Grooved Cam for 65-66 425hp Big Block

[Ronald L.]

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

Joe,
I appreciate the second opine on this, as there was a time as metallurgist, I was there checking tin on pistons, gears, cams, rocker arms, r/a nuts, studs, even the rod nuts we heat treated. Even when they tore out furnaces from the 30/40's to make way for nodular iron gear heat treating.

[Duke W.]

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

Ronald------


Yes, the engine plants did manufacture the camshafts from cores that I believe were produced at GM foundries. They produced camshafts for both PRODUCTION and SERVICE.

I think that Flint manufactured most camshafts right up until its closure. I don't know if Tonawanda manufactured SERVICE camshafts after 1975 when big block use in passenger cars ended.

Also, each cam part number was ground from a unique core that was cast close to finished dimensions. This minimized machining time. Nowadays all SB flat tappet cams - both GM and aftermarket - are ground from a single core supplied by the CWC division of Textron, and I think the same applies to big block cams.

The early big block cams have the rear journal groove cast in. The drawings for the later non-grooved cams have a note that the earlier part numbers can be created from the grooveless core, but the groove must be machined to the dimensions called out on the earlier drawings for grooved cams.

Duke

[Clem Z.]

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

Clem,

Could it be possible the new rear camshaft bearings are produced with a smaller .062 hole so no need for the caution note or are they all .250".

You are right about the evolution of the 265 small block and rear camshaft bearing with regard to oiling the lifter galleries. That's a mistake you would think GM would not make again..

Pat, With a higher volume oil pump what is the relief pressure in the spring..

even the later L-88 short blocks i bought to turn into race engines the ones that had the grooved cam had the large oil feed hole. either GM back then did not think it was a problem or did not care as they were using up the 535 cams. the cam that GM sold over the counter for short track racing 340282 did not have the groove. the only cams i remember that were grooved was the 535 1st design L-88 and the 143 street cam you bought over the counter were grooved as long as i remember. the 362 street cams were not grooved which were the 143 replacement.

[John H.]

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

Wayne;
Thanks for taking the time to share this information and pictures on machining the groove into the "65-66" camshaft. If my memory serves me right, the distributor also has a special groove for oil passage.

Jeff -

The full vs. partial annulus groove in the distributor housing makes no difference; the full 360* groove works for any application. The 1st-design partial groove can cause oil starvation if the distributor isn't oriented exactly as specified.

[Michael H.]

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

the cam that GM sold over the counter for short track racing 340282 did not have the groove. .

Not trying to change the subject but, I agree, that 340282 was a wonderful cam, and not just for short track. Had one in that black 67 at Road America years ago.

[Clem Z.]

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

Jeff -

The full vs. partial annulus groove in the distributor housing makes no difference; the full 360* groove works for any application. The 1st-design partial groove can cause oil starvation if the distributor isn't oriented exactly as specified.

i understand that was done to cut down on internal oil loss in aluminum blocks because the distributor and lifter bores in the aluminum blocks opened up when hot and that was the reason for the high volume oil pump in the ZL-1 aluminum engines. the 360 degree groove would allow the oil loss all the way around the distibutor housing where the 180 degree groove would cut down on the internal oil loss . we "O" ringed the distributors where it fit into the lifter oil gallery used on aluminum blocks to prevent the internal oil loss.

[Clem Z.]

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

Not trying to change the subject but, I agree, that 340283 was a wonderful cam, and not just for short track. Had one in that black 67 at Road America years ago.

it worked good for auto trans on the street vs the 180 cam that came in the LS-7 crate engines.

[Joe L.]

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

even the later L-88 short blocks i bought to turn into race engines the ones that had the grooved cam had the large oil feed hole. either GM back then did not think it was a problem or did not care as they were using up the 535 cams. the cam that GM sold over the counter for short track racing 340282 did not have the groove. the only cams i remember that were grooved was the 535 1st design L-88 and the 143 street cam you bought over the counter were grooved as long as i remember. the 362 street cams were not grooved which were the 143 replacement.

clem-----


The only difference between the 3863143 and the 3904362 was the rear journal groove. Otherwise, they were the same. Although the 3863143 was sold in SERVICE for many years for all 1965-71 SHP (i.e. L-78, L-72, L-71, LS-6) applications, the 3904362 was the camshaft actually used in PRODUCTION for the L-71 and LS-6 applications.

I expect that the reason that GM supplied the 3863143 in SERVICE for all the SHP applications was that it was the closest things to a "one size fits all". In other words, it could be used either for the 65-66 applications or the 67-71 applications. The 3904362 could not be used for 65-66 applications without machining the groove.

[Clem Z.]

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

"the 3904362 was the camshaft actually used in PRODUCTION for the L-71 and LS-6 applications".
this sort of proves that GM thought was better to use a non grooved cam in later blocks.

[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.

I got my Sealed Power CS-165R cam, and I must say I am disappointed with at least one aspect of it. The lobes of the original GM cam are about 0.575" wide while the lobes of this cam are only 0.52" wide. The timing specs of the CS-165R cam are identical to those of the TRW TP-165 cam, but the lobe width of the TRW cam is 0.58", essentiallly identical to the original GM cam. A friend told me his Crane cam for a 67 big block had narrower lobes than a GM cam, and had the opinion that this contributed to that cam wiping out. While his case may have had more than one contributing factor, reducing the surface area of the lobe by almost 10% is certainly not helpful at a time when the oil formulations have become less friendly to wear on sliding surfaces.

[Ronald L.]

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

Patrick, Bingo.

Might not be an easy calculation, but the spring force through the rocker and push rod to the lifter on the cam lobe and the bearing surface is reduced 10%, what increase in coef friction is required to over come this?

[Patrick B.]

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

Patrick, Bingo.

Might not be an easy calculation, but the spring force through the rocker and push rod to the lifter on the cam lobe and the bearing surface is reduced 10%, what increase in coef friction is required to over come this?

I'm not sure what calculation you are suggesting. I do not intend to change from the stock Chevy valve springs, so the contact pressure between the the cam and the lifter will increase by some amount between zero and 10%. If the lifters were truely flat, it would be about 10%, but the spherical nature of the lifters complicates matters. If the contact were only a small patch at the point of the sphere, the lobe width would not matter and only a narrow line of parkerizing would be worn off the tip of the lobe. However, all the cams I have seen with any wear at all have the parkerizing worn off the whole width of the point of the lobe, although there are places on the flanks of the lobe that do not appear to receive contact with the lifter. It certainly appears that the width of the lobe would have some effect on contact pressure even if it is less than a simple area ratio. Maybe some of the engine design specialists on our panel can explain the effect of cam lobe width. My point was that the CS-165R cam was changed from the GM spec in the direction of higher lifter contact pressure, adding to concerns about break-in and oil additives that are much discussed here.

[Joe L.]

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

I'm not sure what calculation you are suggesting. I do not intend to change from the stock Chevy valve springs, so the contact pressure between the the cam and the lifter will increase by some amount between zero and 10%. If the lifters were truely flat, it would be about 10%, but the spherical nature of the lifters complicates matters. If the contact were only a small patch at the point of the sphere, the lobe width would not matter and only a narrow line of parkerizing would be worn off the tip of the lobe. However, all the cams I have seen with any wear at all have the parkerizing worn off the whole width of the point of the lobe, although there are places on the flanks of the lobe that do not appear to receive contact with the lifter. It certainly appears that the width of the lobe would have some effect on contact pressure even if it is less than a simple area ratio. Maybe some of the engine design specialists on our panel can explain the effect of cam lobe width. My point was that the CS-165R cam was changed from the GM spec in the direction of higher lifter contact pressure, adding to concerns about break-in and oil additives that are much discussed here.

Patrick-----


The width of the finish-machined lobes is a function of the width of the lobes in the raw casting. Apparently, at least some of the generic cores currently being manufactured for big block Chevrolets have a narrower lobe width. I cannot imagine why, though. CWC-Textron manufactures most of the cam cores being used today.

[Patrick B.]

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

Patrick-----


The width of the finish-machined lobes is a function of the width of the lobes in the raw casting. Apparently, at least some of the generic cores currently being manufactured for big block Chevrolets have a narrower lobe width. I cannot imagine why, though. CWC-Textron manufactures most of the cam cores being used today.

Joe---
The TRW cam has CWC cast on it, but I did not see the familiar CWC casting mark on the Sealed Power cam.

[Joe L.]

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

Joe---
The TRW cam has CWC cast on it, but I did not see the familiar CWC casting mark on the Sealed Power cam.

Patrick------


Then I'd say that Sealed Power must be using another core supplier which is probably why the lobes differ in width from the TRW and original GM.

Many iron castings these days have their origin in China. Maybe Sealed Power obtains theirs there. Or, maybe the finished camshaft, too. Is there any country of origin information on the box?