COX 010 TeeDee prop screw

balogh Thu Jul 06, 2023 5:58 am

I am actively using at least 2 of my several COX 010 TeeDee engines in the Lil'SpeeDee as well as the Sharkface RC planes. The stock prop screw is single slotted mushroom headed, and its single slot does not hold the screwdriver tip well - especially due to the tiny dimensions.

I have found a web-based distributor in Europe (England in fact) of American screws and ordered hex head socket cap screws sized 2-56 x 5/8 (same as the stock slotted), that now will replace the stock single slot screws.

https://www.westfieldfasteners.co.uk/UNC-Bolts-Screws/Socket-Head-Cap-Allen-Screw-UNC-2-56x5-8-inch-A2-Stainless.html

These are much easier to handle and to give them the right torque when mounting the prop, without the risk of the screwdriver tip slipping out of the single slot and damaging the engine or, your finger.

I would encourage Bernie and Matt to stock these hex socket cap screws for all COX engines...especially for non-US based COX engine users, who do not have hardware stores selling US sized screws on every corner.

For the 020 size TeeDee and Pee Wee engines, one of the hex socket head engine mounting screws sold by Bernie is a good replacement, if you have a spinner hub, instead of aluminum spinner, (that aluminum spinner would need a 3/4" long screw) :https://coxengines.ca/mounting-screws/cox-049-engine-mounting-3-48-x-1-2-socket-head-screws-3-4.html

For the 049 size engines our CEF friend dckrsn already sent me some courtesy socket head screws - that I cannot thank him enough for - , but others, living outside the US, may also be interested...

For the 09 size engines Matt used to sell such socket head screws together with the aluminum spinner, but these are not in his stock anymore http://www.exmodelengines.com/product.php?productid=17816&cat=254&page=1

GallopingGhostler Thu Jul 06, 2023 10:28 am

It is good that you found an EU supplier of ANSI (American National Standards Institute) sized screws. Yes, Matt used to offer them, but I bet he discontinued because more buyers wanted the factory styled hemispherical dome head screws to maintain Cox stock appearance for historic collector reasons (and the pan head for the Pee Wee and Babe Bee). Those who fly often though will prefer the socket head screws for practical reasons.

I bought a Tee Dee .09 spinner with the socket head screw for my Medallion .09 R/C from Matt a couple years ago, because just like you, I wanted it for better prop security and historic appearance was of less importance. I've already had my share of chewed up prop screw heads from multiple prop changes on all my Bees. (You fly enough, you break enough props.)

balogh Thu Jul 06, 2023 10:40 am

Yes George, I have mixed emotions myself when seeing a COX engine made to look non-authentic with post COX era aftermarket components added, no matter how finely made these aftermarket parts are...I try to keep the authenticity of not just my shelf-queen but my work-horse engines too, as much as possible...the socket head prop screw is just a minimal compromise to authenticity, worth, however, the use vs those vulnerable stock screws.

GallopingGhostler Thu Jul 06, 2023 11:01 am

András, I am more a practicalist. Just seeing a historic Cox engine in use, even with a few non-stock accessories is satisfying.

When I worked:

rdw777 Thu Jul 06, 2023 3:35 pm

Agree with you Andras, Socket head cap screws are much easier to manage in small sizes….Better feel for torque as you mentioned as well…. When I started messing with small engines again I ordered a little pack of 2-56 hardware mainly for mounting the engines…. It had both socket head machine screws of different lengths and # 2 socket head wood screws …. You may already have the tool to drive your cap screws…. I made mine from
“L” shaped wrenches …. Epoxy’ed into a dowel….

The hardware stores here generally don’t have machine screws that fit our engines…. However there’s one hardware store in town that caters to shooting sports and has screws that are common to firearms…. The only difference is that they are fillister head instead of socket heads…. I picked up some anyway…. 3-48 for .020 and 5-40 for .049….
Socket head and fillister screws are generally much harder than the factory screws ….I think the hardened screws may help protect the crankshaft in event of a hard impact…. Particularly with the PeeWee’s…. The cranks are thin and fragile…. I know I broke one when I was a kid….

balogh Thu Jul 06, 2023 5:12 pm

Thanks George and Robert.

George, I tend to be practical in technical matters too, unless emotions play into them. I see in COX engines the object of my childhood yearning when continents separated and politics isolated me from access to these gems...now that it is only the matter of time and money to get any COX engine I want, I want to get and use the "genuine stuff" that I could not afford as a child. Hence my insistence on as many old stock parts in my engines as possible. I like the aftermarket parts invented and made after the heyday of COX, but would rather stay with the "antique" components that made thses engines "the COX"..

Robert, yes, I agree, the prop screw may add to the strength of crankshaft splined end, providing the screw is long enough to penetrate deep enough in the threaded shaft cavity, especially beyond the countersunk transition between the splined end and the journal bearing where the shaft tends to break.

Unfortunately the socket head screw I bought is only 5/8" long and it's free end, after the spinner and prop are pulled on the screw, is just enough for a solid mounting of the prop, but not long enough to penetrate beyond the splined end.

gkamysz Thu Jul 06, 2023 5:59 pm

You see many earlier PeeWee with the drive knurl broken off the crank on thEbay. Early PeeWee .020 (with the necked crankcase) have a smaller diameter knurl for the drive hub, which seated against the resulting step. Later versions (straight neck case) have a larger knurl and the drive hub seats against the end face of the crank. I don't know when the change was made, but I think the case design is definitive. I think many PeeWee were supplied with very short prop screws, which didn't help.

Early TD .020 also have a smaller knurl for the drive hub, but I think was changed to the larger size fairly early.

andrew Thu Jul 06, 2023 8:50 pm

balogh wrote:................
Unfortunately the socket head screw I bought is only 5/8" long and it's free end, after the spinner and prop are pulled on the screw, is just enough for a solid mounting of the prop, but not long enough to penetrate beyond the splined end.

gkamysz wrote:............
I don't know when the change was made, but I think the case design is definitive. I think many PeeWee were supplied with very short prop screws, which didn't help.

I only own a couple of .020's, but quite a number of .049's. Not being a collector, I always replace the slotted prop screw with an allen head machine screw. Since I usually buy screws in bulk, I will purchase the longest that I think I will need and cut to length. I try to set the prop screw length so that it will almost bottom out in the crankshaft when fully tightened -- my reasoning is that the screw will help support and stiffen the end of the crank.

GallopingGhostler Thu Jul 06, 2023 9:01 pm

For the 4-40 screws, I buy the longer length socket heads in bulk, have a bolt cutter in my electrical crimp tool to trim those easily to length. Works great on the Testor McCoy .19 & .35 and K&B .35's I have.

Don't have such yet for the 2-56 screws, if I could find a similar tool for easily cutting them, would be great besides using a cutting wheel & filing.

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