Sportster Bottom End Limits

[bitpusher]

Originally Posted by Turbo Sporty 48

Sky,
Are you about to "check out and do up" the race crank?
Looking forward to hearing about that.
What happened?

nothing happened. yet. when i tore down i found a few things that warrant a closer look. there is a little more runout than i (and the stator) would like to see.

so yeah, the insides need a checkup. i sniped up another stock '99 crank on the bay to swap in (if it is ~true) while i ponder and learn how to true (if necessary) the monster crank.

[Turbo Sporty 48]

Here is a thread from the XR1200 owners forum:
http://www.xr1200ownersgroup.com/sit...nsion-finished
It seems the frame is a big limiter to a well tuned turbo Sporty. Have referred to this elsewhere but it is relevant here too i think.
Of course this is on a rubber mount frame, not solid mount, the stronger frame IMO.

[maru]

Very few streetbikes are going to end up breaking rubbermount frames, turbo or not. There are plenty of things to loose sleep over,but frame breakage is not one of them. It is just not that easy to make the kind of power that is likely to do that and nobody even knows if power had anything to do with it.

It is hard to imagine what vibration can do, but unusual harmonics from that 100ci engine could have been just as likely the real source of the problem. Power could also have been the problem, but I would not leap to that conclusion.

In any event, that combination was a very unusual set up and until others start breaking frames, I would put this in the "cross that bridge when you come to it" category. The rubbermount frame is far from frail.

While it is good to think ahead, one can spend an incredible amount of time, energy, and money solving problems you don't have. Even those with above average resources have a limit with regard to time, energy, and money.

[bitpusher]

i am not going to go into gory details but.....

if the frame that i chopped and welded can hold up to 140hp through the abuse i have lavished upon it, there is no way in hell ANY engine you can fit in an unmolested frame is going to hurt said unmolested frame.

[Turbo Sporty 48]

I hear you both.
Right now, I'm pretty convinced that the bottom end and frame are good for all I intend on throwing at them.
Now that suspension, maybe I should rigidify it like you LSR bath salts guys so I can feel your pain. And I wanna go back to that canyon again...

[A 4 liter V8 eater]

Originally Posted by aswracing

I worry about Sky's. We pulled out all the stops when we prepped the crank, using all the tricks I've learned over the years doing my Bonneville cranks, and there are several things we do specifically to fight this spread issue, but still, at those power levels, you're fighting an uphill battle.

What are some of the tricks?