HI all, I am rebuilding the 364 from my 1958 Buick and I have some questions.. The shop manual recommends a piston to bore clearance between .0008" and .0014" and a minimum piston ring gap of .015" I have bored and honed the block to have a .0008" clearance with the new +.030" pistons supplied by Russell Martin. Now the ring gap is only .008" I asked Russell about this and although I was first told to go by the shop manual specs, after this difference occurred, he advises me to use a piston to bore clearance between .0018" and .002" and says that should open up the ring gap. If not, file fit the rings he says. He also advised that he likes to use a ring gap of .017 or .018 I just want to check with you guys what clearances you use. The new piston clearance he has advised to use, is way over the shop manual specs. I don't want to end up with the bores too big and the pistons lose .. causing a smokey engine. Please advice.
I would go to .001" to 001.25" clearance. This should take care of the ring end gaps. I wouldn't use .0008" as my finished clearance. You MUST remember on initial 1st. time start the pistons are gonna "Grow" more than usual because of added heat & friction. Then they will get scuffed on the sides. You WON'T end up with smoke with this clearance. A "Nail" will normally put out a puff when started because of the guide clearance & no guide seals especially on the exhaust. Intake seals are OK to use, but you will normally still get a "Puff". Tom T.
Generally speaking, going an extra .0006-.001" more on bore with cast pistons, and an extra .002-.003" on gap is not going to make an oil burner... Retarded timing could make that a tight fit quickly.
go with Tom's recommendation.... and rather than mess with piston/bore clearance,,,, file the rings..... I like to stay with stock specs on the pistons and rings...
Most modern pistons have the minimum clearance built in to them. Mike the skirts perpendicular to the wrist pin bore, generally full skirt pistons will have some taper built in to them (At the very bottom the piston will measure about .0075-.001 larger then it does up by the wrist pin). Set your skirt clearance with the smaller measurement taken up by the wrist pin. A 364 is standard 4.125 bore if you are going .030 finish bore size should be 4.155. Those antique shop manual specs don't mean much anymore. Piston alloys and piston ring design have changed by leaps and bounds in the last 60 years, to boot today's fuel burns almost twice as hot as the old leaded stuff. Old rings were dependent on tension to seal where as modern rings are gas loaded. For engines with 4.5 or smaller bores Hastings recommends .004 per inch of bore diameter 4.155 x .004= .0166. I would be scared to set that engine up with that tight of ring end gap and skirt clearance.
