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Merlin plugs etc for Norvel ?

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Merlin plugs etc for Norvel ?

Old 09-24-2011, 06:46 PM
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danilo-2
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Default Merlin plugs etc for Norvel ?

Recieved my Merlin Head clamp and plug for my Norvel. Seemed fine.. but on closer study, not so sure.
The Plug insert does have a wee bit More volume than the Norvel plug. It's of Plated metal rather than Ali But it's diameter does seem to be very close to the Norvel plugs' Diameter.
The head piece, which 'seems' a direct copy of the Norvel one, isn't a direct copy, it's oddly off in a couple of dimensions.
The notable difference that I care about is that it has a larger diameter hole for the plug insert than the OEMone. Oversized enough, that it seems to me at least, a bit of a sloppy fit.
Cause for concern here or what? I'm seriously thinking of reboring a spare "early' Norvel head to an ahem.. accurate.. insert hole size. Again: Paranoia or Clever?
Old 09-24-2011, 08:02 PM
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Default RE: Merlin plugs etc for Norvel ?

I think it is made for mainly the Merlin plug insert.  If the others are sloppy I believe each piece would be self centering on their own.  Any clearance would maybe let some air circulate.  The clamping only needs to be on the outer lip of the insert.  I just looked at mine, seems ok.  Never run it yet.
Old 09-24-2011, 08:46 PM
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Jaspur_x
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Default RE: Merlin plugs etc for Norvel ?

I prefer to use the merlin flatcoil plugs in all my models that I can, seems to be higher compression than any other plugs.
Old 09-24-2011, 09:04 PM
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Default RE: Merlin plugs etc for Norvel ?

Does the Cox head / Insert from Bernie (The New Cox / Cox International ) work on a Norvel
Old 09-25-2011, 05:53 AM
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Default RE: Merlin plugs etc for Norvel ?

I think all of the inserts work on everything up to the .06, even the Wen Mac/ McCoys. (Whatevever they are??) They are the same thread but compression varies a lot.  I had a norvel that would not even run with a 6" 3" prop because the compression was too high  with a Tee Dee head.  It worked great with a dished Baby Bee low compression head on the big prop but not record breaking.  It also worked very good with the Tee Dee head on a 5" 3" prop.  So yes it will work.  Maybe order a few head gaskets at the same time to experiment.
Old 09-25-2011, 08:48 AM
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danilo-2
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Default RE: Merlin plugs etc for Norvel ?

Thanks for the replies gentlemen. All input is appreciated..
Firstly these ARE the Merlin bits ( sold by "Bernie' as clamp / insert A ) as I was told by him.
Yes I realise that the Clamp force is all that's strictly necessary , but then there is the issue(?) of heat transfer . Minimal contact with the finned 'head' can also mean heat issues. Are these designed in / compensated for effects or is that just wishful thinking :-)
The Merlin inserts are the of the same external diameter as the oem Norvel plugs (I have a few 'spares' :-)
It's the oddly oversized hole in the Adapter that irks. Plug fits into OEM Norvel heads is loose but by no means sloppy.
Barring any other info input I can see no genuine reason for this except lax production tolerances?
IMO,COX #702 heads are barely worth fitting in any Cox. I havent for decades, especially on my TD's
A standard Cox head gives a better/consistent run with a documented (somewhere in the dim past) 500 Max rpm loss, easily compensated for by a wee shot of extra Nitro :-) and the lower compression is wayyy easier on the fragile cox cranks.
IMO and experiences it's the squish band area design that's desirable in a 2 stroke cyl head. Not necessarily an elevated compression ratio
Thank you: Jaspur X for the flat coils info.
I have history with Nelson plugs and flat Globee type coils have proven desirable..
Just didn't know if the Merlin ones were worth buying variants. Will try a couple then :-)
Old 09-25-2011, 04:05 PM
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Default RE: Merlin plugs etc for Norvel ?


ORIGINAL: danilo-2
...The Merlin inserts are the of the same external diameter as the oem Norvel plugs (I have a few 'spares' :-)
It's the oddly oversized hole in the Adapter that irks. Plug fits into OEM Norvel heads is loose but by no means sloppy.
Barring any other info input I can see no genuine reason for this except lax production tolerances? ...
NORVEL changed plug size mid stream when they created the "Freedom plug". The Freedom plug operated on a little less power and made provisions to use a plug-on booster.

Both the plug and the adapter were changed and the parts were NOT interchangeable. Perhaps you have a mismatch.

George
Old 09-25-2011, 04:32 PM
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Default RE: Merlin plugs etc for Norvel ?

Merlin plugs have a bigger hole in to accomodate HIS buttons.  I think they work on other brand plugs too though, just with a bit of slop.  Like I said before they will still centre themselves seperately.  The extra gap would be maybe better for air to enter for cooling or not better for heat transfer with other plugs.  You could likely contact Al Kelly at Merlin and ask him.  He is quite knowledgable in motors.  I would just use them and see, for whatever plug will go in.  His are not alum. likely for better spotwelding, but maybe alum. is not better,  I was going to try some heads of alum. brass, steel and maybe plastic or ceramic to see if there is any difference some day, on a .15 or .40, but....
Old 09-25-2011, 05:42 PM
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Default RE: Merlin plugs etc for Norvel ?

Yes I was planning to call and ask.
Despite all explanations It does remain as Odd to me.
OEM Norvel plugs, the later larger versions (I have the earlier Norvel plugs and heads as well and am Not confusing them) caliper out as virtually Identical OD to the Merlin ones. No explanation there
Again: the Only apparent deduction for the too loose fit is Manufacturing Sloth.
Other avenue.. Beyond stocking up on Galbraith heads and Nelsons :-)
is to pay the Extra $2 and buy the Genuine Norvel plugs and heads directly from Norvel now that they are available again.. No more oddly fitting Clone Copy parts with their inherent back of the mind: 'is it good enough' doubts. Getting too old to tolerate 'not quite right'. :-)
Old 09-25-2011, 06:00 PM
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Default RE: Merlin plugs etc for Norvel ?

Have you run it yet...?
Old 09-25-2011, 06:19 PM
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Default RE: Merlin plugs etc for Norvel ?

Yup..some :-) seems to run OK onna test stand  .. so far.  Not quite as many revs as the oem head / plug on same jar of fuel and same prop..but not yet done enough time to be definitive.. either way.
 Just now realised that the pesky Merlin Head clamp that had me going is a $3 !! item      
At that price it's More than expected :-)
Old 09-25-2011, 07:47 PM
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Default RE: Merlin plugs etc for Norvel ?

That's been my experience with Norvel engines. You can't do any better than the original head.
Unless you are flying for trophies, the last XX number of rpm isn't that big of a deal. You can get great performance and the lowest running cost I know of by using Nelson plugs.
Old 09-26-2011, 07:37 AM
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Default RE: Merlin plugs etc for Norvel ?

I don't think you need to have a tight fit between the plug and the clamp. The pressure area will provide a good enough heat transfer and both are made from aluminum which is a good conductor of heat.

FWIW, The "new" engines from NV are delivered with the old narrower plugs and the modern larger clamp. The same goes for the spare glow plugs that they sell. Apart from the slightly narrower base, they are also easily recognizable by the square tip on the top for the contact.

One of the problems with the old plugs is that they really do require 1.5V though to light up properly (e.g. from a dry cell) and the now fashionable handheld 1.2V glow drivers don't cut it, unless they are absolutely fully charged (1.4-1.5V). This a potential pitfall I think, as the engines get really hard to start using the hand held drivers that I guess most people are used to nowadays.
Old 09-28-2011, 06:53 PM
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Default RE: Merlin plugs etc for Norvel ?


ORIGINAL: combatpigg
Unless you are flying for trophies, the last XX number of rpm isn't that big of a deal. You can get great performance and the lowest running cost I know of by using Nelson plugs.
No... no more trying for Trophies since I realised that even Younger Son is easily capable of humiliating me in a match.
Gotta love those split minute reactions.
Am at the entertaining myself stage. Good performance is " just fine" thanx :-)

Was just overreactng to what was/is a sloppy fit.
After all it costs not a cent more to bore the correct size hole .


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