M8 117 Engine resonates at mid range, normal?
Thread Starter
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5th Gear
Joined: Sep 2012
Posts: 9
Likes: 2
From: webster, ny
M8 117 Engine resonates at mid range, normal?
Hey everyone, Ive got a 2025 Fat Boy with the Milwaukee-Eight 117. I love the bike, but Ive noticed its not as smooth as my previous Fat Boy with the Twin Cam 103. Specifically, theres a noticeable resonance around mid-range RPMright around 3,000.
Its smooth at low RPMs, but once it hits that mid-range, you can feel a tingling through the floorboards, mirrors, and grips. Im calling it resonance rather than vibration, since vibration is considered normal by most Harley folks. But this feels differentmore like a harmonic buzz thats present in specific ranges.
I also test rode an M8 117 Breakout and noticed a similar sensation, though maybe a bit less pronounced. I wouldve expected the newer engines to be smoother at cruising speeds than the older Twin Cams, but in my experience, theyre not. In fact, it feels like a step backward in terms of smoothness.
Anyone else noticing this?
Its smooth at low RPMs, but once it hits that mid-range, you can feel a tingling through the floorboards, mirrors, and grips. Im calling it resonance rather than vibration, since vibration is considered normal by most Harley folks. But this feels differentmore like a harmonic buzz thats present in specific ranges.
I also test rode an M8 117 Breakout and noticed a similar sensation, though maybe a bit less pronounced. I wouldve expected the newer engines to be smoother at cruising speeds than the older Twin Cams, but in my experience, theyre not. In fact, it feels like a step backward in terms of smoothness.
Anyone else noticing this?
Thread Starter
|
5th Gear
Joined: Sep 2012
Posts: 9
Likes: 2
From: webster, ny
Its the motor. Just reving it up in the garage does it. Its not bad...it is very minor. However a brand new motor with counter balancers shouldn't resonate at all. Seems like the people who design the motor and frame aren't doing there job very well, or they don't care about vibrations that much. I test rode a 117 Breakout and it has a similar resonation. My older 103 Fatboy is butter smooth, literally zero vibration or resonation.
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,147
Likes: 11,220
From: San Diego, CA
Hey everyone, I’ve got a 2025 Fat Boy with the Milwaukee-Eight 117. I love the bike, but I’ve noticed it’s not as smooth as my previous Fat Boy with the Twin Cam 103. Specifically, there’s a noticeable resonance around mid-range RPM—right around 3,000.
It’s smooth at low RPMs, but once it hits that mid-range, you can feel a tingling through the floorboards, mirrors, and grips. I’m calling it resonance rather than vibration, since vibration is considered normal by most Harley folks. But this feels different—more like a harmonic buzz that’s present in specific ranges.
I also test rode an M8 117 Breakout and noticed a similar sensation, though maybe a bit less pronounced. I would’ve expected the newer engines to be smoother at cruising speeds than the older Twin Cams, but in my experience, they’re not. In fact, it feels like a step backward in terms of smoothness.
Anyone else noticing this?
Kind of like the old story of the "Princess and the Pea". Everybody has a different threshold for what is normal or excessive.
If you feel the bike has excessive vibration, then have the dealer check it over, it could be the harbinger of a problem...
But FWIW.....
When Harley was developing the M8 engine, their balancers removed almost all vibration. It was decided that it ran "too smooth" for a Harley.
The M8 engine balancers are now set up to only remove 75% of the vibration. They left some in to give it the "Harley" feel.
You can google "Harley M8 vibration" and get a lot of reading about the issue, and other's impressions of M8 vibration.
Let us know if you bring it in and they find an issue...
Last edited by hattitude; Aug 27, 2025 at 11:05 AM.
1st Gear
Joined: Jul 2025
Posts: 5
Likes: 14
From: South Florida
I'm experiencing floor board vibrations on my 2025 Fat Boy that start about 55 mph and the vibration continues up to 80 mph, I'm not comfortable taking the bike any faster with vibrations, feels like the steering get very wobbly. The dealer looked my bike over at the 1000 mile service and 3 people that work at the dealership say everything is normal, I pushed back and asked to Test ride another new Fat Boy, that one Rode 1000 time smother. Store managers response was "no two machine are the same". Why do these bikes have some much wheel weights on them? I've had mud tires on trucks with less weights. I'm not sure what the engine RPMs are at those speeds. don't feel comfortable to look down at the gauge. Went back about 2 weeks late after a long group ride and I could not keep up on the highway due to vibrations. Went back to the dealer and insisted that the wheels/tire be checked for balance and that rear tire is properly set up. Again after inspections and many people test riding I'm told nothing is wrong with the bike. they offered to sell me a Road glide. I love my Fat Boy. I'm going to take the bike to an independent motorcycle shop to get an inpartial option on the vibration and have the shop check the tire balance.
Kind of like the old story of the "Princess and the Pea". Everybody has a different threshold for what is normal or excessive.
If you feel the bike has excessive vibration, then have the dealer check it over, it could be the harbinger of a problem...
But FWIW.....
When Harley was developing the M8 engine, their balancers removed almost all vibration. It was decided that it ran "too smooth" for a Harley.
The M8 engine balancers are now set up to only remove 75% of the vibration. They left some in to give it the "Harley" feel.
You can google "Harley M8 vibration" and get a lot of reading about the issue, and other's impressions of M8 vibration.
Let us know if you bring it in and they find an issue...
If you feel the bike has excessive vibration, then have the dealer check it over, it could be the harbinger of a problem...
But FWIW.....
When Harley was developing the M8 engine, their balancers removed almost all vibration. It was decided that it ran "too smooth" for a Harley.
The M8 engine balancers are now set up to only remove 75% of the vibration. They left some in to give it the "Harley" feel.
You can google "Harley M8 vibration" and get a lot of reading about the issue, and other's impressions of M8 vibration.
Let us know if you bring it in and they find an issue...
While ordering a crankshaft for a friend from Darkhorse, I notice that they have a notice that says if your engine has dual balancers, they will need to be installed. I guess that could be a solution, but a very expensive one.
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Road Master
Joined: May 2005
Posts: 1,100
Likes: 419
From: Pennsylvania
Hey everyone, Ive got a 2025 Fat Boy with the Milwaukee-Eight 117. I love the bike, but Ive noticed its not as smooth as my previous Fat Boy with the Twin Cam 103. Specifically, theres a noticeable resonance around mid-range RPMright around 3,000.
Its smooth at low RPMs, but once it hits that mid-range, you can feel a tingling through the floorboards, mirrors, and grips. Im calling it resonance rather than vibration, since vibration is considered normal by most Harley folks. But this feels differentmore like a harmonic buzz thats present in specific ranges.
I also test rode an M8 117 Breakout and noticed a similar sensation, though maybe a bit less pronounced. I wouldve expected the newer engines to be smoother at cruising speeds than the older Twin Cams, but in my experience, theyre not. In fact, it feels like a step backward in terms of smoothness.
Anyone else noticing this?
Its smooth at low RPMs, but once it hits that mid-range, you can feel a tingling through the floorboards, mirrors, and grips. Im calling it resonance rather than vibration, since vibration is considered normal by most Harley folks. But this feels differentmore like a harmonic buzz thats present in specific ranges.
I also test rode an M8 117 Breakout and noticed a similar sensation, though maybe a bit less pronounced. I wouldve expected the newer engines to be smoother at cruising speeds than the older Twin Cams, but in my experience, theyre not. In fact, it feels like a step backward in terms of smoothness.
Anyone else noticing this?
2025 Fat Boy owner as well. I know what you mean, but consider it normal.
I dont notice it as much with the RS528 cam I installed but its still there.
Doesnt really bother me
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Road Master
Joined: May 2005
Posts: 1,100
Likes: 419
From: Pennsylvania
I'm experiencing floor board vibrations on my 2025 Fat Boy that start about 55 mph and the vibration continues up to 80 mph, I'm not comfortable taking the bike any faster with vibrations, feels like the steering get very wobbly. The dealer looked my bike over at the 1000 mile service and 3 people that work at the dealership say everything is normal, I pushed back and asked to Test ride another new Fat Boy, that one Rode 1000 time smother. Store managers response was "no two machine are the same". Why do these bikes have some much wheel weights on them? I've had mud tires on trucks with less weights. I'm not sure what the engine RPMs are at those speeds. don't feel comfortable to look down at the gauge. Went back about 2 weeks late after a long group ride and I could not keep up on the highway due to vibrations. Went back to the dealer and insisted that the wheels/tire be checked for balance and that rear tire is properly set up. Again after inspections and many people test riding I'm told nothing is wrong with the bike. they offered to sell me a Road glide. I love my Fat Boy. I'm going to take the bike to an independent motorcycle shop to get an inpartial option on the vibration and have the shop check the tire balance.
Have someone at dealership run the thing up to 80 mph on the highway and see if they notice what you are talking about...
