babbah

My neighbor has a 65 vette w/ 396 BBC and this weekend it started to backfire and was making a intermiitent loud noise. Noise started a week or so ago but would go away...otherwise ran fine...

We pulled the valve covers and found #8 cylinder exhaust valve was hardly moving when engine was being cranked. All other cylinders were fine. We figured collapsed lifter....Pulled the intake maniforld and found the camshaft lobe for #8 exhaust was completly gone and bottom of the associated lifter was badly worn with concave instead of flat bottom....I have bever seen such wear on these components before.

I have heard that the 396 big block motors were noted for this problem, something to do with the oiling or something, related only to early 396 big blocks......I see that the 396 bbc camshafts rear bearing journal has a slot grove in it, unlike all other bbc cams that dont have this slot.

I wanted to ask any of my fellow forum members if this is true and what actually causes this camshaft lobe failure on 396? Thank You All.....

67L36Driver

Mine lost #5 intake lobe, lasted 2000 miles after build. The second time it lasted only 15 minutes on the run in stand. #5 intake lobe again.
Never have had cam problems with a SB.

babbah

67L _
What was the root cause of the problem?

rgs

If it was recently rebuilt, I would suspect the lifter. We've had so much trouble with the cheap import stuff being sold even through good name stores that we now use only GM lifters.
My 396 has never lost a lifterr/lobe.

435Randy

I have had the cam lobe go out in the last 2 BB cars I have had, one 396 and the other a 427. Since that time I have been amazed at the number of people on this Forum who have had the same issue. I just got my car back from the last rebuild in January so I have not driven it let, my fingers are crossed. The first BB car I drove 60 miles after I bought it before it went. I traded in on the second car after I rebuilt the motor and it went 100 miles before the cam went. I have spent 8K to drive 160 miles, next car will be a small block.

67L36Driver

Never figured out exactly what caused the #5 intake lobe to go flat twice in a row. Only suspect we had were both were aftermarket cams. First was a Comp cam and second was a Crane, both near duplicates of the L36 in duration and lift.
Everything was carefully checked. After the first cam went we even shimmed the cam foreward .030" for better lobe/lifter alignment. Oil passages were clean and clear, lifter/bore clearence was fine, used EOS on assembly, left out the inner spring for break in etc.
What really burned our butt was the very short time it took for the second cam to fail. Metal particals wiped out the crank and bearings the second time.
The best reccomendation I can make is to use a factory cam which has a phosphate or parkerized coating where aftermarket has none.

Ironcross

Gentlemen, do not blame the, or a cam issue on a BB. All of the engines are basically the same and just merely pumps. The bigger the pump the more power it can develope. Most if not all camshaft problems are directly related to the installer. These cams were perfect from the grinder or factory but many are not merely drop in operations. Incorrect lash, wrong proceedure of adjustment, or serious head work that is required on many cams because of the lift and ommited will quickly result in cam failure. Get help from a local racer if your in over your head on a cam change. I`m sure they would be more than glad to help with a correct installation.

67L36Driver

Ironcross
I have overhauled or rebuilt Ford flatheads, Olds 324, Desoto 341 (hemi), Dodge 383, Dodge 318, Ford 351, several SB Chebbys and even an International 330 (what a slug). The ONLY one I have had any cam lobe issues with have been the BB Chevy with an aftermarket cam.
None of thease other engines have had any trouble including some that had new lifters installed with a worn cam, used cam installed with used lifters mixed up on lobes, even one with a used cam from another engine against lifters mixed up.
With the BB Chevy you just have to cross your fingers and hold your breath.

Mike Smith

What kind of oil was he using?

http://www.ncrs.org/forum/tech.cgi/n...15483&expand/1

http://forums.corvetteforum.com/show...645&forum_id=4

AZDoug

I had a factory SB 307 lose a lobe and lifter as described on a factory cam and lifters. Never had a problem on either BB I owned, including two cam upgrads using GM cams.

use a factory, parkerized cam,and factory lifters and buy a can of the cam break in lube, GM EOS, Engine Oil Suppliment (almost pure manganese compound, and I don't have a part number) and liberally apply to base of lifters before dropping them into the holes,a nd also rub it onto the entire cam surface prior to installing the cam.

Pour the remaining EOS onto the cam thru the lifter gallery slots prior to dropping the lifters in. Spend ZERO time at adle and run the engine between 1500-2000 RPM for at least 15 minutes (assures good oil supply) to break in the new cam

Doug

67L36Driver

What gets to me is that the factory does not go through this monkey business. They fired 'em up at the engine plant on natural gas & air mix to set the timing and check for oil pressure, at best run a couple minutes. After that the engine was started and run only long enough to get the car off the end of the assembly line and to a storage lot.

Moral of the story: Avoid aftermarket cams unless you'r building a race motor.

AZDoug

It was cheaper for the factory to do a few warranty repairs than spend break in time; plus back in the 1960's, warranty period was only good for 3 months in 1960, up to maybe a year by 1969, and the chances of finding a bad cam lobe or lifter was pretty small in that time period. I think GM used the EOS durign engine assembly, though.

Doug

AZDoug

Oh, yeah...

The '65-'66 BB cams had a rear groved journal and grooved rear cam bearing, the '67 and up had a groove machined in the block where the rear bearing presses into, IIRC.

Do NOT use a non-grooved cam in a early BB or a use a grooved cam in a later BB.

Doug

Ironcross

All thats necessary if done correctly.

gilmore1967

I can't believe COMP or CRANE would have those type of quality problems. It just does not make sense. Just my 2 cents. I would look for another root cause.

JohnZ

Warranty was 12/12 (I think) starting in 1963, and went to 5 years/50,000 miles (for the powertrain) from 1967-1972. Factory cams were Parkerized to retain oil for initial break-in, and there wasn't much time for cam/lifter preparation at one engine every twelve seconds.

00fxd

You can have problems with both bb and sb chevrolet engine cam lobes going away. At any time through their service lives. No one knows why [spec] . The more engines you have owned or will own the more chance of it happening to you. My next engine build WILL be a roller for this reason.

iniguy

No expert but I think it has something to do with the chemical constiuents in todays oil. Especially bad for solid lifter cams. I've been told to run oil compatible with diesel applications i.e. shell rotella and chevron delvac

435Randy

I have owned over 50 cars, 48 small block's, 2 Big Block's. In that time I have had 2 bad cams and both were in the Big Blocks. It could be just bad luck but sinse I have posted on this forum the feed back has been about 10 to 1 BB's over SM's. I am basing my assesment on statistics. It could be that I have the BB curse, I will let you know at the end of the summer, I have not driven the car sinse the last rebuild.
Randy

GregP

I had a lobe go flat on my SB Chevelle (factory cam). Never had a problem on the BB's in the boat (at least with cams) even with fairly high lift race cams (Crane). I think it is probably a fairly rare and random occurance.

-Greg