jmcowart

Selection and fitting of propeller for the O.S. 61 I am installing in a Tower Trainer .60 is causing me grief and frustration.

No doubt the great part of this comes from my ignorance and inexperience, but it is none-the-less real from my perspective.

I started out to use an O.S. FS-.95V on the trainer. Ihad one available, and I like the way they sound.Itwould not fit due only to the fact the the left-side rear mounting screw on the provided generic engine mount is in the same place as the needle valve and it can't be reached. The engine just fit in the provided engine mount and everything was lining up real well - it flat won't work, or at least it is beyond my limited capability to make it work. Perhaps I was just too lazy to change engine mounts and rework the firewall at this stage. I also didn't want to shange carburator around since Ihad just solved the four stroke throttle linkage jigsaw.

Of course then it was necessary to makea trip to the LHS. Purchased one of the engines listed in the instruction book: O.S. .61FX. Selected prop from the middle of the recommended list: 12X 6. They had APC electric, wood and Windsor Master Airscrew K Propeller glass filled nylon. Best for 4-stroke, but good for 2-stroke also. Bought the K Prop 12 X 6.

Got them back - way back - to shop.

Engine crankshaft is 5/16" 24. Propeller hole is 1/4" front and 5/16" back. Had to ream it to fit onto the threaded portion of the crankshaft. That is now a 5/16" hole all the way through. And of course it will not go onto the unthreaded portion of the engine crankshaft because it is slightly too small.

I sat there in a silent turmoil of frustration about why can't there be standardization and common usages and measurements across the board. Just for a while though.

Now Iask for any advice or explanation as to what Ishould do next. Idon't have a drill press or a machine shop. I would be faced with similiar problem with wooden prop, as they have 1/4" hole all the way through.

What am Idoing wrong? What am Imissing? What don't I understand? What other brand prop should Iget? Obviously this problems is not a problem to others, and it has doubtless been solved countless times in the past. Ijust am fuzzed up with the thing right now. Can anyone offer me some simple suggestions or advice to get me back on track?

Thank you the chance to vent if nothing else. Happy Halloween. Mike.

As my always helpful wife suggested, perhaps I should go out in the front yard and eat worms.

delman

To mount the four stroke you can put the mount bolt in from the bottom and put a lock nut on it under the needle valve. On the prop, just ream out the back a little with your next step of the prop reamer - keep the front half diameter at 5/16.

airtime82

My Feedback: (3)

i used a metric reamer to get the prop onto the unthreaded portion of the .61fx shaft.
its weird but it is metric. I wanna say it was 8mm but dont take my word for it because I dont have that reamer here right now.

downunder

I don't have that engine but it sounds like the machined area of the crankshaft is 8mm which is .0025" larger than 5/16". Not much difference but enough to stop the prop fitting over it. With so little needing to be bored out of the prop there's no problem with using an 8mm drill but a reamer would be better because you'll need it for the next prop you get. Ream (or drill) the prop all the way through because the important part is where it fits on the machined area, that's what keeps the prop aligned not the threaded area. And there's nothing weird about it being 8mm either because OS is made in Japan which, like the rest of the world outside America, uses metric measurements.

JohnBuckner

My Feedback: (1)

A basic tool that needs to be included in every modelers Kit is a simple step reamer and I keep both the SAE as well as the metric versions.

http://www3.towerhobbies.com/cgi-bin...?&I=LXEGH7&P=7

It is not practical to manufacture every prop size in multiple cranshaft sizes. With many basic prop sizes there can be several different shaft hole sizes with various engines. So props tend to be supplied with the smaller shaft hole size likely for that particular prop and the end user may find step reaming is often neccesary.

John

cutaway

Irwin makes a metric 4mm-12mm Unibit.

Your OS isn't the only engine afflicted with this feature. Its very common on ST's.

tacx

My Feedback: (1)

Get a tapered reamer. It's metric, SAE, and everything inbetween.

jmcowart

Thanks much for putting me on the right path. I have both the SAE and metric reamers, so I just did the 8 mm ream from the rear side of the hub and the prop went on like a dream. Thanks again. The info that the unthreaded portion of the crankshaft is 8 mm was news to me and I'm very happy to learn that. It is, as you say, logical that it is metric, I just didn't think of that as they only describe the crankshaft as "5/16" X 24."

On the attempted installation of an O.S. FS-.95V, I tried using lock nut on top,but I just could not fit the nut in and hold it in place. I have used lock nuts on all four retaining bolts with the .61 engine. The original instruction just listed plain No. 4 nuts...

I have the throttle linkage completed, gas lines and filters in place and the gas tank siliconed in place. That's right. Silicon out of a squeeze tube, as directed, described, and pictured in the assembly manual. I used no foam padding. Apparently the design counts on the anti-foaming formula of the glow fuel. Ihave read that the foam is limited to a thin layer next to the tank walls only. I guess I will see. An interesting experiment. But that's what the book says.

There is no effective book with the Senior Telemaster Iam also working on, and I put about twenty pounds of foam padding all around that tank. Man, I'm just doing the best Ican.
Next step is to start install of the servos and pushrods, control horns, etc. The instruction manual for the Tower Trainer is excellent and is truly helpful for a novice. I wish the Senior Telemaster had such a great instruction book for the "ARF" assembly.

Thanks again to everyone for the instructive and very useful information. Mike.