I posted this question over on the mechanical side and got mostly negative responses in favor of the S&S 124 engine. But one poster suggested this board for I own a 2015 Breakout and want some more HP.

Are these engines reliable in terms of mileage? I know it's a performance based design but can one expect the engine to have some longevity with proper break in and maintenance adherence? Thanks.

 

Should, backed by the MoCo's warranty. I suspect that with Harley putting the 110 in the "S" models now, the 120 will be in next year's CVOs.

 

Its all metal, i think if you don't beat on it all the time, its very reliable. I have the fuel moto 107 and i am very sure its reliable if you treat it right, but let me tell you thats hard not to always want to get on it.

 

I would look into how good the crank is. There have been quite a few tc crankshaft that have scissored with modified motors making a lot of torque. S&s crank and rods are vary good compared to stock and possibly the 120r motor. Do research on this If this is the way you want to go. Also depending on how much power your looking to get you may be able to get there with the motor you got. Swapping cams and drive pullies really help these bikes out

 

I have a 120R in a 13 Street Bob. Over 3,300 trouble free miles so far and 47.4 mpg.

Then I have a 120ST in a 15 Freewheeler that has gone over 3K so far. Both have the SERT tunes and are pure pleasure to operate.

The only difference between the R and the ST is the cam. Then it can be the size of intake and injector size that the owner selects.







Dealers have installed many 120's since they came out. None have ever heard of one scissoring. Exceptionally rare even in built motors and more likely from abuse.

 

One thing to note. The 120r motor has no warranty from the moco. It is a race application only.

Currently there is no 120st for softails.

 

I'm getting a much more positive feedback on this section in the HG forums vs the mechanical one. I'll ask around some more but I find it hard to believe HD would put out a higher performance engine such as the 120R only to have the engines fail in their early stages. It would be very bad publicity for starters. THANKS to all of you for replying. Much appreciated.

 

I've only seen one that had a lifter go bad, i've heard other stories but have not seen them first hand so I can't comment on them. The ST version can be covered on a year warranty, you should be aware to get the warranty the bike must run the SE street performance tuner with a EPA calibration in it. Some dealers will do a warranty with other parts, but be aware, this is a dealer only warranty and not backed by the MoCo. Another option would be to go with the S&S 124" hot set up kit (with or without heads). It would require boring your cases but the parts are hands down the best. Just another option you may want to consider.

 

http://hillsidecycle.com/engine-kits/

Here you go. Many happy customers from this shop! Will be building mine once I get some money together.

 

120R installed by dealer, 12k miles, lifter collapsed. Replaced with Feuling lifters and oil system to get more flow. No warranty but who wants stock parts?
I think too much valve spring pressure for high lift and high rpm is too much stress on the valve train. Still like that it is 99% Harley. We will see how this holds up now.