Jett .50 Crank Stud Length ?  
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Jett .50 Crank Stud Length ? - 1/8/2003 8:19:02 AM   
JoeMamma



Posts: 165
Joined: 11/15/2002
From: Lenox Township, MI, USA
Status: offline 		Hello Bob and Dub,

Received my second Jett Sport .50 as an Xmas gift.

This second engine is going into a Lanier F-4 Phantom.

I purchased a 2.25" Great Planes polished spinner for this aircraft and planned on using an APC 10x6 prop. I used the Jett supplied .25" x 28 x 1.5" crankshaft stud, but found it a little on the short side using this spinner and spinner backplate. A Tru-Turn .25" x 28 spinner adapter is also to be used.

After a phone conversation with Dub last year on my first Jett engine, he told me this stud does not need to be tightened firmly in the crankshaft.

What is the minimum depth this stud can be loosely screwed into the crankshaft and still retain strength ?

After screwing the stud in loosely into the crankshaft to approximately .25", I still have .25" remaining to attach the Tru-Turn Adapter.

From what I (vaguely) remember from high-school shop class, a bolt or stud only needs to be installed to a depth at least equal to its diameter; anything deeper is redundant.

A .25" x 28 x 1.75" high-grade stud would be ideal using this particular spinner, but the only source I can find is a box of 50 for $41.00 ! Ouch !

Thanks Again,


_____________________________

Joe Mamma
       Post #: 1

Jett .50 Crank Stud Length ? - 1/8/2003 9:45:39 PM   
bob27s



Posts: 4833
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: online 		Hi,

Thanks for writing.......

The stud should engage the crankshaft about .25". Just as a note, the stud should never be tightened to bottom out in the crank.

With an Tru-Turn spinner nut, the 1/4" of exposed thread for the prop installation is sufficent since the bolt goes though the washer.

If you find that you need a longer stud for a particular installation, you can first try emailing Dub at [email]jett@jettengineering.com[/email] to see if he can supply one longer that the one you have now (you may already have the longest one)

Next option (which you began) is to find a commercially available replacement. There are a bunch of studs and long set screws available which will work quite well. McMaster Carr has part 91565A574 which is a 2" long full thread stud. They have similar 1/4-28 studs up to 3" long. Package of 25 is $6.21. The jump from 1.5" to 2" may be too much though for spinner installation, but for you to determine. [url]www.mcmaster.com[/url]

Next (and I have done this myself) is to try using a piece of all-thread 1/4-28 rod, cut to length. This is not the most precise or strongest stuff in the world, but it can work. Cut to length (careful not to bend it), carefully debur the ends. When you install it, make sure it engages the crank shaft no more than 2/3 of the total possible thread depth. When installed in this way, there is a very slight amount of 'wiggle' in the stud. This is important. The drivewash, collet and crank shaft align the prop.... not the prop stud... so the prop will maintain square alignment. When you tighten the prop nut, the stud will actually move a tiny bit to square up with the rest of the drive.

I hope this has been helpful!

Bob Brassell

< Message edited by bob27s -- Jan 8 2003 4:54PM >

(in reply to JoeMamma)
       Post #: 2

Jett .50 Crank Stud - 1/9/2003 6:32:04 AM   
JoeMamma



Posts: 165
Joined: 11/15/2002
From: Lenox Township, MI, USA
Status: offline 		Hello Again Bob,

Thanks for the tips on installing the crank stud.

I had some .25" x 28 threaded rod laying around, but after using my "file test" I thought the rod must have been grade 2 or less.

The McMaster-Carr grade is higher. I just ordered the 2 incher's using their on-line service.

Thanks Again,


_____________________________

Joe Mamma

(in reply to JoeMamma)
       Post #: 3

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