Ok, so im replacing the cam bearings in my 305 TBI (along with many other things), but the aftermarket cam bearings I got (Clevite brand) have one cam bearing with 2 oil holes, and the rest just have the one.

My question is really twofold

First, my block has channels for the oil to the cam bearings instead of holes. Which position is the best to place the holes in the bearings. My understanding is approx. 2 o'clock with the engine right side up (which should be about 8 o'clock with the engine upside down.

Two, I figure the bearing with two oil holes was designed that way for a reason. Where in relation to the other ones do I install this one.

Thank you in advance!

 

The one with two holes goes in the front. Keep in mind that the O.D. of the others are different, so you can't just put them wherever.

 

There are 3 different ODs in the group.

Put the oil holes at about 4:30 - 5:00, viewed from the front of the block. Remember, ALL the force on the cam, is pushing it straight toward the crank, and it's ALOT of force (from all the springs on all the valves that are open); therefore there is ALOT of clearance at the top of the bearing, AT ALL TIMES. If you put the bearings in with the oil hole toward the top, you will have 5 MASSIVE internal oil leaks, resulting in chronic low oil pressure. Put the front one in with one hole at about 4:30 and the other at about 7:30.

 

I must admit that I always have my machinist install cam bearings for me. So honestly I don't remember much about them. As Apeiron says, they are individually sized so they will not interchange. Also, as I remember, you want to be sure that the front and rear bearings come out last and go in first. I believe that the oil holes on the front bearing should point towards 3 and 9 oclock. Oil holes in bearings 2-4 should point towards 5 oclock, and the rear bearing should point towards 12 oclock. This is veing the engine right side up.

Again, Im not real solid on this. Hopefully someone who has recently done cam bearings will verify this info.

 

I do em somewhat regularly.

 

After some internet research, I ended up installing Dura-bond Cam bearings with the oil hole location: #1 @1 and 5 o clock, #2,3,4 @3 and #5@1-2

http://www.dura-bondbearing.com/Port...20Bulletin.pdf

http://www.dura-bondbearing.com/Port...20Bearings.PDF

 

Id recommend using alum. bi-metal cam bearings if you intend on using aftermarket springs. My experience with the standard tri-metal babbit ones is that they tend to wear quicker than the newer alum. alloy type since theyre softer. Im using the speedpro aluminum ones and they seem to be holding up much better. The oil is clean and there seems to be very little wear as opposed to when I was using the standard tri-metal ones before.

The clearance on the top of the bearing will only be a few thousanths initially, but with the tri-metal bearings, the cam tends to sink over time, creating a lot more clearnace. If your using tri-metal, avoiding the 12 o'clock position is good advice. I know after about 100k+ on my first set, they where pretty much all down almost to the copper.

I put mine in with the oil holes at the 2 o'clock position to set up teh wedge (Im sure there are lots of other variations). The one place you absolutely cannot put the oil hole is between the 4 - 8 o'clock position, because this is where the oil film is that supports the load. The pressure there is much higher than oil pressure, so if you put the oil hole in that area, it will cause the film to collapse.

As for the position, they should be labeled on the box as to which one goes where. Just make sure that they go in teh right place. Also make sure that the oil hole is centered over the groove. Drive it in most of the way, and once you start getting close, check the oil hole position and ease it on in until its centered.

 

Also, after you get the old bearings out, make sure you thoroughly clean the cam bearing bores in the block with a lint free cloth and solvant. Small ammounts of metal can shave off the backs of the bearings when theyre driven out. if you leave it in there, the first place it will go when you start the motor is right into the main bearings since they share the same oil passage as the cam bearings.

Also, which tool will you be using? I used the cheapie one, and had lots of fun with it: https://www.thirdgen.org/forums/tech...ecide-try.html

 

All SBCs have "channels" behind the cam bearings for the oil.

The oil system is:

From the oil pump, dirty oil goes through the rear main cap, into a passage that is drilled vertically all the way to the top of the block, at the place the OPSU goes behind the dist. There is a plug installed (by the machine shop, or by you, in a rebuilt motor) in this passage about 1" above the main cap parting line. Just below this point, there is a horizontal passage leading to the outer par of th eoil filter. The oil passes through the filter, inwards, and goes into the fitting it screws into. This passage goes up at an angle, and intersects another horizontal passage which meets the vertical one just above the plug. (If the plug is not there, the oil filter is essentially out of the circuit, and becomes just an oil tank, with no flow through it.)

The oil goes up the back of the block toward the OPSU. It passes through the groove behind the rear cam bearing. There are 3 2 other holes in that groove, in addition to the 2 from the vertical passage passing through it, one on each side; 2 of those go to the lifters.

The oil comes into the groove from below, passes around th eback of that bearing, and reaches the other holes. One goes back down and carries oil to the rear main bearing. The one at the very top continues up, and intersects a horizontal passage drilled all the way from the front to the rear of the block. There are 3 such drillings: they all have small plugs at both the front and rear of the block, around the cam bearing. The outer 2 feed the lifters. The center one makes that "spine" looking feature above the cam, down the center of the intake valley.

The oil passes from the rear of the block toward the front in that horiz passage. At each cam & main journal (the mains are directly below the cams, exactly the same spacing) a passage is drilled from the center of the main saddle, through the groove behind the cam bearing journal, and up to the horiz front-rear passage. Oil passes down from the horiz one, around the back of the cam brg, and down through these to each main. As the crank rotates, the holes drilled through it line up with this hole from time to time, delivering oil to th erods.

This explains why cleaning out all those little holes, and BRUSHING the grooves behind the cam brg, is SO IMPORTANT when prepping a motor for a rebuild, especially if its prior build blew up. Just dropping a block into a vat with the cam brgs still in it, isn't a guarantee that any metal chips in those grooves, get cleaned out. Then when the "new" build fires up, those chips only have ONE possible place to go: RIGHT DIRECTLY INTO your brand-new bearings.

 

Ok, new problem - none of these things are marked like they should be, and theres no instructions or info in the packaging that would be considered remotely useful, so I have no easy way to tell what fits where. Does anyone have the Cam bearing diameters for the actual housings handy? Id hate to screw up a set putting them in in the wrong order making a trial & error attempt haha.

 

The O.D.s are 2.020, 2.010 and 2.000, but you don't need to measure, it's readily apparent which goes where. If the bearing locations are numbered 1-5 from front to rear, the smallest-sized two go in the #3 and #4 spots. Put these in first. The middle-sized two go in the #2 and #5 spots. The largest goes in the #1 spot, and is the only one that has two holes.

 

Yeah they're definitely not set up for first-timers... after you've done a few sets though, it becomes second nature.

Your bushing tool should be the kind with the plastic guide cone to keep it straight.

Put the rear ones in from the front of the block, and the front ones in from the rear. Easiest to keep the tool perfectly straight that way. Be careful on the rear one, that the bearing doesn't get driven too far rearwards; it will interfere with the thin "freeze" plug that goes back there. On all of them, make a point of looking at the oil hole to be sure it's over the groove, as that journal will run dry and wipe out if the hole is covered up.

When you put the "freeze" type plug in, wipe a little bit of sealer around the edge (I like either Permatex 300 or that purple Permatex stuff, I forget the #); drive it just below the surface of the block, maybe .020" or so; then use your finger and wipe whatever sealer is exposed, around the edge of the plug, to make a little "dam" to help keep the plug from blowing out. Make EXTRA SURE the oil drain hole between the bearing and the plug, is free and clear; the plug will DEFINITELY blow out if the hole is blocked, because eventually that space will fill up with presurized oil.

 

I dont think all blocks have that. I dont recall my goodwrench having it as I specifically remember thinking about how the oil would return behind the cam. But, all the cams Ive come across have drain holes drilled thru the rear of the cam to give the oil a return path.

 

Have you checked over the entire package? On mine, the installation order was on the bottom flap of the box, and where not immediately apparent. If you dont have calipers, Id return them and get another set. They can only be installed once, so if you screw one up, you have to drive it out and get a fresh one. I had that happen with that cheap *** pro-form tool. The tool was the wrong size, and it got wedged in the bearing, trashing it. Once I fixed the tool, it was fairly easy to install them, just took a little time to get them lined up. if your using that tool, measure the driver to be sure its the same size as a cam journal. The bearings contract when theyre driven into the block due to the press fit.