Spark Plug threads in Aluminium heads

Niceonetidy · May 23, 2013

Hello,

How do you Engineers fit spark plugs in Aluminum cylinder heads? Do you thread the head and fit the plug, or fit a bronze insert in the head to make it more reliable and a better life?

Thanks in Advance for any replies,

Colin

Longboy · May 23, 2013

.....You can just bore, tap and thread your plugs dirrectly. I use some anti -seize on the plug threads. This should last till around......2073 or longer.

enfieldbullet · May 23, 2013

seen it done both ways.

also seen on old VW's a nut inserted in the head and crimped in place.

Coilmotorworks · May 23, 2013

Use a good quality tap and die (if you make your own plugs), a little lube on the threads and things will be just fine. Pull the plug(s) just before you store your engine, dry out and lube the cylinder(s) and leave the plug loose until you run the engine again.

lohring · May 25, 2013

I race model boats that use Zenoah industrial style engines. They have plug threads tapped directly into the die cast aluminum cylinder. I've not heard of a stripped plug thread. I bet this is the same with most low cost gasoline engines.

Lohring Miller

ConductorX · May 29, 2013

On VW engines it was common for spark plugs to strip out. We would buy a special tool to ream out the old threads and then the same tool would tap new larger threads. Afterward we would screw in a spark plug with a "Heli-Coil" (brand name) insert. The insert would stay in the head and provide a new steel lined threaded hole with the proper 14mm threads.

"G"

Tin Falcon · May 29, 2013

in the air force we leaned about slimserts.

Everything and more you want to know about them .

http://www.electronicfasteners.com/pdfs/linecard_rosan_slimsert_inserts.pdf

Tin

Philipintexas · Jul 20, 2013

Also, don't remove the plugs from a hot engine.

Philjoe5 · Jul 20, 2013

Or an engine that's running :hDe:

Phil

robcas631 · Jul 20, 2013

Tin those inserts work!

robcas631 · Jul 20, 2013

Colin,

I'd try a threaded steel insert.

gartof · Jul 20, 2013

On aircraft engines we take the plugs out hot every year or 50 hours very rarely is there a problem. When they go back in we use a grafite based antisize sold by Champion and torqued with a calibrated tool. I think the special spark plug antisize is the key.
Gary

wakeup · Jul 21, 2013

My dear old Dad was an engine fitter in the RAF during the war. He suggested a really soft pencil, something like a 2B or thereabouts, just rub the lead of the pencil up and down the thread, depositing a little bit of graphite, screw the plug in tight, slacken and nip up. It needs to be tight enough to seal, that's all, many plugs are overtightened. This process worked for me for 50 odd years in alloy heads.

Don't use any wet lubricant, grease or oil etc.

cheers
Bill

gus · Jul 21, 2013

Tin Falcon said:
in the air force we leaned about slimserts.

Everything and more you want to know about them .

http://www.electronicfasteners.com/pdfs/linecard_rosan_slimsert_inserts.pdf

Tin

Thanks and I did not know this inserts exist.

When installing spark plugs into motorcycle engines ,do take care to ensure
plug is well position and aligned before screwing in to avoid stripping threads.
A friend of mind was stranded in the middle of no-where in the Malaysian Jungle with his bike kaput.Lucky for him a truck passed by before it go too dark.A night in the jungle is very frightening with wild boars and predators after them.Did my jungle training in survival school. Was told to finish all food and bury used food cans deep to avoid attracting wild pigs.

Wizard69 · Jul 24, 2013

Niceonetidy said:
Hello,

How do you Engineers fit spark plugs in Aluminum cylinder heads? Do you thread the head and fit the plug, or fit a bronze insert in the head to make it more reliable and a better life?

Thanks in Advance for any replies,

Colin

We use these at work extensively: http://www.timesert.com/. It is a slightly more tedious installation than Heli-Coils but they are also more reliable in my estimation. In fact I've grown to hate Heli-Coils. If you look through Timeserts catalogs you will find a number of special purpose inserts, including 1/4-32 glow plug inserts.

As for your engine I'd drill and tap a naked thread and worry about thread inserts later. The problem is you will spend a lot of money for the kit even though your threads will likely hold up for years. By the time you will need new threads the engine will likely need a rebuild already. Honestly I'd be more worried about the head bolts and other highly stressed threads.

wings_of_fire · Jul 25, 2013

Niceonetidy said:
Hello,

How do you Engineers fit spark plugs in Aluminum cylinder heads? Do you thread the head and fit the plug, or fit a bronze insert in the head to make it more reliable and a better life?

Colin

Apart from the suggestions others have given, I would like to point out that you also need to use a thin copper washer between the spark plug seat and the aluminum head. Copper is pretty ductile and it creates a good air tight seal under squeezing pressure created by torqued spark plug and aluminum head.

Niceonetidy · Jul 26, 2013

Hi,

Thank you everyone that has contributed. Some good stuff here. I like the thin inserts. And, npt too keen on Helicolis.

Regards

Colin

Walltoddj · Jan 2, 2014

Niceonetidy said:
Hi,

Thank you everyone that has contributed. Some good stuff here. I like the thin inserts. And, npt too keen on Helicolis.

Regards

Colin

Reading the different post I thought I'd put in my two cents. When racing go-karts back in the 70's the first thing we did was insert a Heli-coil insert due to the threads striping out from high compression and a 3/4" length. In 93 I moved to GM Powertrian in Buffalo, NY and all the aluminum heads they used a forming tap, they told me that the form thread is stronger because the aluminum is compressed not cut. I have almost all the different sizes steel inserts, heavy steel inserts, Heil-coil(Recoil), and aluminum I find if done properly all have their advantages but I tend to use the wire inserts the most.

Walltoddj · Jan 3, 2014

Just a point of interest I found CM6 or 5812 plugs at AutoZone today $2.99 each 10mm compact size for Lee's Radials. I bought what they had in stock in my store.

Goldflash · Jan 3, 2014

When I was a young airman I bought a BSA Bantam for about $50 and just used it for riding around base. the spark plug thread in the head was a bit stripped. Used to wrap a bit of aluminium foil around the threads on the plug and screw it in. was good for about 10 miles then it would blow out with a bit of a bang. Didn't keep it long before I gave it away so it became someone else's problem.

Spark Plug threads in Aluminium heads

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