Mill the head instead of buying pistons?

I was thinking of buying the 1075 pistons which I think have 10.5:1 compression. Well, as the displacement is not much different from stock, what if I milled the head instead? Would the results be similar to buying the hi-comp pistons?

Keep my stock pistons, fresh rings, clean up the head, all else stock. Cheap performance boost. ????

Be careful so the pistons don't kiss the valves. Ed

650ed wrote:

Be careful so the pistons don't kiss the valves. Ed

That is exactly what would happen unless you machined out the valve pockets, plus the domed would be smaller than the crowns. This would mean you would also have to machine the crowns to match the domes. Next you start having problems with cam shaft adjustment because you change the distance of the cam sprocket to the chain drive sprocket. You will have to install adjustable cam sprockets to accommodate. 60cc is a 6% displacement increase. That is a lot.

ye gods! Well I thought about things like that, but I swear I've heard of guys doing this without doing all that other stuff. Surely it all depends on how much material you take off...?

I don't know how much piston/valve clearance is stock, I would guess there's some room to work, but maybe not.

I was planning to oval the cam sprocket holes and degree the cams anyway - that's free.

To stay within allowable limits of the head, you might raise the compression 1/3-1/2 points, never to 10.5:1. Milling the head is a one time proposition. Once done the head is junk. It is not a wise move to do.

Done this lots of time no probs.
There's plenty of room before you risk valve/piston contact, just measure the clearance you have before stripping the motor to be sure ,
A blob of oily plasticine (to stop it sticking to the valve or piston) inserted through the plug hole on the end of a piece of welding wire will do the trick ).
Just took 1.5mm off my latest build with plenty more to spare.
Also measure the combustion chamber volume with piston at tdc this will give you an idea of how much needs to be removed for a given compression ratio.
You can slot the std cam sprockets with a needle file as they are soft, just be sure you know what you are doing when degreeing them back in (110 degree lobe centers is std and a good start point)
Forget about the combustion chamber dome being a smaller 'dome' than the piston crown,it already is! (66mm chamber - 70mm bore)
Be more concerned with the pistons themselves as the std ones are cast as opposed to the stronger forged items supplied by wiseco etc.
As long as you don't go mad with the compression ratio and use premium fuel you should be ok.

You could ring your pistons and get some drop in cams for less money than a bore kit and bore job while gaining some performance. $350 - $400

Nice idea Larry. What cams would you recommend? I like torque: 3000-7000 rpms.

Zed - how do you decide how much to take off?

if the head is flat id take it off bottem of cylinder myself,once you mill the head much your stuck with it cylinders on other hand are easy to find.
pull the head and measure how far down the hole the highest piston is after you scrape the carbon off to get an idea how much you can gain.

Nelson wrote:

Nice idea Larry. What cams would you recommend? I like torque: 3000-7000 rpms.

Zed - how do you decide how much to take off?

New cams, Web 118 grind or Cam Motion Z2 grind

If you go the used cam / Ebay route and can fine as good set for little cash outlay, Andrews 1x or 2x.

If you deck the head or block as well, you can't really call those drop in cams anymore because you have reduced clearance.

All the KZ heads that I do get resurfaced and it takes generally .008 - .010" to get them nice again. That little bit won't affect a drop in cam but if you go trimming the block or the head.....that changes.

otakar wrote:

To stay within allowable limits of the head, you might raise the compression 1/3-1/2 points, never to 10.5:1. Milling the head is a one time proposition. Once done the head is junk. It is not a wise move to do.

id rather see 9:1-9.5:1 for a streetable motor anyway,then tweak the rest of the topend around it .
i wish piston makers would lower compression pistons besides turbos for air cooled motors