head skim

[superls]

hi all, as i will be removing the head to replace the head gasket, is it worth having the head skimed? ive heard of it being done before as a proformance upgrade iirc? what if any gains will i get, and if using a standard head gasket how much is a safe amount to take off of the head?

im also looking in to uprated cams, what cams are available for the ma12 and what gains will it give and how much roughly are they?

cheers superls

 

[curtis]

slight difference noticed, increase the compression iirc, about 0.2mm iirc

ask ed, he'll know.

 

[ollie240585]

Think Ed will do a K10 cam for £140, PM him.

 

[frank]

superls

a 1.5mm skim will give you about the same c/r as a 1.0 5 speed
i had about 2.5mm took off mine but had to adjust the valve timing to suit

 

[superls]

so with a 1.5mm skim would i be looking at a 5 bhp increase, like the 1 litre 5 speed has over the lower compression 4 speed?

 

[frank]

superls

in theory yes !
it will retard your valve timing a bit tho, so the powerband should be a bit higher in the rev range
i advanced the cams on my k11, i prefer a bit more grunt, its an option ?

 

[superls]

what do u mean by advanced the cams?

u got msn?

 

[frank]

superls

i hav,nt configured msn on linux yet
i filed a flat on the locating dowels and rotated the cam sprockets
a k10 would need the top pulley holes slotting ( would have to be engineered right, they are prety thin iirc )

 

[superls]

yea they are very thin

 

[frank]

superls

the timing difference will only be about 3 or 4 deg, about the same as an old belt vs a new belt imo

 

[Craig]

Sorry for the silly question, but why does a skim retard you valve timing?
Also - Frank, you slotted the dowel on the cam gear on your K11 - what kind of accuracy do you have for advance/retard as I've been hinking about oding it myself?
Cheers Craig

 

[frank]

craig

the head will be 1.5mm lower, so when you adjust the belt to suit, the top pulley will turn anticlock to take up the slack (retarding the valve timing)
a stretched belt or chain will have the same effect
the accuracy is down to timing with a protractor or crank pulley marks
a 1mm flat on the dowels is about 5 deg iirc

 

[Craig]

Ah, I see - youre keeping the pistons at TDC and the extra slack is taken up by the cams, that makes perfect sense.
How well has the cam stayed in it's position with the dowel enlarged, do you know?
Craig

 

[frank]

craig

i filed a flat on the dowels, which leaves a gap on the other side
i drove it for 2 weeks (500 mls) then checked whether they had slipped (no)
but to be sure i made some little steel shims and slid them in the gap (the big fat washers hold them in ok)

 

[Craig]

Steel shims - that's using your noggin, I like it - think I'll have a go over the weekend at it