Rod Oil Clearances
 

Building a short block for a customer and getting some rod oil clearances up to 0.0030". I know that is high and not desirable, but I want to hear from people who have run those clearances on the street. I just want to know if this thing will live. I have gotten rod bearings coated from Calico before to adjust oil clearances, but I'm trying to avoid this since it's a budget build.

What brand are the Rod bearings and what is the average Rod side clearance your seeing?

Here’s the spec’s that HO racing use to call for, so I would not be concerned in terms of the bearing clearance.

What I would be concerned with is if you have more then .030” side clearance because then you will move a lot more oil out of the bearing clearance that you do have .

Street/strip or strictly a street engine?

Strictly street I think, maybe at the track once a year. I just put the crank and RMS in today so have not measured rod side clearance yet. The rods are Eagle so I can look up past builds to get an idea of side clearance.

Here’s what Federal Mogul says for a street motor.

I don't run them that big. When I have a situation like that I get another set of .001 under bearings and start combining sets till I get something more acceptable.

Is this crank your using still std on the Rods and Mains?

If the crank was cut I have found it never pays to do so before you have the Rods and Rod bearings in hand to measure up.

As opposed to bearing failures from not enough clearance I have never seen a rod bearing issues or failure from having good clearance, even if on the high side of good.

Are the rod journals 2.50" Pontiac size or the common 2.200 BBC size? +.001-.001 readily available for the BBC size. Not sure of ready availability for Pontiac stock size. I would start with a 1/2 shell STD and 1/2 shell -.001. That should put you at .0025" clearance. .0023-.0027" is ideal for a Pontiac street engine IMO. It will live at .003 but not ideal. May run only 10-12 PSI oil pressure with an auto trans and the AC going @600 RPM in drive.

Rod journals are std at 2.500", couldn't find any 0.001" oversized bearings. It's an aftermarket crank and the OD of the rod journals are on the small side hence the big oil clearance. Anyone that has run this big a rod oil clearance? Thanks all for the replies, trying to make this work.

Both Butler Performance and Rock Auto show -.001 bearings available on their web sites. I imagine other vendors have some too. That would enable you to dial in the clearance closer to what you are looking for.

FWIW, I once had a 301 that I slammed together that the crank was .010 under on the rods only from the factory. The mains were standard. I put standard bearings in it inadvertently and drove it about 50 miles. Other than low oil pressure at idle it was surprisingly quiet and when I took it back apart I finally realized that Pontiac had put it together with a undersized crank with Moraine factory bearings.

I just swapped the standards for .010 bearings and it was fine. No metal transfer, and the rod throws were clean, and round. Now this was just highway driving, and not hammering it, but with .010 + oil clearance I was quite surprised there was zero damage and lack of any unusual noises.

Yes, there are 0.001" under for extra clearance but no 0.001" over to reduce clearance. Wish I was dealing with 2.200" journals.

What mgarblik described is what I do in situations like that. You may only need to mix half shells like he said, just takes a little time to find the right mix that gets you where you want to be.

I had a similar problem with a new aftermarket scat crank on a recent build 6 months ago. Rod journals were a hair on the small side and I didnt like the clearance. It was either send the crank to be turned to one of only a couple crank machines in the state, spend $300 and hope it comes back right, or buy another set of .001 under bearings and start mixing shells.

I opted for the latter and it worked out fine. I ended up with .0022 to .0024" after a couple hours of mixing and measuring and a set of rod bearings were only another $150

Happened to me and I just got coated bearings. Fantastic oil pressure at all RPM.

I use coated bearings in everything from either King or ICL. Ive still needed .001 under bearings on occasions when I run into this deal.

I guess it depends on how picky you want to get. Some roll the dice and it works but likely won't have decent hot oil pressure. I want my bearing clearances where I feel they should be, I like my hot idle oil pressure lol.

My 400 built by BES Racing shows .003 on the rods . I have about 9k miles on it and a dozen or so drag strip runs with no issues . 10w30 is a bit light on hot idle psi - 15 or so on my rally gauge . I found a light 50wt that I like - stays about 25 at idle .

I believe you will find that a set of -.001 bearings are what you need to tighten up the clearance a little. This is based on a crankshaft that was ground small, say 2.4992" as an example. The same way a -.010 bearing is made for a crankshaft ground to a nominal 2.490". To get extra oil clearance, you would need a bearing marked "X" for extra, or some mark them +.001 for a crankshaft that is too large like 2.5008" for example. Either way, I think both are available. Just a little harder to find for a Pontiac. Good luck with your build. I also wish you had a nominal 2.200 rod journal. I keep STD., +.001, -.001, -.009, -.010, -.011 in stock here.

The last time I talked to Ken Crocie he was still recommending.002 clearance on both rod and main bearings in 3” main Pontiac street performance engines.

Got it. On Butler's site it stated," -0.001" extra clearance." If that means it will tighten up the clearance I'll get them.