Ok I知 on my 5th belt in 2 1/2 years I知 fed up and beyond frustrated because I can稚 figure this out, engine mods 103 top end upgrade, polished headed and port matching, S&S551 came, updated clutches and spring, solid 34 T compensator sprocket, power vision Target tune kit, sprockets look healthy, alignment is good and minimal run out I know im not making enough power to keep ripping these belts apart and yes I知 checking tension and deflection thinking does anyone know what I知 missing here or

I should just slap a chain drive on it and roll with it also looking for advice on that front as well as far as ratios for for good medium between acceleration and 80mph cruise speed thanks in advance

 

How do you ride it? That, probably more than anything else, will determine belt life.

If you like hole shots, burnouts, lofting the front, being the first away from the light, etc, you're going to break belts.

Belts also fail or break in different ways. No images of the failure, so beyond guessing, none of us have anything to go in.

 

I ride it hard maybe a 3rd of the time hard accelerations buts it痴 a fatboy it won稚 do burnouts the last two just snapped before then I was shearing teeth off them

 

It didn稚 start doing this till about a month after I installed the 103 top end

 

Tempting to blame the engine, but I rather doubt that's it.

Shearing teeth is generally a tearing action, from either too little belt tension for the load, or too sharp or much a load for the teeth.

It's not far from shock loads breaking the belt.

One that I do often see around here is violent engine loaded downshifts. Lots of folk here seem to enjoy the chirp of the rear tire as they downshift. They are folk that probably complain about belt life.

I've a friend who takes pride in destroying belts with clutch dumps. But at least he knows what he's doing while he does it.

Some good guides and information on diagnosing belt failures can be found on the web. Here are two:

​​​​​​https://www.linearmotiontips.com/syn...ys-they-occur/

and

​​​​​​https://www.royalsupply.com/download...ysis_Final.pdf

 

Belts are actually very strong and long lasting.... but as mentioned, riding style greatly affect their longevity. A hard riding style can damage/break a belt on an OEM set-up...

You have increased displacement (power & torque), you have removed the driveline shock absorbing properties of the compensator by adding a solid engine sprocket, you have improved your clutch so it will better transfer the extra power to the rear wheels, and you ride it hard.... That's a perfect recipe for a broken belt.

It may be a blessing those belts broke, instead of your your crank.... Did you do any bottom end work during your mods? What was your run-out ?

As hard as you are on that drivetrain, and with no compensator but a solid engine sprocket, I wouldn't switch to a chain if the bottom end hasn't been addressed...

The weakest link will always give first... The 2009 engine is in the era where the Harley cranks were getting some distressing run out numbers, and the MoCo in it's wisdom (or better stated "protection of corporate profits"), just kept increasing the allowable maximum run out numbers. I believe they got as high as 0.012" allowable run-out. That would be funny if it wasn't so ridiculous...

I fear without an improved bottom end, if you go to a chain, you will have crank issues instead of belt issues...

If I were you, unless the bottom end has been modified/strengthened, I would ensure the belts are kept properly adjusted, double check the final drive belt pulleys to ensure they are in good shape, not damaged so to possibly adding to the belt breakage, then realize you have a cruising bike, not a race bike. I would try to modify my riding habits to avoid shock loading the drive train.

OR...

Send your bottom end to Dark Horse CrankWorks, have them do their magic, and switch to a final drive chain. You can then drive it like you stole it with more confidence....

For a counterpoint: I have a 2016 Ultra Classic with a 124" S&S crate engine by FuelMoto. It was dyno'd at 135HP/151TQ. I "play a little" now and then, but certainly don't abuse it. My bike is heavier, my bike has high HP/TQ, and it too has a solid engine sprocket with clutch upgrade components.... I have 40K miles on that bike, 20K with those mods. I still have my OEM belt, and it looks to be like new....

Good luck with your decisions and driveline mods...