good idea, bad idea?

fireblade · Post by **fireblade** » Wed May 06, 2009 5:21 am

would it be a smart move to machine material from the bottom of the jug where it bolts up to the crankcase, to raise the deck height of the piston and increase compression? Or is there some pitfall in doing this?

bakaracer · Post by **bakaracer** » Wed May 06, 2009 5:39 am

its easier to deck the top.but what reason are you decking it for?

Post by **noiseguy** » Wed May 06, 2009 9:45 am

The reason guys used to do this on some bikes was to alter all the port timings. Frankly, unless you understand and are comfortable changing port timing, I wouldn't do that. Just knock the material off the head instead.

fireblade · Post by **fireblade** » Fri May 08, 2009 3:37 am

what about removing material from the top of the jug?

Post by **noiseguy** » Fri May 08, 2009 8:18 am

Well, the head is easier to machine and cheaper to replace. I guess I don't see why you'd mess with the jug at all.

burnt_toast · Post by **burnt_toast** » Fri May 08, 2009 9:39 am

indeed, head is aluminum jug is cast

keithw · Post by **keithw** » Sat May 09, 2009 10:48 am

The port timing on these is very conservitive. Machining the bottom of the cylinder will lower the ports reducing performance. Some actually spacer up the cylinder to raise the ports. The easy answer is mill the head. If you want to get fancy spacer up the cylinder then cut down the top of the cylinder the amount of the spacer. Make sure you understand what the ports are doing and the port angles before and after.

keithw