1970 GTX breaking up after 2500 rpm. Failing cam?

[BeepBeepRR]

I have been working on this issue all day. The car is a 70 GTX 440. The car has valvetrain noise all the time. And I have been trying to trouble shoot the problem.

Thought it was fuel starvation. replaced a worn fuel pump rod. Didnt help.
Checked timing. Didnt help
Checked plugs all looked decent and were not either white or black.
Swapped carbs to a known good carb. No change in the engine.
Checked the rotor button and cap both looked good. This is a fairly new MSD RTR distributor.
It has a new set of MSD 8.5mm wires. They are all in good shape.

It was running fine until Friday. All he did to the car that day was change out the air cleaner. I checked coil voltage 13.64 when running. Im boggled and wonder if the cam is wiped and that is why its breaking up above 2500 rpms. I think its more between 2100 and 2500.

Any good way to check the cam for wear besides just pulling it?

 

[T2R9]

I would pull the intake and take a good look while rotating the crank by hand.

 

[Kern Dog]

A compression test will help. If one or more cylinders show more than a 15% variance, you may have a problem.

 

[BeepBeepRR]

I can check that. Just so happens I bought a tester a while back. Thanks.

 

[66 Sat]

This doesn't explain the valvetrain noise you've been chasing down, but there wasn't a cellophane wrapper or anything on the air filter element that you forgot to remove?
Just thinking of easy dumb stuff we all do sometimes...

 

[BeepBeepRR]

This doesn't explain the valvetrain noise you've been chasing down, but there wasn't a cellophane wrapper or anything on the air filter element that you forgot to remove?
Just thinking of easy dumb stuff we all do sometimes...

Its not my car but he put his old air cleaner back on due to the intake being too high. Which is in another thread. I'm sure that is not the issue. I even asked him if there was any chance he could have dropped a nut,washer,bolt down into the intake. He assured me that nothing like that happened. I suspected a washer was stuck in a valve or some crap like that. But he said he was careful.

 

[AR67GTX]

Are you running points? Possibly worn upper distributor bushing. That will cause breakup as engine speed increases and it can be seen on a dwell meter as the engine is revved up. If you are running electronic ignition I don’t think they are as sensitive to loose, worn bushings.

 

[Kern Dog]

Oh yes they are, especially the factory based units. The reluctor wheel and pickup are set to a .008 clearance so if there is wear, the two points meet and shuck the teeth from the wheel!

 

[BeepBeepRR]

Are you running points? Possibly worn upper distributor bushing. That will cause breakup as engine speed increases and it can be seen on a dwell meter as the engine is revved up. If you are running electronic ignition I don’t think they are as sensitive to loose, worn bushings.

No it has a practically new MSD RTR distributor and new MSD coil.

 

[#41]

I would suggest pulling valve covers and checking for excessive play at the rocker arms. If so, then pull the intake too and see what is going on....

 

[BSB67]

It was running fine until Friday. All he did to the car that day was change out the air cleaner.

My money is it is something he did.

The new problem of it not going over 2100 rpm is not a wiped cam.

 

[furious70]

I can't see a wiped lobe causing break up at the low rpm. Irratic idle, oil smoke, fouled plug yes

 

[440 Charger]

I have been working on this issue all day. The car is a 70 GTX 440. The car has valvetrain noise all the time. And I have been trying to trouble shoot the problem.

Thought it was fuel starvation. replaced a worn fuel pump rod. Didnt help.
Checked timing. Didnt help
Checked plugs all looked decent and were not either white or black.
Swapped carbs to a known good carb. No change in the engine.
Checked the rotor button and cap both looked good. This is a fairly new MSD RTR distributor.
It has a new set of MSD 8.5mm wires. They are all in good shape.

It was running fine until Friday. All he did to the car that day was change out the air cleaner. I checked coil voltage 13.64 when running. Im boggled and wonder if the cam is wiped and that is why its breaking up above 2500 rpms. I think its more between 2100 and 2500.

Any good way to check the cam for wear besides just pulling it?

Have to look into it more my guess cant tell yet could be so many things.

 

[BeepBeepRR]

I can't see a wiped lobe causing break up at the low rpm. Irratic idle, oil smoke, fouled plug yes

It idles fine and once you get above 2500 rpms it starts to miss really bad. I'm going to change the oil and see if there is any shavings in the filter. This is the second fuel pump rod I have put in this engine in 6 months. Here is a picture of the new vs old one I just took out of the car.

 

[BeepBeepRR]

I would suggest pulling valve covers and checking for excessive play at the rocker arms. If so, then pull the intake too and see what is going on....

Yup good idea. I will do the valve covers first then the intake. Its just odd that it ran fine prior to the air cleaner swap. The Guy who owns the cars has had muscle cars all his life and I trust what he tells me. But the timing is very odd. I would agree. I did also check all of the wiring to and from the MSD RTR and coil. Seems to be fine. I racked my brains in the sun for almost 4 hours. My last guess is valvetrain. Since he got this car it has always had a weird sound in the bottom end. And then the rockers make a crap load of noise. He did tell me that one of the rocker arms for number 8 was loose. So Maybe this is going to get interesting. Either a lifter is failing or a bent push rod.

Thanks for the help guys/gals I like the investigation and trying to figure it out but swapping carbs,coils,checking plugs and all the other crap I tried is wearing thin.. I was stumped but the suggestions are good and helps me think Im not crazy.

 

[Don Frelier]

Fuel filter?
Water in the gas?

 

[BeepBeepRR]

Oh yes they are, especially the factory based units. The reluctor wheel and pickup are set to a .008 clearance so if there is wear, the two points meet and shuck the teeth from the wheel!

View attachment 1165689

I pulled the cap but didnt pull the rotor. Will check the reluctor next time around. There was some carbon on the tip of the rotor button but I got that cleaned up. Also checked the cap and the contact points were a little crusty as well and I cleaned them up a little. But didn't think about the reluctor wheel and the pickup coil.

 

[440 Charger]

It idles fine and once you get above 2500 rpms it starts to miss really bad. I'm going to change the oil and see if there is any shavings in the filter. This is the second fuel pump rod I have put in this engine in 6 months. Here is a picture of the new vs old one I just took out of the car.
View attachment 1165780

Thats about wrong.

 

[BeepBeepRR]

Fuel filter?
Water in the gas?

Good question not sure.. I didn't notice anything weird when I swapped carbs. Then I actually bypassed the mechanical fuel pump and stuck a electric one in line and it worked fine filled the QFT carb in a matter of seconds. I thought it might have been fuel starvation. But with the electric pump it made no difference. But water in the fuel is and could be a suspect.

 

[BeepBeepRR]

Thats about wrong.

The first one I changed out was worse. Almost a full quarter inch of it was gone. This one is about an 8th inch gone. Comp Cams push rods suck *** and they are made of chinesium butter steel.