Is this a NOS L79 "151" camshaft, or something else?

[Scott S.]

From research here on the NCRS forum, I understand that the service part number is 3863151 (hence "151", consisting of the dowel pin assembly) and the finished camshaft part number is 3863152, which should be cast into the blank, or at least the last four numbers, "3152".

In preparation for a rebuild of my original L79 engine, I located a NOS GM 3863151 camshaft (still can't find motor mounts). The camshaft tube certainly appeared to be unopened. I had read Duke Williams' advice on the CF to check the lobes and journals for any corrosion, and if it's clean, it should be fine to use with new lifters, so I had the camshaft opened and examined by an engine builder, and he said it looked like it just left the factory. No problems.

When I examined the camshaft myself, I was expecting to see the casting number "3152", along with a vertical diamond casting symbol (Alan Colvin, 'Corvette by the Numbers', p. 341). Instead, at one end I see "CMC" ("CWC" on opposite side), and on the other end the casting number "1539". I can't find that casting number anywhere in the camshaft chapter of Colvin's book (1955-1982).

On the very end of the camshaft, there is a number stamped that it hard to read, looks like maybe 9A4878, and the end of this number crosses over a much lighter stamped number that appears to be 38_3151 (the 3rd number being a "6" by inference). This "3863151" is so lightly stamped that I can't get it to show up in photos.

What exactly do I have here, and how can I be sure?

[Clem Z.]

Re: Is this a NOS L79 "151" camshaft, or something else?

From research here on the NCRS forum, I understand that the service part number is 3863151 (hence "151", consisting of the dowel pin assembly) and the finished camshaft part number is 3863152, which should be cast into the blank, or at least the last four numbers, "3152".

In preparation for a rebuild of my original L79 engine, I located a NOS GM 3863151 camshaft (still can't find motor mounts). The camshaft tube certainly appeared to be unopened. I had read Duke Williams' advice on the CF to check the lobes and journals for any corrosion, and if it's clean, it should be fine to use with new lifters, so I had the camshaft opened and examined by an engine builder, and he said it looked like it just left the factory. No problems.

When I examined the camshaft myself, I was expecting to see the casting number "3152", along with a vertical diamond casting symbol (Alan Colvin, 'Corvette by the Numbers', p. 341). Instead, at one end I see "CMC" ("CWC" on opposite side), and on the other end the casting number "1539". I can't find that casting number anywhere in the camshaft chapter of Colvin's book (1955-1982).

On the very end of the camshaft, there is a number stamped that it hard to read, looks like maybe 9A4878, and the end of this number crosses over a much lighter stamped number that appears to be 38_3151 (the 3rd number being a "6" by inference). This "3863151" is so lightly stamped that I can't get it to show up in photos.

What exactly do I have here, and how can I be sure?

a quick check would be put the cam in a lathe and use a dial indicator to check the lobe lift. the lobe lift X 1.5 should equal .447 on both lobes

[Scott S.]

Re: Is this a NOS L79 "151" camshaft, or something else?

a quick check would be put the cam in a lathe and use a dial indicator to check the lobe lift. the lobe lift X 1.5 should equal .447 on both lobes

Hi Clem,

Unfortunately I don't have a lathe or a dial indicator. I will have the engine builder measure it for me when I get to that point, but is there any other way to tell for sure in the mean time?

[Duke W.]

Re: Is this a NOS L79 "151" camshaft, or something else?

CWC is a division of Textron that casts the ONE SB flat tappet cam blank that is used to grind ALL current SB flat tappet cams - whether "GM" or aftermarket. As sold by Textron, the pin is installed and all machining is done except lobe grinding.

If you chuck it up in a lathe or mount it in V-blocks and check total lobe lift, they should all be 0.29807".

You can also measure the total "heel to toe" dimension with a caliper, which is from the top of the lobe to the base circle. All should be nominally 1.53223", The base circle radius is 0.61608/0.61808", so two times the nominal radius plus the lobe...

I've seen many cases where the cam in the tube doesn't match the part number on the tag. There are lots of shenanigans going on out there.

Every vintage OE camshaft is available from reputable suppliers like Federal Mogul. It makes absolutely no sense to buy a "vintage" camshaft off ebay or any source that may even be slightly questionable.

No one can see that the blank is not a GM original once the engine is buttoned up, but you can be sure that any F-M or Dana Corp. camshaft is manufactured to the original GM drawing and some are well under $100 retail.

Duke

[Clem Z.]

Re: Is this a NOS L79 "151" camshaft, or something else?

Hi Clem,

Unfortunately I don't have a lathe or a dial indicator. I will have the engine builder measure it for me when I get to that point, but is there any other way to tell for sure in the mean time?

the engine builder should have a dial indicator to check the crank end play and a lathe to polish the crank shaft journals

[Scott S.]

Re: Is this a NOS L79 "151" camshaft, or something else?

CWC is a division of Textron that casts the ONE SB flat tappet cam blank that is used to grind ALL current SB flat tappet cams - whether "GM" or aftermarket. As sold by Textron, the pin is installed and all machining is done except lobe grinding.

If you chuck it up in a lathe or mount it in V-blocks and check total lobe lift, they should both all be 0.29807".

You can also measure the total "heel to toe" dimension with a caliper, which is from the top of the lobe to the base circle. All should be nominally 1.53223", The base circle radius is 0.61608/0.61808", so two times the nominal radius plus the lobe...

Thanks Duke, I have copied the information.

I've seen many cases where the cam in the tube doesn't match the part number on the tag. There are lots of shenanigans going on out there.

I was hoping that hadn't happened here, but it seems like it has. This is the second time now (two different engine builders) that an experienced engine builder has examined a camshaft for me and doesn't seem to know or recognize the first thing about it. Is that normal? Is the L79 (or the base-engine 350-300hp cam in 1969) an unusual thing to an engine builder with 25+ years of experience? In the normal course of opening a sealed NOS camshaft and examining the condition, would it not be expected that he would notice the casting number didn't match the number on the tube?

Is the fact that the casting number is not "3152" mean this can't be an L79 camshaft?

Every vintage OE camshaft is available from reputable suppliers like Federal Mogul. It makes absolutely no sense to buy a "vintage" camshaft off ebay or any source that may even be slightly questionable.

The previous owner bought this car in 1972, and I have been able to contact him. He said it ran incredibly strong, and he drag raced it for two summers in "B" stock. Then he rebuilt the engine and says he put a 350/350 cam in it, and it never ran right again. He sold it to my Dad in 1976, and it never ran right for my Dad, either.

When the (first) engine builder disassembled the engine last winter, the camshaft that was actually in the engine had a casting number "6930", along with "GM 116" and a horizontal diamond. According to Colvin's book, "6930" is short for casting number 3896930 (part number 3896929), which is the base engine 350/300hp camshaft (not the 350/350 as the prior owner believed), beginning in 1969. This is a numbers-matching engine with original correct-date heads, production line carburetor, intake manifold and original distributor, and it still had TRW 11:1 pistons in it. Just the camshaft was changed. The only other variance from stock I am aware of is that the heads measured 68CC each, instead of 64CC.

No one can see that the blank is not a GM original once the engine is buttoned up, but you can be sure that any F-M or Dana Corp. camshaft is manufactured to the original GM drawing and some are well under $100 retail.

Duke

I understand that no one will see it, but given the problems my Dad had with getting it to run properly, and all the time I have spent so far trying to learn about and make this car like it was in 1967, when the opportunity presented itself to get a real GM "151" camshaft back in that engine, it seemed like the right thing to do.

[Scott S.]

Re: Is this a NOS L79 "151" camshaft, or something else?

After doing a little more research, it appears that:

A) "CMC" stands for "Camshaft Machine Company". (multiple forums)

B) "CWC" stands for "Campbell Wyatt and Cannon Foundry" (multiple forums)
I read that both "CMC" and "CWC" were GM OEM markings at some point.

C) "1539" may be the cam "blank" number (Hotrodders.com Forum)

All of these marks (and a few others, like "D3", "12") are cast into the shaft itself. Supposedly, the actual cam grind number is stamped on the end. This camshaft has two numbers stamped on the end, in two different fonts, one deeper and one very light.

The more deeply stamped number appears to be 904879 or 904679 (or could be something else). The more lightly stamped number on the end is 3863151.

As for the green stripe on the end (and what looks like a light blue dot of paint and a yellow dot), all I could find was:

"The early chevy hi perf cams were all identified with painted codes on the cam gear end of the cam. When I locate mine I will post the color code, I believe it is a single white stripe. I bought the cam new in 1970 and never used it. The L-79 cam had 3 colors, green, orange and white." (post 8, Team Camaro Tech Forum, 2008).

"Back in the day I installed many of the L-79 cams for my customers, everyone L-79 cam I ever purchased had the same stripped colors. This was recently confirmed again when I overhauled a friends number match 66 Corvette. I pulled the cam and there were the colored stripes, guaranteed you never noticed them." (Post 11, same Thread)

"Cam 3736097 used in Corvettes to 1964 had one green stripe, that turns brown with age." (Post 12, same Thread)


What all this means, I'm not sure.

[Steven B.]

Re: Is this a NOS L79 "151" camshaft, or something else?

I was hoping that hadn't happened here, but it seems like it has. This is the second time now (two different engine builders) that an experienced engine builder has examined a camshaft for me and doesn't seem to know or recognize the first thing about it. Is that normal?

Scott, every community in this country has an engine builder and most, if not all, will tell you how great they are. If you have an engine you want restored or modified you need to really research to get a good and competent one, just like any restoration. The things I didn't/don't do myself I researched by asking NCRS members, getting recommendations and looking at the work and watching them in their shops. You really want someone who lives and knows these things, which eliminates most of them. Be certain you have the right guy because you can't redo alot of things. I suggest getting recommendations from members.

Steve

[Duke W.]

Re: Is this a NOS L79 "151" camshaft, or something else?

Thanks Duke, I have copied the information.


This is the second time now (two different engine builders) that an experienced engine builder has examined a camshaft for me and doesn't seem to know or recognize the first thing about it. Is that normal?

Yes. To most of those guys "parts is parts"!

That's why I always harp about MANAGING your engine restoration project. The owner should SPECIFY exact brand and part number for all new parts and the work order should specify the exact machining operations, some of which may be contingent on measurements. The final invoice should include manufacturer and part number for all installed parts, which should all be on the preapproved list.

Don't buy "NOS" parts on ebay or from any other source unless they come in sealed unopened boxes.

Most "engine builders" will resist this level of supervision. If they do, keep looking, but most guys don't and end up getting screwed with a crummy engine. Maybe you joined the club, but before anyone jumps to conclusions, get a caliper and make the measurements I discussed in a prior post.

Yes, all GM cams appear to be coded with colored paint, but I've never figured it all out nor have I seen anything that specifies all the coding. The easiest and most expedient way to check a cam is the heel to toe dimension. All GM cams are different and may be different for inlet and exhaust lobe on the same cam.

You can buy a decent .001" graduated caliper for about 20 bucks. Every tool box should have one.

Duke

[Scott S.]

Re: Is this a NOS L79 "151" camshaft, or something else?

I was hoping that hadn't happened here, but it seems like it has. This is the second time now (two different engine builders) that an experienced engine builder has examined a camshaft for me and doesn't seem to know or recognize the first thing about it. Is that normal?

Scott, every community in this country has an engine builder and most, if not all, will tell you how great they are. If you have an engine you want restored or modified you need to really research to get a good and competent one, just like any restoration. The things I didn't/don't do myself I researched by asking NCRS members, getting recommendations and looking at the work and watching them in their shops. You really want someone who lives and knows these things, which eliminates most of them. Be certain you have the right guy because you can't redo alot of things. I suggest getting recommendations from members.

Steve

Thank you for the reply, Steve.

I was new to just about all of this when we began the restoration in Summer of 2008. I try to do a thorough job researching even the smallest things, but I have not made much progress on the engine since last November when I picked up the disassembled engine from the first engine builder. He's a racing engine builder, and I don't doubt he's very good at what he does, but he doesn't speak "NCRS", and while I have read countless engine rebuild Threads and articles over the last year, I don't speak "engine" very well.

I have never had an engine rebuilt before, and I have to get it exactly right the first time, because as you said, there's no second chance if something goes wrong on a numbers-matching engine. Since I don't have any hands-on experience in engine building, it only takes a couple of questions or comments from an engine builder before he's talking over my head.

What I would like to do seems relatively simple: a stock L79 rebuild with OEM or OEM-equivalent parts, with forged dome pistons, built to a true, measured 10:1 or 10.5:1 SCR. Leave the block alone unless it absolutely positively needs to be decked, in which case I need a machine shop with a 3-axis (or 4-axis) cutter, to avoid touching the engine-pad area, but decking the block shouldn't even be necessary.

Crower Sportsman connecting rods seem to be an acceptable replacement for original connecting rods, they're American-made and supposed to be close in weight to original connecting rods, but may not be necessary, if the original connecting rods pass magnaflux testing. On the other hand, the original connecting rods do have a finite lifespan, and a set of Crowers might be good insurance for a numbers-matching block. I have read the 'pros' for hypereutectic pistons and Keith Black pistons, and I'm sure both are excellent, but I'm reluctant to deviate from the original design, unless there is a compelling reason not to use forged domed pistons.

Nearly everyone seems to recommend an OEM-equivalent parts rebuild, to a measured compression ratio of 10.25 to 10.5:1 (i.e., factory rated 11:1 SCR was likely closer to a true measured 10.25 or 10.5:1 in actuality), and I agree with the reasoning behind doing it the "factory" way. If I understand correctly, the L79 cam design has late closing intake valve timing which bleeds off cylinder pressure, resulting in a dynamic compression ratio around 8:1 at a static compression ratio of around 10.5:1. It should run fine on premium pump-gas, which many people here on the Forum do, even though most engine builders I've talked to claim that's not possible.

[Scott S.]

Re: Is this a NOS L79 "151" camshaft, or something else?

Yes. To most of those guys "parts is parts"!

That's why I always harp about MANAGING your engine restoration project. The owner should SPECIFY exact brand and part number for all new parts and the work order should specify the exact machining operations, some of which may be contingent on measurements. The final invoice should include manufacturer and part number for all installed parts, which should all be on the preapproved list.

That is what I would like to do, and I have read your recommendations to that effect on many occasions. I have worked up a parts list (next post), but I'm not sure how to "manage" the engine rebuild. I've never done it before, and I don't have an example to go by.

Machine Shop
The first engine builder (who specialized in racing engines) disassembled the engine, shot-peened the connecting rods, magnafluxed the crank, rods and block (block was also pressure checked). Everything checked out fine, except the crank was .004 T.I.R., which he said could be fixed.

Each corner of the deck measured:
LH (driver) front: 9.029
LH (driver) rear: 9.023
RH (passenger) front: 9.023
RH (passenger) rear: 9.032

Boring and Honing
If I don't have the engine decked, the engine builder would have to bore off the mains if I understand correctly, but do you still use a torque-plate in the process? Should I have the mains align-honed? What are the other "Do's and Don'ts" for the machine shop, besides making absolutely sure the engine pad isn't messed with?

Heads
Three-angle valve job (30 degree top cut, 45 degree seat, 60 degree bottom cut). The first engine builder marked each head "68 CC", which I thought was supposed to be 64 CC. I'm almost positive they are the original 462 heads, dated December 2nd and December 12th, 1966 (car is #07873 with 1/11/67 build date).

I do not need every last drop of horsepower, or to push the envelope on compression ratio, but I don't want to go too low with the L79 cam either. Long term reliability is important. From all I've read, it seems hardened valve seats are unnecessary, but won't hurt (except for potentially cutting into the water-jacket). I will need to use special oil or ZDDP additives with the "151" L79 camshaft.

Pistons
I would like to use TRW forged pistons, and there seems to be three kinds: domed, flat and 'scalloped'? What I don't want to happen is to need racing gas to stop knocking and pinging if I go with 11:1 factory pistons, but if I understand correctly, that should NOT be a problem if I get everything else done correctly. The original block (factory rated 11:1 SCR) was probably only 10.5:1 when it was new, and that was with two steel gaskets. With a thicker composite gasket, a slight overbore (.030 or .020 if I can get away with it), and measured 68CC heads, are OEM (or OEM-equivalent) forged/domed 11:1 pistons the correct choice? I'm almost certain the engine builder is going to suggest something other than forged domed 11:1 pistons, but if that's what I should use, that's what I'll do.

Balancing
Is requesting that everything be balanced to within 1 gram reasonable?

[Scott S.]

Re: Is this a NOS L79 "151" camshaft, or something else?

L79 Rebuild Parts List:
If the NOS camshaft in my opening post is not a real "151" cam, then:


Camshaft - GM 3863151
Discontinued, replaced with GM PART # 12364050 on GMPartsdirect website, says: "Single pattern, blueprinted replacement for factory P/N 3863151 with 350 hp and 327 cu. in. camshaft. Small Image Technical Notes: Basic rpm range is 2200 - 5200; cruise rpm at 60 mph is 3000 - 3400 and compression ratio is 9.5 - 10.75. The duration at .050 lift (intake/exhaust) is 222/222 degrees, and the valve lift is .447"/.447". Lobe centerline is 114. This camshaft kit is designed and manufactured by Crane Cam Co. & reg. It contains one camshaft and 16 tappets"


Pistons - The original pistons wereGM #3866954 GM AA TRW (11.0:1)
If I understand correctly, the current forged/domed OEM-equivalent piston is designed for closer fitting tolerances than original spec?


Push Rods - GM #3796243
Discontinued, replaced by GM #14095256, welded ball type.


Lifters - GM #3799644
Discontinued, replaced by GM #5232720


Rocker Arms - GM #3843359
Discontinued, replaced by GM #10089648, self-guided type.


Valve springs - GM #3911068 (available)


Key (keepers) - GM #838029
Discontinued, replaced by GM #24503856


Cap (retainer) - GM #3896934
Discontinued, replaced by GM #14003874


Valve, intake - GM #3849814
Discontinued - GM Parts Direct: not available
What OEM-equivalent brand & part number?


Valve, exhaust - GM #3849818
Discontinued - GM Parts Direct: not available
What OEM-equivalent brand & part number?


OE Replacement Moly ring set - What OEM-equivalent brand & part number?


Final invoice - to include manufacturer and part number for all installed parts, from the pre-approved list


Where do I find the L79 correct OEM-equivalent part numbers for these?

Rod Bearings - OEM-equivalent?
Main Bearings - OEM-equivalent?
Cam Bearings - OEM-equivalent?
Fel-Pro Gasket set (head gasket thickness needs to be determined)
Timing Chain Set - Sealed Power OEM-equivalent? "Silent" chain set?
Oil Pump - OEM-equivalent, Sealed Power or Melling standard M55 oil pump?


Extras:
Add a "roller thrust bearing" between the block and the upper cam sprocket?

Enlarge the main-feed oil passages with core drills?

Tap the main oil galleries for screw-in plugs?

Screw-in studs for the heads?

ARP rod bolts?



What am I missing or forgetting? Is this what you mean by "managing" the rebuild, and just keep looking for an engine builder until I find one who will do what I'm asking?

Thank you very much for any guidance,

Scott

[Clem Z.]

Re: Is this a NOS L79 "151" camshaft, or something else?

if you use the self guided rocker arms you will need to enlarge the push rod holes in the heads to remove the original "double D' push rod giude holes

[Duke W.]

Re: Is this a NOS L79 "151" camshaft, or something else?

There are way too many questions here for me to answer with my tired fingers that have just finished a 6300 word article for The Corvette Restorer, so I emailed you to call.

One thing that caught my eye is the .004" TIR runout of the crank. If it's that much I don't see how it could even turn in the block. So my first question is why was the engine torn down. Did it seize?

Clem, what do you thing about that amount of crankshaft bend?

Also, Clem, are you sure the pushrod holes have to be enlarged for self-aligning rockers? I know that's the case for guideplates.

Duke

[Clem Z.]

Re: Is this a NOS L79 "151" camshaft, or something else?

There are way too many questions here for me to answer with my tired fingers that have just finished a 6300 word article for The Corvette Restorer, so I emailed you to call.

One thing that caught my eye is the .004" TIR runout of the crank. If it's that much I don't see how it could even turn in the block. So my first question is why was the engine torn down. Did it seize?

Clem, what do you thing about that amount of crankshaft bend?

Also, Clem, are you sure the pushrod holes have to be enlarged for self-aligning rockers? I know that's the case for guideplates.

Duke

they can straighten the crank in a press. i have seen them bend from the way they were stored. you are trying to line up 3 points if you don't enlarge the original push rod guide holes.the holes,the stud and the valve stem tip and also the rockers move slightly sideways during the lift .