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Author Topic: Cox .049 Glow Plugs  (Read 1434 times)
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dputt7
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« on: August 15, 2014, 10:44:38 PM »

Hi All
Could someone please advise me on the best option for replacement of the Cox .049 Glow Head. To my knowledge there are 3 options, the Standard Cox head, the head with a replaceable insert http://coxengines.ca/cox-.049-glow-plug-adapter-insert-style.html and a head that takes a normal glo plug. http://coxengines.ca/cox-.049-glow-plug-adapter.html
It appears the Insert type head requires a bit of trial and error to obtain the best result by altering the number of head gaskets to get the best comp ratio. The head that takes the standard type plug can reduce the revs by up to 500 rpm. I assume this must have a lower comp. ratio.
Which is the best all-round type to use or is there another option.
regards Dave
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Ployd
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« Reply #1 on: August 16, 2014, 12:44:54 AM »

In order of preference: Modified head to take a Nelson plug (or OS turbo plug), Glo Bee plug and clamp or Cox TD plug. Would not consider the head tapped out to take a standard plug.

Ployd in OZ
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NormF
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« Reply #2 on: August 16, 2014, 12:54:55 AM »

The standard for hi perf Cox heads has been the Doug Galbreath, Nelson conversion see: http://www.the-printer.net/DookCat.html

Norm
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ffkiwi
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« Reply #3 on: August 16, 2014, 02:17:22 AM »

The use of a tapped out head for a 1/4-32 thread plug -or a purpose made adaptor for such a plug-invariably results in a loss of performance when used in a Cox engine, regardless pf whether it is a std 325, Texaco, or 1702 hi compression head. This occurs for several interrelated reasons-including an interrupted head surface, and greater 'dead' volume which reduces the effective compression ratio, as well as the internal geometry of the glowplug element cavity compared with the Cox glow head. You can fiddle the changes all you like-but the result is always inferior to an intact Cox head.

In terms of sheer outright performance though, there are some heads that are superior to the standard Cox ones-the Galbreath Nelson one already mentioned above, and the various aftermarket ones that take a turbo plug [both similar in concept but not interchangable]-the GloBee heads-of which there are mixed opinions (and the originals are well out of production in any case)-but Merlin plugs does current equivalents. They also do insert plugs-similar to the Norvel ones-in styling which are at least as good as the std Cox heads-and for some purposes-superior.

 The only issue is that you have to spend the time testing and optimising any of these replacement heads, whereas a Cox original is largely 'fit and forget' until it needs replacing.  Bear in mind for example-that even with the Galbreath head-there are 3 different Nelson plug heats, plus 2 flat coil inserts-plus the current Merlin Nelson equivalents -which adds up to a lot of possible combinations-and there is similar diversity in Turbo plugs

The insert heads have at least 2 (when I last checked) heat ranges-and as well you have the gasket shimming to deal with-which will be driven by a combination of prop load and the fuel you use.

 ChrisM
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dputt7
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« Reply #4 on: August 17, 2014, 04:50:25 AM »

    Thanks Fellas that's given me a steer in the right direction, Chris, I appreciate your detailed description.   I can just remember in the early 60's my Dad drilling and tapping a stock head because there were no replacements available and it never performed as good, he put that down to the wrong heat range. I think that was in a Veron Colt control liner I had.
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ffkiwi
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« Reply #5 on: August 17, 2014, 04:35:41 PM »

Dave it is just possible-that with a lot of work and experimentation-you might repeat might-be able to find a particular combination of tapped out Cox head and normal 1/4-32 glowplug that came close to the performance of the standard OEM head-but it would take a lot of luck, as there are so many variables to play with-plug brand, plug cavity volume, element length (no of turns in the coil) , element wire thickness, element wire composition-all  have an effect on the heat rating of the plug-and you have no control over them whatsoever-other than choosing the brand and heat range.
  Fortunately there are now plenty of alternatives....just be grateful-as the alternative choices for the smaller and larger Cox sizes 0.010.020 09 and 15 are very limited compared with the 049/051-with the 010 you have no choice at all-its OEM or nothing; with 020 there are a couple of people who can modify a burned out head to take the Nelson insert, there is a 1/4-32 adapter for the 09-with the expected drop in performance and ditto for the .15 The 09 head cannot be modified to take a Nelson plug or insert as there isn't enough metal left once its been drilled for tapping, and while the .15 head can be, no one does this on a commercial basis-though Jon Fletcher will machine them for you on a custom basis for a price.
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dputt7
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« Reply #6 on: August 18, 2014, 06:37:37 AM »

Chris, I just want a reliable easy starter so I'll probably go with the OEM head but I might just try an insert head as well just out of curiosity. I have a Rev. counter somewhere so it should be easy to compare
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faif2d
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« Reply #7 on: August 18, 2014, 02:46:07 PM »

The big plus with the Nelson plug conversion is the life of the plug goes WAY up.  I would guess at 5X the life when running high nitro.  You get the added bonus of 500 or so extra RPM these are both compared to the std. C*x comp plug.  The .09 head can be modified for this insert as well,  I had a machinist friend do 5 or 6.
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« Reply #8 on: August 18, 2014, 03:44:27 PM »

Maybe I missed it, but dputt hasn't said what engine he has, yet most of the replies make the assumption it's a TD.

If it's reed valve engine, using a head with a standard glow plug probably won't cause too much loss of power, and putting a bit more nitro methane in the fuel would probably restore that, and improve the running (nitro in the range 15-30% I would think).
I'm guessing here - I've never owned a Cox reed valve engine.
JB
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ffkiwi
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« Reply #9 on: August 18, 2014, 03:52:41 PM »

The big plus with the Nelson plug conversion is the life of the plug goes WAY up.  I would guess at 5X the life when running high nitro.  You get the added bonus of 500 or so extra RPM these are both compared to the std. C*x comp plug.  The .09 head can be modified for this insert as well,  I had a machinist friend do 5 or 6.

A very good model engineer-Jon Fletcher-who does a lot of engine work-will not do 09 heads (I've asked him to do some for me and he declined) because in his professional opinion, there is not enough metal remaining after the head is drilled and tapped for the 11/32-32 Nelson thread, and the seat cut to prevent distortion when the plug is inserted or removed. I would like to know how your machinist friend managed it...........

 ChrisM
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dputt7
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« Reply #10 on: August 19, 2014, 04:07:48 AM »

   Yes, its a Reed engine
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faif2d
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« Reply #11 on: August 19, 2014, 05:02:48 PM »

FFkiwi, I had the plugs done about 7 years ago and no longer remember the details.  Several went to Jim Thomerson a CL guy from south Texas.  He is the one that furnished the burned out glow heads.  I seem to remember that one or 2 were low compression heads and the rest were the high comp heads.  I do remember that the shoulder that the base of the plug stops against was 87 degrees which happens to be the same as a normal drill bit tip angle.  I think my guy only scraped 2 of the heads that he started with.
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ffkiwi
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« Reply #12 on: August 19, 2014, 08:35:51 PM »

I might revisit the whole thing then-I have four TD09s-and parts are drying up-venturis and NVAs in particular-which have applications in other areas as well. [they make good retrofits for some diesels] Cox Int'l are getting quite a few replica parts made for 049s, but show no inclination to do any runs on 09 part-not enough demand I suppose. 09 heads per se are getting harder to get-but MECOA is supposedly producing them. I have good supplies of Nelson plugs and inserts so would like to get the 09s done-bringing them in line with my 049/051s and .15s. Jon F will machine me up  09 Nelson heads from scratch-(at an eye watering price)-but he won't convert burnt out standard ones....

 ChrisM
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danberry
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« Reply #13 on: August 20, 2014, 07:26:35 PM »

A problem with converting old glow heads is the softness of the metal.
At least that's what a guy told me.......
I think it was Doug.
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ffkiwi
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« Reply #14 on: August 20, 2014, 08:24:38 PM »

A problem with converting old glow heads is the softness of the metal.
At least that's what a guy told me.......
I think it was Doug.

That was the other part of Jon Fletcher's reluctance to convert my burned out 09 heads to Nelson plugs-by the time the old element and stem is removed and the remainder faced drilled and tapped 11/31-32, the remaining wall thickness plus the softness of the metal rendered the result problematic.....
   It is by no means impossible that Cox used different alloys for heads over the years-in which case depending on the alloy, some heads might be harder or softer-and hence the modification might work with some but not with others. I know for example, that heads are not always a simple two piece assembly-the Fox 09 glowhead has the entire element assembly-stem, coil and outer alloy housing-pressed into the overall glowhead unit from below. Attempting to tap a burned out one of these for a std 1/4-32 plug is an exercise in frustration........the pressed in outer portion loosens up when you try and tap it...[ask me how I know.........]

 ChrisM
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