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16/8 Prop

Old 03-17-2011, 05:12 PM
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Default 16/8 Prop

Today when I went out to preform a final engine test of Saito 1.50 on my hanger 9 1/4 scale piper cub, the prop flew off at around 75% throttle. My setup then had been 2 washers and a simple nut on the shaft bolting the prop to the engine. Would adding a lock washer solve the problem? What have you guys been doing? Thanks for the help! I would rather have the prop fly off now then in the air!

(Just in case you wanted to know the Crankshaft Threads are M8X1.25mm)
Old 03-17-2011, 05:24 PM
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Default RE: 16/8 Prop

Why add a lock washer? Try using double nuts with one washer between them and the prop. Tighten the first nut against the washer and then tighten the second nut against the first one to lock it in place.
Old 03-17-2011, 05:53 PM
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Default RE: 16/8 Prop

A similar thing happened with me with my 4 stroke 2 cylinder OS Gemini. Although the nut was on very tight there was a <u>"woodruff key" </u>missing from the shaft that made the hub and shaft one, excuse my termenology. So as the throttle was also, as in your case, on practtically full throttle. When the engine picked up speedsuddenly after the second glow plug kicked in theprop took off..... lucilyno one was infront of it.

So my suggestion is to check for that key in case yours is missing also.
I also invested with a double nut arrangement. Now it works well.
Old 03-17-2011, 05:56 PM
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Default RE: 16/8 Prop

Get a set of Saito prop nuts and washer. http://www.horizonhobby.com/Products...ID=SAI170R3135

As Laird SS stated tighten it, Really tighten it. I fly a lot of four strokes and they will spit a prop when they over heat and suddenly seize or backfire. Iuse a thick piece of leather on the prop and an exact fitting open wrench on the nut Position the wrench and nut so that when you squeeze the two together, the nut tightens. When you run out of movement, flip the wrench 180 and that will give you a half flat more to work. Keep this up until you can't get any more movement. Imean any. Then tighten it another half turn. Now do the same with the lock nut.

Spitting a prop not only looses your prop and may crash your plane, but it is just plain dangerous to people around you. I saw one fly from the back of the pits to the opposite end of the flight line a couple weeks back. It was on a Saito 120. I've spun props, but never lost one with the nuts tightened like I suggest.

Don

Old 03-17-2011, 05:59 PM
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Default RE: 16/8 Prop


ORIGINAL: Laird SS

Why add a lock washer? Try using double nuts with one washer between them and the prop. Tighten the first nut against the washer and then tighten the second nut against the first one to lock it in place.
You are running a Saito 150. That engine (especially early versions that had higher compression) is known to throw props ....... IF you run it lean! Crank the needle down a bit too much and no prop nut combination known will keep the prop in place! Now run it correctly a bit on the rich side the stock double nut arrangement will work just fine. I wouldn't recommend any kind of lockwasher arrangement on a prop nut. I'm not sure why you're running (2) washers?? Do you have the correct large steel one that came with the engine? Is your prop a wood, plastic or composite one?
Old 03-17-2011, 06:28 PM
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Default RE: 16/8 Prop


ORIGINAL: rafeeki

A similar thing happened with me with my 4 stroke 2 cylinder OS Gemini. Although the nut was on very tight there was a <u>"woodruff key" </u>missing from the shaft that made the hub and shaft one, excuse my termenology. So as the throttle was also, as in your case, on practtically full throttle. When the engine picked up speedsuddenly after the second glow plug kicked in theprop took off..... lucilyno one was infront of it.

So my suggestion is to check for that key in case yours is missing also.
I also invested with a double nut arrangement. Now it works well.

The Saitos use a tapered collar to lock the drive hub to the shaft. The tighter you tighten the prop, the tighter the hub is locked to the crank shaft.

Don
Old 03-17-2011, 06:31 PM
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Default RE: 16/8 Prop

It is a plastic 16/8 prop. I bought the engine used so it did not come with the large washer manufactured with the engine. I will buy that and it should solve the problem. I meant to say 1 washer above. Thanks for the help.
Old 03-17-2011, 06:35 PM
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Default RE: 16/8 Prop

Thanks for pointing ot the difference between the OS &amp; saito.
The double nuts on the OS shaft fit as this: The second nut is on a long shaft that fits into the back of the first. When u tighten the second the shaft expands and prevents the first from loosening. So far so good but the best tip was to start the engine on low throttle, step back out of the way then throttle up. So far so good. I was using a 17"x8 prop
Old 03-17-2011, 08:27 PM
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Default RE: 16/8 Prop


ORIGINAL: pipercub4

It is a plastic 16/8 prop. I bought the engine used so it did not come with the large washer manufactured with the engine. I will buy that and it should solve the problem. I meant to say 1 washer above. Thanks for the help.

Get the set I gave the link to, not just the washer. The nuts and washer are heat treated and are way more precise that hardware store stuff. They will give you a sloppy fit and may cause problems if you try tightening the to the same torque that you can tighten the Saito set.

By the way, you have a great engine. Just keep the high end a little on the rich side as pointed out before.

Don
Old 03-17-2011, 08:32 PM
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Default RE: 16/8 Prop


ORIGINAL: rafeeki

Thanks for pointing ot the difference between the OS &amp; saito.
The double nuts on the OS shaft fit as this: The second nut is on a long shaft that fits into the back of the first. When u tighten the second the shaft expands and prevents the first from loosening. So far so good but the best tip was to start the engine on low throttle, step back out of the way then throttle up. So far so good. I was using a 17"x8 prop
Doesn't the Gemini have a thrust washer the is tapped for four screws through the prop? Ibreifly had a 300FT and it was. Ijust assumed al of the FT series were allthat way. That would stop the spitting of the prop, or at least really reduce the chance. The O.S four stroke will detonate and spit a prop same as the saito if run on the lean side.

Don
Old 03-18-2011, 06:37 AM
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Default RE: 16/8 Prop


ORIGINAL: pipercub4

It is a plastic 16/8 prop. I bought the engine used so it did not come with the large washer manufactured with the engine. I will buy that and it should solve the problem. I meant to say 1 washer above. Thanks for the help.
IIRC, ALL the engine manufacturer's recommend that you use a double nut setup as described above, on their 4 stroke glow engines 'cause the little beasties WILL backfire on occasion and that usually happens during initial setup if they're a bit lean.

Buy the geniune hardware as mentioned.... [8D]

Do not "assume" that they are tight after the first run either; mine usually require a couple of checks for them being tight after the props are removed for any reason and it's a good idea to check those periodically before you fly. Nylon/composite type props don't usually require as much attention as wood props since they don't compress like wood, but too many modelers don't check their props after the initial install.
Old 03-18-2011, 09:15 AM
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Default RE: 16/8 Prop

Yes, always use a double nut on a 4-stroke and make sure both are tight. I check before every flying session. Also, Harry Higley makes what they call a 'safety spinner nut'. Check their website. Use that safety spinner nut against the prop washer and one of their 'hubs' and the prop will NEVER come off. I've got them on 2 Saito 1.50's and one 1.80 and never lost a prop.
Old 03-20-2011, 07:31 AM
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Default RE: 16/8 Prop

The Gemini has that option to drill through and use the through bolts. However after I made sure I put back in the "key" on the shaft and had the double nuts I had no problems any more although since I crashed the cub with the Gemini in the nose I cracked up the rear of the engine. Have been taking my time in repairing it...

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