My heads have been reworked with larger valves, porting, and decked .020. Engine is supposed to have 9.8:1 CR with 9.4:1 pistons, .020 decked heads and .040 head gasket. The builder never cc'd heads though, so actual static CR was unknown. Well, I am changing cams again, so I pulled heads and cc'd them to know what exactly I am working with. They cc'd at 84 and 84.5. This would put them at 87 - 88 cc as they came from HD. This probably explains why I never felt the bike had low end torque I expected with 9.8 CR with SE204 cams.

With this in mind, I have a few questions:
1. I have read I can safely deck heads .050 or .060. Is this based on 85 cc spec'd head? If so, can I deck heads more since I started with 87+ cc?
2. Using Big Boyz calculator, I tried to measure deck height at piston TDC. My pistons are flat tops and I am estimating deck height at 3/16 to 1/8" below cylinder deck. Granted, this was not done rotating engine, but measuring carbon buildup at top of cylinder. Is this normal or is my deck height way too low? Putting this into BB calculator, my compression is dropping way too low. If deck height needs to be reduced, how do you do that - deck cylinders? That would involve a lot of decking,
3. I want to get static in the 10.2 range, and was thinking of decking heads an additional .020 -.030 and use .030 gaskets. Is this safe or too much? Final head volume will be around 79 - 80 cc.

I thought about installing higher compression domed pistons, but don't want to spend that much boring cylinders, etc. Installing TW6-G cams with 4 degree advance key. I thought once I pulled and cc'd heads, I would have a good game plan with the engine, but this deck height issue complicated things. Any help is appreciated.

 

Personally, I would rather add pistons than deck the heads, that's how I would go

 

you're working way to hard, spending to much money, time and effort for such little gain. Put some domes in and go with what you got. how much HP and torque gain for the $$$ do you think you're going get for going from 9.8 to 10.2?

 

$40 per head to mill and maybe $60 for head and rocker box gaskets - don't think I could put new pistons and rebore cylinders for close to that price. Not sure what kind of power gains I will see with tw6 cams and bumping compression a little, but I want the compression to be in the right range for the cams. From what I have read, these cams really benefit from the extra compression.

 

I was looking at Big Boys site at an article on checking deck height. One of the pics showed them rotating engine to TDC and the other cylinder looked just like my cylinders - a ring of carbon buildup at the top of the cylinder bore wall. The measured deck height was zero. I will turn motor tomorrow - I just assumed the carbon buildup was occurring at TDC and my piston was way below the deck.

 

even if your deck height is zero, the top ring is still .060--.080 down from that, so you will still have some sort of carbon ring .

 

By pulling that head down to the chamber volume you need for the 6 cam, your going to run into intake manifold fitment, and IF you ever decide to go to a larger engine, then those heads may be fubared for that.
I'd ditch the 4* advance gear thought, buy some pistons, and set the compression where you want it for that 6 cam.
I know you don't want to spend the dough, but you'll be better off doing it that way.
Scott

 

Thanks - that makes sense. I am trying to do this cam change without spending too much money, and when I saw the buildup I just assumed I ran into another issue.

 

Thanks Scott. As far as future engine upgrades, I think I am done, or if I ever come into extra cash, I would probably get a new 120 or something along those lines. Kids are starting college next year and I don't see any free $ for years, and that's a big reason to do this as cheap as possible - already getting bills for admission fees, dorms, meal plans, etc.
In your experience at what milling point do you usually start running into intake fitment problems? I saw this formula to calculate how to mill off intakes to align everything: amount milled off heads /.050 x .016
I don't have any fitment issues now with .020 decked, so plugging an additional .030 into calculation would deck .010 off intake.

 

I am all too aware of the finacial needs of a college student, as my daughter goes into her senior year at Utica College, in the fall, said the proud father.....
Around .070" is where we see intake fitment issues.
Scott