Big Block Cam /Journal Grooves

[Joe S.]

I have a question concerning big block cam journals. I'm sure that this has probably been beat to death over the years, but the information that I have received so far is rather conflicting. In 1965/66, the block's rear cam journal bore was not grooved. Both the cam's rear bearing and the rear journal bearing were grooved. Oil entered the rear bearing via the hole in the bottom of the bearing, traveled around the passage formed by the matching grooves in the cam and journal bearings, and exited the top of the bearing to supply oil to the top end of the engine. Beginning in 1967, the block's rear cam journal bore was grooved. Neither the cam's rear bearing or the rear journal bearing were grooved. Oil entered the rear journal bore via the hole in the bottom of the bore, traveled around the passage formed by the groove in the bore and the backside of the cam journal bearing and exited the top of bore to supply oil to the top of the engine. I am rebuilding a 427/435 with a September 1, 1966, #3904351 block. The rear cam journal bore of this block is not grooved. I purchased a new GM #3904362 solid lift cam (superceded original #3863143 cam in 1988). The cam's rear bearing was not grooved. My machinist installed a grooved rear journal bearing in my block and ensured me that I could run either a grooved or non grooved cam. During engine assembly, I saw that "How To Restore Your Big Block Chevy" was very specific about decreasing the size of the journal bearing oiling hole when using a grooved cam in a later grooved block but was unclear as to how to approach a non grooved cam in an early non grooverd block. "The Chevrolet Power Parts Book" had a similar discussion. I called the "GM techline" (800)222-1020 and was informed that all blocks were grooved (Apparently they didn't have information on the early big blocks). I found an article in "the NCRS Encyclopedia" that indicated that GM had determined that the above mentioned modification was not required, but again no mention of how to handle an early non grooved block was made. I asked several locals who felt that with a solid lift cam, anything I did would be fine. ???Opinions and Comments???

[Joe L.]

Re: Big Block Cam /Journal Grooves

Joe-----

As you are probably aware, the biggest problem encountered when using early, non-grooved blocks is the use of a non-grooved cam AND non-grooved bearings. That occurs sometimes with unsophisticated and unsavvy rebuilders.

I believe that the use of the grooved bearing will eliminate any problems and your engine will experience absolutely no problems they way it is presently configured. The modification that your machinest made using the grooved bearing is a common one and has been used successfully for many years.

However, if you're uncomfortable with this for any reason, and I can understand that discomfort, simply return the engine to it's aoriginal configuration----have the machinest machine the appropriate groove in the replacement cam and install a non-grooved bearing. It won't cost that much and, in my opinion, it's unneccessary, but if it makes you feel better about the whole thing, it might be worth it.

[Joe L.]

Re: Big Block Cam /Journal Grooves

Joe----

I did a little more research on this one. It seems that certain pros advise that on the 65-66 "non-grooved" blocks, the cam should be machined with the groove, as the original cams were. This might not be necessary with solid lifters, but I now think that it might be worth the effort if you can easily remove the cam at this point.

[Joe S.]

Re: Big Block Cam /Journal Grooves

Thanks for your research Joe! Unfortunately, I already have the engine assembled and obviously don't want to pull the cam unless it's a "must do." No plans on firing the engine for several months, so I could pull the cam to cut the groove, but is it worth the effort at this point?