Swapping a Twin-Cam for an M8: Crazy or Genius? What’s up in the Forums

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Harley V-Twin M8 Swap

Don’t like the way your M8-equipped Harley sounds? Is it so crazy to reverse engineer a Twin Cam motor into it?

For most, the new Harley line of Milwaukee-Eight engines represents an upgrade over the old V-Twins. They’re smoother, make good power, and respond well to mods. But that doesn’t mean there aren’t a select few out there that would rather have an older Harley mill in their modern bikes. Like HD Forums member LaLleguaNegra, who recently pondered doing the seemingly improbable backwards swap.

“I have a 2017 FLHXS, and I simply hate how it sounds. Can’t trade or sell the bike because I will lose my butt. So I am wondering if I can pull the M8 and install a Twin Cam like the 120″ from HD, or the 124″ from S&S. Will the tranny line up? What about the engine mounts, wiring harness, and computer?”

Harley V-Twin M8 Swap

If the idea of backwards engineering a new Harley sounds crazy to you, well, that’s because it probably is. OldEnuf2NoBtr kicks things off by giving the OP a general idea of how difficult such a swap might be.

“It’s not going to be a direct bolt-in swap. Gonna take quite a bit of re-engineering on you’re part if you’re capable of that sorta’ thing. Fuel-Moto has a 120″ M8 upgrade. Give them a call.”

As cvaria points out, there’s probably a much easier solution to this little problem. 

“What?! Get a twin cam bike. have someone take over the payment or swap payments with someone. Use all your resources. See to your dealer for help getting out of the bike.”

And as QNman says, it’s better to lose money on the bike swap than the engine swap.

“That’s pretty damned extreme to get the right sound. Plus, no matter how much you lose selling the bike, it’ll be less than replacing the motor and engineering a twin cam to fit. Sell the bike, take the hit, buy a twin cam.”

Harley V-Twin M8 Swap

Or, you could just do some work to the existing Harley motor and get similar results, says Doshounds.

“Add compression, a cam, a good 2-1 exhaust, 117-120 big bore, throttle body, injectors. It will sound like a Harley and be a lot cheaper than a motor swap.”

Sadly, swapping engines just isn’t as easy (or cheap) as it once was. Which, of course, makes the thought of going backwards in an M8-equipped Harley pretty improbable. But we still want to know what you think. If you were in the OP’s situation, what would you do? Head over here and let us know!

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Brett Foote has been covering the automotive industry for over five years and is a longtime contributor to Internet Brands’ Auto Group sites, including Chevrolet Forum, Rennlist, and Ford Truck Enthusiasts, among other popular sites.

He has been an automotive enthusiast since the day he came into this world and rode home from the hospital in a first-gen Mustang, and he's been wrenching on them nearly as long.

In addition to his expertise writing about cars, trucks, motorcycles, and every other type of automobile, Brett had spent several years running parts for local auto dealerships.

You can follow along with his builds and various automotive shenanigans on Instagram: @bfoote.

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