Here is another question for you:

How much do you think can safely be milled from the heads on a 04 1200?

I am aware that cam duration will have an effect on piston to valve clearance.

I just plan on installing the 04-05 specific SE cams and will be using the stock head gaskets. Everything else is stock.

I know there is a formula, but do you think that if I can safely mill the heads .030" that it will increase the CR from the stock 9.7 to about
10.0-1? ... Maybe mill .040"?

I want to increase the CR a little due to the loss of static compression the higher duration cams will cause.

Thanks,
Ron

Hey Ron,
Can't answer your actual question, but when you increase compression you might want some compression releases installed while the heads are off to save the starter. I had starter problems on my BT until I added 'em (even with the heavy-duty HD starter). I'm running close to 11:1.

Thank's Jim ... In my case, the cams I am installing will decrease the cranking compression a little just because they have more duration and slightly more overlap than the stock cams. I am just tying to get back that static compression from whats lost as a result of the bigger cams.

I just hope that I can safely mill the heads .030"-.040" without having piston to valve clearance problems.

....wow, I didnt realise that the stock 1200's were running 9.7 to 1 compression ratios....My S&S conversion was only 9.2 to 1 and I pulled 80hp/79lbs on the Dyno.....9.7 should be pretty impressive.
....seems to me that milling the heads is a inefficient way of trying to increase compression....Im probably wrong, but Im thinking that compression is a function of the crankshaft/pistons-combustion chamber.....more than valve-train/cams.
....Ive always thought that compression was measured when the valves were closed on the compression stroke....wouldnt overlap occur on the intake/exhuast stroke?

...Just my $o.o2

Turbota. I'm going to do a similar setup. Justin, at Nallin, said taking off .015" will get approx. 10.2:1 cr. Milling off much more might cause push rod issues.

G'day Turb

BEFORE ya mill anything off anywhere MEASURE what ya got first.

Good engines are NOT built on guess work, you may find that your particular set of heads has a small enough combustion chamber to give you an actual 10:1 (although I doubt it).

When you do your dissassemble do a dumy fit with the cmas and your existing head set up and use platicene in the vlave pockets in the pistons.

Remove the heads and cut the plasticene in half so you can measure the depth.

You want at 0.100" on exhaust and 0.080" clearance on inlet

An easier trick is to use 0.030" solid copper head gaskets which will take up your compression a touch...I have all the figures written down in my tuning book in the workshop, I'll get it later if I remember.
I've calculated out how many cc's for each size head gasket and therefore how much compression rise or fall.

Thanks for the info Stevo ... I figured it certainly would be best to check piston to valve clearance after installing the cams ... But, so many engines (non-motorcycle) I am familiar with can take at least .030"-.040" cut from the heads without any issues even with big cams ... I just don't have any experience with these Harleys ... I'm pretty much V-Twin illiterate at this stage!

wabiker ... Milling the heads is as effective of a way to increase the engines mechanical compression ratio (CR) as is decreasing the heads chamber volume or changing pistons. It all effects the actual compression ratio. The problem with milling the heads is that you can only mill so much before you have piston to valve clearance problems ... And of course, since the Sporty V-Twin does not have adjustable rocker arms, if you mill the heads, you need to install shorter pushrods in order to maintain the proper valve lifter preload (there hydraulic roller lifters). In all reality, if you milled .040" from the head, you would need a pushrod that is .040" shorter than stock (or I guess you could do the same thing with an adjustable length pushrod).

As far as a long duration cam with lots of overlap (ie: 'big' cams) .... It don't change the mechanical CR of the engine ... that's fixed ... but, it reduces the cranking compression (static compression) because these 'larger' cams keep the valves partially open for a longer period of time on all 4 strokes of the engine, to include the compression stroke.

And that's why even Harley recommends high compression pistons be used when installing some of there larger SE cams. And that statement is found right there in the SE catalog.

Ron,

"And that's why even Harley recommends high compression pistons be used when installing some of there larger SE cams. And that statement is found right there in the SE catalog."

.....You said your using stock everything else. So I was wondering why ya were not going with the pistons. Or would ya still have to make the head mods too...? Milling the heads seems like a lot of work to keep stock specs.

Well, milling the heads is certainly cheaper than installing a new set of pistons ... But, if you are going to pull the heads to have them milled, the ideal thing would be to have them ported at the same time.

In my case, I'm not doing a 883-1200 conversion. My bike is a XL1200 to begin with. I don't want to change pistons unless I absolutely have to.

At this point, I am just going to dyno it next week to get a baseline. Then install just the cams and re-dyno. Then make up my mind what I am going to do about the heads at a later date .... Of course, the ideal time to pull the heads would be when you change cams because ya got to remove the rocker boxes anyway ...... So ?

http://img.photobucket.com/albums/v248/Turbota/holeinthewall.jpg

I thought the High Compression pistons from SE (22694-01) gave a higher compression ratio (10:1) without the need to skim the head? Trouble is they only list upto 03, not sure about 04/05/

You know those old 1200 Sports that are advertised at 10:1? They're not. I cc my set up and it was barely 9.8:1. As Stevo said, measure what you have. CC the chambers, measure the deck height and know where you are starting. Instead of milling the head, I didn't use a base gasket.

You can always use a copper headgasket. They are .0027 thick which is about 1/3 of the stock headgasket and see hown she runs. That would give you the effect of milling without actually doing it. I did this with milled heads and my bike ran like a rape ape until the headgasket started leaking. They only lasted 5000 miles or so but it sure was fun while it lasted.

Well Tubota.....Thats kinda along the lines I was thinking.....as you know its a snowball effect. Ya reach a certain point where just swapping parts aint enough....It becomes a case of "well since Ive gone this far, I might as well do this...and this....etc".
Ive known guys that mill/deck heads for that last little bit of compression gain as a final tweak...usually after all the cam, valve train, piston, chamber, port, stroke etc etc work....
Just struck me as a little odd to go from swapping cams straight to milling heads is all.....at least thats what I picked up from your thread....any how, good luck.

Turbota,
I would think you could get a good jump in compression just by using thinner head gaskets. The Ross Racing pistons link below has a cool calculator. Just plug in the data and it will give you the compression ratio. You can change the head gasket thickness and see the compression delta between the gaskets. I plugged in my numbers and reduced the total gasket thickness (base+head) from .070 to .035 and gained .8 compression.
Techrep

http://www.rosspistons.com/calculator.php