mgnostic

I've been on a bit of a 1/2 a engine kick lately. I snagged a box of sure starts the last time Cox was selling them and snag old Coxes any time I see one at a garage sale or auction and so on. I just got a Baby Spitfire the other day and I have scrounged several OK Cubs. I'm not one of those gotta be pristine wall hanger kind of collectors. I like running engines and so to my question. I haven't had a chance to run my latest find. It is a Cub with a venturi extension. I am guessing that the smaller bore of the extension makes for better fuel draw. My only experience with Cubs so far is an open venturi version. Can anybody compare and contrast the two?

forsakenrider

The extension is actually a sleeve that can be pulled out if you try. I have one on a C/L mouse trainer and i flew it back to back with the extension and without with no noticeable differences. The stinkin engine is hard to start no matter what!

gcb

Cubs are low compression engines. Use 25% nitro and at least 20% lube. Some have needles that need more taper (slobber rich to peak in about a turn).

Remember they were mostly designed over 60 years ago.

George

mgnostic

The one of my Cubs that I have run started easily enough. I was running Hobbico 1/2a with added castor. It was probably 20-25%. My thought is that the extention was supposed to be an improvement to the venturi but it seems pretty crude. I know it is a matter of operating on a massively different scale but I have a book on hopping up british car engines (Dave Vizard's book) It points out that venturi shape and length can make a lot of difference. I know Cubs aren't known for being powerhouses but I like playing with older machinery and I will probably put it on an airplane at some point. I know it will never turn a lot of RPMs but I want to get as much as I can. One weekend when the weather is pretty I will try the engines back to back with the same fuel, prop ect.

PeterC

The OK's with the venturi extension are (I believe) later reproduction engines. Whether these were made with surplus inventory from days past or new castings I don't know. These later engines were sold in a plastic bag through mail order for around $7.95. The only difference I have noticed is that they seem a little cruder than the originals. I do believe the venturi extension was an attempt to improve fuel draw which was always a problem with the little Cubs.
Peter

build light

I have seen a few of the extensions and I think they are simply a friction fit and should remove easily.
I do not recall the cubs to be sold off the shelf with one. (see ads below)


Robert

PeterC

You are right. The originals never had the venturi extension. I believe the repro's were advertised in Flying Models magazine only a few years ago (5 maybe). The extensions were an attempt to improve fuel draw. I have never run my "new" Cub so I can't comment on its effectiveness. A pair of needle nose pliers should pull it right out but I would try with and without to see if there is any improvement.
I think the extension is a 3/8" long piece of K&S tubing.
Peter

ffkiwi

OK are still in business-largely run by the grandson of the original founder. In terms of QUANTITY they were nearly as prolific as Cox-so there may well be tons of inventory left, from which engines are being assembled and sold. In terms of QUALITY of course they fall well below Cox-but bear in mind-as has been previously said-that these are 60 year old designs, and were produced on the machinery of the era. The needles in particular are very crude, and the handling can be improved by either grinding a better taper on the needle, or better still retro fitting a fine thread NVA which are available from Texas Timers. Also be aware that in some respects Cubs are 'flimsy'-there is not a lot of meat in the crankcase casting, and the design renders it prone to distorting if tightened up too much-leading to the dreaded 'tight over bottom dead centre' syndrome. The same can apply to the head. Getting Cubs to run well is an art in itself-and a few people have done it-usually by a) a lot of trial and error and b) having several examples available to mix and match parts from. For a history-get your hands on 'They Should have Kept the Bear' by Ted Brebeck (the grandson referred to earlier)-I think Peck Polymers stocks it.

ChrisM
'ffkiwi'

build light

Quote by ChrisM 'ffkiwi':
"For a history-get your hands on 'They Should have Kept the Bear' by Ted Brebeck (the grandson referred to earlier)-I think Peck Polymers stocks it. "

Peck does stock it and Virginia Hobbysports carries it for $10.35.
For a laugh do a search on Amaon .com for this title. Prices (used) range from $58.17 to a whopping $125.00!!! Used! Heh.

Now for the needle valve. I started a thread about the Texas Timers NV assembly to replace the OK cubs and Wen- Macs and such only to find out thaat many of us have the same NV assembly in or own boxes.
That thread is here:
http://www.rcuniverse.com/forum/m_8020914/tm.htm

This NV replacment is probably the best single mod you can make to these engines that does not require special tools or skills outside of a drill.

Robert

jeffie8696

I have a much better time with the later model Testors/McCoy .049s. they are slightly smaller overall and they are very reliable in my opinion. they may not have as much power as some but they appear to start and run a lot more reliably.

Strat2003

My Feedback: (1)

I guess I have one of the good "new" Cubs. I have it in a little free flight FuBar with an eyedropper tank and I start it by hand...just a couple of flips and it goes! It does seem to like to be wet for starting and I agree that the blunt needle makes it pretty sensitive.
I'm still running the little soft red plastic prop it came with but have been warned that they can fly apart, so I do my best to stay clear of the prop arc!