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tightening prop

Old 10-13-2010, 07:04 PM
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mistermnkim
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Default tightening prop

any specs in inch pounds guys are tightening props? i was mounting a new prop on my rcgf 64cc tonight and was just curious? my engine has 4 small bolts around 1/8 inch but im sure they are metric.
Old 10-13-2010, 07:14 PM
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ggraham500
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Default RE: tightening prop

Also is there a difference in torque for a 4 bolt pattern versus a single bolt pattern? Wood vs composite vs nylon vs carbon fiber?
Old 10-13-2010, 07:19 PM
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Default RE: tightening prop

If they are M4 they are 1 1/2 to 2 ft/lbs, M5 about 4 ft/lbs . You will not easily find a ft/lb torque wrench that goes that low, so you would need an in/lb torque wrench. 1 ft lb equals 12 in lb.
Old 10-13-2010, 07:45 PM
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Tired Old Man
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Default RE: tightening prop

40-45 inch pounds covers the m4 and m5 prop bolts for a wood prop. 65 inch pounds handles a carbon prop. Keep in mind that a lot of carbon props have wood cores so the folks that like to hunker down on their prop bolts are screwing up their props and risking broken prop bolts. Torque the screws in an opposition, or "X" pattern.

A good rule of thumb is that if your propeller has an indentation from the propeller hub on it's back your bolt torque is way too high. You want clamping force, not crushing force. Unequal bolt torque is also a problem because it permit the prop to "wobble" a little bit on the end of the crank. As that happens the other bolts are driven deeper into the prop, crushing the hub a little each revolution. Pretty soon the hub becomes loose around the bolts and crap happens. Crush the hub a little too much and longitudinal splits can occur the length of the blade on a wood propeller.

It's your prop, engine, and airplane. Only you can decide if a $20.00 torque wrench is worth it to you.
Old 10-13-2010, 08:15 PM
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w8ye
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Default RE: tightening prop

With wood you need to retork a few times until it settles down
Old 10-13-2010, 08:20 PM
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Default RE: tightening prop


ORIGINAL: Tired Old Man

A good rule of thumb is that if your propeller has an indentation from the propeller hub on it's back your bolt torque is way too high. You want clamping force, not crushing force. Unequal bolt torque is also a problem because it permit the prop to ''wobble'' a little bit on the end of the crank.
TOM, while I have always agreed with your torque specs for the most part there are exceptions. Denting the prop hub is simply unavoidable with some of the softer woods used in some of our more common props .... including the smaller Xoar sizes. For example, I have props that have been used on engines for years with little or no denting ... these are mostly 50 cc and larger engines and their related prop sizes. But then I have props I've been using on my DLE 30 and other smaller gassers that dent the first time I tighten them and NO, I'm not over tightening them. These smaller props have all been Xoar standard wood props. Switching to the laminated Xoar props on these smaller engines has reduced or completely eliminated the denting problem.

Frankly, any torque will cause denting of the softer props where even over tightening will not dent the harder ones. The soft props will not accept or hold torque well. Laminated and harder props seem to hold torque extremely well after a couple of tightenings. Same problems exist for single bolt of multi bolt hubs. Solution ... buy the harder solid wood props or spend a bit more for the laminated ones. You can usually pick out the harder ones just by looking at them... they're also a bit heavier.
Old 10-14-2010, 07:19 AM
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Default RE: tightening prop

The MSC hard rock maple and Xoar beech are good examples of what you're talking about. The Xoar will crush no matter what. The MSC won't crush one bit with same torque. I love MSC props. Oh and they are close enough to the same weight....22x8 VS 22x8.
Old 10-14-2010, 08:20 AM
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ec121
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Default RE: tightening prop

I have noticed the same thing. There seems to be a surface crushing with the Xoars. Then it firms up and stops. I am using 45in/lbs. I am evolving over to the laminated type as I need props.
Old 10-14-2010, 04:49 PM
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Tired Old Man
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Default RE: tightening prop

Truckracer,

I don't disagree with you at all in this regard, but the problem is not limited to smaller props.

I have seen a few Xoars in 27", 28" and 32" sizes that could not be torqued to any usable value without crushing the hub. I even had one (28") develop a longitudinal split at 40 inch pounds of torque. There's little to be done when props are made from materials incorrect for the application. That problem will not be resolved until people stop buying those products. Manufacturers have no incentive to fix their mistakes as long as they are profiting from them. Not too many products come from China that don't have a shortcut somewhere in their manufacuring or materials selection process
Old 10-15-2010, 06:26 AM
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FentonFlyer
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Default RE: tightening prop

I've often wondered if a bushing installed in the bolt holes would be beneficial in our applications. Simple lengths of steel tubing with an ID sized according to your application that are maybe a milimeter or so shy of the hub thickness. This would control the crush and allow you to achieve and maintain the proper clamping force.
Old 10-15-2010, 09:06 PM
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Tired Old Man
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Default RE: tightening prop

A metal bushing does not allow for expansion and shrinkage of a wood prop during weather extremes. The bushing would have to be marginally shorter than the thickness of the prop hub.
Old 10-15-2010, 10:55 PM
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Default RE: tightening prop


ORIGINAL: FentonFlyer

I've often wondered if a bushing installed in the bolt holes would be beneficial in our applications. Simple lengths of steel tubing with an ID sized according to your application that are maybe a milimeter or so shy of the hub thickness. This would control the crush and allow you to achieve and maintain the proper clamping force.
Fenton Flyer....I think you have a good idea there. Maybe some prop manufactures should experiment along that idea. Best Regards, Capt,n
Old 10-16-2010, 01:15 AM
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w8ye
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Default RE: tightening prop

The only advantage I can see for metal sleeves around the prop bolts would be to keep the wood from compressing against the threads of the bolts.

The disadvantage would be that the sleeve would have to be shorter than the compressed thickness of the prop hub.
Old 10-16-2010, 08:38 AM
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Default RE: tightening prop

Yep. Hard to apply a clamping force if a material is present interfering with the compression action of the screws and washer.

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