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Old 01-13-2019, 12:06 PM
JBHansen JBHansen is offline
Join Date: Jan 2015
Location: Simi Valley
Posts: 28
Default Spark Plug Threads

I need to chase the threads for one plug. How do I keep the shards out of the cylinder?
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Old 01-13-2019, 12:40 PM
Mike S's Avatar
Mike S Mike S is online now
Senior Curmudgeon
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 14,730

Dual plug engine?

Take an old plug, break out the insulator, glue/solder/weld in a coupling for an air line.

Blow air into one plug hole while chasing the other plug hole. Valves should be closed.

This is guaranteed to get crud in your eye------wear goggles.
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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Old 01-13-2019, 02:51 PM
gnuse's Avatar
gnuse gnuse is offline
Join Date: Jan 2005
Location: Georgia / 0GE5 / KSSI
Posts: 379

Grease on the tap is an easy way.

"God does not deduct from one's time on earth that which is spent in the air."
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Old 01-13-2019, 05:52 PM
rongawer rongawer is offline
Join Date: Dec 2007
Location: Brentwood, CA
Posts: 447

I second the use of bearing grease on the tap, but if you have BoeLube, that works even better. I would combine that with the idea of blowing air into the other plug hole as Mike said. If you don't feel like welding, I'd recommend using a compression tester and plug low pressure air onto the fitting.

Knowing that you'll be looking down the hole while crud is coming out, I would not use more than 30 psi, and I second the use of safety glasses plus a face shield.
Ron Gawer

- RV10, Build in progress.
- RV12, N975G, "The Commuter"
- Several others that are now just great memories for me.
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Old 01-13-2019, 06:02 PM
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DaleB DaleB is offline
Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 2,049

Slickest solution I found -- search Amazon for "back tap". You put a coat of grease on the threads, slide it INSIDE the head, expand the tap to engage the inner threads, then back it out. Do that a couple of times. It will chase the threads from the inside out. All the chips end up outside the head, AND you don't have to worry about starting the tap crooked. I bought the 12mm size to correct a slightly buggered up plug hole on my Rotax, and it works great. Well worth every penny I spent on it.

And no compressed air required.

Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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Old 01-14-2019, 10:16 AM
JBHansen JBHansen is offline
Join Date: Jan 2015
Location: Simi Valley
Posts: 28

thanks for the info
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