Skimming head with gear driven cams

[shadowhawker]

Is it possible to skim a head for more compression on gear cam drive engines.
Move the gear carrier mounting holes so the gear carrier can be moved sideways and down a fraction?
Anyone done this?

[Drunkn Munky]

Yes, pretty much every V4 400 race motor has skimmed heads

[shadowhawker]

So how do you alter the gear train to maintain mesh clearance?

[CMSMJ1]

you space it up....

Get thee to the search tool - it is in a few threads relating to the NC30s..

[shadowhawker]

Nothing in cam spacing, head skim, cam gears, cam gears shim, camshaft gears, skim.
There is a reference to taking half a mill off the head in Sparkly race bike, but it just says.".head back on..."
Did get this, but no how to.
viewforum.php?f=24&start=4775
and a diagram of shims
I would prefer to modify the gear carrier rather than shim the gear carrier.
The info on doing the shim is contradictory.Just shim the amount taken off, or measure seperately.
I am looking at all the threads individually now....220 done...

[steve92]

I'd also like more info on this if anyone would like to share.

[blueflag]

Did it on my Triarm. Quite a performance really and I wouldn't bother again.
The idler gear assembly that sits in the middle of the barrels needs the side plates cutting horizontally to allow the bottom gear to be offset, thereby putting backlash into the gear train then welding up again. If I remember correctly I offset mine about 5-6 mm. (more than that and I had clearance issues on the casting.
That allowed me to run without a base gasket (.25mm).
Bottom line, it ran well for 2 seasons then I started feeling a slight vibration on the overrun during a couple of races and it finally let go in the last race of the season last year (weld on the side plates cracked) costing me a very comfortable 2nd in the Forgotten Era championship I was in. Bitter? ME?
VFR pistons, that's the easy way!
HTH.

[shadowhawker]

Ouch..that's a bit of a bastard, as they say in racing.
I still think the carrier mod is worth doing..with judicious strengthening.
Thanks for the info, been at this all night....
.

[Cammo]

As blueflag says, using rvf400 pistons (vfr are discontinued) will increase the compression ratio. Easier than skimming the heads and the rest of the work.

I don't know how much this increases the c/r by, anyone have any idea?

[shadowhawker]

£674 a set Plus rebore/ gasket set well over £700.

Gear mod £0 skim £30 Gasket set £30 = £60

Leaves £640 for drugs n whores......or race wheels....