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pre-1955 glow head thread spec #302

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pre-1955 glow head thread spec #302

Post  DougW on Wed Jul 13, 2016 11:03 am

Does anyone know the thread pitch/diameter for the early Thermal Hopper glow head ? Please don't do a lot of research on my behalf but if you know it offhand let me know. Would like to find the correct die in order to re-thread a Cox International insert adapter to the old size. Also, is there a reason why this would not work well ?
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Re: pre-1955 glow head thread spec #302

Post  Mark Boesen on Wed Jul 13, 2016 2:15 pm

Doug, you might consider looking for an old basket case O.K. Cub .049 head, they were the same diameter/thread and already tapped for a glowplug?
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Re: pre-1955 glow head thread spec #302

Post  balogh on Wed Jul 13, 2016 2:46 pm

DougW wrote:Does anyone know the thread pitch/diameter for the early Thermal Hopper glow head ? Please don't do a lot of research on my behalf but if you know it offhand let me know. Would like to find the correct die in order to re-thread a Cox International insert adapter to the old size. Also, is there a reason why this would not work well ?

I have measured the outer dia of the threads on the pre-1955 head is 12,1mm, and the same on the present-day heads is 13,4mm. I could not measure the depth of the threads but the profile of the threads on the two  seems pretty identical.

I figure that as long as you do not touch the shape of the combustion chamber/dome inside the head when machining the current head to the smaller dia, you will probably not impact the engine running characteristics.

Though small, the 049 engine is probably sensitive to the shape of the dome. In the high compression head of early TD-s the dome was convex, then changed to concave on later heads- or the other way around.
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Re: pre-1955 glow head thread spec #302

Post  DougW on Wed Jul 13, 2016 3:07 pm

Thanks for the dimensions. I don't know whether the threads correspond to a standard die or whether they are specially machined. I think the older heads may have been concave since in the USA vintage f/f gas event the high compression heads are not allowed.
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Re: pre-1955 glow head thread spec #302

Post  DougW on Wed Jul 13, 2016 3:20 pm

Thanks for the suggestion to use an O.K. Cub .049 tapped head. Will look into it if win the auction for engine. Have a glow plug tap and a Unimat, could maybe tap the #302 head if the element burns out. Not quite sure how drilling it would work out considering the presence of harder metal in the battery lead terminal and that I am not a great machinist. That the Cub head fits is encouraging; this thread may be a standard one with dies available. I have no threading attachment for my lathe.
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Re: pre-1955 glow head thread spec #302

Post  Oldenginerod on Wed Jul 13, 2016 6:49 pm

Keep in mind that the early Cox head (#302) seated at the top of the cylinder, as with the Cub, where the #302-1 or #325 Cox heads (larger diameter heads) seated on a step in the cylinder below the thread.
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Re: pre-1955 glow head thread spec #302

Post  DougW on Thu Jul 14, 2016 11:50 am

Thanks Oldenginerod.
Did not know that. Maybe re-threading won't work, or the insert adapter will need additional machining. Can't quite visualize how #302 plug would sit inside cylinder with no ledge. But don't worry to spend time explaining to dense Canadian, should be able to tell whether my replacement scheme is possible if obtain the engine and am committed already. Auction ends tonight. Very light engine, remarkable for f/f gas.
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Re: pre-1955 glow head thread spec #302

Post  Mark Boesen on Thu Jul 14, 2016 4:01 pm

http://www.ebay.com/itm/Vintage-OK-Cub-049-Engine-/112053225537


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Re: pre-1955 glow head thread spec #302

Post  Oldenginerod on Thu Jul 14, 2016 8:02 pm

Mark Boesen wrote:http://www.ebay.com/itm/Vintage-OK-Cub-049-Engine-/112053225537
Mark, didn't the first 049 Cub have a different head to the subsequent models?  I think the "A" & "B" heads were the ones that will fit.
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Re: pre-1955 glow head thread spec #302

Post  getback on Thu Jul 14, 2016 8:59 pm

I have one I am selling but the glow doesn't work (( I probably have one if you don't and let me know))  http://www.ebay.com/itm/282081868696?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649   Eric
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Re: pre-1955 glow head thread spec #302

Post  Mark Boesen on Fri Jul 15, 2016 10:30 am

Oldenginerod wrote:
Mark Boesen wrote:http://www.ebay.com/itm/Vintage-OK-Cub-049-Engine-/112053225537
Mark, didn't the first 049 Cub have a different head to the subsequent models?  I think the "A" & "B" heads were the ones that will fit.

The early engines were the same as early Cox, I guess Leroy must of figured why not use the same diameter and threads as Herkimer. Later after Cox went to a larger diameter for a better seal, Herkimer did as well, copying Cox. The Cub didn't go to a intigrated glowhead until 2-3 years after Cox did. They'll work on a Cox, but pretty low compression.
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Re: pre-1955 glow head thread spec #302

Post  DougW on Mon Jul 18, 2016 10:51 am

Thanks guys. Have bought a glow plug O.K. Cub .049 from Texas on eBay, 42.80 Cdn with global shipping Priority Post. Would be able to use this engine in the power pod for a Frank Zaic "Scout" r/c glider and share its head with the Thermal Hopper for f/f gas.

As well, the Herkimer head may help me to see how best to tap/spot face a burned out #302 Cox glow head, or to re-thread the Cox International insert head, which latter should not cost any rpms.

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Re: pre-1955 glow head thread spec #302

Post  Mark Boesen on Mon Jul 18, 2016 4:58 pm

Doug, if it a one piece glowhead, it's not gonna fit, the later glowhead is the same size as the later cox engines. What you need is the head with the seperate glowplug, i'll look i think i got one if you need it.
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Re: pre-1955 glow head thread spec #302

Post  DougW on Mon Jul 18, 2016 6:50 pm

Thanks Mark. The eBay photo shows a glow plug screwed into a tapped head. It's an old model, no beam mounts, large diameter circular back plate, quite unlike newer models A & B. Have never seen it before, although I had a model A or B and an .075 diesel when I was 13 or so around 1958. I would have pasted in a link to the eBay item but the forum rules don't allow new members like myself to post links. However, your comment saved me from buying a Cub integrated plug/head since I had forgot they would not fit. Was considering it.

Engines were a mystery to us. A friend bought his Cub as a kit, and did not know what to do with the needle valve spring. So he installed it vertically inside the cylinder above the piston. Fuelless drive ! I also remember a magazine note that a kid had grounded the second lead from his battery to a large metal stake he drove into the ground, instead of to some place on the motor other than the glow plug. I was hugely ignorant and always on the lookout for the most recent hottest engine even though my chances of actually trimming out the model were quite low. So many times I got the model finished in the wee hours of the morning before going to the contest, and ended up crashing the model or losing it, due to fatigue, haste, frustration and general desperation. Now I know that long before dreams of glory should come learning how to consistently start the engine, remain calm, regulate it, get the d/t fuse lit, properly set the timer, check the wind, launch carefully. This could be easier with a less hot model and engine to begin, except one might be laughed at. Trimming really needs long grass, seldom available at contest fields, because one never knows about transition on initial short runs and it can also save a power on crash from damage. u/c I did not understood what a free linkage, pushrod keeper or good leadouts were nor how to set up to de-sensitize the elevator and to move the whole arm not the wrist. Too sure I knew it all. Yet I had a U-Reely. Totally wasted on me.

A drive for glory instead of appreciating engines and models for their inherent interest, which after all gives one a better chance. I really liked Bernie's info on Cox engines and fuels, that 1/2 A's like nitromethane and it is not just for max power but also smooth running and less internal stress. But I was always after the hottest fuel, even Franny's "This is it" even when I barely if at all had the models under control. So I outgrew that. But don't know what is wrong with me now, like back then I did not realize what is now clear. Must be something. Anyway I went through a lot of good engines I did not deserve.
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Re: pre-1955 glow head thread spec #302

Post  straitnickel on Tue Dec 06, 2016 2:25 am

i'm looking for the thread count per inch cause I have threads that need to be chased, does anybody know the number?
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Re: pre-1955 glow head thread spec #302

Post  Oldenginerod on Tue Dec 06, 2016 5:30 am

straitnickel wrote:i'm looking for the thread count per inch cause I have threads that need to be chased, does anybody know the number?

All head and cylinder threads on Cox .049s appear to be 40 tpi.
http://www.mh-aerotools.de/airfoils/cox_techinfo.htm

Hope this helps.
Rod.
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Re: pre-1955 glow head thread spec #302

Post  straitnickel on Tue Dec 06, 2016 5:43 am

Oldenginerod wrote:
straitnickel wrote:i'm looking for the thread count per inch cause I have threads that need to be chased, does anybody know the number?

All head and cylinder threads on Cox .049s appear to be 40 tpi.
http://www.mh-aerotools.de/airfoils/cox_techinfo.htm

Hope this helps.
Rod.

Rod,
yes it does thanks.
regards, joel
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