Spark plugs
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Road Master
Joined: Oct 2009
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From: Wisconsin
Spark plugs
I know the owners manual says to change plugs every 2 years or 30,000 miles. Is this the rule of thumb? How often do most of you change out your plugs?
Thanks Jonnierock
Thanks Jonnierock
Seasoned HDF Member
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From: State of Confusion
I changed my first set at 27K and they looked great and I could not tell a difference at all in how it ran after replacing them..FF to now and I'm at 28 K on them and it runs exactly the same as it ever has so I'm waiting until 30K per schedule..I go by mileage on plugs instead of time since I average close to 20,000 miles a year riding .. M8s are more efficient from epa requirements so they last longer than their predecessors
Last edited by mjwebb; Sep 11, 2022 at 10:35 PM.
Stellar HDF Member
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From: Massachusetts
I changed my first set at 27K and they looked great and I could not tell a difference at all in how it ran after replacing them..FF to now and I'm at 28 K on them and it runs exactly the same as it ever has so I'm waiting until 30K per schedule..I go by mileage on plugs instead of time since I average close to 20,000 miles a year riding .. M8s are more efficient from epa requirements so they last longer than their predecessors
Seasoned HDF Member
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2 years or 30K go with it.
The reason for the 2 year thing is crap builds up they may be harder to get out.
No reason to remove them just to clean and gap unless you are running some wild tune with a real rich fuel.
Not like the M8 is an old shovel
The reason for the 2 year thing is crap builds up they may be harder to get out.
No reason to remove them just to clean and gap unless you are running some wild tune with a real rich fuel.
Not like the M8 is an old shovel
Seasoned HDF Member
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From: England
The reason for the 2 year thing is crap builds up they may be harder to get out.
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Intermediate
Joined: Sep 2019
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From: Ky
When you do change them out, it wouldn't hurt to blow the area around the plugs out before removal. Going that long there will be a lot of road grime and grit to accumulate around the plug that can fall down into the plug hole when they are removed. Also be sure to coat the new plugs with some anti-seize so they will come out the next time easier.
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From: Lititz Pa
I changed them at 30K and they still good in my M8. Maybe the next time I will go to 40K unless something happens. Just like oil few years ago I sent my Moble 1 synthetic oil to Blackstone labs test results 76% life left. I still do 5000 on changes. Realistically I would not be surprised if you went 100K on plugs and 10K on oil you would most likely be ok.
HDF Community Team
Joined: Mar 2017
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From: Texas
Here's a recent thread that was made on the same topic. You'll find plenty of answers there: https://www.hdforums.com/forum/milwa...ht=spark+plugs
and another: https://www.hdforums.com/forum/2018-...ht=spark+plugs
Here's what mine looked like. First post is after 2 years, 18k miles. Second post is after 2 years, 8k miles. The only issue I see with them is the amount of corrosion on the plugs on top of the engine as it traps water - no issue with the actual function of the plug. They were not difficult to remove as I torque to spec and use anti-seize as the service manual states (I know the newer service manuals have removed this).
and another: https://www.hdforums.com/forum/2018-...ht=spark+plugs
Here's what mine looked like. First post is after 2 years, 18k miles. Second post is after 2 years, 8k miles. The only issue I see with them is the amount of corrosion on the plugs on top of the engine as it traps water - no issue with the actual function of the plug. They were not difficult to remove as I torque to spec and use anti-seize as the service manual states (I know the newer service manuals have removed this).
Last edited by BrandonSmith; Sep 12, 2022 at 07:16 AM.