Spark Plug Heat Paste for Rotax engines

[WestCoast]

What heat paste is everybody using on their spark plugs? I have been told that Rotax only approve the use of Wacker P12 however it is hard to come by and I believe there is only one supplier in Australia who charge AUD$157.85 for a 90 ML tube.

 

I have in the past bought the plugs from this supplier and they charge AUD$1.50 to apply paste to each plug, however I recently bought a bunch of plugs from the USA at a great price, so would like to paste them myself.

 

Dave

 

 

[Guest ozzie]

I used champion anti sieze paste on GA engines it can be found at most aviation suppliers and has been seen in repco stores. use SPARINGLY. just a dab as if it finds it's way onto the electrodes it will short the plug out.

 

 

[airangel]

I understand there is available from electronic outlets a paste that is used as a heat transfer medium for heat sinks I have yet to chase it up, but on the face of it may be OK

 

 

[Yenn]

Airangel. That paste may not be suitable as it may not be electriclay conductive and also would not be designed for the high Cylinder Head temps. Some of those pastes are also carcinogenic.

 

I use never sieze, available from engineering supply stores.

 

 

[airangel]

Maybe....Need to do more research, However I am not sure an anti-seize is necessarily a heat sink paste which is what Rotax call for....More research needed

 

 

[vk3auu]

Why do you think you need an anti seize paste anyway. A correctly torqued plug should not come out.

 

David

 

 

[Yenn]

vk3auu.

 

That is the problem. It won't come out.

 

I very much doubt that there is any need for a paste to connect the plug to the head for temperature transfer, but it is a good means of preventing damage to the aluminium threads in the head to use an anti seizing compound.

 

 

[Guest jsg]

We use Unick (silicone heat transfer compound) comes in a tiny 10gm tube, got it from a electronics shop (Jaycar) does not seems to dry or cook, goes a long way for such a little tube, probably done 24 plugs. Prior to that we use the antiseize as was concerned about possible plug grab of the cylinder threads!

 

 

[vk3auu]

I see where you are coming from. Must have been having a "Seniors" moment. The most important thing to stop threads seizing or otherwise damaged, is not to overtorque the plugs.

 

I have an old Honda 6.5 HP motor with virtually no thread left in the head. I need to put a helicoil in it. It used to fire the plugs out after a while. I lent it to the builders to run a 240 volt alternator to run their docking saw while they were building my house and came in one day to find a couple of slivers of wood driven in beside the plug to keep it in. Not the sort of thing you would need in an aeroplane.

 

David

 

 

[airangel]

Thks jsg, You have helped by confirming its ok, That is what Rotax specify, A silicon hear transfer paste

 

 

[WestCoast]

Thanks all for the feedback on this subject. I have ordered some Unick silicone heat transfer compound from Jaycar and will see how it goes.

 

Dave

 

 

[Methusala]

I'm not an engineer or scientist but on first principles it elludes me as to why a heat conductive medium should be required between mating surfaces of steel and alloy.If I touch a hot surface i feel the heat more or less instantly. Water does not boil any faster in a pot treated with an intermediate substance. I do, however, use anti-seize compound to prevent inter-granular binding between 2 dissimilar metals. I hope this provokes further dicussion on this worthy topic. I think that silicone based heat transfer paste is used in electronics to promote heat flow from a device to a heat sink across what would normally be an air gap. Kind regards, Don.

 

 

[Guest Nelson Smith]

I agree with you don,what is all this yap about heat sink compounds on spark plugs.Are you trying to soak heat from the plugs to the heads or from the heads to the plugs?The paste that should be used on the plugs (sparingly) is to minimize pickup of the aluminium

 

threads by the plugs when screwing the plugs out.It should be an anti sieze compound.

 

Jabiru specify Nickel Sieze.

 

 

[WestCoast]

I agree with you don,what is all this yap about heat sink compounds on spark plugs.Are you trying to soak heat from the plugs to the heads or from the heads to the plugs?The paste that should be used on the plugs (sparingly) is to minimize pickup of the aluminiumthreads by the plugs when screwing the plugs out.It should be an anti sieze compound.

Jabiru specify Nickel Sieze.

Nelson...I started this thread (Spark Plug Heat Paste for Rotax engines ) as Rotax are very specific on the subject and I was interested to learn what others were using. Below is some documentation from Rotax and you will see what I mean:-

 

 

 

[Guest Nelson Smith]

Yes Westcoast I see what you mean.

 

Thanks

 

Nelson

 

 

[Methusala]

I apologise to any who may have taken offense when I entered this thread. I am also, I add, not a Rotax engine specialist and have, as I had hoped , gained more info on the subject. Kind regards, Don.

 

 

[WestCoast]

Don....no offense taken, in fact quite the contrary as I greatly appreciate all of the discussion on this subject. There are quite a few things about the Rotax where I can't quite see their logic and even though my engine has less than 150 hours on it, it is now out of warranty so if there is another product that will equally do the job, then I am prepared to investigate it.

 

Thanks again to all that have contributed to the discussion.

 

Dave

 

 

[allowera]

Anyone tried Wurth CU800?

 

I know it's good stuff on the spring loaded exhaust ball joints.

 

It is a copper paste in an aerosol with a good capillary and adhesion

 

medium, originally formulated for Disc Brake Pad backing plates.

 

Using a fine 'straw' applicator I have had great results in automotive

 

applications wherever extreme heat or pressure is encounted.

 

Any thoughts?

 

 

[Guest ozzie]

Hi all, i have been looking at the replies to this thread and seeing how there are are lot of different opinions on this, i sent an email off to Roy at Ultraflight Radio and asked him to run it past the resident rotax guru. Great question was the reply so good that they are going to disscus it on this weeks show if you can't stay up in the wee hours tonite and listen i will post the mp3 link here when it is available in the next few days.

 

www.ultraflightradio.com

 

ozzie

 

 

[Guest ozzie]

OK here is the segment from Ultraflight Radio were they have a quick explaination on the spark plug paste. it is 22 minutes long but it is the last two minutes that covers this. basically it is both a heat transfer paste AND an anti sieze compound.

 

Is there a cheaper alternative that is equal to the expensive Rotax product. Yes but you will have to download the segmant to find out. Maybe Ian can import it for the shop.

 

 

regards

 

Ozzie

 

 

[WestCoast]

Ozzie....thanks for providing the link to that U.R. Podcast. Interesting that there is a cheaper alternative as I always thought that the price of the Whacker P12 paste was a bit O.T.T.

 

Would be great if Ian could import it for the shop but for anyone that wants to investigate what was recommended, here is the link: http://www.rotaxparts.net/scripts/prodView.asp?idproduct=245

 

Regards

 

Dave

 

 

[Admin]

Dave

 

I will look into it in a few weeks - thanks!

 

 

[facthunter]

Heat transfer.

 

The best way to cause a correct plug to overheat is to not tighten it to the specified torque.Ie. (leave it loose) The PRIME purpose of putting anti-seize paste on plug threads is to prevent aluminium bonding to the threads (near the tip) and wiping out the thread as the plug is unscrewed. A helicoil is the cure, but prevention is better. Since the heat travels down the insulator into the plug body then to the cylinder head proper mainly through the sealing washer area, and not through the much smaller cross sectional area to the threaded section, I cannot see that a paste, designed to increase conductivity would achieve very much. A little thought to what is actually taking place here would have to consider that due to the plug being tightened up, the top part of each thread would be in actual contact with the head metal anyhow, thus ensuring an adequate ( and predictable ) heat flow path. If this is all so critical, then a slightly worn thread in the head would cause a major change to the situation, and I have never observed this. Nev...

 

 

[airangel]

Nev, West coast started this , and it is important to remember that the thread refers to a hear paste recommended by rotax for their engines. Maybe it it is because they have water cooled heads that their specified heat paste can or is able to draw more heat away from the plugs than may be able to occur on an air cooled engine.

 

I dont think the original query by west coast related to a anti seize as has been the subject of many statements and that in itself is another topic.

 

 

[facthunter]

Function.

 

An anti-seize capability would have to be part of the original specification, or there would be a potential problem there. ALL alloy heads recommend it. I would not use a LAME or L2 who did not use an anti-seize on spark plugs. The silicone based paste used on some electronic applications (heat sinks) would not be appropriate in my opinion. Nev...