i have an 86 1100 thats due for a top end job. what do i need to do to go with 1200 pistons and bump the compresion a notch? didnt the 1100 have bathtub heads like the 883?

Yes, those heads have a bathtub similar to the XB or 04-05 XL1200 head. Not sure of the volume off the top of my head, let me research it. It's a damn rare head and we haven't had one come through the shop in years.

I suspect, though, that they could be configured to handle an angled dome piston, like a Thunderstorm style. If you don't want to do chamber work, an XB domed piston *may* work, if the dimensions are correct.

Any competent head shop should be able to measure the chamber volume and let you know what your options are and the pros and cons of each.

The valve job will add a little volume, keep that in mind.

Aaron

I think the 1100's had the same size valves as the Evo big twins from memory.
Havn,t seen a set in years..

I remember some of our local "experts" tellin me the angle of the valves was different between 883, 1100's, 1200's and big twins and ya couldn't fit big twin valves in a 883, 1200 sporty head unless ya welded 'em up and changed the included valves angle..

Harley Myths are a wonderful thing :)

Stevo ... you're right ... 1.840 intake valve, 1.610 exhaust. Chamber is 62cc. These things aren't terribly different from XB heads!

Elmo, those heads are giving 9:1 or so with flat tops at 1100cc. At 1200cc with no changes to the chamber and flat tops, they'll give about 10:1. That's the simplest thing to do. Just watch the volume after the valve job. When you cut the seats and face the valves, it sinks the valves a little and makes the chamber a touch bigger. You often have to cut the deck a little to get the chamber volume back down to where you want it.

so i could just order a regular set of 1200 flat top pistons and have the jugs bored to fit them correct? i dont want to get into and head work as far as porting and stuff... my main concern is a quick and easy turn around since its the only vehicle i own

elmo ...

Just my opinion, but if my motorcycle was my ONLY form of transportation, I would leave it stock and not mess with it.

id love too but my bike has more miles backing up to bar curbs than most do going forward so its due for a rebuild anyway...( erie noises from top end) and i think 1200 pistons are cheaper and more readily available than 1100 pistons anyway...( dealer told me good luck finding them). so anyway my plan is to just pick up the 1200 ones have the cyl bored to match them shave the heads to make the surface nice and flat and put it back together. if i can get a little more compresion and help out the 2 up riding then thats a bonus...sorry about the long run on sentence i aint figured out how to make seperate paragraphs in forums yet

I'm with Aaron

Just take it out to 1200 with flat tops and bet the heads re conditioned .....

You've got bigger valves than any other sportster cams out with already