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Spark Plug Insertion Issue

WingedFrog

WingedFrog

Well Known Member
I changed all Spark Plugs during my annual. Seven out of eight spark plugs went in easily but one wont go. It seems to grab the thread but after about one turn it gets hard and wont turn by hand. I tried to turn it 1/4 to 1/2 turn with the wrench, hoping the resistance would subside but no luck. I got advice to use a tool called M12-1.25 Spark Plug Chaser which delivery I am waiting for now (M12 is not a common size you can find in auto parts stores). The Spark Chaser is not a Tap, it has a tapered thread that will grab the existing thread and should restore the part that is obstructing the path of the plug. I had like to know if anyone had such problem and/or advice on how to proceed with the Spark Plug Chaser. The Spark Plug I retrieved is showing a thread that is intact, i.e., no cross thread sign so I suspect the damage/obstruction is limited to the first threads in the cylinder head's hole. Luckily the hole in question is looking downward which will prevent any debris to fall into the cylinder.
 
Will any of the plugs thread in? How about the one you took out? I would be reluctant to chase threads this soon without more info..
 
Having replaced thousands of plugs in aluminum, I NEVER use thread chasers, they have sharp edges on the outside of the threads.

I do chase the threads though. I take a spark plug and cut relieve grooves in the side with a dremel cutting disc, at least four of them, with a radial cut on the leading side and a shallow angle on the passing side. Then take the cur plug and buff with a wire wheel on the bench grinder to ensure no sharp edges. Then use this plug as the "chaser"

Just thread in and work back and forth. It removes the carbon and does not yield aluminum in the process. Remove often to clear the grooves.

YMMV. Good Luck.

Only do this if the offending plug bore and plug showed a lot of carbon relative to the others. It could be a cross thread, so be very careful to assess that the plug is going in straight. I always thread the plugs in by hand. i.e. no pull handle. You can slip some fuel hose over the end to help with odd angles and difficult to reach situations.
 
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Do you have access to a bore scope to check the threads?

Are you using the thermal paste as a lubricant? I use a graphite paste from the auto store that seems to work well as both a thermal conductor and anti-seize lubricant. All my plugs go in finger tight right up to the point where they need to receive final torque. I also use a q-tip with alcohol to clean the threads every time I pull plugs. If you use the graphite paste make sure to keep it off the two threads closest to the electrode to avoid any chance of shorting them.
 
An old toothbrush with a bit of grease on it can be used to clean the threads of any loose debris. Follow this up with some solvent on the brush and then the appropriate thermal paste.

ps -- Make sure you don't borrow your wife's toothbrush for this. Somehow they always find out.
 
You are not supposed to get the thermal paste near the first several threads that go into the hole.
 
You did the right thing by not forcing it and making matters worse.

A spark plug thread chaser doesn't have sharp edges like a regular tap, they are more rounded. They tend to reshape the threads and not cut new ones like a standard tap. I have 6 of them for varying plug sizes. I have used this chaser many times. It could be dirt, corrosion, but more likely some carbon. Maybe starting a plug you may have dinged a thread? Put a drop of oil on the chaser or a tiny smear of the silicone thermal paste and I'm sure it will screw down into the threads and clean them up. Take a clean rag and wipe the threads out. Once done my bet is you won't have to do it again.
 
An update

This is an update for you fellows that might face my predicament one day. I thought with confidence that my spark plug was able to grab the first two threads before blocking. In these conditions it is tempting to force it further with a wrench. Roger Lee's advice saved me for doing that, thanks Roger. It's not that I was wrong but this morning I used the thread chaser and lo and behold, it worked. after a few wrench turns the resistance decreased and I was able to screw the tool by hand. After removing it I found this: this tool has three longitudinal groves which purpose is to collect the junk it is pushing out of the thread. Indeed there were metallic parts that looked like steel wool in the grove. Not a lot but if I had used the spark plug instead of the tool, this junk could have damaged more threads and eventually finished in the cylinder.
Now my spark plug screws in by hand, I'm safe!
 
Good deal. Glad you were able to get it cleaned up without damage. Thanks for posting the update.
 
I find them sometimes troublesome to get started threading in, but taking time and not forcing (hand start only, no wrenches) is the key to success. I also always have a fresh coat of anti-seize on the threads which serves as a thread lubricant.
Dick Seiders
 
Anti seize is not supposed to be used on Rotax plugs (service bulletin) and no lube is to be used on the 2 strokes. Those plugs are a cold dry torque.

Anti seize is an old school hold over from the Cont / Lycoming early days. You are supposed to only use the thermal conducting paste that Rotax suggest. There is more than one MFG that makes it. Anti seize has no thermal properties and only lubes the threads. The silicone based thermal paste recommended by Rotax does two things. One it does lube the threads, but more importantly it is a thermal conductor and is used in the electrical industry just for that. It's more a heat sync. It helps make the heat between the head and plug more even. It actually helps the plug more by removing as much as 40+F from the plug. What does this do? It helps keep detonation at bay. Many of my friends at my airport with Cont. & Lycoming's have switched to the thermal paste. It does the same thing as anti seize only better. It takes old school thinking into the 21st. century.
 
Roger,

I'm familiar with the argument for thermal paste, but I don't agree with all of it. The thermal paste applied at the factory did not evenly cover the threads, so the heat transfer was only I partially enhanced. I evenly coat my threads with a graphite based anti seize paste that fills the microscopic gaps between threads for the entire circumference.

All my plugs have a light tan patina when I pull them at annual, and the engine runs great. Seems to work for me. Is there something else I should be looking for?

Rich
 
Hi Rich,

It shouldn't change the color of your plugs. That's a direct result of the burn at the tip. The paste doesn't need to cover every microscopic part of the plug to transfer and sync the temps. If the paste is not perfectly applied to every part of the plug it gets spread as it is threaded into the plug socket. Anti seize will not transfer or help sync the temps and it won't help if the engine were to get close to a detonation scenario which will happen so quick you probably won't be able to correct for it.

Anti seize isn't going to make it run bad it just has no benefit for the intended purpose and spec Rotax ask for.

If someone didn't do a good job in applying the paste it can always be corrected.

Rotax still doesn't want anti seize used.
 
not aware of the thermal paste issue. Will research my Rotax manual. If it calls for it I will likely use it. I have not had any problems with the anti-seize method thus far. I do however replace plugs with new at each annual Cond. Inspection. It's a great forum as I am always learning something new.
Dick Seiders
 
Roger,

You have piqued my interest. I am going to check the anti seize label and see what, if any thermal conduction benefit it may add. In a past life we used neolube which is graphite powder suspended in alcohol. The stuff I use has a grease-like suspension.

Rich
 
Hi Rich,

You will find in some publications that anti seize has some thermal properties. The issue is that the silicone based thermal paste made just for heat transfer and nothing else is head and shoulders above what little thermal conductivity that anti seize has. Like I said the anti seize won't hurt anything, but it isn't doing what Rotax has intended for a spark plug paste.
 
I ordered some from Lockwood:

(here's the link)

The Rotax Material List calls for Wacker P12 - says no substitutes allowed: (link)...hard to find

But here's the front and back of the $3.49 heat sink paste from my local radio shack:

33usyrp.jpg


11vp20g.jpg
 
Here is a good substitute. I have been using it for over ten years. The Rotax thermal paste is a European brand and is quite expensive at around $160. This amount would last the average owner 2 life times. This brand is what other people use to.

http://www.amazon.com/MG-Chemicals-Silicone-Transfer-Compound/dp/B005DNQWQU


This is like the gearbox sealer Loctite 5910 that Rotax recommends (European market name), but the US equivalent id Loctite 598.




Some batteries from Europe are Hawker brand in some aircraft from Europe. The same company and identical twin is the Odyssey battery name in the US.
 
Thanks Roger. Just ordered some thermal paste. Are there any other common equivalents to the gold-plated Rotax specified consumables or service items?
 
A number of the Rotax consumables are from the European market. Rotax says (except for a few products) that you can use any product that is equivalent to their recommendation. Several items that can be found here in the US is the Loctite equivalents to the European ones.
 
read the 173 page manual and found the thermal anti-seize requirement. Rec'd a couple tubes from Lockwood today. Thanks for the tip.
Dick Seiders
 
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