Regrinding a Camshaft?????

[Clem Z.]

you MUST use the single hole redrilled to .062

in all 67 up blocks when you use a cam with the grooved rear bearing journal because the groove in the cam journal will allow too much oil to pass thru the oil hole of a bearing using the standard size hole. NEVER use a 65-66 rear cam bearing in a 67 up block because you will have a even larger internal oil loss due to the 3 holes in the bearing even using a non grooved rear journal cam. the oil flow is limited with the .062 redrilled hole. the oil flow is limited in the other 4 bearings because the non grooved cam journal is being pushed down against the oil feed holes. on small block chevys you should install ALL the cam bearing oil feed holes at 5:00 position to allow the oil to be "pulled" to the bottom of the cam journal for correct oiling. if the oil hole is in any other position you will also have a internal oil leak causing some oil volume loss to the mains because cam bearings have .004/.006 clearance.

[Terry F.]

Re: Addendum

You don't feel comfortable with it???? How about me? Joking aside, I can give my engine man a call and he can probably tell me. I have heard of rear bearings that were designed for both cams but like I said, my memory on it is vague and I am likely totally wrong. I will search out the cam bearings. Thanks, Terry

[Terry F.]

Re: the 65-66 rear cam bearing has 3 holes that

Clem, the guy that first built my engine soldered the one hole shut and re-drilled through that same spot with a .062 drill bit. I ran my engine for a short while and gave up. It took forever for the oil to reach the lifters on the front of the engine and I was getting only small abouts of oil to the rocker arms in the front. The engine is ok but..... I am getting geared up to pull it and put it back together right. What a shame. I didn't know exactly what was wrong but I knew something was up when I had to stand there with my engine running squirting oil on the rockers to keep them happy . Live and learn. Terry

[Terry F.]

Re: you MUST use the single hole redrilled to .062

Clem, Thank you for adding to the discussion.

So, it seems that in 67 and later big blocks, the block determines the rear cam bearing NOT THE CAMSHAFT. Regardless of what camshaft design (grooved/not grooved) you must use the same rear camshaft bearing. But, if you use the grooved camshaft, you must solder the oil hole shut and redrill the hole at 180 degrees with a .062 bit.

In 1965 to 1966 big blocks, you must use the three hole grooved bearing and you must use the grooved camshaft, period!

Sound correct?? Thanks, Terry

[Jack H.]

Well...

I will admit we've seen a handful of 'escapes' over the years. I'm talking about cam shafts that were mis-ground or improperly hardened causing them to go 'flat' very quickly after engine rebuild. But, every mfgr has his quality control horror stories too!

The only way to positively guarantee a given cam's grind is to profile it and that's a LOT of hand labor for an ordinary street engine. You WILL find serious racers profiling their cams and that's typically done for two reasons: (1) they need to know that what they installed is what it's supposed to be, and (2) using eccentric fasteners they can 'tweak' the timing gear mount as part of the engine's blueprint process....

[Clem Z.]

if your block is a 65/66 NEVER solder up any

of the cam bearing 3 original holes as they are needed as produced along with a grooved rear cam journal to get oil to the lifters. any reduction in the oil supply to the cam lobe lifter interface will cause premature wear to the cam and lifters

[Clem Z.]

correct,you have stated it correctly

any other way you will either have too much or not enought oil to some parts of the engine

[Joe L.]

Re: the 65-66 rear cam bearing has 3 holes that

Duke-----

There's absolutely no reason, at all, to use the 65-66 rear cam bearing in a 67+ block.

[Clem Z.]

correct as you would have a very BIG internal

oil leak from the 2 top holes that feed the lifter gallery in the 65/66 block. you would have thought that GM would have learned from the SBC lifter gallery oil feed changes they made and to do the exact same thing to the 65 BBC and have to change it also. no wonder they are in trouble as it sounds like the right hand does not tell the left hand what has been tried before

[Duke W.]

Re: correct as you would have a very BIG internal

GM continued to confuse the issue when (in the Chevrolet Power Manual) they "explained" how to modify an early bearing to work in a '67-up block with the photo showing the '67-up single hole bearing that needs absolutely no modification.

Given the the proper bearing for '67-up blocks became available concurrently with the new block design, there is absolutely no reason to modify an early bearing to fit a '67-up block.

Just use the proper bearing.

Duke

[Wayne M.]

Here's an original? one in a 961 mid-May '65 block

The pan is off, so I could look up and see the other 2 holes in the upper half. If I can't figure out what the cam is, (grooved rear journal), I may post here for help.

Really good stuff, you guys. This board is the best !

[Duke W.]

Re: GM #3967810 Cam Bearing

Joe - can you measure the diameter of the oil hole in that 860 bearing?

Duke

[Joe L.]

Re: GM #3967810 Cam Bearing

Duke-----

Well, I "sort of" can. The problem is that the hole is not, at all, perfectly round. It's more of an "oblong" hole. This is also true of the 65-66 original bearing---the holes in that one are not perfectly round, either. Anyway, the hole in the 3967810 bearing is 0.173" long and 0.142" wide.

[Joe L.]

Re: GM #3967810 Cam Bearing

Duke-----

I don't know what the differences are between the 2 referenced bearings. However, I have no reason to believe that there was any major configuration difference between them. More likely, it was just a change to a different manufacturer.

None of these bearings, including the current ones, are really what one would call a "very high quality" bearing. That's because the bearing shells are of the "interlocking seam" type. The best cam bearings on the market are manufactured by Durabond and use a seamless shell. That's all that I use.

Most Chevrolet cam bearings, including all of the GM iterations, use babbit bearing material.

[Clem Z.]

i bet the hole was put into the material before

the split bearing was rolled into a circle causing the oblong shaped hole