spark plug compression leak
 

what would you guys suggest to seal up the spark plug i am getting a little leak through the threads. masters metallic comes to my mind but 2 probs 1 getting some in the jug and 2 that stuff is the pits to get a thread apart later. any other suggestions???

RE: spark plug compression leak
 

What kind of engine do you have and what kind of plug are you using.Did you buy it used?Are you using a 5/8 peanut plug with a taper seat in a standard plug with a flat gasket.If its the flat gasket type is the plug gasket even there?
Are you sure the plug isnt cracked?

RE: spark plug compression leak
 

I am using a zenoah glo plug adapter on a poulin pro model 114 engine. yes the engine is old but it ran as a gas engine. I am trying to convert it to gas glow. There is no gasket on the adapter itself, it never came with one. should there be?

RE: spark plug compression leak
 

If your threads are shot you would probably not be able to tighten it completely. Does the plug seem to tighten to a point where significant resistance is felt. If it does you may have conditions as described by AAis4ne. If your threads are shot the proper way to repair it would be with a helicoil kit.

Bill

RE: spark plug compression leak
 

k thanks for the replies. i'll take another look in the morn and see where im at. i thought i had it good and tight but tonight when i tried to turn it over slowly by hand without glow plug lighter on it! i noticed a slight bubbling for the thread so i figured it wasnt starting for me due to the loss of compression so i was thinking of using thread sealant to rid the prob and try again. but im not so sure that sealant is a good idea. also im trying to build this on the cheap. and the other problem is the closest rc store to me is in london an hr away...arrgg

RE: spark plug compression leak
 

does the adapter have a flat face where it meets the engine or is it tapered? if it isn't tapered, pull a gasket off of a spark plug and put it on your adapter, or make a washer out of thin aluminum or copper sheet metal and use that, should seal it up

RE: spark plug compression leak
 

The Zenoah glow plug adapter has a taper for a taper seat; no gasket. His engine probably had a gasketed spark plug.

You can try adding a gasket. Another way would be to machine a short taper in your head to match the taper of the glow plug adapter. I don't recommend any sealer...

AV8TOR

RE: spark plug compression leak
 

Try wraping the adapter threads with teflon pipe tape...then thread it in just like a pipe plug. I have read some guys use same tape on Saito exhaust threads??? Capt,n

RE: spark plug compression leak
 

the teflon pipe tape works great. I have used it several times. Plug comes out easily.

RE: spark plug compression leak
 

No sealers are recommended on spark plug threads as it can inhibit heat transfer from the plug into the head with it's cooling fins.

If possible, machine a taper in the head to match the taper on the sealing surface of the glow plug adapter. The taper wouldn't have to be very deep.

AV8TOR

RE: spark plug compression leak
 

This was for a person who does not have a way to machine a taper. Just use the real narrow tape and do just the first portion of threads so the upper part is still contacting metal to metal. This is just for this one engine...kinda a experiment "if you will" There is good product called Anti-seize that is good for the threads of spark plugs. Capt,n

RE: spark plug compression leak
 

ill give te tape a try to see how it works. im affraid of the taper idea cause if ya muck up its all done. all i have for a dril is a hand held I havent got a drill press...maybe for my bday :D

RE: spark plug compression leak
 

I would hope that not too many modelers subscribe to this practice of plumbing tape thread and, seat repairs. Reminds me of auto exhaust repairs with muffler patch,and bailing wire.

Take a look at this NGK tutorial. You really should get/make a flat seat style adapter, or have a Buddy add the taper to the seat as was suggested.

Partial NGK quote:
"The spark plug works as a heat exchanger
by pulling unwanted thermal energy away from the combustion chamber, and transferring the heat to the engine's cooling system.

http://www.ngksparkplugs.com/techinf...000&country=US

RE: spark plug compression leak
 

I had the same problem, but what I did was to take the gasket from an old spark plug and put it to the adapter, it worked great.
Good Luck and Happy New year to all of you converts.
Bill Pomplun.

RE: spark plug compression leak
 

IF you noticed it is actually the ceramic insulator around the center electrode that does the heat transfer to the combustion chamber which is surrounded by "wet" coolant -or more technically-the heat range of the plug-also 2 strokes in small engine applications - AIR COOLED - do not use coolant jacket style heads-only air around the cooling fins of the head and cylinder -which is true of the statement from NGK-2 different cooling systems-"wet" and "dry"
Further discusion here
http://www.liquidcooledairpower.com/lc-ridofheat.shtml

RE: spark plug compression leak
 

The heat extraction from the plug does not care if a water jacket is present.The finned thermal mass takes care of that process of heat transfer just fine in the "little" motors.The 911 Porsche
did not seem to mind the lack of water either.

The body does conduct the heat into the head,just as NGK says it does.
The heat conduction path is through the nose and into the metallic plug body.
The heat range is determined by the length of that path.

Adding "plumbing tape" insulation to that path,just adds another tuning variable.

RE: spark plug compression leak
 

OK then use Copper anti sieze - there ya go[>:]
never stated about plumbing tape-just heat absoption and disipation-liquid cooled versus air cooled - i agree with ya - not against you

RE: spark plug compression leak
 

AV8TOR...where did you read sealers are not recommended on spark plug threads? Capt,n P.S. Happy New Year!

RE: spark plug compression leak
 

Hell I don't remember Captain. It is something I learned many years ago building high performance engines.

It is common knowledge among race engine builders that you don't want anything impeding the heat flow from the spark plug to the surrounding cooling surfaces, whether they are air cooled or liquid cooled. It can really mess up your heat range selection of spark plug, and in extreme cases can cause engine failure because the spark plug can't cool itself and overheats. Usually before it fails completely it starts acting like a glow plug and causes preignition and engine failure.

When we set the spark plug depth, and look to ensure that no threads are exposed into the combustion chamber either of the plug or the threads in the head, we are advised by the spark plug companies not to even use two gaskets if we need to space the spark plug out a bit. The proper procedure is to use a special solid gasket that is thick enough to provide the clearance you need, and this is something that Champion and other companies offer for that purpose. Even the practice of using two regular spark plug gaskets if needed to obtain proper thread depth is not recommended, as it can also impede heat flow.

AV8TOR

RE: spark plug compression leak
 

AV8TOR, You know...I did read about that using a extra gasket is bad like you say. I guess it exposes the internal threads that have sharp edges. What can happen a edge can glow and cause pre-ignition in some engines that run full out, kinda like a truck going up a long hill! Well we are into the New Year now! I sure hope it is a good one?? A local club near Muskegon always get together and have hot food and open flying. I guess the temp may get near 30 degrees. Just may go if I can talk my Granson into going! Yup we fly togeher a lot. Take care, Capt,n;)

RE: spark plug compression leak
 

umm hey i was thinking about this for a bit-HE IS USING A GLOW PLUG ADAPTER!!!!!-so spark plug heat disipation and absorption is kinda null on this discussion.

RE: spark plug compression leak
 

Well, glow plugs come in heat ranges as well, and this is how the ignition timing is "set" on a glow engine. So if the glow plug and it's adapter aren't flowing heat into the head properly, the glow plug would run hotter than normal, and advance the ignition. Possibly to the point of causing problems....

AV8TOR

RE: spark plug compression leak