valve, lifter or something else?

[coronet66]

i have a 70 383magnum. I installed a new cam, lifters and springs. Everything was fine for about 3 weeks and a couple car shows of course! Then i started it one day and the motor was running real rough., I had to keep giving it gas so it wouldn't stall. I checked the wires, plugs, fuel all fine except # 8 plug the core was black instead of grey like the others. would that indicate valve problems?

 

[67 B-body]

was it a flat tappet Hyd camshaft?

 

[coronet66]

yes it was.Comp 274-286, 488-491.

 

[67 B-body]

Well,,,, I had terrible luck with the first cam in my new engine! Mine ran real good for a short time then all went to hell! I spent a tone of time diagnosing that damn thing, hoping it wasnt internal! I had several lobes wipe out on the camshaft because todays oil SUCKS! I also had two valves bend due to this while diagnosing the problem. A couple revs had the pushrods jump up onto the lifters lip and had valve strike.
Short of it all, I tore down the engine, fixed everything up with new cam and lifters, a couple valves, and Brad Penn oil. All is well and running good now.

 

[coronet66]

I used the same break in oil. How can u tell if it's a lobe? I now have the heads , man, vally pan off, so I can see the cam.

 

[Big Jim]

If the lobe is REALLY wiped out, you could actually see the lack of an offset- if it's hard to see good/bad, set up a magnetic base dial indicator on a lifter and rotate engine by hand; check actual measurement. For this purpose, Harbor Freight sells a mag-base and indicator for under $30- handy for a lot of other things a well-but for anything high-dollar I'd use a better quality indicator- (I'm a machinist by trade- love my MItutoyo/ OLD Starret stuff)

 

[coronet66]

could I just measure it with a micrometer?
:blob1:

 

[Cranky]

Yeah but it's not too easy with the cam in the block....

 

[67 B-body]

look at the face of the lifter.... I have never seen a lobe go bad without the lifter failing too.... The failure is almost always caused by the lack of rotation from the lifter, and the wear pattern is typicaly evident with inspection...
I can get a good picture of a bad lobe and lifter posted if you wish to see what happens... LOL!

 

[lewtot184]

you don't think that maybe you over revved the engine floated the springs and pumped the tappets up causing some piston to valve contact? 68-70 383's with stock pistons don't have a lot of extra piston to valve clearance. i know, i've literally broke a head (valve guide boss) missing a gear in my 68 road runner. there's also the possibility of retainer to guide clearance isses that will at the least wreck the valve seals. also if you have adjustable rockers and don't check the true rocker ratio,.....well surprise, surprise!

 

[coronet66]

No, I had just started the car when all this happened. I actually turned it off and started it again and the same thing, so i just shut it down. I did notice on the top of the # 8 piston a half moon black mark. Don't know if that means anything? Unfortionately I'm a shade tree mech. Wish I knew more em, this is driving me crazy I've called 4 different shops and get 4 different answers

 

[lewtot184]

hopefully its something simple, but an "eyebrow" on the piston could be suspicious. if you have an air compressor or access to one try bringing the piston up to top dead center, both valves closed , and pressurize the cylinder. see if you can hear air coming thru the carb or exhaust. if so there's probably a bent valve. if not, then i'd check for a clobbered valve seal. usually its the intake valve that makes contact with the piston on a 383. as far as being a shade tree mechanic, we all are or have been. i've got a friend who says i'm one step above a shade tree mechanic because i have an air compressor!

 

[67 B-body]

Poor some solvent or gasoline into the combustion chamber "I think you've removed a head" of the cyl that had the half moon mark in the piston. If you bent a valve, it should leak solvent through the valve seat even if it's closed.

 

[coronet66]

hopefully its something simple, but an "eyebrow" on the piston could be suspicious. if you have an air compressor or access to one try bringing the piston up to top dead center, both valves closed , and pressurize the cylinder. see if you can hear air coming thru the carb or exhaust. if so there's probably a bent valve. if not, then i'd check for a clobbered valve seal. usually its the intake valve that makes contact with the piston on a 383. as far as being a shade tree mechanic, we all are or have been. i've got a friend who says i'm one step above a shade tree mechanic because i have an air compressor!

well your're one up on me, I don't have an air compressor! but i like that saying

 

[coronet66]

lots of good info. When u put a new came and lifters in do the valve stems need to be ground?

 

[Big Jim]

Valve stems don't need to be ground but you do need to check for coil-bind at full lift in addition to valve to piston clearance. Seen guys get away with out doing it but after spending the money for new cam/lifters/springs just cheap insurance.