Geez.....looking at the video, it is starting to look like a cam timing or distributor timing issue to me. Have you taken a timing light to it to see exactly what your timing is doing at various rpm's? I'd try that first (easiest). 2nd, if the timing all looked good, I think I'd pull the timing cover and see what I see. It's not that major of a job.

OK, just to be clear.... is this a relatively new build or recent overhaul OR did the engine run great for years & now all of a sudden it won't rev past 4 grand?

I will eyeball the rockers but will likely go ahead and pull the timing cover. The more it sinks in the more I think it’s in there wrong. I just am crossing my fingers that valves didn’t kiss pistons.

Rookie move! Thanks all, I’ll keep you posted

You may get lucky as most of this mostly stock stuff has piston to valve clearance that can be measured with a yardstick.

Hopefully you get lucky.

Again, this is why you always degree the cam. Not only can there be errors in machining and tolerance stack up but there can be human error. If you degree the cam you eliminate all but the human error and reduce the human error to almost zero.


We can never eliminate human error. We are...human after all.

Are you sure you dont wanna check "rockover" as opposed to pulling the dampener/pump/tcover/new gaskets? (that's alot of work!) You know I ain't sure how a way advanced cam would affect compression but just me (I'm lazy) I would pull the plugs & do a compression test & even just (1) cyl would tell something (assuming a compression test will be way off if the cam is way off). I ain't a cam guy but if my thinking/math is right with a 23/46 tooth SB timing set, one tooth adv would adv the cam 15.7 degrees in addition to the built in adv (from LCA). Holler how it turns out, this is the weirdest one I have seen in a long time! I cant wait...

I haven't gotten my entire game plan together, but I may quickly check the "rockover"...I bet it's off.

All this talk reminded me that this happened to me in 1991.
I had a short block assembled at what should have been a respectable shop...Was charged on the invoice for degreeing in the cam and everything...
This was a dirt track 340 motor with a 284-484 Mopar Performance camshaft.
There were 3 marks on the timing gears the triangle...the square and the dot. They lined up the dots but the dot on the outside of the crank gear wasn't stamped well.
After two weeks of no RPM's...Changing intakes and carbs and distributor I pulled the timing cover...
Instead of the crank keyway being at about 2:00 and the cam at 4:00 and the dots aligning the cam was at 4:00 and the crank was at 12:00. The dots were aligned but it was the wrong dot on the crank gear.

When I pulled the "X" heads after finding this it had lightly hit the valves...
I remember that motor had a very small sweet spot where it would start easy and if the timing was off just a little it wouldn't start...
Worst thing about getting old is the things you forget...

What Madscientist said made me think of something to try: bump the dampener to TDC on the tab & look at the dist rotor & if it is at #1 then pull the pass VC & see if the #6 rockers are even & if rotor is at #6 then pull the dr VC & see if the #1 cyls' rockers are even. Alot of chain slop might mess this up, but just a thought.

Before I tore the motor down, I would check the ignition timing at 2,000 rpm and be sure the dist advance is working correctly.
I had one dist that had worn slots in the advance plate and it would actually retard the timing at higher RPMs. With a different dist, that motor made great power and spun as fast as you wanted it to go. Gene

Eyeballing rockers on overlap wasn't working for me. It's timed right. I was nearly certain I didn't pay special attention to other dots, but apparently I did.

The distributor advanced fine to ~35°, I checked it prior to tear down.

I'm back to square one, well actually square -1 on the issue.

You are up late. This must really be digging at you, huh ?
This stuff can really suck...You don't want to let them WIN...

I’ve been building motors for a long time. I did not always have the tools to degree a cam. I have run across it twice in my lifetime where the cam gears were not marked correctly. One motor was off 8 degrees and the other was off 16. These were factory assembled motors that had been running. Both were 340s and both were dogs. You must always degree your cams.

Yep. With two little kids I'm stuck working on things late at night, unfortunately this vehicle stays outside, so that adds to the fun.



Statistically another gear set would almost guarantee me to not have that problem, if it were the case. I'm only partially kidding, however

I need to see what it takes to degree a cam, with the head on, and the intake on, in the truck....

Good for you for getting back into it right away. I also have worked many late nights on stuff like this and can relate somewhat.

Yes definitely figure out how to degree it before putting it back together.

I bet it is not easy to do in the truck which I have never done before, so good luck with it.

FWIW years ago I rebuilt/ installed cams at least 5-6 times without degreeing the cam with no problems.

But in the last 20 I have degreed everyone since then.

Quick story, when I was running alcohol dragster I was stuck at 259 mph, Tom Conway who was helping tune the car always questioned if I had the cam degreed in right. So one year I took my engine stand to the US nationals and took the motor out of the dragster and put it on the stand to have Tom check my cam timing. We were changing the motors anyway so it was a good time to check and Tom would be there for the long weekend.

The cam timing was just where he said it should be. Still the car did not MPH like it should.

A month later I moved the cam myself different from where he said it should be and the car went 265MPH and did a big wheel stand on the first run.
So you never know until you know to begin with where the cam is in at then you can make changes to experiment.

Good luck with yours.

There is a simple way to degree a cam using feeler gauges.

Essentially when the cam is installed "straight up" the intake and exhaust lifters should be at the same height at TDC. Put a straight edge across both (sometimes you may need to substitute deep well sockets to get enough height)and measure any gap. No gap means straight up installation. If there is a gap then it's not installed straight up. How much gap and which one is low will determine advanced/retarded and how much. But I forget those details it's been a long time.

That tach might have a rev limiter in it, move the redline needle higher.

^^^ that's (way) too easy!

Have you checked to make sure the throttle cable is adjusted to allow full throttle opening? Yes, I have experience with such things.

I see you checked the cam timing. Your post says it has stock ignition. The pickup coil has a polarity, the engine will run if hooked up reverse polarity, but it will run like you describe. The stock mopar distributor has a plug so it can not be switched, but aftermarket distributors may be wound wrong polarity on the pickup coil. MSD had a tech bulletin about this problem. http://documents.holley.com/techlibrary_pickups.pdf

Is that a paint mark on the cam gear? Never saw one before....always had a machine mark. Is there a machine mark under it? or elsewhere

The AFR going lean makes me want to say ignition, coils are cheap and easy.