Let's let the opinions fly!!
Rebuilt my 96 road king, Crane hi-lift cam, head work, cylinders 10 over, 10.5:1 compression kb pistons, ultima programmable ignition (dyna 2000I) Oh and of course m and m ignition converted to carb!
So how should I break it in? I've heard 50 really soft miles then 500 nice miles, I've heard 50 and I'm good, I've heard build it and throw it right on the dyno... opinions and reasons please!!!

 

This is from the S&S web site

1. On initial engine startup, don’t just sit and idle motor while you admire your work, or tinker with minor adjustments. Heat buildup can be
excessive. Do not let engine overheat.
Proper first time engine start-up and break-in for first 15 minutes is critical to achieve permanent and lasting head gasket seal. Upon initial start-up, idle
engine at 1000–1500 rpm until cylinder head temperature reaches about 250°. Do not crack throttle or put any load on engine during this time. Heat
buildup is necessary to cause heads and cylinders to expand and seal. Do not let heat get excessive. Prior to initial start-up, a .003"-.005" “feeler gauge”
will fit between head gasket and head and cylinder gasket surfaces stopping at fire ring on head gasket. Warming engine as instructed will tightly close
this gap producing a good, lasting seal.
2. First 50 miles are most critical for new rings and piston break-in. Most engine damage will initially occur during this period. Keep heat
down by not exceeding 2500 rpm. Vary speed. Do not lug engine.
3. Next 500 miles should be spent running engine no faster than 3500 rpm or about 50–55 mph. Do not lug engine and continue to vary
speed.
4. For balance of first 1000 miles, speed can be run up to 60–70. Continue to run engine at all different speeds including lower 40–45 mph
ranges. Do not lug engine.
5. 1000–2000 miles basically same as before but a little more liberal with rpm range. Avoid overheating and lugging engine—no drag
racing, trailer towing, etc.
6. 2000 miles and up—have fun!

 

Ride it.......stick to the speed limit and keep the revs spinning, don't labour it....has worked for me since 1979.

 

....and me since the '60s! Stop reading the internet and ride.....

 

If it's not puking oil after the first 50 miles, ride it like a rental.

 

I have always done a first start, let it warm up good, shut it down. Let it cool, start it up and ride it easy but, no lugging. After the first 100 miles I ride it a little more like normal but I ride easy for 600 miles, then an oil change and ride normal.

When I worked for Piedmont Aviation many years ago I tested radial and horizontally opposed aircraft engines. We started them, let them idle a while and over the period of 2 - 4 hours depending on the size of the engine. Within 4 hours we were running Pratt and Whitney R-2600's at redline. That engine is way, way bigger than anything HD ever made. Heck, the carb for an R-2600 is the size of a Harley Big Twin. The R-2600 with a flight prop threatened to tear the whole building down. Plus we had to put some strong pitch on the blades to get proper cooling and manifold pressure. Every time was three and a three quarter hours of boredom capped by fifteen minutes of sheer terror. But, I digress..

 

When I bought my new Buell Firebolt I was given some instructions about running it in. That went in one ear and out of the other, but I rode it home gently, before reading the manual. That told me to keep it below the equivalent of 90mph in top, for the first 50 miles! For my Evo it was max of 2,500rpm for the first 50miles and max of 3,000rpm for the next 500. The truth lies somewhere between those limits! So lets stop fussing over this and get ridin'......

 

Spanners and I rebuilt the top end on my bike before Christmas new pistons, reconditioned heads, V thunder 3000 cam and lifters, we started it and let it warm up checked for leaks etc.. then we shut it down. Put our riding gear on and went for a 15 minute ride. I rode it as I would normally ride but being careful not to lug the engine and keeping it in the correct gear and not over revving it ( well most of the time ). Changed the filter and oil after 500 miles and just rode it as normal. Now at about 1500 miles it has loosened up and I have given it some real hard throttle and it loves it. No smoke or rattles, just my take on it.

I have rebuilt many top ends on aircooled VW motors and have done the same and never had any problems.

 

Opinions, Opinions, check for leaks, recheck the oil and run it like a normal day. Don't baby it, don't rev limiter it, don't let it idle long, listen for noise, don't listen for noise and ride it.

Posted a article a while back on putting it on a dyno and letting it eat, very popular break in procedure.

 

Ha ha! You nailed there mate!