soft cam lobes?

[79gmcclassic]

hey guys long time no talk! but i got some questions for all you hardcore gm truck guys! i have had my truck for around 4 years now and it has never exactly ran correctly and smoothly, at an idle its the worst it will run really rough and have a hesitation where the truck just wants to go and me and my dad have the idle screw turned slightly up because thats what we thought the problem was. and we have also gotten the quadrajet rebuilt, i always run 91 or 93 octane fuel. we also have had the assumption of a burnt valve or carbon stuck on the valve so it doesnt seal but my grandpa recently said that he thinks the cam is soft and then i recently also heard that small block gms are noted for soft cam lobes in this era...so i was wondering if you guys have ever had experiences similar? i was thinking of doing a top end kit and ditching all the emissions junk, because it doesnt burn a drop of oil and the seals are still doing good as well after 35 years of never bein opened up! thanks in advance!

[geezer#99]

Look at it this way!
If your cam lobes where soft then they'd be just round lobes in a big hurry.
Your grandpa was referring to the poor metal cams where made of and the resultant flat lobes.
Your rough idle could be caused by a lack of timing and a carb that's trying to idle on the power circuit.
What's your initial timing set at?

[Mr.Chevy4x4]

Yep, I agree. When a cam lobe starts to go, they go FAST. From my experience it is more often an exhaust lobe. Once it's gone you would experience back firing through the carb. When the q-jet was rebuilt, were throttle shaft bushings installed? If not, you could have a healthy vacuum leak past the shaft. Have you checked for vacuum leaks elsewhere? What about the vacuum advance? Need to make sure it is working correctly, and check base timing. Lots of things it could be, but that is where I would start.

edit: Oh yeah...and a compression and leak down test will tell you a lot!

Mike

[INSIDIOUS '86]

76-79 was about the years. Typically you will hear the lifters and rockers smacking around as they wont hold thier preset lash. I think the lifters and cams then were suspect. Seen a lot of cupped lifters out of engines like this.

[motornut]

called "candy cams" hard like a candy cane outside.
softer inside...
I've seen nylon gears that split/pulled off the gear too.
I only found it because i went in to replace the timing chain,
couldn't see the crack,till it was off.
work threw it checking for vacume leaks,and a slight tap on each tube in the carb.
be sure they are seated,
my 3/8 from the carb base to the charcoal was split,bad,couldn't see it

[bnoon]

I had the cam go flat on three lobes of two cylinders on my 454 orange '76 and it eventually spun a bearing on a third cylinder. It still ran decent going down the road, but boy did it lose some power near the end! It took a good 5-6 months to burn down those lobes completely.

If you suspect cam lobe failure and want to be certain, pull the valve covers off and rotate the engine over by hand using a long breaker bar and a socket on the balancer bolt. Measure lift at the pushrod tip. Stock cams have somewhere in the neighborhood of .2 to low .3 inch of lift before the rocker's 1.5 ratio and all should measure about the same.