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Low Budget 350 Chev - Page 7
BORING THE BLOCK Time to get the block bored. I had ground as much material as I had thought was needed to allow clearance for the conrods without having a piston to hold the small end central as I turned the crank. if I had old pistons I could have used one of those on each rod to get a better idea. Do the best you can with what you have.. Do as much grinding as you have to now before boring. At first I couldn't work out why I had so much grinding for clearance then remembered the rods were used before in a 327 which is about a 1/4 inch shorter stroke.. At the time of writing, looking back I might point out to check the camshaft clearance with longer stroke engines (377 383 etc) or when using alloy rods!. These hit the lobes in cyl1, cyl4 and cyl6. After reading articles on the net regarding the boring of engines I decided to spend a little more and have the block bored with torque plates. The idea of torque plate boring and honing is to attempt to imitate the stresses and forces placed on the block when the heads are torqued down. Apparently the bores will remain true after assembly creating a better ring seal and ultimately more horsepower. Two local engine machine shops did not have torque plates to suit a small block Chevy so the block was taken to Townsville and given to Ken Melvin to do the honours.. He required to know what head gaskets I intended to use, what torque settings on the heads.. Talk about fussy!. I also had to install the main studs and caps and torque them into place before taking the block in. This saved Ken some time and ultimately me some money. Each piston was measured individually and the result written on its top. Each bore was then done to suit each piston. The instructions for the pistons indicated a minimum of .001" clearance was needed due to the lower expansion rates of hypereutectic pistons. This low clearance would have been to suit the expansion rate of the bores in a normal block, but after some discussion regarding the fact the expansion of the bore may be restricted by the grouting, it was decided to run a clearance of .002". I was given the opportunity to watch the last hour or so of the process. The block was mounted with a 2" bar through the main journals and set up so it could be rocked from one bank to the other in order to keep each bore true to the crank line etc.. Someone with more knowledge of machining could explain the reasons better than myself. All the bores were honed a bit at a time and left to cool while working in another bore. This was to keep the whole block cool and more even. The bore was checked up and down for taper and the hone set to dwell at different positions to get it all true. The amount of checking was unbelievable, the honing head would only go up and down the cylinder twice and then taken out so the bore could be checked. Ken was as fussy with the old budgie block as you would expect with a top dollar race engine block.. After seeing what was envolved in this process, using torque plates and a reputable machine shop, the extra money spent was well worth the excercise. Next... Trial Assembly.
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