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CROSSFLOW HEAD MILLING

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Any idea what the limit would be to mill a 55cc xe head ,like is it possible to take 10cc or more out of it ,im just dabbling with the idea off flat tops instead of 20.5 dish,to get close to 11.1 the head needs around 40cc ,pistons and rings and head gasket ect is gunna be about 500 bucks or mill the head for a cheaper rate but will need shorter pushrods,so cost is about the same but less effort to take the head off.

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11 hours ago, ando76 said:

You may want to factor in your piston to valve clearance.  Personally I wouldn't hack that much off a crossy head. 

Yep, what he said.  With a high lift cam, etc...may need eyebrows cut in the pistons.

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Yep, it's basically the same, but, the combustion area is shaped differently, all the combustion with flat tops, is done in the head cavity. Don't know how that would affect a Crossy, Slydog would prob be the best fella to answer this. Obviously pulling the head off would be easier than engine out, and piston swap. 2mm is a fair chunk off alloy to remove, and it's bit harder to put it back. Can use copper head gaskets, (Cometic ? I think) but they're pricey. And any head swap in the future will need the same machining, as the original. 

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Skimming the head on a quench type combustion chamber needs more meat off than an open chamber, as part of the bore area is already flat so is not included in the CC calculation. Every head design is different but for a closed chamber clevo, 5 thou off removes 1CC of chamber. I should imagine crossys to be similar since although the bore is smaller, the quench area is proportionally less than on a clevo.

Another very important aspect is quench distance. If your pisons are down the hole, no amount of head machining will fix the poor quench that results, regardless of how high your compression is.

Example: If i had my time over again, the clevo would've copped a set of proper zero-deck pistons instead of the Hypertec rebuilders, which sit down the hole too far. Either that or skim the block to get to zero. I ended up taking 0.025" off the heads to get to a bit over 10:1. If I'd have taken the meat off the deck instead, it would have only needed 0.015" to achieve the same cc, with improved quench.

Best quench distance is generally said to be 0.040", which happens to be the thickness of a standard head gasket. People do go thinner than this but are pushing the envelope for kissing the head with the piston top.

Sent from my CPH1607 using Tapatalk

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Gerg is on the money pretty well. 

Next thing that may be interesting is my current head has had the chamber opened out a far bit (thanks to previous head porters) and as such quench area is huge but running flat tops with a zero deck helps this along with a low cranking psi. Engines rattle on the torque peak more often then they do @ hp peak. 

Next thing is my block was decked 45th or so to get zero deck with the slugs use. Next is my cyl head is all but flat on the indicator and as yet both have given me zero issues from doing such. 

Food for thought.

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so yes or no for milling a heap off the head with dish pistons ? while on the subjevt i saw a keith black 1120 piston to suit usa 200 engine,with a smaller dish but the comp height is smaller does anyone no the dish size it says .085 ?

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