CO2 Motors - repair and maintenance

Last months AeroModeller had a very good article on maintaining and reconditioning CO2 Motors. I have rather large collection, but following the use of some special lubricant, advertised as a 'low temperature oil ideal for model CO2 motors' most of them are non-runners due to seal failure caused by the 'special oil'...

Anyway, the article came up with some very good suggestions and following the advice, together with slices of a small 'O' ring and some material cut from fine-bore silicone tube, I've managed to get two of them running sweetly this afternoon!

They're both Davis Diesel conversions of Cox glow motors, the large one being an 0.049 and the smaller an 0.020. For size comparison the large motor has a 10" prop and the small one a 5".

Now, all I need to do is find suitable models to put them in......









Coincidently, the last page of the article suggests using rubber props for the GM120, taking care to chose those with a large enough hub to take boring out to the right diameter for the prop screw and the power of the motor.

They're both Davis Diesel conversions of Cox glow motors, the large one being an 0.049 and the smaller an 0.020.

I had no idea this was even possible, CO2 conversion of a glow engine !!! I'm guessing that the engine is single speed unless they've managed to engineer some kind of throttle in there too.
What sort of power do they produce ?

I read the article to too. It's very good , I even bought some Labelle 108 synthetic oil which apart from being quite expensive seems to work well in my engines...hopefully this won't attack the seals

I think it was back in the 1980s that Davis Diesel (DD) produced different heads for Cox motors to convert them to diesel or CO2. I didn't bother with the diesel heads, but I bought a CO2 head for the Cox 0.020 and a full motor and head for the 0.049. The cost was about $25 and $50 respectively.

The CO2 head replaces the glow head. The inner with the ball valve screws in and out to throttle the engine. The power produced is pretty good, but they do need a much larger prop than when under glow power. However, I believe the Gasparin motors are more efficient as CO2 requires a much longer stroke than available with a glow engine to realise the available power. At the time, the biggest CO2 motors available were the Brown Twin and the Modella, so the Cox conversions filled a gap, which Gasparin later exploited.

The DD CO2 conversions are occasionally available on eBay, etc, if you keep your eye's open.

If you're interested, I'll bring the motors to the next few meetings I go to (SAM35 Buckminster on Thursday, the BMFA RC Nats, and Peterborough Flying Aces) so you can have a closer look.

It would be good to see them close up. I can't make Buckminster but I plan to be at the Nats hopefully Sunday, if you remember

Just idle thought but would blocking of the intakes on the Cox engines make any difference ?

one tenor wrote: Just idle thought but would blocking of the intakes on the Cox engines make any difference ?

Good question John. I leave them open too allow the crankcase to breathe, to allow internal pressure to equalise and to give access for oiling.

Sounds about right andy Thanks

On the subject of props for CO2 I have been using these 7" props from Flitehook on my GM 300 and they work well.

I thought they were Modella props but the moulded logo says SW.




I was using the much larger 9 1/2 " plastic rubber props from Flitehook but I found on 30" vintage models the prop was so big that where it stopped would effect the glide path. I nearly lost a model in a wheat field at Middle Wallop thanks to that.. and I'd set the D/T. They work with the bigger engines and bigger models but you need to carve the freewheel moulding off.





SAMS used to do a prop kit that came with loose blades and a hub , you can make them as 2 , 3 ,4 bladed units with the different hubs. They work well too. I'm sure Kevin will correct me if they don't do them anymore




For the smaller Telco sized engines, as well as the Telco prop, I've used the KK rubber prop that used to come in the kit again with the rubber drive bit chopped off.

Is the loose blade job one of the SAMS props?

Is the loose blade job one of the SAMS props?

Yes they come in a little packet and you have to assemble the blades into the hub yourself.

I just checked SAMS site and they don't list them anymore but the KP props look similar

Squirrelnet wrote:

Is the loose blade job one of the SAMS props?

Yes they come in a little packet and you have to assemble the blades into the hub yourself.

I just checked SAMS site and they don't list them anymore but the KP props look similar

Thanks Sq I'll check when the time comes Whenever that is."2" hubs supplied or do you specify which?

John have a look at this they come in various sizes.

www.samsmodels.com/products/propellors

Its worth checking with John at Flitehook too , he doesn't have any CO2 props on his site but I sure he had some red Modella ones last time I saw him

Thanks for that but it will be quite a while till I am able to do anything with this info as A) I 'm still waiting for hips replacements and( my only CO2 motor needs new tubing ,tank valve etc Still nice to know Do you know best suppliers for this gear by chance? Regards John O/T

my only CO2 motor needs new tubing ,tank valve etc Still nice to know Do you know best suppliers for this gear by chance?

I don't know of any where selling parts in the UK . Black Sheep lists tubing but as they are US based any order over £15 will incur a £30 handling and customs charge !

blacksheepsquadron.com/index.html

My best bet would be eBay for a non runner of the same type

edit - Actually the tube is fairly easy get even eBay lists short 2m lengths of .5mm copper tube. you'd need to check the size for your fittings obviously.

The .5mm quoted is the wall thickness. The tube inside diameter is 3mm and the outside 4mm.