Moparts Tech Archive

Big Block

big block oiling mods

other than installing a 1/2" pickup and reaming the passage between the mains and cam to 9/32 is there anything else that should be done? it looks like the main to cam passage can be enlarged to 3/8 as that ist the size of the hole in the main saddle.

I don't enlarge the oil hole between the main bearings and cam bearings. The hole more commonly enlarged to 9/32 (or 17/64, etc) is the angled hole from the main bearings to the passenger side oil galley (lifter galley). This feeds oil to the mains.

When adding the 1/2 NPT oil pickup, I recommend checking that oil passage and enlarge it to 5/8". For comparison, the drill size for the 1/2 NPT tap is 23/32 (0.7188") and for 3/8 NPT it is 37/64 (0.5781"). The connecting passage to the oil pump can be enlarged to 5/8" also. I have found some already that size and some only 9/16".

Also, from the rear of the motor, take out the oil galley plug on the drivers side of the motor and push a freeze plug into the bore just past the feed that goes to the oil pressure guage ports. It's a 15/32" I think, I'll have to look at my papers at home. Do this mod only for a solid or roller cam as it blocks the oil off the lifters. You can drill a 0.10" hole in it to let a little bit of oil go through if you want. This mod greatly increases the amount of oil availible for the main and rod bearings.

I believe that plug is 19/32". I just helped a buddy with his B-engine stroker. We found this info in Hensley's Racing Ent. "Little Purple" Book that Herb McCandless wrote. Yeah, it's for solid & roller cams only

IMO it's also good idea to groove the fourth cam journal for full time oiling to the rocker gear.If you do this you should install a .060 orifice in both heads to control oil flow.I would like to hear other opinions on this mod.

when i did my 383 block i also tapped the passages to all the cam bearing and installed allen head set screws with an 1/8 th hole drilled thru it to restrict oil flow to all cam bearings except #4 which feeds the rocker gear , i got this from a sheet on doing the mods from herb many years ago .

the front cam bearing is done from the camshaft end , i guess an easier way would be to drill smaller holes in your new cam bearings and install with that smaller hole over the feed passage . i do like the idea of grooving the #4 bearing , what's the best way to do this in a lathe ?

oh and joe , i just used an aircraft drill bit to open the passage , not a reamer . worked fine , did it with a pistol drill and lots of oil .

Yes, you can either drill and tap the head or block deck and install a drilled set screw, or go another route. A short piece of 1/4" rod will fit into the rocker stand side, and the 3/8 hold down bolt will capture it. There is some clearance between the 1/4" restrictor and the hole, so you probably wouldn't want a .063" orifice. In fact a flat filed on the restrictor would work, but its a little more difficult to calculate the orifice size then.

thanks for the clarification on the groove , i thought you cut the groove in the cam BEARING cutting it tin the cam never even crossed my mind , much easier . i'm guessing you put the plug withthe orifice in the head oil passage ? another no brainer .

When you drill and tap for the 1/2 pickup, don't go too far with the tap, or else you may not get the pickup to snug down...as I recall that's a tapered pipe thread that's required...count the # of threads before drilling the hole oversize and duplicate that # when retapping....you should also consider radiusing the 90' bend between the pickup threads and the pressure side of the pump, the MP manual gives a good picture of where to grind, just do it carefully with a LONG carbide ball bit or you may grind the opposite spot close to the pump mounting boss and ruin the block....I've seen it happen!

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