The Renault manuals nominate a maximum removal of 1/2mm from Ventoux cylinder heads. While that's no doubt conservative, 1/8'' would be very risky. The problem is the bottom 'deck' of the head is fairly thin. While it is stiffened by the vertical walls of the combustion chamber, that leaves sections of the liner periphery relatively unsupported. I'm a coward - I removed 1mm and wasn't game to go further!Hi Stan
You are over-thinking this looking under the bed for boogey men. Extra CCs are good, no down side really. (except cost ?) Forget about valve shrouding and air flow etc etc that is all BS in this circumstance. If you can clean a few casting dags and match the manifolds better and even clean out the valve ports a bit, it will feel good. If not then just settle for the 7%. Shave the head while it is off to get the compression up to a modern figure. You might have to retard the ignition because the engine runs so much better as the combustion is faster. In times past on old Citroens I just asked for 1/8" off the head. No down side ! I probably shaved a few 750 heads too but forget now. They were meaty thick alloy castings if they are not corroded badly. Gees the difference the good coolants made there. The R4 was an early model with a 750 engine and the head was just the same as the 750 heads as I remember ! I put a hot cam in that too but it was really too wild for a 3 speed and front wheel drive, but a small cam would be good too !
Back in the good ol'days, say about 1965, we had a 750 we acquired from somewhere and drove it around a newly laid out subdivision with dirt roads behind my mates place. Heaven sliding it around till somebody rolled it. So we went and cut the roof off with a can opener and a hacksaw on the pillars and frame members. Left the doors on "for safety" as no belts in those days. I think we rigged up a can and hose so "no one else could drive it", and had to tie the center pillars together with a rope to hold the doors from drooping when opened That kept going for quite a while till it just disappeared one day. Ahh well, easy come, easy go !
We had earlier (or later) done a similar thing with a Fiat 500 Toppolino fitted with a Triumph 500 twin motor. It was fun for a while 'up the back' of another mates place. Then he came home one day and a dozer had cleared the area and dug a big hole for the rubbish and made it all go away, before the subdivision started. Bugger !
Hmm had a Honda 50 step thru that did good service for a long while through the bush again. My mates wife was the quickest till she found out it had brakes. When the bike fell apart I fitted the motor to an old kart frame for my kids to drive around. Not a bad unit for a freebee either. I wonder where that went in the end ?
Cheers Jaahn