Big bore kit or new engine
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Stage II
Joined: Nov 2022
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From: Alabama
Big bore kit or new engine
I’ve got a 2008 Fatboy with about 68,000 miles. I was talking to a guy at a dealership service department about putting in a big bore kit when he warned me that doing that with such high miles would cause the engine to tear itself apart. He recommended either building a new motor and transmission or buying one. Is he right?
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I’ve got a 2008 Fatboy with about 68,000 miles. I was talking to a guy at a dealership service department about putting in a big bore kit when he warned me that doing that with such high miles would cause the engine to tear itself apart. He recommended either building a new motor and transmission or buying one. Is he right?
YMMV
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Joined: Sep 2008
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From: San Diego, CA
I’ve got a 2008 Fatboy with about 68,000 miles. I was talking to a guy at a dealership service department about putting in a big bore kit when he warned me that doing that with such high miles would cause the engine to tear itself apart. He recommended either building a new motor and transmission or buying one. Is he right?
This is all IMHO...
There is some truth in what he is saying, but I will disagree with the "guy at the dealership service department"... There is more to an engine's ability to handle additional power, than just the mileage.
I agree that if the bottom end is loose, damaged, or badly worn.... the addition of a big bore kit most likely would be more than it could handle....
I will also agree that the higher an engine's miles, the more careful you have to be about adding power.....
But to make a blanket statement that a 68K engine will "tear itself apart", is a BS thing to say...
How big of a displacement increase? How much of a compression increase? How much of a HP/TQ increase...?
Unless he had worked on your engine and knew something specific about your engine's condition, or you were inquiring about a radical, high HP Big Bore Kit, it sounds like that "guy at the dealership service department" was trying to sell you something....
When speaking as an "expert", a true expert should be more careful with their words.... IMHO, his advice should have been offered as a risk v benefit discussion, or even a cost v benefit discussion, educating you about the potential risks..... rather than issuing a blanket doomsday statement...
There's a big difference between saying, "I wouldn't recommend it at that mileage", or "it may be better to", then to say it "would cause the engine to tear itself apart."
His "expertise" would have lost any credibility with me, due to that blanket statement....
Last edited by hattitude; Nov 16, 2022 at 09:00 PM.
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Stage II
Joined: Nov 2022
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From: Alabama
This is all IMHO...
There is some truth in what he is saying, but I will disagree with the "guy at the dealership service department"... There is more to an engine's ability to handle additional power, than just the mileage.
I agree that if the bottom end is loose, damaged, or badly worn.... the addition of a big bore kit most likely would be more than it could handle....
I will also agree that the higher an engine's miles, the more careful you have to be about adding power.....
But to make a blanket statement that a 68K engine will "tear itself apart", is a BS thing to say...
How big of a displacement increase? How much of a compression increase? How much of a HP/TQ increase...?
Unless he had worked on your engine and knew something specific about your engine's condition, or you were inquiring about a radical, high HP Big Bore Kit, it sounds like that "guy at the dealership service department" was trying to sell you something....
When speaking as an "expert", a true expert should be more careful with their words.... IMHO, his advice should have been offered as a risk v benefit discussion, or even a cost v benefit discussion, educating you about the potential risks..... rather than issuing a blanket doomsday statement...
There's a big difference between saying, "I wouldn't recommend it at that mileage", or "it may be better to", then to say it "would cause the engine to tear itself apart."
His "expertise" would have lost any credibility with me, due to that blanket statement....
There is some truth in what he is saying, but I will disagree with the "guy at the dealership service department"... There is more to an engine's ability to handle additional power, than just the mileage.
I agree that if the bottom end is loose, damaged, or badly worn.... the addition of a big bore kit most likely would be more than it could handle....
I will also agree that the higher an engine's miles, the more careful you have to be about adding power.....
But to make a blanket statement that a 68K engine will "tear itself apart", is a BS thing to say...
How big of a displacement increase? How much of a compression increase? How much of a HP/TQ increase...?
Unless he had worked on your engine and knew something specific about your engine's condition, or you were inquiring about a radical, high HP Big Bore Kit, it sounds like that "guy at the dealership service department" was trying to sell you something....
When speaking as an "expert", a true expert should be more careful with their words.... IMHO, his advice should have been offered as a risk v benefit discussion, or even a cost v benefit discussion, educating you about the potential risks..... rather than issuing a blanket doomsday statement...
There's a big difference between saying, "I wouldn't recommend it at that mileage", or "it may be better to", then to say it "would cause the engine to tear itself apart."
His "expertise" would have lost any credibility with me, due to that blanket statement....
This guy started by saying it would be better if I paid to have a new engine built and then said if I was going to do that, that I might as well just buy a brand new bike with one of the 114 Milwaukee 8 engines. So, his recommendation cost went from about $3K to about $6K to about $26K. That’s quite a jump.
Seasoned HDF Member
Joined: Sep 2008
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From: San Diego, CA
I’m thinking of going from a 96 to a 103 and throwing in some screaming eagle racing cams.
This guy started by saying it would be better if I paid to have a new engine built and then said if I was going to do that, that I might as well just buy a brand new bike with one of the 114 Milwaukee 8 engines. So, his recommendation cost went from about $3K to about $6K to about $26K. That’s quite a jump.
This guy started by saying it would be better if I paid to have a new engine built and then said if I was going to do that, that I might as well just buy a brand new bike with one of the 114 Milwaukee 8 engines. So, his recommendation cost went from about $3K to about $6K to about $26K. That’s quite a jump.
Yeah, he was trying to make some money....
I have no idea about your riding habits, maintenance routine, or current mods.... so I hesitate to offer advice...
However.... if it were my bike, and...
I like the way it is set up...
I am planning on keeping it for awhile...
It is my one and only bike or reliability is extremely important...
I would rebuild the engine rather than adding a big bore kit at that mileage.
I would certainly consult a shop on what components in a big bore kit to choose, to reach my performance goals.... Consulting a shop is a good idea. You want components that work well together, If you just pick several brand name components and throw them together, you may be short changing yourself.... Most shops have combinations that they use and know work well together.. And as always, after all the mods are done, the tune is very important...
Depending on the planned HP increase, I would probably also spend the money to have the bottom end done by someone like Darkhorse Crankworks, then do the new top end myself...
I would then have an extremely solid, well built engine that IMHO, would be better than any OEM HD engine... It would certainly be much cheaper than a new M8... and (depending on component choices) it would run every bit as good as an M8...
If I was just doing mods on a 2nd bike, and/or one that's mostly a local cruiser, I would first check the crank runout. If runout was good, I'd just do a Stage II with a bolt-in cam. I'd get it tuned well by a reputable tuner.... then run it...
Good luck with your decision(s)....
Grand HDF Member
Joined: Sep 2022
Posts: 4,471
Likes: 3,853
From: Florida
I’m reluctant to give any advice on an m8 or Twinkie because I’ve never been inside one. However.. a motor is a motor is a motor. If this was an EVO, I’d say if you can do some labor yourself, I’d get heads ported, good valve job, new springs and cam(s), hone (depending on the cylinders) and just get higher compression pistons. This way not a lot of money is thrown on top of a half used bottom end and the power gain would be good with little investment. Then in another 50,000 just buy a crate engine or sell the bike.
I would not pay for all that labor and new parts of big jugs on a bottom with close to 70k on it.
I would not pay for all that labor and new parts of big jugs on a bottom with close to 70k on it.
Last edited by Rains2much; Nov 18, 2022 at 03:19 PM.
Stellar HDF Member
Joined: Dec 2010
Posts: 3,275
Likes: 669
From: The Rust Belt!
I’m thinking of going from a 96 to a 103 and throwing in some screaming eagle racing cams. This guy started by saying it would be better if I paid to have a new engine built and then said if I was going to do that, that I might as well just buy a brand new bike with one of the 114 Milwaukee 8 engines. So, his recommendation cost went from about $3K to about $6K to about $26K. That’s quite a jump.
Last edited by Zakk13; Nov 20, 2022 at 03:19 AM.
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Seasoned HDF Member
Joined: Mar 2010
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From: Poolville
Start with checking the run out on the pinion shaft.. If you're at .003-.005".I would go for it.. I'd also go with a Andrews TW 48, Wood tw 222, or tw 5-6..
Trans should be fine..
Trans should be fine..
Last edited by 98hotrodfatboy; Nov 28, 2022 at 05:47 PM.
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Joined: Dec 2006
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From: West Texas Sandhills
I say do the big bore kit if that’s what you want to do. I had a S&S 97 inch big bore installed on my 06 Heritage a few years ago with close to 90K on the clock and have had zero issues. I also went with the Screamin Eagle ported heads and already had 510 gear drive cams installed. I’m calling bullshit on the dealer telling you it will tear itself up. Sounds like a sales ploy to me.
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Oct 31, 2019 11:47 AM