Short threads on Brodak .40 crankshaft

[Dennis Heckel]

Hi all,

I put a plastic spinner (Dubro) and prop (wood Master Airscrew) on my Brodak .40 so I could set the engine in the Twister I'm building to see how far back I need to cut out the fuselage and get the spinner as close to the front of the plane as possible.

The problem I have is that with the spinner and prop on the engine the nut only has about half of the threads on the crankshaft. How are you guys fixing that problem or is it something I shouldn't be concerned about. I am a mechanic and things like this drive me nuts, if all the threads were covered and the nut was even with the shaft I wouldn't worry at all about it. I put an APC 10 X 6 prop on it and it seemed to be even worse. I plan on using an APC 10.5 X 4.5 prop.

I was thinking of removing the nut and washer and using a prop spinner nut under the plastic spinner if it will fit. Do you think that would be a good idea or will I just be causing myself more grief?

Thanks,
Dennis

[tom hampshire]

Hi Dennis - You have one of the first production B40's.  The problem was fixed after the first 100 engines.  You can either run an oversize diameter nut with no washer or a shaft extension nut which extends down over the crankshaft and has an OD of 5/16 (.312)  The latter requires reaming props to fit.  Both work fine.  Tom H.

[Alan Hahn]

This is what I have used on my B40. The extension (other side on the nut) extends just inside the washer, giving you that many more threads to grab onto. There are other versions, but this one worked for me.

Here is a link
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXB938&P=0

[Dennis Heckel]

Thanks for the quick reply, it helped a lot.

Dennis Heckel

[Steve Helmick]

You'll like the Thunder Tiger "Cyclone" 11 x 4.5 prop better than that APC (which is a good one!). Be sure you have enough LG to clear the 11" dia.    Steve

PS: Plastic spinners aren't all bad...but the (much too thick) plastic backplates ARE ALL BAD! Look at the Great Planes spinners. They make one with an aluminum backplate for about $6.95. MANY stunters are using these now, because they're lighter than any aluminum spinner you can buy. Theoretically, they're only available in 2-blader configuration, but Mike Haverly adapted a (DuBro?) 3 blade cone to a modified GP aluminum backplate. The spinner works ok, but neither Mike or I have had any real luck with 3 blade props.

[Rod Claus]

Dennis,
My early B-40 had shorter threads.I gave a call to John Brodak about this.My later B-40 has longer threads.The Thunder Tiger cyclone 11X4.5 really works well on this engine.The RSM 11x6 propeller works well also if you like wood propellers.We launch at 9800 rpm using 10-11/11 fuel and a .290 venturi.Jim Lee can male you a venturi very quickly.
Also,we get a du-bro mufler pressure outlet and drill a #30 hole about 1/2" in front of the split in the muffler.The fitting will "self-tap" its way into the thin muffler housing and then you put the nut on the inside and tighten it with a small wrench.We are getting a very stable engine run by using pressure.
The spinner that my buddy Steve suggested is what a lot of us are using here in the rainy northwest.
Have fun.....

[Bob Reeves]

Another opinion on the Great Planes spinners.. Personally I hate the darn things. It's very difficult to get the prop lined up and then it may move as you tighten it. Once you get the prop where you think it needs to be and tight then you find you can't get the two little machine screws started because the prop isn't really in the right place.

Trying to move the prop in relation to the back plate you cut your fingers on the sharp edge they machined at the outside rear of the back plate. After some use you find the little sandpaper disks need replacing so you either have to cut new ones or order replacements. Changing or even tightening a prop in the field is a crap shoot and heaven forbid you drop one of the screws.

Be forewarned I personally think the Great Planes is the worst designed spinner that can be purchased, I would much rather use a Dubro or SIG.

Oh ya..... Brodak aluminum spinners only weigh 1/4 ounce more, look better, come with a recessed prop nut and you can get them in 3 blade versions.

[Paul Smith]

The Great Plains spinner can be upgraded by replacing the quiche' eating Phillips screws with real man 4/40 Allen bolts and Nylock nuts.   Despite the stated shortcomings, it accomodates the shortcoming of certain crankshafts.

[Phil Spillman]

On my short stubs I use a True Turn adapter nut assembly to hold it all together! Works on early Brodak Engines as well as Fox's older short stubby shafts. Phil Spillman

[Wayne J. Buran]

Brodak spinner has my vote, light, runs true, aluminum nut and washer and it has a nice look.
Wayne

[Bob Reeves]

The Great Plains spinner can be upgraded by replacing the quiche' eating Phillips screws with real man 4/40 Allen bolts and Nylock nuts.   Despite the stated shortcomings, it accomodates the shortcoming of certain crankshafts.

I don't think so... The aluminum back plate is taped for metric screws, might be able to re-tap it 4-40 or get the proper metric screws in a hex head.. But that still doesn't solve the prop alingment issue.. Nylon lock nuts are out of the question unless you want them sticking out the back of the back plate.. Regardless why bother as we have much better alternatives.

[Dick Fowler]

On my short stubs I use a True Turn adapter nut assembly ......

Hey Phil, What do you do when "nature calls"?

[Allan Perret]

I don't think so... The aluminum back plate is taped for metric screws, might be able to re-tap it 4-40 or get the proper metric screws in a hex head.. But that still doesn't solve the prop alingment issue.. Nylon lock nuts are out of the question unless you want them sticking out the back of the back plate.. Regardless why bother as we have much better alternatives.

I like the GP aluminum backplate spinners.  First thing I do is throw away the 2 philips head screws and replace with readily available socket head M3 x 6mm, the heads are a perfect fit in holes of the cone.  You wil need 2.5M ball driver. 
I actually use M3 x 8mm cause I have a bunch of those. They protude out of the backplate about 3/32" but are easily trimmed down flush with Dremel tool. 
Prop alignment, no sweat.  Trim openings to fit your prop if necessary,  then mount cone on backplate without prop.  Put a couple of tick marks on edge of backplate corresponding with prop openings so you have a reference when mounting / tightening the prop.  I dont use any sandpaper washers and never have any issues.  Sometimes you will get a soft wood prop that comes loose but that is going to happen no matter what spinner you are using. 

[Phil Spillman]

Hi Dick, I answer the CALL quickly if at all possible! Phil Spillman

[Wayne J. Buran]

Hey Phil, see you Sunday.
Wayne