SonexBuilders.net

Maybe this has been discussed .. i couldn't find it.
I had the threads strip in one spark plug hole. I've previously had to clean them up with a
thread chaser. My manual (2012) says to torque plugs to 22 ft lbs. That's what I did
early on .. even though I thought it too much. Later on I noticed Sonex changed the
torque spec to 12 ft lbs so I started using that. When did this happen? Why wouldn't a service bulletin be
issued?
Any one else have issues with this? I feel the threads were weakened early on by the
excessive torque.

RT

Common problem: http://sonexbuilders.net/viewtopic.php?f=7&t=3948

I was not aware the torque spec had been changed, but I looked now and you are indeed correct. 12 seems like a much more reasonable value. Edit: Looking at what I wrote in that thread, apparently I'm misremembering...

The NGK ER9EH spark plugs we're using now have a spec that says "Torque Specs: Aluminum: 5.8-7.2 lb. ft."

So even 12 is ~twice as high as they say.

Does the manual suggest using "spark plug anti-seize and thread lubricant compound" on the threads of the spark plugs? We use this on our certified airplane engine's spark plugs. Lightly coat the threads of the plugs with this prior to installing on the engine. See: http://www.aircraftspruce.com/menus/ep/ ... seize.html

I use anti-seize, then tighten until well seated. I broke a spark plug off in the hole early on trying to torque to the high specs. I don't bother with torquing the spark plugs, honestly. Just seat them and give them a little more twist to make sure the crush washer has crushed and the spark plug is well seated. Even so, I eventually stripped a spark plug hole when removing a plug during an annual. So I put Time-Serts into all 8 holes after that. No more aluminum threads. I have the tool for the Time-Serts available for loan from the Sonex Foundation web site:
http://www.sonexfoundation.com/Tool_Loan_Program.php

mike.smith wrote:I use anti-seize, then tighten until well seated. I broke a spark plug off in the hole early on trying to torque to the high specs. I don't bother with torquing the spark plugs, honestly. Just seat them and give them a little more twist to make sure the crush washer has crushed and the spark plug is well seated.

Good post! Many used to iron heads will torque to a high setting but with aluminum I've learned that all of that isn't necessary. On the Corvair I use anti seize (iridium plugs) and torque to 100 inch lbs (8.3 foot lbs). No issues with stripping a plug or any coming loose. Sometimes after a short engine run I will recheck the plug torque.

Mike is correct that you can feel the crush/sealing washer when it stops seating. If I don't have a torque wrench available (I usually always do) I can set the torque with a "stubby" ratchet by feel and be pretty close.

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

lutorm wrote:Common problem: http://sonexbuilders.net/viewtopic.php?f=7&t=3948

The NGK ER9EH spark plugs we're using now have a spec that says "Torque Specs: Aluminum: 5.8-7.2 lb. ft."

I've continued to use the 4163 plug. How does the ER9EH work?

RT

Thanks for the input. I've thought I've been careful putting them in. I use anti-seaze and replace them yearly at
annual. I emailed Sonex support .. but their reply was basically they think 22 ft lbs is valid and they're not
responsible for how plugs are installed. I have a repair kit ordered. It's not the Time Sert .. hopefully that works
or I'll be buying a new head.

RT

I would recommend that you exercise caution in attempting to repairing the spark plug threads with anything other than the time-serts. This is not an area where you want to take risks. People have reported problems with helicoils and their spark plugs. Another tried some other repair and his engine spit out the spark plug in flight.

There is a time-sert tool in circulation with the members here that you can use or you can bring your heads to a machine shop to have it done.

Jake

lutorm wrote:Common problem: http://sonexbuilders.net/viewtopic.php?f=7&t=3948

I was not aware the torque spec had been changed, but I looked now and you are indeed correct. 12 seems like a much more reasonable value. Edit: Looking at what I wrote in that thread, apparently I'm misremembering...

The NGK ER9EH spark plugs we're using now have a spec that says "Torque Specs: Aluminum: 5.8-7.2 lb. ft."

So even 12 is ~twice as high as they say.

*******************

The NGK ER9EH is an 8 mm plug though as opposed to the 12 mm Autolite 4163?

Terry
Sonex #1508
N296SX
AeroVee #0736
Tail Dragger
http://www.mykitlog.com/SNX1508

I've been using NGK dr8ea