www.zxrworld.co.uk

my brother has a zxr 400 L1 1991 the head gasket went so he went and got a 1996 engine but did the same to that so he has two engines and wants to build one out of the two would he gain much in having it polished and ported and skimmed would he need a dyno jet kit if he did and can the cams be fine tune on the sprockits any help would be great

cam sprockets are fixed unless you are running SP cams, this limits how far you can skim/deck things before losing cam timing.

cleaning up the ports wont hurt if you know what you're doing, but will if you dont..

i've done a couple of heads, reckon im starting to get there but my bike's no 75bhp+ rocket ... yet

easiest thing to do is skip the base gasket on re-assembly, safely tightens the squish up a bit... and tbh, if its a road-bike and the head isnt warped thats really all i'd do

Yes & No,

Removing just the casting marks will make for a smoother responce - you might gain a pony or two top end.

Unshrouding the valves certainly helps any engine tune state and you'll need to forget about fixed "jet kits" to get the benefit.

if you've two engines needing work then personally I would go the full hilt on one, I've got 5 working motors and one of them is getting laid into !

1 motor 1 chance then no - go full free flowing pipe, carb's and rolling road to get the most.

MM!

as i am doing head gasket and cam chain on my bike while i have the head off i am cleaning all the valves and ports up, cleaning up casting marks, re-lapping valves etc.
when you say skip base gasket do you just take it out clean up the surfaces and bolt it back together or do you have to you sealant or something?

Use sealant.