Question Do we need copper crush washers with Denso IK27 automotive plugs?

[Neal]

A friend of mine is about to change his plugs in his FX-3 and he’s being told to use copper crush washers. I don’t know anything about this and just use the two washers that come with the plug. Can someone educate me on the proper procedure to change these plugs and parts required please?

 

[Neal]

In further conversation it seems he was talking between the step down adapter and the cylinder and not between the plug and adapter.

 

[Cactus Charlie]

The washers you show in your post are solid copper washers/gaskets not crush washers. But yes, needed between adapter and cylinder not between IK27 plug and adapter.

They can be re-used if you anneal them. Hang on a wire, heat to cherry red with a torch, quench in water.

I see no reason to remove the adapters unless you need the larger hole for borescope inspection. If you use appropriate torques at assembly the plug should come out without disturbing the adapter.

 

[Neal]

One other question @Cactus Charlie - what torque are you using on the Denso plugs? I know CubCrafter's AMM says 15 ft-lbs, I believe Denso says 15-21, and I think Klaus says 20 in the Lightspeed ignition manual, but don't cite me on that. What are you using?

 

[Cactus Charlie]

Tight enough but not too tight. I don't use a torque wrench on these plugs.

Denso says - Torque Specs Cast Iron: 26-30 lb. ft. Aluminum: 15-22 lb. ft.

The adapter is neither cast iron nor aluminum. I run them in until the crush washer touches then add about another half turn. You feel the torque ramping up as the washer starts to crush. (It's a year since I pulled mine and I may have a better answer next week.)

As an aside - at one PA-28 annual my IA told me of an owner who used a torque wrench to secure prop bolts and sheared at least one. That owner had either used the wrong spec or set the torque wrench incorrectly. Had no idea what a reasonable torque would feel like so just kept pulling until the bolts sheared.

 

[Cactus Charlie]

I run them in until the crush washer touches then add about another half turn. You feel the torque ramping up as the washer starts to crush.

Much less than half turn when re-using a spark plug as the washer is already crushed.

 

[Neal]

I was wondering about that. When removing a spark plug, is it okay to re-use the washers?

 

[Neal]

I misinterpreted these washers as shown in the original post. They are for the 18mm adapter and not for the 14mm Denso IK27 plugs. The denso plugs have built in washers that are to be used.

Another interesting bit of information is the Light speed installation manual specifies the torque on the adapter (35-45 ft-lbs) but also specifies 20 ft-lbs as the torque for the Denso plugs, yet CubCrafters specifies 15 ft-lbs in the AMM.

 

[Cactus Charlie]

You are making this far too complicated. The plugs need to be screwed in tight enough that combustion gases don't leak past the threads and washer/gasket and not so tight that that the thread is stripped. There is a huge range of torques that meets both requirements.

 

[Neal]

I respectfully disagree. If there is a published torque value for something I'm going to use that. The problem with the Denso plugs is there are varying bits of information, however, all fall within the published range by denso, so pick your torque (or technique).