Regrinding a Camshaft?????

[Joe L.]

Re: Addendum

Terry----

The GM #3904359 camshaft assembly is the camshaft assembly that was used for 1967-72 L-36, L-68, and LS-5 (also, Chevelle/Camaro L-34). Earlier versions have the embossed number "3904364" which is the camshaft part number AND also the casting number for the core (since no other camshafts were manufactured from this core, the casting and finished part numbers are the same). In any event, whatever you want to call it, either GM #3904359 or GM #3904364, there is NO rear journal groove.

[Duke W.]

Re: Addendum

One should also be conscious of rear cam bearings. The 986 camshaft assembly to service all '67-'72 427,454 Corvettes with hydraulic lifters is the early one with the groove, and the parts manual also calls out different service rear cam bearings for up '65-'66 and '67-up. I expect that there is a difference in the service '67-up rear camshaft bearing that makes it compatible with the service grooved rear camshaft in post '66 blocks, and I would be willing to bet that its configuration differs from the OE rear cam bearing that was used with non-grooved OE camshafts after 1966.

So make sure the installed rear cam bearing is GM 3967810 or an exact equivalent, which is called out for all '67 to '74 427, 454 that originally had non-grooved camshafts.

In the absence of firm evidence to the contrary, it's reasonable to assume that the 3967810 bearing is compatible with a grooved camshaft in post '66 blocks.

Duke

[Terry F.]

Re: Addendum

Joe, thank you for being patient with me. I think I know when I am being frustrating. Your information is incredibly helpful. Tomorrow, I will buy the camshaft. Thanks, Terry

[Terry F.]

Re: Addendum

Going from my depleted brain cells. I believe the rear cam bearing will have an actual groove in it. Though I am not certain of it. I will surely find out though. Thanks, Terry

[Duke W.]

Re: Addendum

I don't know the difference between the 3967810 rear camshaft bearing called out for '67-up and the 3876863 called out for '65-'66. Assuming these parts or supersessions are still available from GM, it might be a good idea for you buy one of each to determine physical differences.

This whole BB early/later grooved/non-grooved rear journal has always been confusing, and I don't feel totally comfortable with it.

A note was added to the 144 camshaft drawing that the casting for the 364 camshaft can be used to grind the 144. Of course, the groove has to be machined in. The casting for the 144 has the groove roughed in and only required finish machining.

The converse is not true. The 144 camshaft casting cannot be used to make a 364 camshaft.

Duke

[Duke W.]

Re: Addendum

If you buy an original 360 camshaft assembly, you're going to have to make absolutely sure that you have a rear cam bearing that is compatible with the no-groove rear journal. As I previously stated, I suspect that the parts book callout is different than OE in order that a grooved journal camshaft can be run satisfactorily in a post '66 engine.

Whether you buy this 360 camshaft assembly or not, let us know how and where you found it. Being as how it was never offered through service parts (or maybe it was for a brief period in the last sixties; my oldest Corvette P&A catalog is '77) I wonder how there could be any floating around out there unless it was removed from an OE Tonwanda built engine, in which case it is used, even if the engine only went through hot test and was never started after that.

Duke

[Clem Z.]

the 65-66 rear cam bearing has 3 holes that

must be aligned with the 3 holes in the block. the 2 top holes feed the lifter gallery and the bottom hole feeds the oil from the rear main so if you do not use the correct rear cam bearing you will get little if not any oil to the lifters. the later blocks use a groove in the blocks rear cam bearing bore to allow oil to reach the lifter gallery. the groove in the early rear cam journal was the oil path to the 2 upper holes to feed the lifter gallery. you can use a grooved cam in later blocks by soldering the single large oil hole closed and drill a new .062 hole not in the soldered area but 180 degrees off. i have done this with dozens of BBC with no problems. if you do not do this you will have a LARGE internal oil leak in the engine which could starve the lifter gallery.

[Joe L.]

Re: Addendum

Duke-----

I assume that you're talking about the GM #3904359 camshaft assembly. This is the combination of the 3904364 camshaft + dowel pin. It's the non-grooved rear journal equivalent of the 3883986. The GM #3904359 camshaft was once available in SERVICE (see attached photo). It was available from ABOUT 1991 until just a few months ago. As I mentioned previously, though, the parts labels on these pieces are, curiously, early 1970's style labels, even though they were not available in SERVICE until ABOUT 1991. You can see the label style in the photo.

As far as the cam bearings go, here's the deal:

1965-66 big blocks used, of course, a camshaft with a grooved rear journal. This was used in conjunction with a rear bearing which was also grooved for its full ID circumference. This bearing was GM #3876863. It had THREE holes in it. One hole was about 5/16" OD and the other 2 were about 1/4" OD. The 65-66 blocks had no annular groove in the rear journal bore. So, upper engine oiling was delivered through the combination of the groove in the camshaft journal, the groove in the bearing, and the holes.

1967+ blocks used the camshaft with no rear journal groove. This was used in conjunction with a rear bearing with no groove and a single oil hole of about 1/8" OD. However, there was an annular groove in the rear cam journal bore. So, upper engine oiling was handled through the block's annular groove. The rear cam bearing used for these applications was GM #3967810. Contrary to what it says in some GM parts publications, this bearing CANNOT be used for 1965-66 engines. It CAN be used for the #2 camshaft bearing position in 1965-66 engines, but it can't be used for the #5 position.

The 1965-66 engines MUST use a grooved rear journal camshaft + the special camshaft bearing, GM #3876863 (or, aftermarket equivalent).

1967+ big blocks can use either a grooved or non-grooved camshaft in conjunction with the 1967+ style rear bearing. Some say that the oil hole needs to be reduced in size to about 1/16" and some say it's not necessary. I don't know; I've never done it.

The GM #3967810 bearing was discontinued from SERVICE August, 1992 and replaced by GM #12508997. The latter is an identically configured bearing, but it's manufactured by Federal-Mogul instead of the manufacturer that produced the 3967810. It's still available from GM.

The GM #3876863 was discontinued without supercession in March, 1981. Although not available from GM in SERVICE since that time, an aftermarket replacement manufactured by Federal-Mogul and others is easily available.

[Joe L.]

GM #3876863 Cam Bearing

Here's a photo of the 65-66 camshaft bearing:

[Duke W.]

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

Glad you chimed in, Clem. What you describe is certainly different than what's in the Chevrolet Power Manual. It shows a rear cam bearing with a single hole and says to solder it up and redrill to .060". This never made any sense to me. Maybe the photo is of a late bearing rather than an early three hole bearing that you describe.

So the '65-'66 oil feed to the lifter galleries enters the hole in the bottom of the bearing from the rear main, travels around the camshaft journal groove (which also oils the rear cam bearing) and exits to the lifter gallery feed holes through the corresponding aligned holes at the top of the bearing. Makes sense.

If the '67-up lifter galleries oil feed path is via a groove in the rear cam bearing BORE, then why does the cam bearing need three holes? Seems to me that only one hole of suitable size in the rear cam bearing is needed to feed that one bearing, and most of the oil feed from the rear main will travel around the groove in the block bearing bore and enter the two feed holes in the block that lead to the lifter galleries.

What am I missing?

Duke

[Joe L.]

GM #3967810 Cam Bearing

Here's a photo of the GM #3967810 bearing. By the way, this bearing was released in later 1969. So, what was used for 1967-69 big blocks? The REAR bearing used for those applications was the GM #3876861. This was the same bearing as used for the #2 cam bearing position for 1965-66 big blocks. For 1967+, the #2 and #5 cam bearings are the same; for 1965-66, the #2 and #5 cam bearings are DIFFERENT.

[Joe L.]

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

Duke-----

The 67+ rear bearing does not have 3 holes. Only the 65-66 bearing has the 3 holes. The 67+ bearing only has a single oil hole of about 1/8" OD. The 65-66 style bearing is never used in 1967+ blocks, regardless of whether a grooved or non-grooved cam is used.

[Duke W.]

Re: GM #3876863 Cam Bearing

Okay, it's now clear to me. See my response to Clem, but you can ignore it as you have answered my questions. It makes sense now.

The photo in the Chev. Power Manual is obviously the '67-up single hole 810 bearing, but the text describes modifying the early 863 three hole grooved bearing. No wonder I was confused, and a lot of other people, too. In fact, there is absolutely no need to modify the early bearing for use in a '67-up block since a properly configured bearing was available for later blocks concurrent with the design change.

So it's now crystal clear that '65-'66 blocks must use the original type three hole, grooved rear cam bearing along with a grooved rear journal camshaft. No other configuration is acceptable.

And all '67-up blocks MUST use the single hole rear camshaft bearing, but either a grooved or non-grooved camshaft is acceptable, and either will yield essentially the same oiling system performance.

It would have avoided a lot of confusion and probably some busted engines if the Power Manual had described it this way.

The key is that Terry and other BB owners who are contemplating engine rebuilds understand this issue, particularly the danger of using a non-grooved camshaft or single hole rear camshaft bearing in pre-'67 blocks. Either is going to burn up the engine in short order due to lack of oil feed to the lifter galleries.

Duke

[Duke W.]

Re: GM #3967810 Cam Bearing

So this begs the question: What is the difference between the 3876861 and the 3967810?

My '77 P&A catalog shows the 810 for the #2 bearing in all '65 to '74 BB, so it sounds like it superseded the 861 for whatever reason.

In fact the #1 through #4 bearings for all '65 to '74 BB are listed respectively: 3967808, 3967810, 3967809, 3967809, so it appears that all the BB cam bearings were redesigned circa '69, but they had to retain the early grooved three hole 3876861 rear bearing to service '65-'66 blocks.

Duke

[Duke W.]

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

That's what I was asking Clem. What about the other two holes in the early bearings. It appears that at least two holes should be soldered up to use an early bearing in a later block.

The later design is obviously more "fail safe". With the early design, if the rear bearing wears or develops excess clearance for any reason it will flow more oil, which will reduce feed pressure and oil flow to the lifter galleries, which could effectively starve the lifters and top end if the rear bearing clearance opens up excessively.

This can't happen with the second design. The lifter galleries will get oil unless the rear camshaft bearing literally comes out of its bore.

I'm also surprised at the large feedhole on the second design bearing - a 1/8" hole to feed one lightly loaded cam bearing?

For comparison the Cosworth Vega engine has ten cam bearings. They are not inserts - just precision align bores in the cam carrier casting. The oil feed to the top end has a .090" restrictor - much smaller than 1/8" inch - to supply TEN bearings. The front cam jounals are grooved which feeds oil via small radial passages in the journals to gun drilled passages in the center of the cams and remaining journal oiling is via a small radial holes in each journal. The rest of the valvetrain is lubricated by splash off the cam bearings.

It's an interesting comparison of oiling system design.

Duke