Main Bearing Feed Passage Oil Restrictions

While preping a '75 455 this week before sending it to be machined I took a few minutes to revisit the oiling system and the modifications most of us are used to. Since this build should be in the 600-650HP range and 6500RPM without a main girdle I wanted to look close at opening the main bearing feed passages on 2-3-4-5 mains from 5/16" to 11/32" as outlined in Jim Weise's oil mods. Just a note....None of this thread I'm writing relates to #1 feed, as it is plenty large already. I grabbed my 5/16" X 12" long drill bit and slid it up through the #2 main bearing feed from the saddle up toward the passenger side oil galley. Two things came to my attention. The first being that the 5/16" drill bit would not intersect with the galley as it had not been opened up to 5/16" all the way to the top, (#3,4,5 also). The second and most interestion thing was, while I was doing that I stood back and looked at the section of drill bit shank that was exposed in the cam bearing bore....which is where the cam journal receives its oil. I couldn't believe that I had never noticed how much of the 5/16" (.312) passage that feeds the main and rod bearings is restricted by the back of an installed cam bearing. So I grabbed a piece of 5/16" thick wall tube and decided to use it to measure the amount of passage that is blocked. I slid it into the #2 main bearing feed passage and scribed the area of exposure at the cam bore. I then carefully machined out that area of the tube and measured the difference. Once again the standard O.D. of the tube is 5/16 or .312...the section of tube remaining after the removal was .212 measured in the center of the removed section. So what we have here is a .100 reduction in main/rod bearing oil feed at #2,3,4,5 passages. As I see it that equates to about a 33% loss in oil capacity/flow at that section feeding each main/rod bearing. Maybe one of the fluid specialists or mathematicians can calculate the exact amount of restriction for us. Now drilling the main feed to 11/32" and cheating perfectly to the outside of the block (as JW outlined) is definitley going to help but even that will only relieve the restriction by .031 (1/32") at best. And the TA back grooved cam bearing will also help but once again, they have two .022-.025 deep grooves that don't span the whole width of the restricted oil flow area. That is because there is a section of material between the two grooves that is the same OD as the rest of the un-grooved portion of the bearing. Those two combined (drilling to 11/32" & TA cam bearings) still would not achieve the full 5/16" of oil flow though that section of main/rod bearing feed. Now what I plan on doing is taking my 6" long flare burr to carefully relieve .100 on the back side of the main bearing feed passages in the area directly across from each restriction (cam bearing). It will be pretty much a cresent shape (on #2,3,4,5). I feel there is enough material behind each as to not compromise the web. Due to the overall increase in size of that restricted area, I will be leaving all four remaining main/rod bearing feed diameters at 5/16". From all the pictures I can find the engine block's main web breaks on the lower side (below cam tunnel) of the block. I have included some pictures of my findings. I used blue layout dye to help contrast. Don't forget that what you are seeing is what the column of oil that's supposed to be feeding the main/rod bearings would look like if it was not restricted by the back of the cam bearing. I am aware that this thread would not pertain to any engines that are not in need of a top notch oiling system to begin with. I think that rules out the engines up to about 700HP and up to about 7000RPM,..... though when considering all the modifications we do to eliminate 90* turns, blend sharp edges, add balance lines, align bearing feed holes, increase suction system volume, enlarge restricted areas, blueprint pumps, etc. on even mild builds, I feel this is going to be an extremly important procedure I will be performing on every build I do going forward. I'm not trying to re-invent the wheel here.....just build a better Mouse (and Rat) trap.

Larry

 

That's why some on here has used the Ford 351 Cleveland oiling modification on a much high note. The way the Ford boys do it, they tap directly inline with lifter oil galley to main oiling. A couple in here has gone one step farther. They actually drive tubes down in those oil galleys going to the mains and plumbing the tubes directly to the 351 Cleveland oil modification. Basically its a priority main oiling system. Then they went to something that is much simpler and its been proven past 750 horsepower, Robert Makely's and AM&P's Scavenger oiling system. It eliminates 6 to 9 90* turns automatically.one individual says its a pain the arse, but don't be fooled, it works very well. Better then most anything ever tried.

 

I wanted to add this illustration of exactly where the oil restriction/obstruction is taking place. Though this illustration is of a 350 it still depicts the same issue as well as it's location. If you follow my yellow highlighted arrow up to the cam tunnel you can see the dark column of oil and it's reduction in size at the cam bearing. This holds true at cam bearing #2,3,4 & 5. The #1 cam bearing posses no problem as the main/rod bearing feed at that location is larger already. What's funny is how the cam lobe in the picture is pointing right at the problem.

Larry

 

Bluzilla (Larry) your correct but once you go to the scavenger type oil pump from Bob Makely/AM&P your volume is doubled on that side. Now if you decide to go direct (Priority main oiling system) you eliminate that problem all together. You simply can not fix the problem cheaply. The more power you make with this ole block, you gotta band-aid it until she pops. When is that? No one knows.

 

Interesting observations.

Two thoughts come to mind. First is, what size main feed passage do Chevy's have? 5/16? Smaller? Bigger? Second is, what is the diameter of the hole in the main bearing? If its less than 5/16, then the cam restriction may not matter much.

 

Good questions,....I was carefull to have already looked into both of those points along with many other factors before my starting my original thread. 1st: I have an empty 496 Big Block Chevy on a stand in the shop for a customer build right now. Last week I checked the main bearing feeds on that Chevy block and they were .250 which is still larger than the .212 of the Buick's restricted main feed area. 2nd: The Buick's main bearing shell's oil feed (hole) diameter is .312" (5/16") .
A couple of notes about that Chevy's nearly bulletproof oiling VS the BBB is that the Chevy has "Priority Oiling".. Buick doesn't, Chevy has smaller diameter main journals (2.275") VS Buicks (3.25") and the Chevy's rod journals are (2.20") VS Buick's (2.25") resulting in the Chevy having a slower speed at the bearing surfaces, and less volume of oil needed at equal crankshaft speeds. The way I see it, anytime you "neck down" a .312" (5/16") oil passage .... It's never going to flow the same volume as a full length .312" passage (at the same given pressure), unless you relieve the restriction. I also feel that it is easy enough to do and should really payoff especially in the "Higher RPM or Larger Bearing Clearance" applications.

Larry

 

That's why you can make a Buick apriority main oiling system. Its the cost envolved that you won't like, ask Dave Mongeon.

 

So, if a Buick crank is turned down to the same specs as a Chevy, does that improve the situation? That is the basis for some of the bigger inch BBB motors isn't it?

 

Good questions also.
1st: BBB main journals would not be turned to BBC's 2.75" journal size as there is not a main bearing that would be feasible.
2nd: BBB rod journals are often turned down to the BBC size of 2.20" (and widened) as used in the popular 470CID applications as well as displacements.

Note: TA's Tomahawk Raised Cam Block's have 3" mains and priority oiling too boot, along with a host of other improvements.

That takes us back to: Open the oil restriction and feed the main/rod bearings a full .312" column of oil.... which is what this thread is really all about.

Larry

 

Larry, just to point out, the Tomahawk doesn't need to be raised cam to have the 3" mains and priority oiling. You can order standard cam height and have the 3" mains as I have.
Cheers

 

Thanks Slim, I knew they all had priority oiling but didn't know you could order 3" mains on the standard height cam version. Good to know.

Larry

 

Update since I first posted this in October of 2016, ...... these are the two carbide burrs that I used to open up the restricted areas. I used a small hole gauge to check the final size (a small flexible piece of tubing or even a spark plug wire of the correct 5/16 diameter can be used to check). You have to make sure that you can push the gauge or tube flush with the cam bore opening to be sure enough material has been removed. And I found these nifty little cartridge rolls on-line that fit up into the oil passage perfectly. I used them to polish the rough areas the burrs left behind.



Larry

 

Great read Larry, thanks for writing it up!

 

Thanks for the write up Larry. Starting on this with my 430 now. One thing to clarify. Did you chase the main feeds with your 5/16 bit through to the lifter gallery?

 

Yes I did, .... and if I recall correctly, there wasn't a lot of material to clear out up there. You just want to stay away from the cam tunnel as to not enlarge the break through area that feeds the cam journal. I believe JW refers to it as "Cheating to the Outside of the Block".

Larry

 

I have wondered why so much of the material backing the cam bearing is not there. All to feed a little hole. Cooling maby? It may be just the way it turned out in the machining process. Being there was no racing development of any significance done by Buick on this block. It may be that with a slight restriction at that point the feed hole might be fed with higher pressure. Fine for a stock motor. I am glad i haven't gotten my block machined yet because now i have more work to do! Im adding an oil accumulator with pressurized start, a balance line, everything TA recommends and Jim Ws block prep thread. A crank scraper, and a mesh one way flow windage screen. Also some baffle welding in the oil pan. I have a 75 block center sump going in a RIV there in the pic. Great info Larry thanks. How would you or anyone recommend I address the oil pickup tube and screen? I know round is not the ideal shape.

 

Thanks, ..... I would talk to Steve Reynolds (SRE Fabrication) in Whitelaw WI about the pickup/screen assembly.

Larry

 

Mike Philips at American Machine and Performance has pick uptube screens. I bought a couple and they are nice. Not too bad to install, just a little tedious.

 

I took a look at my pickup tube from TA, They already addressed that with a better screen like the one shown on AMP website. Looking at the balancing line. why not plum into the actual main itself in stead of the galley plug? It would seem not much different than addin g the distrruibuter gear oiler. That rear main is also the smallest diameter passage, since its the farthest away. What size are you drillling that one too Bluz.? To fit a carbide down it to pocket out around opposite the bearing opening it would need to be like the number 1 hole. Or do you go through the opening?

 

Well known member Gunther, Why is it you always refer to Mullegun Dave. Dont you think if everybody actually would ask him every time you refer him he would get a little tired of splainin? Could you just cut to it and say it yourself? If I did go ask him, can I use you as my referance? Or would that actually cause Mr. Mullegun to refer me to some other guru?