Hello, i bought a OS .90 2-stroke and the drive washer has a pin sticking out towards the prop, does this take a special prop or do i have to make a hole in it, any help would be great , flyby50...... also maybe someone could tell me if this engine is as powerful as it looks, thanks...

You have to make a hole. I don't think they came that way? Somebody probably installed the pin?

Sounds like an old timer to me. From 1978 until 1985 there was the 90FSR and the 90RSR. In 1985 they brought out the 91

Thanks for your help, yes it is the .90 fsr, do you have any idea how these run, thanks.....

The The 61 FSR has a strong following on here. The 90 is pretty old is not as common and I don't see much about them. I think the are good engines but they just weigh a little more than current 91's

The .90 and 1.08 are the same basic engine...they both run well...smooth and reliable.

My guess why you don't see/hear much about the .90 is because they are the same size, so for the weight, one might as well get the 1.08?

They are schnurle ported just like current engines

At 24 oz. they are as heavy as and heavier than some 1.20 2 stroke engines. Good runners though for sure.

Terry in LP

They were originally delivered with one roll-pin installed and one spare in the box. You can pull the pin out, it serves no practical purpose. These engines handle well and last longer than most. They don't like to be set too rich, often stopping instead of fourcycling. An idle bar plug may make them easier to tune until you get use to it.

Thanks guys for your help, its hard to find info on this engine, i'll have to wait until spring to fire her up, [&o] thanks, flyby50

I have both the 90 and 91 FSR engines and they are great engines. I especially like them in the TF Gold series warbirds where the weight of them eliminates the need for useless lead up front to balance. If you gotta carry weight up front for balance then it might as well be part of the powerplant.
I have found over the years these engines run best on 15% Omega for me anyway. Because they rev pretty high I use wood props either TF or Zinger 14x 6.
They are much quieter than Master Airscrew and the performance is better as there is less flex at the tips. APC props wont work on these engines as the crankshaft is too short to handle the fatter APC hub and then the prop nut is not fully on unless you scrap the stock OS washer and use something thinner. Even then I don't like the fact that the prop nut is not fully threaded on.
As for plugs I use the OS #8. They do a good job and last a longtime. Back in the day the old Fox idle bar plugs also did a good job but they didn't seem to last as long.
Finally you don't need the pin in the thrust washer unless you enjoy drilling holes in the back of the prop. I haven't used mine in years. If you use the wood prop with the supplied prop washer the nut will fully seat and when tightened properly there should be no problem.
Good luck with your motor - you will like it i am sure.
ByronF

my experience with "Heavy" engines is that they run good and last a long time.

In the right airframe they are the best engine to have

Which is precisely why Rossi engines always weigh more, or used to, than the competition.


Ed Cregger