Hi Jem,Jem wrote:Andy,
a friend has asked me to post the following. He has spent time in the past tuning 478/501 motors.
"The 507 barrels are a larger diameter on the spigot and therefore the holes in the crankcase are larger. If he fits 478 barrels they will drop in but won't have the integrity or rigidity as the barrels will be a sloppy fit. When I fitted 507 barrels to a 478 crankcase I had to turn a 2mm (I think) off the spigot diameter. He needs therefore 478 crankcases and to fit 70mm pistons which will bring him up to 496cc just under the 500 limit.
If he intends to race, then he should use forged pistons not the Morini ones with the split skirts as the skirt where the hole ends the split has a tendency to crack and break off. I have rebuilt a number of engines which when on stripping have had this problem either a crack propagating to the edge or the bottom already broken off. The pistons I had made some time ago were forged because at the time Asso only had one piston with no intention of making anymore."
He was offering a 500 which had been worked on, a couple of months ago. I'll ask if it's still available.
Jem
I hope you don't mind my jumping in to your thread,
Please can you find out if the forged 70mm pistons you friend used had the combustion chamber in the piston crown and who made them if so.
Thanks
John