bacon104

So this OS 120 III surpass w/pump is the first four stroke Ive run and a have a question. Ive installed a Master Airscrew K-Series 16X6 prop, and when I install the flat washer in front of the prop, then the first nut, the hub on this nut that goes through the washer to center the washer, hits the front of the prop. This makes the prop washer stay loose when you tighten the prop nut. The nuts and washer came as a pacaged kit in the TF P-40. I have reamed the prop to 8mm for the OS 120, but do I need to ream more out of the front of the prop to allow this part of the nut to go inside the prop? Does not seem correct so I have not done it.

Gray Beard

My Feedback: (-1)

I have one of the OS IIIs and at one point a long long time ago I used a big MAS prop on it. I just went out and looked but couldn't find the prop but the nut on mine doesn't go all the way past the washer. So, either I ground the nut down a bit or I reamed the prop hole a bit?? I switched over to APC props and they already have the prop hole reamed for the longr nuts. If you go into the glow engine forum and go into the OS support you can ask Bill Baxter what he does about it. If you bought the engine used the washer may have been replaced?? The ones I have for mine are really thick and tapered so I may just have the correct washer?

David Bathe

If you've reamed out the prop, you'll very possibly have a flush 90deg edge between the prop hub face and the hole. You'll need to bevel that edge some.Difficult to explain but I'm sure you understand.

Gray Beard

My Feedback: (-1)

David, I have two of these engines and last night I was able to find them both. They both have very thick washers with a bevel and the nut doesn't go through to hit the prop. If i put the nut in any of my flat washers then it protrudes. That's why I wonder if there isn't an after market washer on the IOPs engine??

bacon104

That is it. The washer is the flat washer that came with the plane. I cannot find a beveled washer that came with the engine. I will find one, thank you all!

David Bathe

I agree, the washer on my old Surpass II isn't flat, definately bevelled. Wouldn't us something else.

airbusdrvr

I have a couple of OS FT-160s and FT-120 twin-cylinder motors. They had the same issue you describe with some props with thinner hubs. I had several washers of different thicknesses machined to compensate for this problem when using thinner hub props.

David Bathe

Here's a pic of a pattern 16x10 from my YS 1.40.
You'll notice the slight recessed front of hub hole (stock, not by me) and then the actual hole for the crank.
Hope this helps.
As stated, my old S'II has a beveled washer and the prop nut doesn't protrude.
Having said that, I've seen some that do slightly. On a prop such as the one pictured, this doesn't present a problem.