851SC Spark Plugs

Hi Mike~~

Again you are 100% correct about anti-sieze compound causing these sort of inaccurate over torque issues & the resulting bolt/stud breakage issues !

Cheers !

I am not suggesting to not use anti size. I don't use it on my Auburn plugs but I don't leave them in for 50 years. My negative experiance with anti size is it adversly effects the torq. readings on a fastner. The fastner has to be stretched much farther to get the torque reading you want thus risking breaking the fastner or stripping the threads. Fastners are usually torqued with oil, not antisize. Never use ARP lub. to torque non ARP fastners!! When I was building my Cord engine I used ARP lub. on the main studs and twisted the first one right off. When contacting ARP about this they said to not use it on non ARP fastners, with no warning on the lub. it was a little late. They got to sell me some studs that way and probably better to replace them any way.
CORDially Mike

Hi Mike~~~
You are indeed quite correct that a spark plug gets rid of it's heat through direct contact with the cylinder head's casting & water cooling jacket !
The combustion chamber of a cylinder head is the hottest spot in any engine.

I use two kinds of anti-sieze compound.
one type contains 80% pure aluminum powder mixed with some sort of very thick high-temp lube base~~~

The second type I have used contains 70% pure copper powder mixed with a similar thick high-temp lube base~~~

Both Aluminum & Copper are very excelent conductors of heat.

Both products say that the will easily & efficiently conduct heat because of the metal powder formulations they contain.

I have used these products on my spark plug threads for many years~~

The first antique car I had with an aluminum cylinder head had severly siezed steel spark plugs.
The car had sat in a very damp dirt floor garage for 50+ years before I bought it.
In fact despite my extreme best efforts after 50+ years of storage I stripped at least three of the six spark plug ports after using aero-kroil penetrant which i let sit for weeks & repeated heat & cool cycles in my efforts to remove them.
The aluminum cylinder head'sthreads just corroded and creeped into the ruted steel spark plug's threads.
There was no getting the three wort offenders loose.
I inserted 18mm Heli-Coil tyle Thread-inserts made of stainless steel in the stripped plug ports retained by loc-tite red high-strength # 271.
Thinking back I should have installed similar heli-coil thread inserts on the remaining three plug ports while I was already at it.

I have used aluminum anti-sieze compound ever since this siezed plug episode and the plug are now always easily removed .
I have no plug related heat issues using these two anti-sieze compound types.

If you think about it for a moment the metal paste in the spark plug threads really acts like a very efficient heat sink transfer compound similar to that is used in the electronic industry to mount transistors onto aluminum finned heat sinks.
The anti-sieze compound gives complete thermal contact on the entire threaded surface.
The metal paste gives great heat disapation for the spark plugs~~~possibly much better than dry installed plugs alone~~~~and you Never ever have to worry about a siezed spark plug again.

I now NEVER install ANY spark plugs without some sort of anti-sieze compound.
AND~~~ I never install ANY plugs in any aluminum cylinder heads without this anti-sieze compound .
All new cars come from the factory with this similar compound on all aluminum cylinder heads.
Also most new cars with aluminum heads now almost always come with Stainless Steel spark plug thread inserts factory installed~~~
Lawn Mowers, Motorcycles,also as well as autos.

This has been my long term experience with high priced anti-sieze compounds.
The Aluminum compounds costs $35. a pint.
The Copper compound costs $50. a pint.

There are other "Auto Store" anti-sieze compounds out there at very inexpensive prices ~~~BUT I suspect that they do not transfer heat as efficiently as you have already suggested .

What type & brand of anti-sieze compound have you experienced spark plug thermal overheating issues with ?

I can get you all the brand names & military specs of the two products that I always use.
They are used extensivly in the military & aerospace industry .
They are only sold at high-end professional industrial supply houses.
McMaster~Carr , W.W. Grainger etc~~~
BRAD~~~

A spark plug cools by disapating its heat into the cyl. head. Inserts and antisize impead that cooling.
CORDially Mike

Yoi might want to heat the stuck plug & insert with a propane torch to expand the insert and then use a ubber strap wrench to remove the insert !

Usee red #271 high strength loctight tread-locker as stated above.
When you re-intall your 14mm plugs use aluminum high temp anti-sieze compound to prevent the thread insert from sticking to your plugs.

Hello

you could try this:
Install the plug and insert as a unit, using Loctite, back in the head and leave it alone a night. Then try again to remove the plug. With some luck the insert remains in the head. Its important to clean and degrease the head and insert carefully before using Loctite.

Good luck.

Andreas

My apologies if this topic has been covered before. I am the relatively new owner of a ?35 Speedster. I believe the head was replaced with a reproduction item more than 20 years ago although the car has done only two thousand miles since. When removing the plugs I noticed that they were 14mm type but that the head has reducing inserts but not standard Helicoils. Unfortunately, the front inset comes out with the plug. I?d like to put in a new set of ?? reach but can?t get the insert off the front plug without damage. Did these cars originally have 18mm plugs? I assume the inserts are not a standard fitting. Is it possible to acquire another insert? Any advice gratefully accepted.