I have recently aquired a 454 engine in peices. According to the casting numbers it is a 91/92 replacement LS-6 engine. It has the rectangular port heads and aluminum intake, 4 bolt main block but I am having trouble identifing the camshaft. It has the numbers 299006 or possibly I am reading it upside down and it would be 900662. It also has 3143 stamped opposite these numbers. I would appreciate any help....thanks BJ
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Re: camshaft ID 454
BJ------
The camshaft is a GM #3863143 as evidenced by the "3143" stamped number. This is one of 2 virtually identical camshafts that could have been used in the LS-6 engine.In Appreciation of John Hinckley -
Re: camshaft ID 454
Is there a groove in the rear journal?
DukeComment
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Re: camshaft ID 454
Yes, the rear journal is grooved. BJComment
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Re: camshaft ID 454
Hmmmm! That's what I expected, but I believe that cam was only applicable to 65-66 SHP BBs. Beginning in '67 a different part number SHP cam was used. It has the same lobes and lobe phasing, but no groove in the rear journal.
However, the "143" is the only SHP BB cam listed in my mid-seventies parts manual. If you use a grooved journal cam in a '67 or later block the rear cam bearing feed hole is supposed to be modified. Details are in the Chevrolet Power Manual. Maybe Joe or another BB expert can comment.
DukeComment
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Re: camshaft ID 454
Duke-----
Yes, there were 2 different SHP mechanical lifter cams. The first was the GM #3863143 and the second was GM #3904362. The first was used for 65-66 and has the rear journal groove. The second was used for 67-71 and does not have the groove. Otherwise, the 2 cams are the same, although many references show somewhat different specs for them.
I've never been able to quite figure out the situation with these 2 different cams. GM never catalogued the 3904362 for SERVICE until February, 1988 when it replaced the 3863143. However, I feel very confident that the 3904362 was used in PRODUCTION for 67-71 SHP big blocks, also notwithstanding what some references may say. Instead, the 3863143 was sold in SERVICE for many years (until February, 1988) for all 65-71 SHP big blocks. Also, there was NO SERVICE instruction provided that the rear cam bearing needed to be modified for use of this cam in 67+ big blocks. When the 3904362 replaced the 3863143 for SERVICE, there was no instruction that the rear journal needed to be grooved for 65-66 engines.
Adding to the confusion, I've seen 3904362 SERVICE cams WITH the rear journal groove. I can't say that I've ever seen a 3863143 without the groove, but they may be out there, too.
The 3863143 and the 3904362 were manufactured from different cores. That's because the 3863143 core was cast with the groove to reduce machining operations. The 3904362 was cast without the groove. However, it's very possible that for relatively low volume SERVICE parts manufacture, the groove was added to the 3904362 core in the machining operation. Technically, that would make the cam a GM PART #3863143 while the core identification marks would show it as a 3904362. I think that the "3143" end stamping was supposed to "clear up" this confusion.
I have heard before of these "3143" cams with rear journal groove being used in the old GM #366250 LS-6 crate engine assemblies. Whether the rear cam bearing was also modified in these engines, I do not know. If not, I would expect that the modification to the bearing was not really all that important, notwithstanding what the Chevrolet Power Manual and other references contend.In Appreciation of John HinckleyComment
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Re: camshaft ID 454
Thanks Guys for all the info. I know where to come to now for future questions (that I know I will have) on this project. Thanks again....BJComment
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Re: camshaft ID 454
Joe - I have a 1989 vintage crate LS6 I bought new myself and have had the cam out. It has the groove, and I ASSUMED it was the 4362 based on the listed parts back then for this crate engine. I know if I pull the cam plug I could tell on the end, but it is not convenient right now (even though it is sitting on a stand it is not accessible and is all sealed up. I can tell you, the block was the new style, and I did the power book modifcation to restrict oil flow on the rear cam bearing with a 0.060" hole. The stock hole was the way GM assembled it though. I am guessing I have a 3143 vs 4362, and am now really curious of the casting number as well as stamping on the end.....CraigComment
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Re: camshaft ID 454
Just to remind everyone and, hopefully sort out some general camshaft confusion, the order part number for the camshaft in the parts catalog is really an "assembly" that consists of the finished machined camshaft and the dowel pin. The number cast (or stamped) into the camshaft - either the entire number, or sometimes just the last four digits, is the actual finished camshaft part number, and the parts catalog sometimes refers to this as the "ident. no." (identification number). Sometimes the camshaft assembly and ident. no. are sequential, but not always. Many refer to the ident. no. as the "casting number", but this is a misnomer. All Chevrolet camshafts are machined from their own unique castings, but I have never found any part numbers for the raw castings.
The 3863143 camshaft assembly (3863144 Ident. no.) has the rear journal groove. It is roughed in as part of the casting and finished machined to spec per the drawing. The 3904362 camshaft assembly (ident no.3904366) does not have the rear journal groove, and I can assure everyone from my inspection of the GM drawings that the lobes are IDENTICAL - both the eccentricity data, which is listed to five decimal places every camshaft degree and the lobe indexing.
The last change to drawing no. 3863144, dated 2-17-67 adds the following note" "May be made from 3904366 casting", so it's possible to have a "143 camshaft" with an ident. no. of 4366. In this case the rear bearing journal groove would have to be fully machined since the core did not have a roughed in groove as part of the casting.
The inlet and exhaust lobes are also identical, including the clearance ramps - as is the case with the SB 30-30 cam, but unlike the 30-30, which has the same specified valve clearance for both inlet and exhaust, the SHP big blocks do not, and to add to the confusion, the first clearance spec in 1965 was .020"/.024", and this was later revised to .024"/.028", I think beginning in 1966. Another interesting footnote is that the LT-1 cam uses the same lobe as the SHP BB on the inlet side, but it is indexed two degrees later. (The LT-1 cam exhaust lobe is the 30-30 lobe indexed four degrees earlier.) Also, as is the case with all other vintage Corvette camshafts, except the Duntov, but including ALL hydraulic lifter camshafts, the lobes are asymmetrical, so the "centerlines" do not correspond to the points of maximum lift.
It's clear from the camshaft drawings that the top of the clearance ramp is .012" above the base circle, and if BB rocker arm ratio behavior is similar to SB rocker arm ratio behavior, I believe that tighter clearance is called for. The SB rocker ratio begins at 1.37:1 at the lash point and increases to 1.44:1 at the point of maximum lift for an approximate 0.3" high lobe.
So far no one that I know of has ever measured OE BB rocker arm ratio behavior, and I would certainly like to get the data, as it would benefit everyone to allow better defined valve clearances. Since I don't own a BB, I don't have one handy to measure.
DukeComment
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