New to me Thermal Hopper

duaneh Sat Apr 06, 2024 10:14 pm

But not really new at all...

This one may set a new standard for "grubby". But aside from being dirty, I don't think there is anything mechanically wrong with it. It turns over and has compression. I think initial cleanup will only be soapy water and a toothbrush. Then see if it runs.

The cylinder must be a replacement. I thought all these had a thin wall, dual ported cylinder. This one is a stepped wall single port, and has wrench flats on the top fin. Am I right that the cylinder must be later production than the engine?

GallopingGhostler Sat Apr 06, 2024 11:08 pm

Looks like you scored, cage mount and all! Thumbs Up

Speaking of Thermal Hoppers, I acquired one off E-Bay a year ago, thread:
https://www.coxengineforum.com/t17211-cox-049-thermal-hopper-a-never-ending-story

It was a blessing in disguise, because someone had wrapped the cylinder with masking tape to keep dust out of the cylinder in storage. Didn't look like much, so it went unnoticed until I bought it for a very reasonable price. Removed tape and cleaned up, I scored. Very Happy

Also, it was a learning lesson for me. Apparently on these, you can use a later cylinder and piston. Looks like maybe someone had a bad cylinder/piston combo and replaced it.

Mine is the earlier one (pre-1956) that the cylinder uses an earlier glow head, cannot use the later glow heads as its threads and mounting is different. However, I could change the cylinder for a later one, then use the later heads.

Your cylinder is a later one. If it could talk, perhaps a previous owner needed a new cylinder and piston, mounted what he could buy from whatever hobby supply he visited or mail ordered from.

If you have another engine with earlier thin cylinder and piston, could swap those out and have an "authentic" looking Thermal Hopper. With some TLC, it should clean up nicely. You may have a future Cox Engine of the Month winner. Wink

Ken Cook Sun Apr 07, 2024 6:03 am

The stepped wall cylinder was introduced in the 70's. While it's not original, it will save you the patience of locating the original small glow heads which are becoming harder to source.

GallopingGhostler Sun Apr 07, 2024 6:12 am

Ken Cook wrote:The stepped wall cylinder was introduced in the 70's. While it's not original, it will save you the patience of locating the original small glow heads which are becoming harder to source.

This is true Ken, I guess it depends on how genuine he wants it. Mine is 1955 or earlier, which uses an earlier glow head, cylinder incompatible with later. They continued making the Thermal Hopper past 1955, 1956 went to the "modern" thin cylinder configuration that use current heads.

If heads become problemmatic, I'll borrow a cylinder and piston off one of my earlier postage stamp engines and use that, to keep the historic look of a later manufactured Thermal Hopper.

getback Sun Apr 07, 2024 7:08 am

That will bee nice once you get her cleaned , These are good runners you should at least put a dual port single or duel bypass cly. on it so it can perform like it should . The older 3 piece piston will come apart after a while of hard running . Had one happen to me ! Sad

duaneh Mon Apr 08, 2024 9:45 pm

I got the engine cleaned up somewhat. It needs a new crankcase gasket, and the reed doesn't look too good to me. I flushed it out as best I could, but it's still oozing green. I don't know how to get the reed assembly apart, and didn't want to risk damaging anything.

It does not have the older 3-piece piston. A previous owner replaced the cylinder, piston and glow head with newer parts. Probably it was easier to do that than find the old type glow heads. I put a thin wall cylinder on it to look a bit more original.

roddie Mon Apr 08, 2024 10:33 pm

Great looking little engine Duane! I've been curious about the "Cricut" machines.. and their ability to cut gasket material.. (which it definitely can..) and other parts like the reed-valves for our engines. High-tech... meets Vintage iron... Cool

getback Tue Apr 09, 2024 8:49 am

https://www.mh-aerotools.de/airfoils/documents/cox_test_thermalhopper_049_aeromodeller_february_1954.pdf The reeds are not to hard to get out but need to bee careful with them , it will run off of just the thicker reed by it self if needed .. Just pry the retainer off a little at a time the gasket are available at Cox Inter. >> https://coxengines.ca/back-end/cox--049-thermal-hopper-space-bug-jr--crankcase-gasket-2.html

rsv1cox Tue Apr 09, 2024 5:32 pm

Wow, that one was nasty Duane but a great clean-up.

Mine has the thin wall but someone added a needle extension. I like it. Those spinner nuts are available at MECOA an acceptible reproduction but your's looks decent as is.

rdw777 Tue Apr 09, 2024 7:12 pm

It cleaned up nicely for you duaneh….. Should make a good runner for you…. If it will start maybe that’s the finish cleaning of the reeds Thumbs Up

GallopingGhostler Tue Apr 09, 2024 11:53 pm

duaneh wrote:

It does not have the older 3-piece piston. A previous owner replaced the cylinder, piston and glow head with newer parts. Probably it was easier to do that than find the old type glow heads. I put a thin wall cylinder on it to look a bit more original.

Duane, it cleaned up really good and the thin cylinder restores its post 1955 Thermal Hopper look. Looks like you have a good candidate for the next Cox Engine of the Month contest. Very Happy

Other day, I fired up my Space Bug Junior with earlier head / cylinder, but it would only run on prime. I suspect a venturi leak in the tank, may need to make up a venturi gasket from a slice of silicon fuel line.

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