When I put my 18x8 prop on my moki 1.8 the prop covers the area where the prop is suposed to be and extends about a 1/4 inch out from the smooth surface where the prop lays. Is this supposed to happen?

Can you please reword your question? How does the prop over hang the area where the prop should be? What extends a 1/4" from the smooth surface where the prop should be?

John

Yes this is normal.
I'm running a Moki 2.10 and see the same thing.
I use a Tru-Turn nut that actually inserts some of it's length into the inside of the prop. The prop is bored to 12mm and the nut I think is 10mm.
Perry

who's on first?

No kidding. I still want to know how the prop covers the area where the prop is supposed to be and overhangs by 1/4" past the smooth part.

John

The Moki 180 and I assume the 210 have a prop shaft that is ~12mm in diameter. The front part of the shaft is threaded with a 10mm thread -- the threading process reduced the overall diameter of the threaded portion to 10mm.

If you ream a prop to 10mm it will fit over the threaded portion of the shaft but will not fit over the rest of the 12mm shaft, which is about a 1/8-1/4" in length.

What I did with my break-in prop (I have not installed my Tru-Turn spinner yet, which would just about cover the length of the unthreaded shaft) is to ream the prop for 10mm and ream only through the back half of the prop for 12mm. This gives me a good snug fit for the prop. When I install the spinner back plate I will pay close attention to the length of the unthreaded shaft that still shows and carefully ream only the portion of the prop that will slide over it. You don't want to ream the entire prop for the unthreaded diameter because it will not fit over the front of the shaft snuggly -- potential for the prop to become highly unbalanced.

BTW, this is the only engine for which I have seen this problem -- usually the shaft is threaded from its original diameter which would make the threaded portion of the shaft the same diameter as the unthreaded portion.

Jim, what you say makes perfect sense. Reading back over the first message and filling in the blanks, I believe you have answered the question

John

Ooops, I went to lunch and forgot to hit send. Here is what I came up with ...

I plan on getting a Moki 2.10. I get the impression that the Moki 1.8 and 2.10 have very very short crankshaft threads. Not much room for the prop nut, especially since some of the shaft is taken up by the thickness of the spinner back plate. I take it, this is what Willy RDRC is talking about. Unless the prop has a relatively thin hub, a special prop nut or spinner adapter will be required.

From doing a bit of reading I see that the Moki 2.10 has a 12mm diameter crankshaft (smooth) that is stepped down to 10mm threads. The Saito 120 is similar in that it has a 10mm shaft and 8mm threads.

In any event, the short crankshaft seems to be confirmed by jpmorgan's post since he is referring to a Tru-Turn "short shaft" spinner adapter (which is specifically designed to deal with this problem).

Attached is a pic of the Tru-Turn TT-0105-A adapter (from the Tru-Turn adapter selector). Just look at how deep the nut reaches into the prop hub. According to Tru-Turn, the nut has a 13.5mm (17/32") diameter (I called and asked).

So ... if I want to run a Tru-Turn spinner I am going to need to ream the prop to 12mm and form a 13.5mm (17/32”) counterbore to clear the Tru-Turn adapter. In order to do this, the proper tool is one of those Bennet prop drills. See this page:

http://www.bennettbuilt.com/page9.htm

It would probably make sense to order a 17/32” drill with a 12mm tip so you can ream and form the counterbore in one operation. Are we having fun yet ?

Well, here is some more. The Tru-Turn web site also mentions a special back plate. This no doubt provides a 12mm hole in the spinner backplate. Darn, the bigger you go, the more complicated things get.

So in order to run a Tru-Turn spinner (and I do love Tru-Turn spinners) I have to order a special spinner direct from Tru-Turn as well as ream and counterbore each and every single prop.

I wonder if I can use one of those cone shaped spinner nuts. The problem here is that 10mm is big, I don’t think Du-Bro makes one. I called PSP manufacturing since they sell these “Billet Spinners” (Prop Nuts) in various sizes (not 10mm thread though). See:

http://www.pspmfg.com/

The lady said they would make one in 10mm thread for like $9.00 (would take about a week). Perhaps this is the way to go.

Moses

Moses,
You're making it way too complicated. There is plenty of thread for your prop, spinner backplate, and adapter nut w/washer. My adapter nut is 1/2" wide, so I drill my props to 1/2" and install. It's that easy. I took a pic on my digital camera but the battery just died and I wasn't able to post the pic here.

Ryan, making things complicated is apprently what I do best ... you left out overthinking things as well .

So you just reamed the prop to 1/2" and used the spinner nut to located or center the prop. Some folks don't like to do this, but I have no big issue with it. What did you do with the spinner back plate? - drilled it out to 12mm - yes.

Also, if there is plenty of thread left for the spinner nut then I can use the TT-0100-A adapter (pic below). This will eliminate the need for the counterbore. Then it's just a matter of reaming the prop to 10mm.

Moses

Actually, its not that its too complicated. The prop shaft on the Moki is too short and because of that you have to have a special adapter to mount any kind of spinner. Right now I have a Tru-Turn backplate mounted on my engine, a Zinger 18x10 wood prop, the prop washer that came with the engine, and the prop nut that came with the engine (BTW the prop nut recesses into the prop washer) and I have ZERO more threads on my shaft, i.e., the front of the prop nut is flush with the front of the shaft. The only way I'm going to be able to attach the spinner is with a special adapter that replaces the prop nut. Like the original prop nut it will have to recess into the prop washer to get enough threads to tighten. Moses' picture shows an adapter that goes one step further by recessing all the way through the prop. That gives me more of a warm fuzzy the prop won't fly off the 1st time my engine starts backwards. And, it does happen -- I discontinued my break in sessions until I get my Tru Turn adapter because I've already thrown the prop with my setup. Lucky for me I did not loose the prop washer and prop nut. You should have heard that engine scream with no prop load at full throttle -- luckilly it was running max rich.

Moses, that nut adapter would work well. I have the opposite problem in that the bottom of the nut adapter extends well past the washer, so I don't have a problem using it to center my prop. In fact, I will actually use all the threads on the nut when trying to tighten the prop down, so I got another washer to ensure that the prop gets tightened all the way. Either way, there is plenty of thread for the nut to tighten down on, and the prop is perfectly centered when installed. The spinner backplate was drilled to perfectly fit the crank.

Hilleja, I have not had a problem with the engine throwing the prop unless it is flooded and kicks hard when trying to start it. Then again, I don't try to start it at full throttle. If it starts backwards then I apply a little pressure to the spinner and the engine usually starts turning the correct direction.

When its 30 degree F outside and its only the 3rd time the engine has ever been started you won't get a start unless you have a lot of fuel going to a very hot glow plug. Even a normal single-cell glow starter is/was not enough -- had to connect my power panel and run it up to maximum green to get the plug hot enough. But, one of the problems with that setup was the prop nut is only on the very end of the shaft and no spinner is available to "apply a little pressure". The engine started hard backward and when that happened I purposely moved away from the prop. I circled wide around the test stand and by the time I came up behind the engine to decrease the throttle she threw the prop. She did start backward the 1st time I lit her but quit and then started in the correct direction. I'm waiting on 1) warmer weather, and 2) the Tru-Turn adapter, before I continue my break in. I almost positive the cold weather is preventing me from getting a good start and with the minimal prop nut position I am very much afraid of this engine -- probably rightly so.

One thing I did notice when I ran it the 1st couple of times was that it has no sensitivity to further richening the needle. I'm lead to believe this is due to the Cline Regulator. I went so far as turning out the needle 3 or more turns out more and no effect -- I could have totally removed the needle and she would have continued that way. When I adjusted it the other direction she started to lean out when I had closed it down to about 3 1/2 turns out.

Wish I could comment on the Cline, but I am running a Perry pump and with medium tubing it leans out around 1 1/4 turn, and I am flying it at 1 1/2 turn. I am sure I could get it too rich to run but I haven't tried it yet. If you get a longer adapter than the one shown in post #10 then you will probably feel much more comfortable running it.

Oh, and it doesn't matter how many times it has started or what temp it is outside, the only way I have been able to start mine is making sure the carb is sloppy wet and that I am using a hot plug.

Yep, most of my engines have backfired and loosened up the prop at least once. Usually during run-in and initial set-up. For my two strokes I have been very lucky that the prop did not fly off. For my four strokes I use Tru-Turn set-ups - they really can’t fly off since they use a lock nut.

I appreciate the information guys. It looks like I really need to get the engine and prop in my hands so I can see where I am at.

I actually would rather run a lock nut on the Moki. So I called Tru-Turn and asked. Unfortunately, the tech guy confirmed that they do not have an adapter with a lock nut for this application. They just don't make a double jam nut in 10 x 1mm thread.

They tech guy also said he prefers the "0105" adapter. He says this is a big monster adapter with a big monster 3/4" nut - appropriately sized for the big Moki. The "0100" adapter is sized for the 1.80 engine and he says they are not as strong - Darn it. He even mentioned that the "0100" adapter is less than half the weight of the "0105" adapter ... which weighs a whopping 2.2oz all by itself. This is going to be a heavy set-up.

So I'll order up the engine and see what it looks like.

So far I'm looking at the big "0105" adapter ($16) plus a 3.5" menz cut spinner - with the special back plate (~$80). A bit more than I had intended to spend.

If anybody has a way to get this done safely ... I'm open to suggestions. A 20" prop flying off your Moki 2.10 could ruin an otherwise perfect day of flying.

Moses

I think he just wanted to know if it is normal for the prop hub to be overhanging the drive washer on the engine.

The hubs on big props are quite a bit bigger than the drive washer on the Moki's. It is perfectly normal.

quote from Mendes:
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I think he just wanted to know if it is normal for the prop hub to be overhanging the drive washer on the engine.
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Oh .... that is a different question than what we answered :stupid: .

In any event, I still need to find a good way to get a spinner or spinner nut on a Moki 2.10. I would prefer to forego a counterbore. I would also prefer a lock nut. Any suggestions would be appreciated.

Moses