My Magnum XLS 46 is still on my test stand and runs, sort of. But I'm still having trouble with the prop nut loosening. Seems to me there should be a limit to how much I dare tighten it without danger of stripping threads.

Is there any reason I should not use a lock washer under the nut?

I'd probably use another nut as a jam nut before I'd start adding washers, but that's just me.

Well the first time you tighten the nut you will probably just drive in into the front of the prop hub. If it's loosening just go to your local hardware store and buy a second nut and double nut the thing. You can take the nut you have now and just have them match it.

Thanks for the advice, guys.

Have you ever had to add that second nut. I've certainly used jam nuts before but I'm totally new to model airplanes.

I wouldn't worry about stripping the threads, unless you get the nut started crooked, IE cross threaded. I use a 6" cressent wrench and after getting the nut snugged down, I position the wrench so that when I squeze the wrench and prop, it tightens up the nut. Flip the wrench for another 1/2 flat bite and do it again. When it becomes dificult to gain a little more tightness, you are good to go.

Don't use a lock washer, espically a split washer as it will provide a lopsided tention on the prop. The Jam Nut method is best, and again tighten the jam nut on the same as above after tightening the first nut.

Don

You shouldn't need a jam nut. It sounds to me that the engine is kicking back when you put the starter to it due to being overprimed. You should never fuel a tank, hook up the glow plug and jam a starter into the engine as this is a good way to throw off the prop.

What you should do after you are set up ready to start the engine is to hookup the glow plug, and pull the engine through compression by hand through several turns. If you feel a strong bump doing this, you are flooded. When the bump happens every other turn, the mixture of fuel in the cylinder is almost right (perfect if starting by hand, err, chicken stick). If two turns, and no strong bump, then you are ready for an electric starter.

Also, the above is for two stroke only.

You could also use a nylon lock nut.

Lockwashers and nylon locknuts aren't even allowed to be re-used in some full-scale applications. Every time installed/removed they lose a bit of holding power. On a 2 stroke simply get the nut VERY tight as it is EXTREMELY difficult to damage the hardened steel treads of either the not or crankshaft. Many 4 strokes do use a jam nut system of some sort.

Thanks again, All

Guess I'll try Campgems method of tightening, then the bump approach of High Plains. I've read about that method but this engine doesn't seem to fire without priming it first, even with the electric starter. But I'll try it and see if I can learn something.

I still don't know if anyone ever uses a jam nut, or a nylon lock nut as suggested by broke_n_bummin.

Frank

Don't be afraid to put some serious torque on it. If the nut is coming loose, it is either not getting tightened enough or the engine is backfiring and loosening it up. Both the nut and crankshaft threads should be hardened. Unless you put a 3 foot cheater bar on a 1/2" drive ratchet to tighten it, it won't strip.

Most smaller 2-strokes don't need jam nuts.

Umm you may want to pull it through a few times with the glow *NOT* connected becease if it does fire.......

(yes i know techniclly our engines can start without an ignighter on the plug but its a lot less likely )

Thanks, Bruce

I'll go with that. It's just that I have stripped so many threads in my lifetime due to over-tightening, but I suppose not with the hard steel in these parts.

Hi ChuckW

No 3 ft. cheater bar here, just the 6" crescent wrench as used by Campgems. So I guess I can't hurt it, right?

Flying freak:

I've read that the force generated by a single firing in the method suggested by High Plains is easily accommodated by a firm grip on the prop. I thing the glow plug heater must be connected in order to check for the bump!

Whenever you're starting an engine (by hand or electric) the force needed is trying to loosen the prop nut. When the engine is running the torque at the crankshaft is tightening the prop nut. If the plug is glowing too hot then the engine fires too soon (kicks back) and this loosens the nut.

With everything set up correctly (plug not too hot, engine not flooded) then surprisingly little tightness is needed on the prop nut. For a normal 1/4" thread it should only be tightened to about 6-8 foot pounds. This is just a firm pressure on a proper sized spanner.

On the OP's engine though it sounds like it may be a friction problem which makes me wonder if it's got a plastic backplate spinner fitted. These are too slippery. They can be fixed by making washers out of wet/dry sanding paper to go between the backplate and the prop driver. Or get a better spinner .

The "bump" felt by holding the prop and turning it over compression is just a bump, it's not a hard bang so there's no problem doing it. This is routine for just about everyone who hand starts to check that the prime is correct for a one flick start.

Thanks, du. I'm beginning to understand lots of new things, like absent kick-back there's no mechanism for loosening the prop nut. 8 ft-lbs surely isn't a lot of torque!

I'm not sure what you meant by "OP's engine" but in my case you're right on. I bought a 2" plastic spinner from one of the usual suppliers, yellow to match my plane color. So I should re-do that with a metal spinner and back plate? I guess polished aluminum or chrome would look just as good, maybe better!!

Now if I could just figure out how to get the damned thing to idle at a reasonable speed[].

Frank

Yeah, and if you go to Cermark.com you can get them for $9.00.

http://www.cermark.net/List.php?TID=50

Instead of a crescent wrench which can slip and damage the nut go out and buy a good "combination" wrench
http://buy1.snapon.com/catalog/item....e=snapon-store of the proper size for your nut. SAE & Metric are available. Get it at your local auto parts or Sears cheaper than this though. Good leverage and NO slippage. Get a "6-point" if you can find it.

Lou55 I went to Cermark but I don't know how to read their listings. Are the details and explanations available some where? Thanks

Bruce88123 Your're right of course. I've plenty of combination wrenches left over from my old car hobby, even some 6-point items. I'll likely find the one that fits and use that in the future. Thanks

Frank

The plastic spinner back plates prevent a good seat of the prop and nut in my mind. Like you, I like the colors so I use a combo aluminum back plate with plastic nose. Great Planes makes the ones, I use. You find out right away with a four stroke that the plastic back plates will just not do. If you try to tighten it, it mashes out under the pressure needed to hold a prob on in a back fire.

Downunder is a tad off in his recomended torque. A garden varity hardware store screw of 1/4 in diameter is recomended at 9 Ft/Lbs. A grade 8 whick is closer to the screw makeup on a crake shaft is 14ft/lbs. 5/16" screws are twice that. My grig, I'm guessing is around 75 lbs or so. Figure I have an effective pull of about 4" on the 6" cressent so I'm able to pull down around 25ft lbs all out. I probably don't squeze near that hard pulling a prop nut tight, Maybe a bit to much, but I'll tell you this, I've never stripped out a nut tightening it. I've broke of a number of bolts in my time by over tightening them. This is steel on steel. Glow plugs are a different story where you have a very fine thread in cast alluminum with a steel screw.

Thread damage comes from poorly fit threads. Hardware store nuts are thread formed for the most part and 60% thread are all that is needed. A proper propeller nut is machined and has a fuller thread, as does the crank. No wiggle wobble while the thread is loose. You take a hardware store screw and nut and they rattle around some times. If you want or need a jam nut setup, get a four stroke nut set for a few bucks and rest assured that you have a good setup.

Don

I have this [link=http://www.sears.com/shc/s/p_10153_12605_00947236000P?sbf=Brand&sbv=Craftsman &filter=Wrench+Style%7CCombination%5EType+of+Wrenc h%7CWrench+sets%5EWrench+Sizing%7CStandard&vName=T ools&cName=Hand+Tools%2C+General+Purpose&sName=Wre nches]6 point wrench set[/link] and it goes small enough to take off my Needle or anything else on my Mag 46 XLS

That's a good set. Just remember to use metric wrenches when required. Proper tools make any job easier and safer.
While on the subject of tools let me bring up something that hasn't been discussed lately. Many Japanese products use screws that LOOK like Phillips but are actually JIS screws. Phillips screwdrivers don't fit properly although usually can be made to work. Servos and engines may have these screws among other parts. http://centralhobbies.com/Tools/jis.html is an example of CORRECT screwdrivers for these screws.
JIS=Japanese Industrial Standard