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Cox Engine of The Month
February-2024
1/2A Nut's

"RC Speed Boat Power Drive TD .020"

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Post  Robbasdog Sat Mar 16, 2019 3:27 pm

Hi folks, what's the deal with the two different external shapes on the .15 glow heads? I mean, apart from the combustion chamber shapes--trumpet, conical and hemi-- there's two (that I've seen, maybe more? ) different profiles in the fin-root diameters too. The fins on one are much longer, with less metal between the chamber and the air--was that meant to follow closely the shape of the inside and so cool the head faster for racing with hot fuels? Was one simply an upgrade to reduce costs? Which one came first? I suppose like a lot of tech things on Cox engines, there may be no one definitive answer.
Just curious, and for what it's worth I reckon the longer fins simply proved to be too easily bent so Cox strengthened them by reducing the turning depth.
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Post  KariFS Sun Mar 17, 2019 8:27 am

You got me curious enough to dig out my .15 engines and heads to take a look Very Happy

You have a good eye, I had never noticed the difference. I have three engines, an early Tee Dee, an Olympic and a Sportsman. The Tee Dee and the Olympic have Tee Dee style heads, both with the deep grooves or high profile fins. The Sportsman has a standard head, with the lower profile fins. With all the spare glowheads I have, the shapes are the same, Tee Dee style having the hig profile fins and the standard ones are with low profile fins.

I did not see any difference in fin spacing, but my engines and heads are all from the same era, early ’70s or older. I have three glowheads of both styles.

Pics:

.15 glow head shapes... Ae799610

It’s hard to get a sharp picture of two different heads with my phone camera, but here are crops of two different pics:

Standard:
.15 glow head shapes... 47df6a10

Tee Dee:
.15 glow head shapes... 34a43910
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Post  Robbasdog Sun Mar 17, 2019 8:55 am

Hi Kari, thanks for the input. I had to resist the urge to list what heads are on my .15s simply because after all these years they're not likely to be the originals. What this topic needs is someone with a whole bunch of NIB .15s to give their input, tho' I dare say even that may not be the one-and-only answer! Also I don't have enough engines and/or spare heads to tell whether each of the combustion chamber shapes can come in either of the two external shapes. Obviously I don't have enough engines Eyebrows , I must rectify that!!
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Post  ffkiwi Mon Mar 18, 2019 10:51 pm

This could well be accounted for by nothing more than the mundane reason that a form tool is used to shape the external head profile-and this tool will need to be periodically resharpened-which may alter its shape slightly-and hence the shape of the part it is used on.

ChrisM
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