Saito 91 prop nut problems - RCCanada - Canada Radio Controlled Hobby Forum
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Old 07-28-2013, 09:54 PM   #1
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Saito 91 prop nut problems

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I have a Saito 91 which has a shaft length of only 3cm from front surface of the flange to tip of threads. I'm using the recommend 14x7 prop (can't remember the brand but APC and most others are approx. 2.5cm wide). I know you're not supposed to use plastic spinners, but I use one (again, don't recall the brand) which has a thin metal base plate and a plastic cone. I use this because it is just thin enough for me to get the prop on with the flat washer and nut, grabbing almost all of the threads on the nut, and I think it's a better quality than those "all plastic" ones. Even with this setup (and torquing it down very tight) I have had the nut come loose a couple of times at startup (luckily no props flying off!). I've looked at the Saito web site and know they recommend Tru Turn spinners as well as the adapter kit TT-717A or TT-718A.
Is this (Tru-Turn spinner with TT adapters) my only option?
Will TT-717A or TT-718A resolve my problem without using a Tru turn spinner?
If so does anyone know which one of these adapter kits works better?
What about just using a basic lock washer between the prop and nut?

I have lots of other Saitos but they've never given me this problem, the bigger ones have the jam nut and the smaller ones have just never given me any issues at all.
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Old 07-30-2013, 01:54 AM   #2
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Re: Saito 91 prop nut problems

Hi Andy:
I've noticed the APC props are a bit thinner (approx 1/2" or 1.3cm thick) than a Master Airscrew brand. Was your shaft possibly shortened because my Saito 91 has a length of about 3.6cm from the flange to the tip of the shaft. With an APC prop (14x6) mine is able to install with an aluminum spinner backplate (using plastic or aluminum spinner cone), factory washer, factory prop nut , and a spinner adapter nut (also functioning as a jam nut) for the nose cone. I always make sure they are very tight using regular sized hand wrenches, of which some engines are supplied with when sold new.

I've used spinner adapter nuts for Dave Brown and Tru Turn spinners. They are used in place of the factory jam nut when using a spinner so the bolt can hold the cone tight to the backplate.

The prop coming loose on start-up can be from backfiring if your fuel mixture is too rich ( I think rich???? ---- not an engine expert). For the low speed needle try a bit leaner (1/16 turn at a time) until there's not backfiring to cause the prop to come loose.

A lock washer may be an alternative, but I have never had to use one on any size engine so far. Maybe someone else can add more helpful info on this problem.
Wayne Pinke
MAAC #8730
Sun Parlor RC Flyers (Windsor, Ont)
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Old 07-30-2013, 06:04 AM   #3
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Re: Saito 91 prop nut problems

Hi Wayne, I had 2 Saito 91's at one time and the other one (which I sold) did have a longer shaft. This one I bought used so not sure what the story is on it. Your extra 0.6cm probably gives enough room for that additional nut. The spinner adapter nuts you mention look just like the adapter kits TT-717 and 718. Seems they have a long shaft that runs right through the prop hole to fasten the backplate as you said? and you are probably right that the engine had backfired when the prop came loose, however I just don't like the thought of it coming loose under any circumstances. I will definitely be tuning it up to hopefully avoid any more backfires and I'll have to buy one of these nuts and see how they work. Thanks for your advice!
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Old 08-01-2013, 06:12 PM   #4
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Re: Saito 91 prop nut problems

I converted a YS Helli engine to use a prop. Their shaft is shorter than normal. all I did was get one of those prop washers with a large hole in it so an extended portion of the prop nut goes through it. I made my nut but there are a lot of engines that already have this setup.

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Old 08-04-2013, 12:25 PM   #5
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Re: Saito 91 prop nut problems

+1 on the DB spinner nut. Used it on my .91 GK w/o issue.
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Old 08-05-2013, 07:56 PM   #6
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Re: Saito 91 prop nut problems

Ok, sounds like the Dave Brown spinner nuts are the way to go. I notice there's 4 different lengths and I guess that means I'll have to buy an aluminum spinner for it as well as that uses the bolt through the center instead of the cheaper plastic ones. I saw this from Horizon Hobby..
Thanks for your help.
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