My original camshaft has worn out lobes. I am asking for a recomendation for a replacement although I would like to find a NOS one. Also what other items should I replace.
Thank you John. 35080
Thank you John. 35080
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John-----
If you feel that you must use an original type hydraulic flat tappet cam, I offer the following:
For NOS look for a GM #3883986. You can also use a GM #3904359 if you have the rear journal machined for the 65-66 required oiling groove. This is an absolute MUST HAVE feature for any camshaft you use.
You MUST also install new lifters with a new camshaft.
Also, install a new timing set. I highly recommend using a Cloyes True Roller 9-3110In Appreciation of John Hinckley -
During a restoration of my '67's 390 last summer, I chose the Melling (MEL-22216) which matches the 3883986 profiles. My machinist/builder didn't like the springs Melling recommended - said they were too stiff (125/325). He supplied the springs but I don't recall which he used. Before I asked him to get the springs, he said to look for springs with about 90 lb closed seat pressure and open at about 280 lb (300max).
He broke in the engine with a total run time of about 1 hour – he wanted to make sure the cam/lifters were going to play nice.Comment
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Howard's Cam, Oshkosh, WI and Elgin Cams, Santa Rosa, CA offer exact clones of most OE cams. As Joe stated your '66 vintage block needs the ...986 version that has the groove in the rear journal. The ...359 has the exact same lobes. It only differs by NOT having the rear journal groove.
The high level specs for this cam are:
.050" lifter rise duration, inlet/exhaust: 214/218 degrees.
IPOML/EPOML/LSA: 110 deg. ATDC/120 deg. BTDC/115 degrees
Max lobe lift, inlet/exhaust: .27143/.28232"
Your '66 L-36 was originally equipped with the first design valve spring-damper. AMA specs call out 94-106 lbs. @ 1.38" and 303-327 lbs. @ 1.88" for a nominal rate of 434 lb/in. These springs were subject to failure, especially on mechanical lifter big blocks that were run hard. A second design dual spring with integral retainer and umbrella seal is speced out in the '70 AMA specs for LS5, nominally 105 lbs. @ 1.38" and 326 lbs. @ 1.38 for a rate of 442 lbs./in. So seat force and rate are about the same, but the second design is much more reliable
Absolutely do not install springs with higher seat force and rate than the above, no matter what the cam manufacturer recommends, and slightly less should be okay if you observe the 5300 tachometer redline.
Due to the higher loaded big block valve train these springs have higher seat force and higher rate than small block springs that are about 80-84 pounds on the seat and about 200 open with a nominal rate of 238 lbs./in. but the big block uses the same lifter, so lobe-lifter loading is greater.
Unfortunately GM discontinued the second design spring about 10 years ago, but Joe Lucia found an aftermarket dual spring of similar rate to the second OE design.
There are various reasons stated for what appears to be a much higher flat tappet cam lobe-lifter failure rate than what was typical back in the day. Many blame current engine oils, but current C-category oils have more anti-wear additive than back in the sixties (and more than current S-category oils). I don't blame current C-category oils.
LIfter origins appear to be a bit sketchy, and some say that some current lifters lack sufficient crown on the face that combined with very slight lobe taper should cause the lifter to rotate. I do put some credence into this theory. Some current lifters also have a small hole on the lifter face that feeds pressurized oil directly to the lobe-lifter interface.
If the cam manufacturer offers Parkerizing, absolutely have this process done even if it increases the price. OE cams were Parkerized and this aids break-in. Parkerized cams have a dark gray mottled surface finish other than on the journals, which are polished off. This surface is micro-porous and holds oil, which aids successful break-in. It wears off the lobes fairly quickly, but by the time it does the lobe-lifter interface should be seated and yield long life.
I'm not sure what sources there are for cam blanks, Going back, say ten years or more it was the CWC division of Textron, and they were made in the USA. There was just one flat tappet cam blank for most engine families, and it was used by all cam grinders. You should inquire about the source for blanks by the vendor you choose.
A moly-disulfide grease should be used on lobes and lifter faces during assembly. Use C-category oil with a ZDDP rich supplement like GM Engine Oil Supplement or equivalent. Prefill the oil filter. Also prefill the primary carburetor bowl for a quick cold start and run the engine at 2000-2500 no load for at least 20 minutes. Since the moly-disulfide has a lot of solids that may clog the oil filter, change it after the initial break-in, and top off the oil. Run this oil with the supplement for 500-1000 miles, then change with C-category and you should have long cam life.
It's important for you to discuss cam blank source, Parkerizing, lifters, and valve springs with each vendor, and go with the one that gives you the straightest story and the most confidence.
DukeComment
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