Prop nut threads

[Fredvon4]

Dan Berry's question about spinner tightening

Made me think about a question I have had a long time, but always seems to come up in a post where my question would be a shift or hi-jack

My questions are.. of the 75 engines I have from .020. up to .90, all are right hand thread prop shafts of varying diameters and thread pitch

Is there some engineering logic to right hand or clockwise tightening?
Or is it simply cost concern as CC or left hand thread is harder to cut or source?
Or is it typical availability for hardware store NUTs ...example  RHT 1/4" x 24 or 28 TPI is easier on the owner to replace?

It would seem to me that LH or Counter clockwise tightening would be the preferred design--- to prevent the propeller for loosening or at least requiring the high torque need to keep in in place... 

Of course where I use a grade 8 steel nut this is not much of an issue

But---I like shaped aluminum spinner nuts

I am fairly POed when I over torque a (pricey) one and feel the- you dummy you just stripped the threads,  give....grrr

[Tim Wescott]

I'm pretty sure that on a normal engine the action of the engine is to tighten the nut over time -- but that's the sort of thing that I often get backward.

Regardless of what's theoretically best, I'm really sure that using right-hand threads is cheaper in production, and makes your customers happier in general.

[Target]

And can you imagine many stripped nuts you'd see if they were left hand threads?!

[Brian Hampton]

Torque of the engine helps keep the nut tight with a RH thread but if you have an engine where you can turn the front end 90 degrees for reverse rotation then the torque will try to loosen the nut so a LH thread nut would be better but don't lose it!

[Tim Wescott]

But---I like shaped aluminum spinner nuts

I am fairly POed when I over torque a (pricey) one and feel the- you dummy you just stripped the threads,  give....grrr

Need a spinner nut with a Keensert.  Not that anyone makes such a thing, but we can wish.

[John Rist]

Torque of the engine helps keep the nut tight with a RH thread but if you have an engine where you can turn the front end 90 degrees for reverse rotation then the torque will try to loosen the nut so a LH thread nut would be better but don't lose it!

That's why the prop comes off when you get a backfire   

[Motorman]

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[Fredvon4]

Ah yes the RH is needed as stated above to tend to tighten (at least not loosen) from normal rotation engine / prop torque...
Sheesh and DOH!-- I knew that

Forgot that the pop/bang and loose the hardware from backfire was wrong rotation instant torque...

MM I am going to try my hand at helicoil fixing one of the two that I buggered by too much torque

Also thought trying a trick my dad did decades ago fixing a stripped hole on and aluminum car engine head. Cleaned it good, then again, then flooded with MEK, blew out and packed hole with J&B weld
full two day set then tap and drill... The bolt for the alternator only was 7/16 with 14Lbs torque call out in the Chiltons book

Of course this method for a rotating assy demands the drill and tap process needs to be dead center accurate

Any way guys thanks for the responses. They helped to snap back into the grey matter, all the things, I USED to understand fully as a mechanic

This getting old and the more and more frequent senior moments is a bit disconcerting

MotorMan thank you so much for the offer, I currently have 7 of the typical spinner nuts. I bugger more than the two I just stripped,  I will PM you for details and compensation

[Motorman]

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[Fredvon4]

Thanks MM I may do it anyway just to see... I have many expendable engines and know enough to be out of harms way bench running this lash up

but I think safest is with Keensert or (Helicoil that I have in the proper size)

Just an simple low cost easy to do experiment.... over the years I have been a bit amazed at the uses of J&B weld stuff

A friend stripped a spark plug in a well used Ford truck engine and just J&B welded the plug in....lasted until he sold it years later...NO! I don't recommend this use, but I was amazed it stayed put considering all the thermal cycles

[GallopingGhostler]

My questions are.. of the 75 engines I have from .020. up to .90, all are right hand thread prop shafts of varying diameters and thread pitch. Is there some engineering logic to right hand or clockwise tightening? Or is it simply cost concern as CC or left hand thread is harder to cut or source? Or is it typical availability for hardware store NUTs ...example RHT 1/4" x 24 or 28 TPI is easier on the owner to replace?

I imagine that except for speciality engines for competition, model engines in the past have always been very competitive items price wise. Every penny saved meant another potential sale. Hence use of readily available hardware helped keep costs down.

Two years ago I lacked a prop nut on an E-Bay buy, Enya .35-III TV. Local Fastenal store guy gave me a half dozen 7mmx1 (I think that's the size) for free, which I greatly appreciated. (Farmers and contractors come and buy them in bulk, they don't deal is small quantities.) They were off-the-shelf items, although not common hardware store items.

Where I lacked the prop washer behind the nut, I use common washers and fender washers, just pick a size with hole slightly smaller than shaft, ream out. Sometimes double up washers if too thin.

[Target]

Looking at your post made me realize that if the shaft is long enough, you could double nut the shaft, and I think that would be "backfire-proof" if done properly with two wrenches....

[Tim Wescott]

JB Weld might make a good "get me through the contest" sort of repair, but a Helicoil or an insert would be a forever fix.

The only aluminum spinner nuts I've used are the Higley ones, and I've reefed on them without a problem.  You can come over and be my breaker bar from now on.

[Fredvon4]

Tim I have a few of the Higley version but tend to prefer the better look of other real cone shaped ones. Especially the pretty anodized colored ones in Blue and Red...

of course I trust Harry used a good aluminium and full cut threads

I have nothing but anecdotal to claim the other source pretty ones are much softer aluminum or inferior thread cutting

Thes do what we all know happens... feels tight but needs (in my mind) just an 1/8th turn more... phooey... that felt too easy!!!   GRRRR

[Tim Wescott]

Thes do what we all know happens... feels tight but needs (in my mind) just an 1/8th turn more... phooey... that felt too easy!!!   GRRRR

There needs to be a word for that feeling.  Anyone's who's wrenched on anything knows it, but if you haven't, you don't.

[Motorman]

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[Will Hinton]

I'm sure we've all heard the old addage that proper torgue is to twist it off and then back it up a quarter turn!

[Steve Helmick]

One of the most basic "rules" in machining is that fine threads are NOT appropriate for use in aluminum and other soft materials. The conflicting "rule" (of engineering) is that a fine thread gives more tension per unit of torque applied to tighten said fastener. Boils down to aluminum being a bad choice for prop nuts.

Installing a Keensert would be "da bomb". Unfortunately, a real 1/4-28 Keensert might just cost as much as one of those slick looking spinner-ish nuts. The local Ace Hardware might have a self-locking thread insert that's affordable, but doesn't have the locking pins of a real Keensert. If you have to buy a drill and tap, your frugal repair just cost a bunch of dinero.    Steve

[Carl Cisneros]

If memory serves (and at my age it doesnt really LOL)
Does, any one remember the OLD Chrysler products fromI think the 40' or 50's with reverse
thread on the lug nuts on the passenger side of the cars?

My dad had a Chrysler (can't remember which one), and I can remember him cussing up a storm whenever he
removed and installed the lug nuts on teh passenger side of our car. I believe they did that
due to the reverse rotation of the passenger sides tires.

Carl

[Fredvon4]

Yes Carl, remember them well

I suspect there was a large over order of incorrect axle bolts and nuts and Chrystler was confident they could sell all of them as repair items to every service station in the south....   Gas station Bubba could twist them off easier than the skinny kid in Seattle.... grin

OK poor attempt at humor, but I have seen more than one twisted off by an un-informed guy trying desperately to change a flat tire

[Brian Hampton]

Proper British sports cars like the Triumph TR's and MGA Twin Cam and others with the centre knock off nut were left and right hand threaded, usually with an arrow showing "undo". I remember taking my Jensen Interceptor in for new tyres once and the mechanic came out and asked if all the wheel nuts were a left hand thread because of the big "L" stamped in the top of each (aluminium!) nut. Had me baffled for a moment cos I'd had the wheels off many times then the light dawned on me. It wasn't an "L" for left hand but a "J" for Jensen .

[Tim Wescott]

If memory serves (and at my age it doesnt really LOL)
Does, any one remember the OLD Chrysler products fromI think the 40' or 50's with reverse
thread on the lug nuts on the passenger side of the cars?

That extended at least up to 1968, 'cuz when I hit 14 or so it became my job to switch the cars over to snow tires in the winter, and back in the spring.  Dunno about earlier, but they had a big "L" or "R" stamped on the studs so that you at least had a clue about which way to turn the wrench.

[Steve Helmick]

Just remember, "Righty-Loosy, Lefty-Tighty".   Steve