- valve cover/baffle to roller rocker arm interference
- header leak
- stuck valve
- fuel pump

I'm in the Mojave desert at the moment but before I left I used a
stethoscope on the engine, trying to track down the source of the
noise. However, the stethoscope seemed to pick up the noise any
where I placed the probe. It might have been a bit louder on the
fuel pump but I'll to double check that when I get back to town. Any recommendations on a mechanical fuel pump to feed a street performance type 351C (approximately 400 HP at the flywheel)?

If it were a valve stuck in the guide, would it be noticeably harder
to turn over by hand (as the piston pushes the valve closed)? BTW,
I pulled several pushrods and they were all straight and I spun the
rest in place. Also, if it were a valve, I would think I would be
able to pick up the noise louder in an intake runner or header tube.

It can definately be a header leak. Can you feel around the header flanges while it is running when the engine's cold? You may not have room on theat mid-engine car.

I'll give it a shot. There should be decent access from below.

> When adjusting the valves, did you first listen to each rocker stud with
> the motor running using the stethoscope?

No, I didn't.

> I am sure you have a cut away valvecover

Yes I do but it doesn't work all that well with the roller rockers.
I think I clipped away too much. I was actually thinking of sacrificing
an old tall Ford Motorsport valve cover but I need to find a set of the
long bolts first. Cut out the top and put a hinged cover on it with
one cylinder at a time access would be slick.

> If nothing was banging then I would rule out the valvetrain......

I also thought about pulling all the spark plugs and turning it over
by hand. If it doesn't feel tight on one cylinder, that would rule out
a stuck valve.

It's a tapping noise. It's directly related to RPM and it is slow enough
to be a single cylinder. Bfore I came in to work today, I fired it up
and listened to it with the stethoscope again. I can pick up a similar
sound in each of the header tubes on the driver's side.

"...suddenly there came a tapping,
As if some one gently rapping,
rapping at my chamber door.
'Tis a loose rocker, I muttered,
tapping at my chamber door
Only this and nothing more."

Apologies to Mr. Poe.

> Could be carbon build up on the pistons. You can run the car about 2000
> rpms and slowly pour a cup of water down the carb. This sometimes will
> remove the carbon. RAY

My dad suggested the same thing but I had the heads off less than 10K miles
ago and there was absolutely no carbon build up. I swapped the 4300D carb
for a 735 CFM Holley and did a cam change at the same time. This engine
was just supposed to be in the Pantera temporarily (until I got around to
building a stroker engine for it) so I never bothered rejetting the carb.
I suppose it is possible it's been running rich enough to build up carbon
but 10K miles seems awfully quick for that to happen.

Not really. The sound is more distinct than that. Maybe if
one rocker was way off. I had a bad pushrod (improper heat
treat) one time that wore the end off until it was slapping.
It sort of sounds like that.

> btw, what pistions are in the engine?

The original cast dished pistons. Engine has 25K miles on it from
new (in 1974). I pulled the open chamber heads after buying the
car with 16K miles on the odometer and the pistons were spotless.
A funny thing about the pistons is that only 6 of the 8 had the
complete dish. The other two were only partially dished, as if
they had not been completely machined. I finished the job with
a die grinder when I had the engine apart. I put it back together
with a mild cam and Aussie 2V heads, along with Hedman headers.

> Dan, I seen rich motors carbon up in less than 10k. Try pulling
> one spark plug and starting the engine. Rev it a few times. If
> the noise is still there do the same thing to another cyl.

I'll give it a shot.

> The bad news is, I had the same type of noise in my old 130k
> cleveland. We were sure it was valve train related. WRONG, it
> was a cracked piston. Hope that's not your problem. RAY

I hadn't thought of that. It certainly could be the problem.
I shift at 6000 RPM or so which I thought would be safe but
you never can tell. I probably have some standard bore dished
pistons in a spare short block that could be swapped in but I
really don't want to go to the effort. I just got the heads off
the flow bench for the stroker motor. If it turns out to be a
cracked piston, I'll probably just wait until the new engine is
ready (probably not until fall).

Is there any way to isolate a cracked piston without pulling
the engine?

quote:

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Is there any way to isolate a cracked piston without pulling
the engine?

---

I'm not real sure about that. If you have a loose piston you can disconnect a plug wire to see of the noise goes away. However, I don't know if you can do anything like that with a cracked piston(s).

I built a 351w using TRW pistons. After a few months the engine developed a noise that sounded like the valves needed to be adjusted. After adjusting the valves 3 or 4 times, I came to the conclusion that wasn't the problem... no need to hit me over the head with a stethoscope.

After disassembling the engine I found 3 or 4 pistons where the skirts were completely broke off and 3 that were cracked almost to the point of totally being broke off.

All the broken skirts looked exactly the same. You could take the broken skirts from one piston and place it in one of the others, just like it came from the other piston.

Funny part of this story is, right before I disassembled the engine, we took the car out and was turning the engine over 7k, lol I can?t believe it didn?t come apart.