I need some advice on fully grooved mains. My motor was rebuilt about 5 years ago by the previous owner and has under 100 miles since the rebuild. The engine is out while the engine bay is finished and I am doing a few things to the engine...mostly bolt on items such as CC heads, bigger cam, roller rockers, one piece SS valves, etc. The engine currently has half grooved mains that were put in during the rebuild by the pregious owner, the crank was ground .010 under and polished and then the (stock) rotating assembly was balanced. Should I swap out the main beaings to a set of Clevite fully grooved bearings. One of the changes I'm making is a new cam with a .580 lift with 290 adv duration so it should be able to push 6000-6500 rpm. Is it worth the effort to swap the bearings at this point...will it necesitate a better than stock volume oil pump? Can I do it without a additional machine work to the crank?

I recommend fully grooved mains on anything other than a grocery getter. I was last told the Clevite fully grooved mains were only available in standard size however. I don't know if that's relaible information.

There are a few ways around this, like checking other bearing manufacturers such as King bearing. I know Denny Wydendorf modifies standard sets to make his own fully grooved mains, it would be worth it to contact him via his web site and see if he'd sell you an modified undersized set.

Wydendorf Machine

You should be able to replace the bearings without further crankshaft work. You'll have to disassmble the motor, put the bearings in the saddles & torque the caps in place, measure the ID and compare to the crank journal OD. The ideal clearance is 0.0025", with limits of 0.0024" to 0.0027".

Fully grooved mains are one of the building blocks of a lubrication system equipped for higher engine speeds. There are a few other considerations as well, for instance the proper oil pan. Something to discuss perhaps at a later time.

-G