Here is how to explain what happened in your case:
When a Harley engine is shut off, it will normally come to rest on a compression stroke. If you stop in to fill up with gasoline, the engine will typically be off for 5-10 minutes. During that short interval of time the compression will not have time to bleed off yet. In other words, it will take a significant amount of torque to spin the engine when it is resting on a compression stroke. That is why so many people complaint that the bike only makes the "kickback" or crashing sound when the engine is hot, not when it is cold. The reason is that when the engine is cold the compression has bled off and the starter has a much easier time spinning the engine. Now, if the battery is not quite up to snuff in cranking power and you try to start the engine just after it has come to rest on a compression stroke you will very likely experience what is known as "kickback". The weak battery does not have enough torque to spin the engine swiftly through the compression stroke so when it does fire it will "kickback" and cause the dreaded noise. A fully charged battery with at least 12.8 volts (100% charge) will easily spin through the compression and you will not experience any "kickback". At 12.7 volts the battery is only at a 75% charge.
I hope this makes sense.

 

Makes a lot of sence,as I've experienced this with the old kick bikes. Next quetion.. What exactly makes the (engine is about to explode) sound?

 

Addedum: The battery has good voltage but no capacity.

 

This occurs because for a split second when the starter engages and tries to turn the engine over in the proper direction, the "kickback" occurs and wants to rotate in the opposite direction that the starter wants. The compensator, the primary chain and the inherant slack can make a terrible sound. Once an owner hears that death rattle sound, he is an easy mark for some over zealous or ignorant service department who want to sell parts and labor. Like I said earlier, most will try and sell you a new and "improved" compensator, some will sell you a new "high torque" starter and a few will actually diagnose the cause as being a weak battery (but not many).

 

Great explanation thank you, and you probably saved a lot of members from unecessary expenses.

 

I'm having similar symptoms as the OP. I had my 3.5yr old battery tested at HD and it's 90%. I forgot if the results gave a volt rating. When I plug in my battery tender, it always clicks right over to green.

Should I replace this battery anyway?

My engine is a fresh HD reman big bore 95" with only 500mi on it. I thought my starting issue was related to a "tight" motor and that in time the starter/battery would be strong enough.

**** thinking about this more, the issue precedes the reman engine install, so it's not the new motor that brought this on. I also wonder if what caused my crank runnout at 80,000 mi, (which led to a new motor) and if it's related to faulty starting issues ****

 

How do you loosen an auto tensioner?

 

No not any more. I had this "bang" problem on my '09 RKC with 103" Stage II upgrade. Replaced the compensator with the SE one. Replaced the starter with the 1.4 kw one. Replaced the clutch assy. All that did not cure the problem. Then a few months ago I bought some '12 take off heads with factory ACR's. Spent hours putting them on. Result: No more hard starts. No more bangs and kickbacks. Turns over real nice and civil now. This IS the solution to the problem. It's why beginning in 2012 HD puts the ACR's on most of its bikes.

 

So in other words, too much compression
is what you're saying even with the stock-er heads..w/no ACR's.

 

The only cause for the kickbacks and bangs is the high compression. It has little to do with the compensator. This is especially bad when the engine is hot. Compression releases solve this problem and make starting a breeze.