Just got in the mail my Master Airscrew 12x6 prop to go on my Saito 56. I was under the impression the prop would just slide onto the threaded prop shaft and then you would snug it down with the plate/nut combo. However in order for me to get the prop on my Saito, I have to hold the hub with pliers and screw/thread the prop onto the shaft because apparently the hole on the prop is a tad smaller than the prop shaft. Is that normal? Do I need to drill out the prop hole so that it slides down on the prop shaft? I guess I assumed the pre-drilled prop hole would be slightly bigger than the prop shaft.

Thanks guys!

Josh

I just went through the same thing Josh with the same engine and props. Your going to need a reamer. Don't use a drill bit because they don't make round holes believe it or not. You can end up off center and out of balance. You manual should say what size you need.

http://www.horizonhobby.com/pdf/SAIT...der_Manual.pdf

Props may well have to be drilled out to fit many different engine crankshaft sizes that are out there. I either DRILL or ream whichever is easier at the time when I have the need. It is really not a difficult item. Another tip is that when one drills a tad much or one is using a prop larger than normal, there is an easy fix. The super types may groan however having doing this prop thing since the mid '40s I reserve a right to do whatever works for me at the time a need is there. That is when the prop hole is too big. I simply wrap the shaft with masking tape until a tight fit is made. I have done it many times and it works for me. Just don't do it so the tape bundles up between the prop and the thrust washer.
I find it better to drill or ream properly, however when a need is there I satisfy the need.
The model airplane supplier is not going to custom cut a prop for each size engine. If he should, one would need a LOT more money to obtain such. Believe it or not, there are things that one has to do for one's self. Try it, and I'm betting you will like it.

Here is the reamer you will need to fit props to that engine Ream it out to 8mm

Don't forget to balance the prop too !

You mean like some of us????? Sorry, I just couldn't resist!!!




[quote]ORIGINAL: GaryHarris

You can end up off center and out of balance.

I just want to add a safety note: lightly sand the trailing edge of the propeller blades. This is so you don't slice your finger when you try to flip start. Just remove the flash from the trailing edge and round over the edge. THEN balance. I can show you the scars on my finger from my little .46 prop. Happy flying.

Throw your step reamers away. A tapered reamer is much better. If you use a step reamer you may need both a SAE and a metric. You only need one tapered reamer. Also, When you sharpen a step reamer you decrease the diameter. When you sharpen a tapered reamer it doesn't matter.

Use a tapered reamer and ream from the front of your prop until the rear hole fits the shaft. The rear hole is the hole that is perfectly centered when they mold the props. APC Props recommends reaming props with a tapered reamer.

Read the section titled "Engine shaft hole alignment" in APC Props web site.

http://www.apcprop.com/v/html/tech_s...html#holealign

Prop reams come in metric and SAE, good idea to have both on hand. Ream and balance. Never ever use pliers to hold the thrust washer, they really will booger up the thrust washer. You can buy a piston stop that threads into the plug hole, I make my own, Fill the cylinder with oil and install a glow plug, there are other ways like using cord but a stop is better on a four stroke so you don't harm the valves. A lot of engines put the TDC mark on the thrust washer and a plier will remove the mark. I rebuild used four strokes and have several that the thrust washer is chewed up from people using pliers on them, then I have to use a wheel and cut in my own TDC marks. Use correct tools on an engine, there is nothing on one that calls for pliers.

You can get a tapered proper reamer here:

http://www.bphobbies.com/view.asp?id...mp;pid=V716154

or here:

http://www.rcplanebuilder.com/tools/...apered-1-8-1-2

or here:

http://www.jrhobbyhardware.com/shop/...29478def5da514


Frank

I have a hard time agreeing with using a tapered reamer. I just won't do it for safety's sake. Especially on a 4-Stroke.

And there you have jstyle regardless of the method and the tool you choose to do the job with please do go ahead and do it. Screwing the prop onto the crankshaft should be avoided at all cost such as you described and the reason may seem counter intuitive but doing so will make the chances of loosing the nut/washer/prop and prop drive bushing on the ground or even in flight much greater due to back firing or even vibration in the plane of rotation.

If a spinner is used the problem is even worse.

John

Well it sounds like an order for a reamer is upcoming. Thanks for the replies. Another question now. One of the props I messed up earlier I drilled out and put on the plane for balancing purposes only (putting everything on and in position to balance before I cover). With the tricycle config on the Kadet LT40 and the 12x6 prop I only have like 3/4"-1" of clearance from the tip of the prop to the ground. Is that cutting it close? Should I go for the 11x8 that Saito says the 56 will swing? Kinda scares me only have an inch of clearance between the prop and Terra Firma.

Thanks!

Josh

Safety?

Tell us why you have a hard time agreeing with the tapered reamer issue. Do you think APC is going to give you unsafe info in regards to mounting their props?

The slight taper that a tapered reamer cuts into the hub helps the hub to register (lay flat) against the drive washer. It is not unsafe.

I have many 4 strokes. A 220 Saito being the largest and I have always used a tapered reamer. Believe me once you try it you will always use it.

Although I do have a tapered prop reamer I use the stepped type with the straight shanks. I do not use prop adapters or savers so my props are going onto a straight machined crank shaft and have a slightly snug fit completely through the hole. That's just how I do it and the prop reamers can be found in most hobby shops or ordered through tower. I know people that have knocked out the Tee handle and chucked them up into a drill press for quicker/easier reaming. I do think the stepped reamers are a much better tool for people new in the hobby.
Ground clearance of the prop? A trainer is going to take some hard landings so I would go with the smaller prop. Some of my own planes have less then 1/2 inch clearance but I know how to land them without a prop strike but I have gotten chips taken out of a prop from hitting small rocks on take off more then once.

You could also try a 3 blade prop for a bit of ground clearance. Try an 11 x 6 ( or 8) three blade and see if that gives you more room. If you are flying off grass, you really need the room, the grass has a way of grabbing props.

A tapered bore going onto a straight shaft with 10,000 plus RPM, is something I would never do, or recommend to someone new. And sorry, I won't be always using a tapered reamer for props.

Josh, I have 1 1/2" on my LT40 build right now with a 12x6 prop. I think your cutting it a little close. Just go with bigger wheels. Maybe 3 1/2" on the main and 3" on the front.

I don't see what difference it makes how you size the prop to the shaft, the only thing your doing is centering the prop on the shaft. Once tightened against the drive hub that turkey isn't going anywhere except around and around...

Greybeard... thanks for the tape tip, I can see how that'd work just fine.

Prop installation is one of those little internet myth depositories that just refuses to die. Here are the facts:

1. The kind of hole doesn't matter. The prop is held in place by friction on the backplate or thrust washer by design. All the hole does is center the prop so that the hub will be in balance while the engine runs. You could get a prop centered properly and then Dremel out all around the engine shaft so that it doesn't touch the prop at all and, assuming the prop was balanced right, you'd never know the difference in flying.

2. You should never have to hold on to the thrust washer to tighten down a prop. If you are doing that you don't have enough backplate friction. I can put a prop nut on finger tight which the engine compression is enough to be able to tighten it down, and I can then turn the engine over with the prop. You'll notice the thrust washer has texturing in it to bite into the prop hub. When you use a plastic spinner, you need to add some kind of material to replace that friction. The best thing is a piece of open mesh plumber's sandcloth or either the drywall sandcloth that looks like window screen material. If you use a spinner with a metal backplate, it will have some texture on it that is adequate to hold your prop.

3. (not discussed yet but important) You have to use enough torque, especially with a 4 stroke. The little 4 way wrench you bought for glow plugs probably fits your prop nut. It's fine for snugging down the nut, but break out the box end wrench and really crank down on that thing if you want it to stay on. If you ever use a wood prop, retighten occasionally as the wood will compress a little. You don't need any kind of threadlocker on any engine if you tighten the nut hard enough to begin with.

4. Do not under any circumstances sand off the sharp trailing edge on your props. They are made that way for a good reason- drag reduction. Even rounding it off a little bit can make a significant difference at the 12-13k rpm you'll be running at most of the time. Many people will take off the casting line at the leading edge and maybe sand away the burr at the trailing edge, but you want the back of that prop to be razor sharp.

5. Balancing is worthwhile. I know beginners don't want to spend money on tools, but $20 for a good prop balancer will save you much more than that in repairs caused by vibration and even engine reliability issues cause by fuel foaming. You'll occasionally see someone tell you they have been flying unpteen years and don't bother balancing props on smaller planes. But once you get a few balanced right and get used to see how your plane runs with them, you'll know the difference instantly when you forget and put a new one on that isn't.

Instead of a tapered reamer, you may want to look at adjustable reamers:
http://www.use-enco.com/CGI/INSRIT?P...PMPXNO=3464890

I use them on props in the 15 to 22 inch length. I have found them to work well without the pratfalls of a drill bit.

Bob

yes the back edge can make a few rpms differance. But on a LT40 will it really be worth the cut fingers? Dull the edges, save the fingers.

I have been known to use tape on an over reamed prop when at the field but it wasn't me that said I did it. All my props that go into my flight box are balanced before they ever go into it. I do a lot of prop testing so I have a lot of different sizes of props that have been reamed for different engines. If I break a prop and want to keep flying a plane I often use tape to get it on the shaft tight but when I get home I put a correctly reamed prop on that engine. Tape works but I like things done correctly, just a me thing.
757, an improperly reamed prop will loosen up and create an imbalance. People that know how to correctly ream a prop with a tapered reamer are fine doing it but someone new to the hobby should use a stepped reamer to make sure it is done correctly.

Many Spinners come with a little plastic selection of inserts designed to slip into spinner back plates and allow for many different propshaft size diameters.

These can in some cases to serve in the exact same way for propellors.

Landing Products propellors (APC) in the case of the C-2 and the D-1 hub designs actually come with two stepped holes within the hub. The larger hole approximately half way through the hub is in fact the referance true hole for centering referance. There are machined aluminium center rings or inserts with the appropriate size crank hole that fits the larger centering hole. The small diameter portion is drilled out and the ring will now index the prop correctly to the prop shaft even if you use a toilet auger to drill

Most do not bother with this but that is what the stepped hole in your APC's is all about.

John

Jeez, it isn't some major skill set to get it right with a tapered reamer. You turn it a little and you check it. When you think you're getting close, you make smaller passes with it with less pressure until it just goes on. If you get it a thousandth or two too loose, go ahead and use it anyway. You'll still be within the margin of error that props are built with. Of all the things we do in this hobby, this is one where the learning curve simply isn't hard enough to worry about.