On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Robbasdog Mon Sep 30, 2019 9:39 am

Hi folks,
Dame fortune has smiled on me once again--- I've just found a couple of old Thimble Drome engines dying a slow death in a neighbour's attic, and all I had to do to get them was mow his lawn!
One's a Space Bug Junior missing its tank unit ( beats me how that would happen ) but otherwise in excellent condition, and the other is a Thermal Hopper so well used there's virtually no compression left, missing the spinner and needle, but otherwise complete and tidy.
I've already got a good red-tank and a great clear-tank SBJ, so if anyone has a spare yellow or blue colored tank I could buy, in good-to-great condition, that'd be awesome. Ideally a blue one, but yellow'd be nice too.
I'll try and get the Thermal Hopper up and running soon on a stepped Bee top-end and the other bits from my stash, but I'd love to find a small head-thread cylinder assembly and head to give it back its own youthful pep. Anyone got a good spare set they will part with??
Gonna have plenty of time to play with these, autumn has shown its face already and bike-rides are getting fewer by the week. Doh!

Cheers, Rob

rsv1cox Mon Sep 30, 2019 12:06 pm

Good luck with your search. Hopefully some one here has spares.

Best option though is a continuing ebay search but I seldom see those parts offered.

Robbasdog Mon Sep 30, 2019 12:19 pm

Hi, thanks for that. I have seen the cylinders on feebay, but as you say, not for a while--- and then the seller only posted within the USA. I won't take parts off a running donor engine, even a scruffy one, but if a non-runner with bits missing or damaged turns up I'd be happy with that, as long as the parts I want are good. May not have much of a choice!

getback Mon Sep 30, 2019 12:24 pm

Yes Yellow and Blue are pretty rare even complete Cox has the needle assy.https://coxengines.ca/cox-.049-needle-valve-309.html I got a red one off ebay years ago Nice , but not willing to get rid of it , was in a box with some other stuff LOL Very Happy

i thought they had these too but didnt see them . https://www.ebay.com/itm/Cox-049-Aluminum-Prop-Propeller-Spinner-Space-Bug-Thermal-Hopper-Strato-Bug-049/371651872389?hash=item56882d8685:g:-r8AAOSwyGZaA4J~ If you purchase a rough looking engine with the small glow threads and us on the nicer one just takes time ..

Robbasdog Mon Sep 30, 2019 2:05 pm

Thanks for all the info, getback. I took a spinner off one of my SBJ s and replaced it with a nut and washer as per original and was surprised to find one of the broken Golden Bees in my graveyard box had a good-but-not-great twin-bypass cylinder and a large-head needle, so that now sorts the Thermal Hopper to my satisfaction.
So, now just looking to find a decent SBJ tank...
Just a thought...has anyone tried to expand one of the first-type pistons and hone the cylinder to get a good fit? I've fixed an old long-stroke 5cc diesel like that before, but the piston was cast iron and a whole lot bigger!

dckrsn Mon Sep 30, 2019 3:41 pm

I think there's a SpaceBug Jr tank/backplate in this lot.
https://www.ebay.com/itm/gas-engine-rc-cox-049-or-MRC-enya-035/274023216397?hash=item3fcd0e750d:g:wuIAAOSwM4pdigi0
Bob

ian1954 Mon Sep 30, 2019 6:21 pm

Robbasdog wrote:Thanks for all the info, getback. I took a spinner off one of my SBJ s and replaced it with a nut and washer as per original and was surprised to find one of the broken Golden Bees in my graveyard box had a good-but-not-great twin-bypass cylinder and a large-head needle, so that now sorts the Thermal Hopper to my satisfaction.
So, now just looking to find a decent SBJ tank...
Just a thought...has anyone tried to expand one of the first-type pistons and hone the cylinder to get a good fit? I've fixed an old long-stroke 5cc diesel like that before, but the piston was cast iron and a whole lot bigger!

This is not a recommendation because for "one offs" it is quite expensive and there is a risk of inducing brittlenes. Using a case hardening compound such as Kasenite - heating a steel piston to red and dipping it into the Kasenite carburises the steel and hardens the outer layer,

I have done this on three Cox pistons after making a former to hold the piston and stop the inside being carburised.

However, one distorted beyond recovery and Kasenite is now expensive.

Robbasdog Tue Oct 01, 2019 4:11 am

Thanks for the link, dckrsn, I did see that one. I already have a very rough uncolored one that still holds fuel, if I get stuck.
As for the piston, Ian, I was told a trick by an elderly motorcycle racer ages ago, used to race home-brewed specials he mostly made himself, very much a Bert Munroe type. He used to heat up his old worn out cast iron pistons to a dull red then quench them in tepid water. He had a massive collection of his failures, mind you, but eventually hit on a way to make them end up just bigger enough to go another racing season. He was very proud of his efforts, too, not least because of the money he saved! So when a friend's home made model engine needed more compression I tried the same trick, and by sheer luck it worked. He had to hone out the bore a bit, but the guy that made it reckoned it ran better than when it was new.
I don't imagine it'd be too sucessful with alloy pistons, but steel ones ought to be ok.

coxaddict Tue Oct 01, 2019 6:04 am

Let us know how it turns out. Sometimes when resetting the ball socket something happens to the piston making for a tighter piston to cylinder fit. Some say not to use the piston holder because of this when resetting the ball socket. I started working on a mandrel to try to expand the piston from the inside but ended up not using it. I had the luxury of swapping used pistons to fit to cylinders to make good runners. Might re-visit the idea of expanding the piston without cracking it.

Robbasdog Tue Oct 01, 2019 8:33 am

Hi coxaddict, I agree swapping pistons is the best solution...if you have a stash of 'em, that is! I only have this one 3-piece piston that's not in an engine, and I'm a bit reluctant to risk it on an experiment. I think I'd prefer a bad set to an odd cylinder. I even briefly thought about plating the piston, but I've only done copper and zinc on nuts, bolts and washers, chrome seems a lot more complicated, and there's still the risk of over-cooking the piston...and once it's gone, it's gone... gonna have to think about this one some more...
This seems like a basic question, but will a ball/socket piston work in an earlier cylinder??

Mark Boesen Tue Oct 01, 2019 9:00 am

Yes, it will interchange. For max rpm sometime a loose piston/cylinder fit actually works better. What an engine feels like flipping cold and how it operates hot at high rpm are two different things. Experiment, it's part of the fun. Resetting ball sockets use a thick piece of glass for anvil and lots of light taps.

Robbasdog Tue Oct 01, 2019 9:17 am

Thanks for that, Mark. I just tried the older cylinder on the dead Golden Bee (with its original piston) and it fitted--- once I added another two gaskets so the piston didn't hit the head at TDC. More maybe needed to give enough clearance when hot. Compression better, but even with a new piston it's still below par, so cylinder is well worn, and I can only guess what it's done to the compression ratio. Might not run properly...if at all! But a good basis for more investigation!

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On the scrounge again...Thermal Hopper cylinder and SBJ tank...

On the scrounge again...Thermal Hopper cylinder and SBJ tank...

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Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...

Re: On the scrounge again...Thermal Hopper cylinder and SBJ tank...