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Low Budget 350 Chev - Page 8
TRIAL ASSEMBLY I installed the main studs and caps with the bearings and torqued them down to get a reference size and after measuring the crank main journals, worked out a base clearance. A bit of swapping of bearing shells left me happy with a common clearance throughout. Then I installed the crank and using plastigauge on all the mains I retorqued the caps and once again checked the clearances. I opted to go for more clearance than you would use on a street engine that was intended to last for a hundred thousand kilometers between bearing changes. My thoughts for this were so the crank was not tight in the bearings and with the higher volume oil pump, I would still end up with reasonable oil pressure. Realise I am still only talking about clearances within factory specs for serviceable limits and have intentions of replacing the bearings at the end of years racing. (If the engine lasts!) Once I was happy with the mains I installed one piston at a time without rings and checked big end clearances on the crank. After grinding what I thought was enough off the block to allow the alloy rods clearance, they all still hit the pan rail, so I had to remark the block, disassemble everything and get out the air grinder. This procedure was carried out another four times to get it right! It took me till I was almost finished to realise why I had to grind so much off. I had never put alloy rods in a 350 before as I always used the shorter stroke 3.25 cranks. This crank needed an extra .125 of grinding to get my clearance. One point for guys building long stroke 383 chevs, If you use alloy rods, be prepared for a lot of grinding. I think if I built a 383 stroker, I would be using a set of the easy to get H beam rods as they look like quite reasonable units for their cost. The next problem sent to try me out was when I set up the cam to degree it in.. Four of the ally rods hit the lobes of the cam, so more grinding of the rods was needed to obtain clearance. This is another point to watch out for as I only used a small solid cam, and if I had a roller with high lift the problem could have been worse. Also if you are building an engine, check these clearances before balancing the rods or whole assembly as if you have to regrind for clearance you balance job will be wasted. Ok, everything has clearance, the bearings are OK, now to file the rings to the correct gap (or the gaps I use). The ring manufacturer will recommend gaps for different applications, and there are all sorts of arguments about the first or second ring having the larger gap, whether or not gapless rings are better or not etc. etc. Her in Oz gapless are VERY expensive, (depending on your budget) and if you were building a Pro Stock engine and chasing the last horse probably what you need but for me I like the basic moly top ring set, but to get file backs, the purchase of a set of plasma moly rings are the way to go. The only way to file them back is using the proper tool. Beg borrow or steal one before trying to use a file by hand. If all else fails make up a jig to support the ring square to a good file and take care. This would have to be my least favorite jobs other than cleaning parts when building an engine. After the bottom is clear, I lightly bolted a head on without gaskets (this allows me a bit extra clearance when the gasket is used at final assembly). I installed two valves using a small spring found at hardware shops to check the valves did not hit the pistons. The small solid cam I am using did not have any problems so notching the pistons was not needed. Stips of modeling clay on the top of the piston will give an indication of the clearance, and the head to piston clearance in the quench area. One thing I did at this stage was at every 5 degrees of crank rotation (30 degrees each side of TDC) I pushed the valves down till they hit the pistons and measured the distance. This will give me an indication of clearance if I change cams in the future as to how much lift can be used without having to disassemble and notch pistons. If you are going to put in oil drainback screens in the valley area now's the time. Now the grinding, filing and clearancing is complete the rotating assembly can be sent off for balancing.
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