Making mini sparkplugs.

[Generatorgus]

After making about half dozen 1/4-32 spark plugs and having difficulty turning the teflon core because of lack of rigidity, I tried drilling and inserting a length of the .032 electrode before turning to fit the core.
The extra stiffness makes the chore a lot simpler.
GUS

 

[B-RAD]

Pictures would be great.

 

[Generatorgus]

B-RAD

Sorry, no pics of the build. Next time I make one maybe.
But I do have a couple pics of finished ones.

This is a Stainless steel 1/4-32 long reach I made for my Briesh Little Brother. You'll notice no grounding electrode, it doesn't seem necessary.
This plug now has somewhere over a hundred hours on it and still working good.

This was a leap of faith build of a two piece 1/16-27 pipe thread, agian stainless steel.
I haven't used this one yet, I built it for my 1/2 scale H. Ford engine, I thought the pipe thread would fit in nicely with the pipe fitting engine theme.

 

[Lew Hartswick]

Re- side electrodes: My SAAB 850 GT from the 60 area used what they called "surface gap" plugs (no side electrode) and they
worked just fine.

 

[gus]

SOS SOS .
Just started building glow plug engine and wil need to buy 1/4 x 32 NEF tap and thread die.
I live in Singapore which went metric 40 years ago. Imperial taps and dies are as rare as dinosaur eggs in Singapore..
Please advise advise supplier e-address. Thanks.

 

[tguckian]

Would like to hear more about miniature spark plugs. Am building an IC inline 4 cyl.

 

[GailInNM]

Gus,
The formal name for the thread is 1/4-32 Unified National Extra Fine or just 1/4 UNEF. While quite common in the US, you will probably have better luck getting it shipped from the UK. Most model engineering supply venders there will have at least the tap and often the die. Perhaps one of our UK members can recommend a vender.

Do a search for 1/4 unef tap uk

Gail in NM

 

[GailInNM]

tguckian,
I posted a construction segment on making miniature spark plugs a couple of years ago. The start is here:

http://www.homemodelenginemachinist.com/f14/tiny-i-c-engine-7397/index26.html#post115891
At the end of post 259 is a link to a PDF file of the drawing for the illustrated plug.

I would like to know more about you and the engine you are building. If convenient please post an introduction in the welcome section and start a work in progress post on your engine.

Gail in NM

 

[GailInNM]

Generatorgus,
I have used the 1/32 wire to reduce deflection. It works well.

Using the Teflon as it's own bearing, i have clamped the wire in the tailstock drill chuck and that adds some more stiffness.
More recently I went to Corian for insulators. For low performance engines it seems to hold up as well as Teflon and because it is stiff it easier for me to machine.

Gail in NM

 

[RonGinger]

If you are building the engine and the spark plug forget about US size taps and convert to the nearest size metric thread. There is no magic abut thread sizes.

 

[GailInNM]

Ron,
For spark ignition I agree with you. What ever is the most convenient. Unfortunately, Gus in Singapore said he is building a glow engine and glow plugs are a lot harder to make. Other than a few specials that have been made over the years I think that all the commercial glow plugs are 1/4-32 thread.
Gail in NM

 

[Generatorgus]

Gail, thanks for the input.
I've considered the corian, but haven't yet tried to source it and besides when I started to make my plugs I bought a 6 foot length of 3/8 teflon.
It will take me quite a while to use that up.

I recently bought a 1/4-32 die on Ebay direct shipped from China $ 5.50 with free shipping. What I got was an adjustable die that was not cut and does'nt have an adjuster screw but it worked just fine.
I cut the threads on my other plugs on the lathe, but it's a little fussy for my experience level and the die cut thread has a better fit to my tapped holes.

GUS

 

[donkey1]

Gus.
Tracy tools in the UK stock the tap for spark plugs and they ship worldwide www.tracytools.comthey call it a model engineer tap in the uk.
good luck.
Bri

 

[gus]

Gus,
The formal name for the thread is 1/4-32 Unified National Extra Fine or just 1/4 UNEF. While quite common in the US, you will probably have better luck getting it shipped from the UK. Most model engineering supply venders there will have at least the tap and often the die. Perhaps one of our UK members can recommend a vender.

Do a search for 1/4 unef tap uk

Gail in NM

Hi Gail.

Thanks for the info.
About the machine the crankcase cylinder port on the crankcase.Keeping my self alert.That beware when a 69ner gets tired,he needs a break and if not the last cut could demolish the crankcase.
Will post when I go further.

 

[gus]

Gus.
Tracy tools in the UK stock the tap for spark plugs and they ship worldwide www.tracytools.comthey call it a model engineer tap in the uk.
good luck.
Bri

OK .I did not realise they have UNEF Tap.

Will buy today and wait for tap to arrive to turn the outerhead.
Can I assume 1/4 " Glow Plugs comes standard with 1/4 x 32 UNEF thread.

Thanks for info.

When O/head gets completed,I will post .


Gus from faraway Singapore.

P.S.

I missed the "Potato Skins".Been enjoying this cuisine often when I get stationed in Campbellsville,Kentucky.Also missed the Country Ham.
Here in Singapore,no way I can have these.

 

[gus]

Hi Gail.

Thanks for the info.
About the machine the crankcase cylinder port on the crankcase.Keeping my self alert.That beware when a 69ner gets tired,he needs a break and if not the last cut could demolish the crankcase.
Will post when I go further.

Found and ordered taps from tap-die.com UK.

Now will buy OS Glow Plug. Lets hope the aeromodel engine shop is conversant with UNEF threads. Sadly there are no too many aeromodellers here in Singapore building from Scratch. Most buy ready makes from China and Vietnam. Gus is among the dying specimen. Bet you.I may the only guy making his own aeromodel engines.

Just finished crankcase and cover screwed on.
Two weeks from now when tap arrive ,will machine outerhead.

 

[Jasonb]

Gus, I don't think Tapdie do UNEF taps. Contary to what has been said above they are NOT the same as the 1/4x32 ME taps, the thread angle if different. ME is 55degree, UNEF is 60degree.

If you are ordering from the UK then Model Fixings sell the correct tap.

http://www.modelfixings.co.uk/glow_plug_taps.htm

You will only need the taper one as its a through hole and yes the 1/4x32 UNEF is a standard glowplug thread so they will all fit, OS number 8 plug is recommended.

J

 

[Jasonb]

Gus.
Tracy tools in the UK stock the tap for spark plugs and they ship worldwide www.tracytools.comthey call it a model engineer tap in the uk.
good luck.
Bri

NOT the same tap, see my post above.

 

[waynes world]

dubro products make 1/4-32 glow plug tap and die you should be able to get them from local hobby retailer. or the next best place is tower hobbies on line in the usa. not rare item at all very common.

 

[gus]

Ron,
For spark ignition I agree with you. What ever is the most convenient. Unfortunately, Gus in Singapore said he is building a glow engine and glow plugs are a lot harder to make. Other than a few specials that have been made over the years I think that all the commercial glow plugs are 1/4-32 thread.
Gail in NM

Hi Gail.

Here is my engine. For now it is only a shell,piston,liner,con-rod still missing.
Will be done in good time.Went shopping for glow plug.Saw the exhaust silencer.Bought it to save the hassle of building DIY silencer.
Glow plug fitted on. Next on the list is the carb.Will make it for relaxation before going on to the skill/patience demanding piston and cylinder sleeve.
Would be lovely ,if we could make our own glow plugs too.

P.S. Bought the 1/4 x 32 UNEF from local aeromodel supply shop today.Need it like yesterday as the taps from UK n US has yet to arrive.Soon as I got home the postman called to deliver the UK taps.I have too many 1/4 taps.

Gus from faraway Singapore.