Please identify this BB cam

[Wayne M.]

It was in a 961 mid-May block I acquired (T0607LF which is 396/325hp). Took measurements by rotating cam in its bore with a stem (plunger) micrometer, on the lifter of the left bank (cyls #1,3,5&7). Got lift measurements at intakes - 0.292", 0.291", 0.291", 0.289" respectively. Exhausts - 0.295", 0.294", 0.294", 0.291", again respectively.

Multiply this by the 1.70 rocker arm ratio and it gives 0.496 to 0.491" lift at the intake valves, and 0.502" to 0.495" at the exhausts. Allowing for some wear (cyl #7 ?) and accuracy of measurement, this looks [relying heavily on Colvin's book] like the mechanical cam # 3863143 specs 0.497 / 0.503, except my cam had HYDRAULIC lifters (at least I think they are). I have never run the motor nor know the history.

Here's some other views showing markings. Rear face of cam has stampings but no part #.

At front of cam, between fuel pump cam and #1 exhaust, what appears to be cast "CCO" and under that "CMC" could really be "OCO" and "OMO" if the "C" is a poor die. OMO is what Colvin calls out for the solid 3863143 cam. Opposite side is probably a date casting [screw mark, K18, screw mark] Nov 1, 1968 ?

In the auto-load picture, you can barely make out "C-2" to the left of the distr/oil pump drive gear. Opposite side (no pic) is "D-2" and under that OL-1(? very faint)

So is this a GM cam ? The intake lift is too much for any "hot hydraulic" produced by the General, as far as I know. What kind of wear is acceptable on a used cam (still has its lobe-mated lifters) ?

[Clem Z.]

just because the lifters have a snap ring

holding in the push rod cup does not mean it is a hydraulic lifter as "piddler" valve solid lifters also use a snap ring.

[Joe L.]

Re: just because the lifters have a snap ring

clem and Wayne------

Yup. If you want to know if they're hydraulics or solids, just press down on the pushrods. If they're hydraulic lifers, you'll be able to "depress the plunger". If they're solids, you won't be able to. All big blocks using solid lifters used the piddle valve type lifters.

I strongly suspect that what you have here is the 65-66 SHP cam.

[Wayne M.]

Lifter looks hydraulic to me

Clem, Joe

haven't tried the pushrod force yet.

Is it possible to run hydraulics on an L78 / L72 / L71 solid cam ? This motor was together and was running (the story when I bought it). I'm wondering what to do for lash or pre-load if I re-use the lifters.

Forgot to mention in my original post: the lift measurements I took closely resembled the '65 L78 cam lift spec's (0.497 / 0.503"), but not the 0.520 / 0.520" of the '66 thru '69 L72 / L71 cam. The '66 one used the same part # as the '65, although the lift is different. Still according to Colvin's book, the '67 used a different part # (3904362, cast 366 -- rear journal groove removed ?) and the durations changed from 1965 to 1966 to 1967, but remained constant from 1967 thru 1969. Then, in 1969, part # reverted back to that used in 1965 / 1966 (3863143 (cast 144). Is this for real or just typos on Colvin's part ?

[Clem Z.]

Re: Lifter looks hydraulic to me

they are hyd lifters. i never ran hyd lifters on a solid lifter cam. if you set the hyd lifters any looser than "zero" lash they will "pop" apart because those wire retainers will not hold them together at speed.

[Clem Z.]

PS i would replace those wire retainers with

correct size snap rings which are much stronger.

[Duke W.]

Re: Lifter looks hydraulic to me

The lobe and lobe indexing on all '65-'71 SHP mechanical lifter cams is the same - absolutely identical. Recommended clearances were increased from .020/.024" in '65 to .024/.028" for '66-up so lash point durations decreased and exhaust lash point point duration is less than inlet lash duration for both sets of specs because of the greater recommended exhaust lash eventhough the inlet and exhaust lobe identical. Actual lobe clearance ramp height is .012".

Whenever dealing with camshaft duration/lift data you must know the context or it's worthless. There are many ways to present "cam specs", and often the context is not specified.

Mechanical lifter cam lift is either "gross" including the clearance ramp or "net" which doesn't include the clearance ramp, but varies with valve clearance. Sometimes recommended setting clearance is used. Sometimes "checking clearance" is used, which may be different than recommended setting clearance. The same basically applies to duration, but most mechanical lifter cam duration specs at .050" lifter rise include the clearance ramps, so actual effective duration at .050" lifter rise above the tops of the clearance ramps, which is what you need to compare to a hydraulic lifter cam is less.

The groove/no-groove issue was extensively discussed in a recent thread.

The nominal gross lobe lift on the BB SHP camshaft is .30572", and gross lobe lifts for all Corvette camshafts are listed in the applicable service manual. Given the measurements, it might be this cam, but with some wear.

Another check is to look at the first .012" of lift. It it takes on the order of 60 degrees of crankshaft rotation to go from .001" to .012" lift, it is probably the SHP mechanical lifter cam. Above .012" lift the rate of lift should rapidly increase.

If the .001-.012" lift occurs rapidly, it is a hydraulic lifter cam.

Also, all GM cams should have the finished camshaft part number, or at least the last four digits in the casting. The grooved rear cam journal SHP mechanical lifter cam is 3863144, so the casting should include this number or "3144" if it is the early SHP mechanical lifter cam with a grooved rear journal.

Duke

[Clem Z.]

most BUT not all BBC cams have the last 4

numbers of the part number stamped into the back of the cam rear journal