil, turned the engine making sure the lifters were pushed back down at the correct time and after several turns they freed up and the engine's compression returned.

George

RE: Tired OS FS-90
 

Thanks guys!

Will try these ideas. It really looks to be a fine older unit and I have the perfect home for it. Hopefullt it will just need a little TLC.

GrumpE

Is YOURS the REAR camshaft one?
 

Dear GrumpE:

The PIPE Here yet again...and I'm wondering if YOUR OS FS-90 is the REAR camshaft one...

...if it IS, I've ALSO got one of these...and if you EVER need servicing, feel free to contact:

John Sepe
Seco Enterprises
301 Sabal Ridge Circle, Ste A
Palm Beach Gardens, FL 33418
ph. (561) 625-9671
[email protected]

...as HE's the one who recently installed the new Boca Bearings-purchase set of FIVE all new ball bearings in MY OS FS-90 rear camshaft engine!

I am ITCHING to get mine RUNNING in my test stand to see how WELL it performs with the new bearings (and new VALVE SPRINGS it apparently needed as well)...the New Year's Day forecast for my club's field in Halifax, MA, looks like it'll be 41º out, and I may just head down there with the FS-90 in the test stand to "rev it up" on two 10-oz tankfuls of Red Max 10% nitro, 17% all synthetic lube four stroke fuel to check it all out...it hasn't been run in ALMOST twenty years!

John Sepe ONLY works on OS and Saito four strokers, and he's apparently also got a good enough reputation to have had Stanley Alexander, the AMA mag's RC Scale columnist, recommending him in a late-2003 issue of Model Aviation!

Hint here...if you're going to use one of the Conley/Perry P-20 "shaker" pumps on yours, the one that's "officially" called the "Micro-Oscillating" pump, start out with setting the hex fitting on the OUTLET side to ALMOST a full turn from fully CLOSED (actually about a 330º angle counterclockwise from that "fully closed" position) and you should be "good to go" should you feel you MAY need one of those pumps for more reliable fuel feed!

You can read about what it's going into at http://www.rcuniverse.com/forum/Kit_..._994013/tm.htm ...it's my winter project, and it'll be the very FIRST RC model aircraft I've ever flown TOTALLY by myself right from the MAIDEN FLIGHT ONWARD...even though I've been in the hobby from 1977 to 1986, and AGAIN starting back in RC in 2001!

Good luck with YOUR FS-90...I was just wondering if you DID have the REAR camshaft version, that's all!

Yours Sincerely,

The PIPE! ;)

RE: Is YOURS the REAR camshaft one?
 

Hello; I would oil it up and spin it over by hand enough taht you are sure it is fully oiled. And run it, on a bench mount. It will tell you if it's okay or not. I have run many old engines with no failures to date. If it is well cared for as you say, there is likely many years of fun left in it yet. I have two of those engines and like them a lot. I would try a 14x8 prop and run it a bit rich. It might smoke awhile while burning out the old oil.

RE: Is YOURS the REAR camshaft one?
 

Yes it is. Looks to be in very good shape other than the seemingly low compression. Hope toget a few hours this week to work on it.

GrumpE

RE: Tired OS FS-90
 

I agree with Flyboy,
Reset valves, oil it up and run it! Mo mystery on 4 strokes.

Compression is varible, subjective and over-rated.
Check the RPM's. Thats the objective anyway.

RE: Tired OS FS-90
 

Mighty Mouse,

Will do tomorrow. Right after our anual first flight of the year event of course.

RE: Tired OS FS-90
 

Good deal. I haven't flown all year!!!! :(