Cox .049 Thermal Hopper - a never ending story

pman1111 wrote:The only alternative I see to trimming the screws would be to drill holes in the birdcage to accommodate the screws.

rdw777 wrote:Good luck on the mount George, Rootin for you on that one to compliment you fine engine….. Have you tried the head yet?…. With the general good shape of the engine it may have even never been used…. I’m sure you’ve had the same thought I’ve had on these that are of interest, I’m sure a few Thermal Hoppers powered some early single channel RC types….

I did a little investigating and got some interesting feed back on thin wall cylinders… May be of interest….

https://www.coxengineforum.com/t16250-thin-wall-cylinders?highlight=Thin+Wall

GallopingGhostler wrote:

sosam117 wrote:I hope you get it. It would be a fine addition to your Thermal Hopper!

Thanks, sosam117. Regarding a prop nut source, also thanks. I'm going to wait a little, until I can identify parts for other engines, to offset shipping. Quick question, my 4 crankcase/back screws are longer by 1/16 to 3/32 of an inch. Did your screws require trimming to fit the mount cage?

András, peering into the combustion chamber with piston at bottom, it has two of the largest bypass ports I have ever seen. Now I can understand why even the slightest mishandling of the cylinder can result in its ruin. The boost port machining is immaculate! The top has very nice, smooth, elliptical radiused edges even to its depth, a work of art. Now I can understand why it was considered one of the most powerful .049 engines of its time.

GallopingGhostler wrote:sosam117, I think I have found the answer. The screws installed apparently aren't the original ones it came with. Per photo by H.R. Warring in Feb. 1954 Aeromodeller:



The screws are neatly flush or slightly recessed in the aluminum backplate. This is also verified in Adrian's website,

https://www.mh-aerotools.de/airfoils/cox_earlyengines.htm

According to Adrian, it sold for $6.96 in 1953, which now would be $78.42, about what we'd pay for a performance Cox reed valve engine today.

sosam117 wrote:The screws I got from Burnie (Cox International); they stuck out as far as the ones that were on the engine already. The original screw heads were buggered up, so I replaced them with the one from Cox Int.

I think the originals that was flush with the backplate were done special to "clean" up the look of the engine?
If they are flush with the backplate then the bottom screws will be no longer than abut 1/8" long?

On another Thermal Hopper I received, both of the bottom screws were missing.
Probably vibrated out because of them being so short and the other top screws are almost flush with the backplate.

GallopingGhostler wrote:

sosam117 wrote:The screws I got from Burnie (Cox International); they stuck out as far as the ones that were on the engine already. The original screw heads were buggered up, so I replaced them with the one from Cox Int.

I think the originals that was flush with the backplate were done special to "clean" up the look of the engine?
If they are flush with the backplate then the bottom screws will be no longer than abut 1/8" long?

On another Thermal Hopper I received, both of the bottom screws were missing.
Probably vibrated out because of them being so short and the other top screws are almost flush with the backplate.

That is interesting, sosam117, so having some excess length is helpful.

I think on the cage, when it comes in, I'll carefully mark, drill, and tap with cage bolted to backplate continue thread from the crankcase. Then, the screws will have more "meat" to bite into, so they don't back out so easily. The very think backplate doesn't give much thread for the screws to grasp. Also, I'm wondering if a little thread lock like Locktite might be useful for the engine back screws.

pman1111 wrote:Looks like you're the proud owner of a new birdcage mount! Now if the shipping gods are on your side......

GallopingGhostler wrote:

pman1111 wrote:Looks like you're the proud owner of a new birdcage mount! Now if the shipping gods are on your side......

Interesting, I was the only bidder, but then have found the best time to buy stuff is during major holidays. This is not considered holiday by some employers, but still a lot of people visit family and travel away.

Thanks @pman1111 for pointing this listing out. It does appear to be a quality reproduction. Now, just waiting for it to ship. So far, have had success from that direction in NorCal. If ships right away, should take about a week.

sosam117 wrote:Sometimes that blind squirrel, he finds that nut!

sosam117 wrote:

GallopingGhostler wrote:

pman1111 wrote:Looks like you're the proud owner of a new birdcage mount! Now if the shipping gods are on your side......

Interesting, I was the only bidder, but then have found the best time to buy stuff is during major holidays. This is not considered holiday by some employers, but still a lot of people visit family and travel away.

Thanks @pman1111 for pointing this listing out. It does appear to be a quality reproduction. Now, just waiting for it to ship. So far, have had success from that direction in NorCal. If ships right away, should take about a week.

Sometimes that blind squirrel, he finds that nut!

rsv1cox wrote:

sosam117 wrote:Sometimes that blind squirrel, he finds that nut!

From - The legend of Bagger Vance.  Perhaps the best golfer movie ever.

GallopingGhostler wrote:I think I have my answer on length of screws. Apparently on some, screws were trimmed by factory, for example this pre-1956 version, which is the same that I have:


Cropped Cox International CA photo from
https://coxengines.ca/oem-cox-boxed-engines/-21-cox-049-thermal-hopper.html

Rather than installing longer screws, I think I am better off not modifying the excellently crafted, machined aluminum engine mount and simply trimming mine, use a little Locktite on the threads so they don't vibrate loose.

When I received the Thermal Hopper from Allan Laycock, the engine was missing one screw (2-56") on the bottom of the engine and that "little" screw holds the backplate on.
All the other screws were there. The two long 2-56 screws on the upper hole in the crankcase and the only other "little" screw that was still there on the bottom of the crankcase (though it was loose and probably would have been lost with a few more runs?)



Now for the cage screws.
All three were there but it seems they looked slightly bigger?
The engine's 2-56" screws really didn't screw into those holes very well?
I measured them and they were 3-56" screws?
I don't know if the holes were originally 2-56" or not, and they got stripped out and Allan just tapped them bigger and drilled and tapped the holes to fit the 3-56' screws?

Anyway, they were almost flush mounted and were there, so I decided to use them as there was no problems.
As for the engine screws, I purchased them from McMaster-Carr some 2-56" Filister (cheese head) screws that were 3/4" long.
Their warehouse is only 20 minute drive from my home and I can look over and select the correct screws.
I did trim them down to where all four stick out 1/16" from the cage mount.






Now for the last part:
I screwed the backplate with the 3-56" screws to the cage mount so now both were together.
From there, I drilled (carefully) the four holes where the engine's 2-56" screws are at on the backplate through the cage mount.
Then while the backplate and cage mount were still together, I tapped the freshly drilled holes in the cage mount, starting from the backplate side so that the treads continue from the backplate through to the cage mount.
So, when I screwed the crankcase to the backplate, I have enough threads to really keep the engine together.




And that is how my cage mount is screwed to the Thermal Hopper.
Thank you for reading.

sosam117 wrote:Now for the last part: I screwed the backplate with the 3-56" screws to the cage mount so now both were together. From there, I drilled (carefully) the four holes where the engine's 2-56" screws are at on the backplate through the cage mount.

Then while the backplate and cage mount were still together, I tapped the freshly drilled holes in the cage mount, starting from the backplate side so that the treads continue from the backplate through to the cage mount. So, when I screwed the crankcase to the backplate, I have enough threads to really keep the engine together.

GallopingGhostler wrote:

sosam117 wrote:Now for the last part: I screwed the backplate with the 3-56" screws to the cage mount so now both were together. From there, I drilled (carefully) the four holes where the engine's 2-56" screws are at on the backplate through the cage mount.

Then while the backplate and cage mount were still together, I tapped the freshly drilled holes in the cage mount, starting from the backplate side so that the treads continue from the backplate through to the cage mount. So, when I screwed the crankcase to the backplate, I have enough threads to really keep the engine together.

Thanks, sosam117 on the details for your particular TH mount setup. The mount is such a fine piece of work, and as such, since this is also a collector engine albeit a runner as well, I've decided to take a path that is a little less invasive for now.
(I've had my share of hole drilling screw ups        )

It is fairly easy to trim the screws, and thanks for the Locktite Blue advice, makes sense for screws that will be later removed for servicing, but provide additional leverage to prevent them from backing out during run time.

If the mount plus engine had a certain amount of scarring, I would not be afraid to drill the additional holes. But, I don't have a drill press, just scribes and hand tools. Most of my repairs have been rudimentary.

You see, I can successfully run the engine just by carefully trimming and Locktiting the screws. If I notice during runs, tendency for screws to loosen, then I can go an extra mile. For other more common engines, they can be run until the cylinders, crankcases, etc. need replacement. Parts are still available. With reasonable care, even those last a while (unless I fly on paved circles).

So, there is a little madness in my reasoning.