Spark Plugs
Club Member
Joined: Aug 2008
Posts: 22,855
Likes: 17,906
From: Lafayette, Louisiana
My carbureted Evo runs slightly smoother with AutoLite spark plugs, but that is probably my imagination.
You have to be careful in twin cams and are better off using OEM plugs due to ion sensing.
M8 uses an automotive style knock sensor instead. Given the nightmares experienced by a small but measurable portion of M8 owners, I would be hesitant about using anything other than OEM unless you have extensive modifications anyway.
You have to be careful in twin cams and are better off using OEM plugs due to ion sensing.
M8 uses an automotive style knock sensor instead. Given the nightmares experienced by a small but measurable portion of M8 owners, I would be hesitant about using anything other than OEM unless you have extensive modifications anyway.
Road Master
Joined: Aug 2011
Posts: 1,195
Likes: 299
From: midwest
Fuel injection metering is much better than the old system - just look at your own car these days. When’s the last time plugs were replaced before the 100K mark? I’ve pulled many with mileage over that and found the plugs were like new, though admittedly they were either platinum or iridium.
Bottom line, with fuel injection I’ll replace the stockers with plat. or irid., whichever HD offers. There’s more than 30K on mine and the stock plugs still look fine.
Bottom line, with fuel injection I’ll replace the stockers with plat. or irid., whichever HD offers. There’s more than 30K on mine and the stock plugs still look fine.
Stellar HDF Member
Joined: May 2007
Posts: 3,256
Likes: 522
From: USA
IMO nothing wrong with changing plugs every 5000 miles as the OP does.
Inexpensive, retains best spark, plus one can index the plugs...HD can be a hobby.
Copper core plugs flow electricity very well (do a science search)
If changing plugs frequently, why use exotic metals as those metal do not increase electricity flow, yet do slow down metal degradation?
FWIW Under magnification look at the electrode tip (0K vs 5k vs 10K vs 20K mileage) for its retained sharp edge.
The ground electrode usually wears pretty good yet look at the surface facing the electrode tip for pitting and
again to that electrode retaining its sharp edges.
Plug reading for performance tuning is an art. One reads down the porcelain after doing "throttle chops" at different RPMs. One also reads the electrode tip. Too much art to describe, really helpful to learn this with a two stroke motor, but the ball park read is a darkened tan color over the tip and porcelain. For a street Harley I'll leave this step is open to other co-members.
Using copper OEM spec plugs and indexed is my top tip and so easy to plug & play
.
Have fun.
Inexpensive, retains best spark, plus one can index the plugs...HD can be a hobby.
Copper core plugs flow electricity very well (do a science search)
If changing plugs frequently, why use exotic metals as those metal do not increase electricity flow, yet do slow down metal degradation?
FWIW Under magnification look at the electrode tip (0K vs 5k vs 10K vs 20K mileage) for its retained sharp edge.
The ground electrode usually wears pretty good yet look at the surface facing the electrode tip for pitting and
again to that electrode retaining its sharp edges.
Plug reading for performance tuning is an art. One reads down the porcelain after doing "throttle chops" at different RPMs. One also reads the electrode tip. Too much art to describe, really helpful to learn this with a two stroke motor, but the ball park read is a darkened tan color over the tip and porcelain. For a street Harley I'll leave this step is open to other co-members.
Using copper OEM spec plugs and indexed is my top tip and so easy to plug & play
.Have fun.
Seasoned HDF Member
Joined: Aug 2013
Posts: 35,795
Likes: 38,537
From: Post Falls, ID
Are there any issues with electrolysis of the steel spark plug threads with the aluminum cylinder heads and long change intervals?
Would anti-seize on the threads ensure a clean plug removal at 100,000 miles?
Would anti-seize on the threads ensure a clean plug removal at 100,000 miles?
Stellar HDF Member
Joined: May 2007
Posts: 3,256
Likes: 522
From: USA
Post 16 electrolysis.
This is a known issue in many vehicles.
Yes, I always use a little anti seize...sparingly apply to the plug threads making sure none of the product gets to the combustion chamber or plug electrodes.
Anti seize does not ensure a clean removal at 100K.
If the plug extends into the chamber, carbon can build up on the threads causing major removal issues.
Salt air rusting the metal case and degrading its bond to the porcelain can separate the plug into multiple pieces.
Time can be an issue (the electrolysis action).
For motor cars, it can be advisable to remove and inspect plugs every 5 years no matter the mileage.
HDs are too easy to wait so long.
Just take care to not to over torque your plugs....I like 11 ft lbs.
Did I mention indexing as a winner for this HD hobby?
This is a known issue in many vehicles.
Yes, I always use a little anti seize...sparingly apply to the plug threads making sure none of the product gets to the combustion chamber or plug electrodes.
Anti seize does not ensure a clean removal at 100K.
If the plug extends into the chamber, carbon can build up on the threads causing major removal issues.
Salt air rusting the metal case and degrading its bond to the porcelain can separate the plug into multiple pieces.
Time can be an issue (the electrolysis action).
For motor cars, it can be advisable to remove and inspect plugs every 5 years no matter the mileage.
HDs are too easy to wait so long.
Just take care to not to over torque your plugs....I like 11 ft lbs.
Did I mention indexing as a winner for this HD hobby?
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HDF Community Team
Joined: Mar 2017
Posts: 7,857
Likes: 4,417
From: Texas
The top (or right side) spark plug wire boot is a PITA (or near impossible) to remove without a boot remover tool. I use one of these:
