milling heads

[skeeter91]

i would like to know how much material to mill off to gain 115-120 psi on a set of small bore crossflow heads #545&544.they are going on a 86' 150 that is only run on 93octane etheanol free fuel with 28deg. of total timing.

[bobthebuilder]

Get a piece of real soft lead solder and cut you a small little piece and put it in the head chamber with a little stick um of some kind and with head bolted back on turn it over and then removed the head and measure the solder with a dial caliper or mic.. you need to keep about .040 clearance but I have cut em down to like .037 and that did OK... But OMC Cross flow heads have that issue when you cut them. You cannot just cut a bunch off to a certain CC volume like Mercury heads. I has to have that clearance between the head and piston. Just a heads up for you.....

[skeeter91]

thanks bob,that is great advice.as soon as my tournement season is over,i will be pulling my heads and checking the clearence,so is there that much variation from year to year/motor as far as clearence?

[bobthebuilder]

Yea I sent you a PM. You might just find some older year model heads for it.. They allow for clearance but just close up space in the open areas of the chambers.. All OMC cross flows are like that.. I think it was like 77 thru 79 year engines that were higher compression heads. You can cut yours some but have to keep that clearance in there for it to live... I had a V-6 175 OMC I think it was a 1985 motor and I put older heads on it and compression went from 85# up to 115# just changing them and I also used the thin head gaskets on it too which probably made another 5# compression to get to the 115 otherwise it would probably had been 110 or so... But it made the thing run a lot better..

[495SWIFT]

Has anyone milled the heads on a 200xp looper 3.0 it has 98-100 accoss the board. Looking for 130, can an OMC guru chime in on how many cc's yield that or how many thousandths to mill?

[71V153]

You can mill em purty tight. ~150 psi is not unheard of. Just make sure ya use surface gap plugs ...

[495SWIFT]

Thanks 71V153, I was thinking about milling .030 off or the thickness of the existing gasket. I already run premo fuel but 150!?, what kind of total timing you suggest 20ish? and say... up three jet size equivalents for the fuel?

[skeeter91]

how about starting your own thread instead of jackn' mine?

[skeeter91]

i got this set of heads cheap so i though i would try it.i am having a tough time locating early heads that dont have ring damage on the starboad side.i recently bought two 1976 200's from two separate people,both of them have the good uncut heads(643/644),and both also munched rings on the starboard side.i also just picked up a complete 175 crossflow with 556/557 heads,havent pulled them off yet.know if these are any good or not?

[phase3looper]

I've taken .100 off of 2.7 heads if you have the exhaust relief ports plugged it'll put you right at 150

[495SWIFT]

how about starting your own thread instead of jackn' mine?
just keeping it going..not jacking, glad to know there are others doing this. On my mercs I used to repair ring damage by preheating the head and tig welding and floating the trash out of the bad spots then re shape chamber and mill, hope this helps

[495SWIFT]

how about starting your own thread instead of jackn' mine?
just keeping it going..not jacking, glad to know there are others doing this. On my mercs I used to repair ring damage by preheating the head and tig welding and floating the trash out of the bad spots then re shape chamber and mill, hope this helps