RB main bearing oil delivery passage

After many years of dinking around with this stuff and wondering: 'why did the factory do such a lousy job on the oil holes to the mains that come from the oil galley? They have "steps" them that hurt flow" etc

Well I think I know why they did that, now.

On some blocks, despite appearing big and beefy, the casting isn't especially thick in the area the oil hole needs to be. If you add in just a little core shift in the wrong direction, then try to create a little too large of an oil hole....the SIDE of the oil hole can break through the casting into the crankcase, and you've got next to nothing for oil pressure.

I've recently encountered this exact screw up... the previous owner gave up on the engine because of oil pressure problems. I got the block. Autopsy shows the oil holes to the mains were sloppily drilled to 5/16" + some drill wander slop. And I found a pinhole in the exact location mentioned.

I am pretty sure I can repair it with a tube, which is a puzzle I'd rather not work on, but will save the block as long as the repair is done correctly.

On his site Dave Hughes recommends 1/4", Chuck Senatore recommends marginally larger 17/64" done with a reamer to avoid "wander". So far I haven't seen anyone wholeheartedly recommend 5/16 but it appears someone thinks it is a good idea??

Beware.....Going too far with an idea or executing it the wrong way might create an expensive repair at best, scrap at worst.

Some is good, more is better and too much is just about right. Some folks think that Moore's law applies to every thing. Hope you can fix it.

Brian

I ground the end of a 9/32" reamer about 1/2" back from the lead edge to act as a pilot. Clean out any boogers. I saw a cylinder head oil feed hole into water on a Koleno block with core shift a few years ago.
Doug

9/32 is as big as I go on the main feeds.

I've always question magazine writers that become motor experts and recommend some stuff that doesn't work or are not needed, especially on BB Mopar V8
I was and am privilege to have known and receive mentoring from Mopar drag racing greats like Dick and Mike Landy, Joe Alread, John Deiana (SP?), Bob Lambeck and many other west coast BB and Hemi Mopar drag racers, none of them ever suggested reaming or enlarging the main oil galleys
I have seen oil restrictors in some of the blocks that the Rod Shop had built and sold to one of my customers, they where in all of the cam oil feeds from the main bearing passages, .060 or so.
I am not a all out drag racer, more of a bracket and Super class racer so most of my motors don't see north of 8000 RPM, ever
I am a firm believer in using full groove main bearings and high volume oil pumps and plenty of oil in the oil pans along with a minimum of .001 + oil clearance for each one inch of crankshaft rod or main bearing journal size
IHTH some

be aware that when using a reamer in any drilled hole, the reamer , no matter how it's modified, will follow the hole as drilled. if the drill wanders, so will the reamer. an end mill or boring the hole is the only way i know of to straighten up a mis-drilled hole. and being a long, deep passage, a tube repair is about the only thing you can do to fix the block in question unless it's possible to weld an iron patch of sorts over the pinhole. and that, i believe, would almost be impossible to pull off. just my opinion.

Thanks for all the replies.

I got sidetracked on an ignition system experiment but am going to think about this block repair some more while I do other stuff.



This is how I saw it as well, a tube makes the most sense.
Researching exactly what kind of tube, now.

It sounds funny, but for a time it appeared a (cast iron) valve guide might work. But then I realized I'd have to ream the hole out pretty monsterously huge, like 1/2" for that to work. So for now it seems either 3/8" or (specially ordered) 9mm stainless steel tubing will probably get the nod, and I'll have to get an assortment of reamers to sneak up on it. For now, I'm assuming a .001 to .0015 press fit should be adequate/about the same as a cast iron valve guide(?).

You should be able to get some ultra thinwall brass tubing from Hobby shops. I had a wedge Megablock I bought from Mr Nice guy that had the same issue, and was repaired that way. No problems for me!!

The cylinder head guys use tubes all the time to seal up the oil passages or other things so tubing should be available. I wouldn't think you would need a press fit to hold it in place since it can't really go anywhere. Maybe a little dab of locktite on the outside of the tube when you slide it into place.

^^^^^^^^^^This. You don't need press fit on something like that.

Wasn't really concerned about it falling out or going anywhere.

Purpose of the press fit is to hold oil pressure and seal up the leak. Concern: if the tube has any clearance in the hole at all, oil can leak past the clearance, and I'll lose oil pressure to that main journal.

Is this thought process flawed?

I suspected it might be a more common problem than discussed...thank you
for the comment

I have seen a LOT of Mopar engines just plain RUINED by "tube and peen lifter bores" and drilled out passages
I have NEVER EVER seen a Mopar that failed because it was not drilled out in some way--never seen it where someone could prove that was what happened all that being said I am a 9/32" man when a hole needs the crud knocked out of it
Honestly all that stuff is just where old 4 speed guys were grabbing at straws to keep the crank in one when they were turning them so far beyond what they will stand that is was not funny--a good restrictor every now and then will help-- a bigger hole in a stock block eehhh...
Just my opinion--keep on drilling and screwing them up if you want

I had a 383 stroker years ago that ate a rod bearing on the dyno. When I tore it down I found a main oil passage that was partially blocked. When we built the engine we just never checked the oil feeds but now I always double check them. I don't think they need to be huge but they should be open. I have some extra long 17/64 reamers that I run down thru the holes. Sometimes one of the holes will make a big pile of chips so that tells you that it was pretty tight.

My Indy SR headed 7200+ rpm 446" wedge is a stock '72 440 block out of an Imperial w/ no drilling to any passages. Ran the snot of it for 3 or 4 years w/ no trouble at all. Bearings looked great when I freshened it up. It does have a Milodon single ext. p/u oil system on it...same setup I use on my hemi.

I like to run a 0.257" ream through them. If nothing else, to get the twist drill grooves out. If I'm going full time oiling to the valve train, I'll open #4 to 0.281". As some have said, I suspect that it really does nothing to help.

Good input, thanks.

I'm going to have to go a little farther, get it on a stand, get the small hole gauge in there and see what I've got. I just did a quick check with the block on the floor using 5/16" drill bit, which fell right in...