Grooved Cam for 65-66 425hp Big Block

[Bill W.]

Re: Grooved Cam for 65-66 425hp Big Block

Around 1990 I bought 2 cams for my 396 from my chevy dealer. The first was part # 3904362 . I was told it was the replacement for the discontinued 143 . It did not have a groove . I also bought a 3925535 the 1979 GM parts book called it a 67 to 69 427 heavy duty (L88) & a 1965 /1966 heavy duty. It came with a groove. So which is closer to the OEM and could the 535 be considered correct ?

[Clem Z.]

Re: Grooved Cam for 65-66 425hp Big Block

Around 1990 I bought 2 cams for my 396 from my chevy dealer. The first was part # 3904362 . I was told it was the replacement for the discontinued 143 . It did not have a groove . I also bought a 3925535 the 1979 GM parts book called it a 67 to 69 427 heavy duty (L88) & a 1965 /1966 heavy duty. It came with a groove. So which is closer to the OEM and could the 535 be considered correct ?

your 1965 396 corvette block needs the grooved cam journal. the later 67 and up chevelle and camaro 396 engines can use the cam with no groove. i think GM sold the grooved cam bearing over the counter cams later so people who did not know what block they had would not have a oiling problem if they has a 65/66 block

[Clem Z.]

Re: Grooved Cam for 65-66 425hp Big Block

cam bearings have a lot of clearance .004/,005 and since the grooved cam journal has a open path for the oil to flow thru that groove there is a lot of area around the groove for the oil to flow out fed by 3 large holes in the bearing where the oil is fed into the bearing . the no groove cam bearing journal has only one oil input and that is at the bottom and the cam journal is being pushed downward to seal off that hole where if the journal has a groove there is no resistance to the oil flow. this is why GM says solder up the original 1/4" hole in the bearing and drill a 1/16" hole to act as a restriction to the free flow of the oil into the groove

the above posting i should have said using a pre 67 rear cam bearing along with a grooved cam in a later block. this will cause a even bigger internal oil leak.

[Timothy B.]

Re: Grooved Cam for 65-66 425hp Big Block

Clem,

I may be confused by your post but what I am saying is in a 1967 and later block, using a correct 1967 style cam bearing without a groove there would be no issues using a camshaft with a grooved rear journal.

Where would the internal leak come from, the bearing has one hole for oiling and the lifter gallerys are fed from the annulas in the block? Maybe you are saying the same thing..

[Clem Z.]

Re: Grooved Cam for 65-66 425hp Big Block

Clem,

I may be confused by your post but what I am saying is in a 1967 and later block, using a correct 1967 style cam bearing without a groove there would be no issues using a camshaft with a grooved rear journal.

Where would the internal leak come from, the bearing has one hole for oiling and the lifter gallerys are fed from the annulas in the block? Maybe you are saying the same thing..

the internal leaks comes from the fact that the incoming oil thru the the large single hole in the cam bearing is unrestricted because it will come directly into the groove in the rear cam journal and the clearance in the bearing/journal will allow the oil to flow out. with no groove in the rear cam bearing journal the oil coming in is restricted because the cam bearing journal is covering over the incoming oil hole in the bearing restricting the oil flow .

[Timothy B.]

Re: Grooved Cam for 65-66 425hp Big Block

Clem,

That works for me, as I stated above I would probably find a cam without the groove and not take a chance. BUT, I would think the restriction to flow would be the clearance between the bearing and journal and the orifice in the bearing and groove in the camshaft would not make a difference.

[Clem Z.]

Re: Grooved Cam for 65-66 425hp Big Block

Clem,

That works for me, as I stated above I would probably find a cam without the groove and not take a chance. BUT, I would think the restriction to flow would be the clearance between the bearing and journal and the orifice in the bearing and groove in the camshaft would not make a difference.

the diameter of the hole feeding oil to the rear cam bearing is 1/4" and unrestricted because of the groove in the cam that can flow a lot of oil and possibly starve the rear main bearing were the oil for the cam come from. the clearance in the cam bearings is large and a lot of oil can flow out thru this clearance if it is not restricted by the cam bearing journal without the groove setting over the oil feed hole.the valve springs put downward pressure on the cam causing it to press against the oil feed hole in the cam bearing acting as a restriction to the oil flow. that is why GM recommends using a bearing with a .062 hole to restrict the free flow of oil in to the groove in the cam in later blocks

[Wayne M.]

Re: Grooved Cam for 65-66 425hp Big Block

Another one from my vaults .. this time from How-to-Hotrod BB Chev's, 1972 revision.



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[Christopher A.]

Re: Grooved Cam for 65-66 425hp Big Block

When i built the engine for my car i was not aware of this and installed a non grooved cam. Funny, or not so much, because after i installed the cam i did have a slight memory of seeing a grooved unit in a book, but just assumed i had made that up somehow. This was my first big block car, so dont be too hard on me. Anyway, upon first start up when i noticed that no oil was getting to the rockers after about 45 seconds, my stomach sank and i knew i had messed up big time. I was not so happy when i had to pull the engine back out of the car over fresh paint to pull the cam and have it grooved. I am sure i am not the only person that has made this oops.
Just a note-crane cams will groove a cam for a 60.00-75.00 charge. I know that is what my local machine shop charged to groove the cam that i had to pull back out of the engine. Some people might think that is expensive, but when you calculate in the time to drive to and from the machine shop, gas, wondering if they are actually going to put the groove in the right place and make it the correct size...the extra money is justified in my opinion

[Patrick B.]

Re: Grooved Cam for 65-66 425hp Big Block

Thanks for the lively discussion of the affect of grooved cams. Even if GM dropped its warning given in the Chevy Power Book, Clem's explanation of how the grooved cam increases internal leakage has re-convinced me not to use the grooved cam in my 67 L-71. I ordered the Sealed Power CS-165R which should be identical to the TRW TP-165 except for the groove, and that it is apparently made in China. I am surprised none of the 65-66 SHP big block owners wanted to trade for a high quality TRW cam with the groove they need. I have several early dated 65 396 blocks I will sell this year and I will offer this correct cam to the buyers.

[Bill W.]

Re: Grooved Cam for 65-66 425hp Big Block

Hey Patrick You dont have the block from 65#17346 do you ? mine was turned in as a core in the late 70s..Bill

[Patrick B.]

Re: Grooved Cam for 65-66 425hp Big Block

Hey Patrick You dont have the block from 65#17346 do you ? mine was turned in as a core in the late 70s..Bill

Bill: I have a B-4-5 block with a Z-16 Chevelle code, a B-20-5 block with just the 511 of a Vette vin showing, a D-24-5 that has been decked clean of markings, and a E (or F it very indistinct)-27-5 with original grain that was never stamped.

[Jeff P.]

Re: Grooved Cam for 65-66 425hp Big Block

Patrick;
i need to machine the groove in my 65 396 camshaft, can you tell me how deep to machine this groove. Also what is the distance from the end of the cam in thousandths of a inch, and how wide is this groove ?
This information would be greatly appreciated.
Thanks

[Wayne M.]

Re: Grooved Cam for 65-66 425hp Big Block

....I need to machine the groove in my 65 396 camshaft, can you tell me how deep to machine this groove. Also what is the distance from the end of the cam in thousandths of a inch, and how wide is this groove ? .....

Jeff --- In Colvin's '65-69 Chev by-the-Numbers, on page 249, there's a reproduction of a GM blueprint for cam # 3856534 [I can't find this in the catalogs] which shows the grooved rear camshaft bearing journal.

The centerline of the oil groove seems not to be in the center of the journal, but 0.51" from the flat face of the rear of the cam. The journal itself is 0.98" wide, but the circumference is chamfered to result in an effective 0.88" width of contact surface with the bearing (not counting the center groove). The full depth of the groove is 0.10". The width of the goove is 0.18" at depth, with the circumferential edges chamfered at 45 degrees to a depth of 0.02".

Would be best to examine / interpret this page yourself before giving instructions to your cam guy.

Pics below are of the cam I removed from my 396 961 block, but it may be aftermarket (from long ago). On another forum, John Hinckley mentioned that circle M marking means Melling.








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[Joe L.]

Re: Grooved Cam for 65-66 425hp Big Block

All------


Here's what I don't understand about all this: GM supplied the grooved rear journal cams for years (1965 to 1988) in SERVICE for all 65-74 applications. As far as I know, there were no instructions provided with the camshaft requiring that modifications to the rear cam journal were necessary for 67-74 applications.

If there was a problem installing these camshafts in 67-74 engines I would think that would have been LONG AGO discovered and GM would have ceased specifying the grooved camshafts for 67-74 applications..