I am working on a 383 stroker motor, rod and main bearings have an X at the end of the part number. The info I can find says that means they are .001" thinner for more oil clearance. The problem is that makes my main bearing clearance .0035" and rod bearing clearance .003" this means they are out of spec by all of the books I have. The rods actually feel loose when I install and torque them. The problem is, I have had a couple of people tell me you want them to be loose for more oil clearance for a higher rpm engine. Sounds questionable to me, it's like I am building a worn out motor. This will be street driven occasionally and some casual drag racing. I have built several motors and never ran into this before. thanks for all your help.
some bearings use x as a +.001 oversize ,its ussually varied by brand, find the specifics on your brand! some use thisas an undersize to take up a worn crank, also make sure you havenarrowed or chamfered bearings if you have a crank with a wide radius, most aftermarket performance ones do. as for the clearence you have waaaay to much, youll have very little oil pressure and it wont be long til you loose a rod. small blocks are forgiving but would try to keep the rods from .002 to 0025max and the mains around 2.5 nomore than .003 keep it tight you wont need a h/v pump save some power, remember you only have the oil film between the bearing and crank to loose your film breaks down and your bearings will score.check your rod side clearence , this will keep the rings and cam alive ,often overlooked and dont ***ume your stuff is right just cuz its new, very few rotating ***emblies come in my shop that dont need work, especially low dollar stuff, it usually needs some type of touch up, especially cheap stroker cranks!! also even eagle i beam rods, good rod, but ive never seen one that was round on the big end,etc,etc.i ccould go on forever,bottom line, your spending the money,double check everything! and get it in the published spec, not what sombody thinks is good!your on the right track!
Thanks that is what I was thinking, just have not ran into this before. I had two guys that have built several engines tell me I needed more clearance for this engine, but when I twist the rod on the crank with bearings in and torqued, I know it is going to knock and not live long. I have been checking and rechecking especially after I learned they didn't know what I thought they knew.
Your bearing clearance sounds good too me... I set my small block up with .0035 to .004 on the mains and the rods are .0035 to .0037 with a high volume oil pump and it runs pretty good for a sbc.
The extra clearance needed for a high reving motor is realized when the rods are at .002" and the mains are at .0025"! This would be the target clearances.
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