High Performance help......please.

Hey,

I'm new here, so go easy on me....... Got a question that I am hoping some of you can help me with to save alot of time and frustration.

I just bought a 72 Mercury Cougar XR7 convertible. Nice ride and well restored. The motor is the original 351 cleveland, but was rebuilt about 3500 miles ago, was bored over, had a mild cam installed, a new Edelbrock intake along with a Edelbrock 4bbl carb, and a MSD electrical system installed. Motor is very tight, pushing about 325hp, and runs very well under normal driving conditions with no problems. However, from a dead stop, when you fully (or even moderately) accelerate, I hear a knocking or pinging coming from the drivers side of the motor. ( I am not so sure I would even call it a knocking or pinging... it's more like a rattling... almost like a loose rocker arm, but louder)
I have heard about the knock and ping caused by low octane, and don't beleive that is the case, especially since I have put high grade (93) octane gas in and even threw in a bottle of 104+ octane boost.
I have also heard that this could be caused by poor air-fuel mixture, which leads me to beleive that this may be my problem as the previous owner stated that he had problems with the old carb and had just recently put this one on.
The car runs great otherwise, especially near the top end.... (I can floor it after I am already going more than 40mph and I don't get the sound).
For giggles, I also added in a bottle of Rislone to the oil to see if that might help. No luck.
Any suggestions would be helpful. Thanks

It May be caused from a lean mixture. try fooling around with your carburator jets and if you put a rich one in and it stops then it was caused by a lean A/F mixture. keep leaning the mixture out untill you get just below the jet that causes that knocking sound.
It may be a loose push rod rattleing around. Since it was rebuilt they who ever did the work may not have gotten the rocker arm tightened all the way down. if this is the case you need to take the heads off and all and take a look. if there is any damage you will need to replacethe push rod and maybe even the rocker arm. if not just itghten it down properly and it should stop.
Im no mechanic so dont take my word for it.

Thanks. You were getting me excited there until I read the last part of your post........"I'm no mechanic".......... just kidding. I appreciate the advice. I figured I would start with the carb adjustments since those are the easiest. Next question...... which way do you turn the screws for lean and which way for rich?? (clockwise/counterclockwise??)

Best case scenario (for you), and best guess coming from someone like me, is that is, in fact, valve rattle.

Try retarding the spark advance a few degrees (at the distributor). Then try it advanced, to see if it gets worse.

That's worth a start. Good luck.

Thanks rollin....
I had tried to mess with the timiing the other day, but I started by advancing it, and ran out of time. It did not go away or get worse by doing this. I will also try retarding it tomorrow.

Its been so long since ive worked on a carburator... in some carburators you have to completely replace the jet, in others it is usually clockwise lean (in, making the gap slightly smaller) and counter rich (out, making the gap larger alowing for more fule).
Try what ^^ said first though. but like i said im no mechanic. just a guy who has messed around with enough lawnmower carburators to melt down and build a car out of and with some experence (for my age) with cars, mostly fule injected however.

All the advice provided is valid, but its more likely the timing. Get a timing light, unplug the vacuum advance at the distributor and measure a baseline static timing at idle. The factory timing should be 10 degrees BTDC.
However, the mods you have, especially the camshaft can change the ideal static timing requirements. So, I would suggest set it to 10 deg and see how it runs. If there is no ping, advance it 2 degrees at a time until it starts pinging, then back it off 2 deg.
It is also possible the distributor is set up with too much ignition advance at low engine speeds, that is, the full advance at 3000+ RPM may be fine, but at lower RPM, the advance is more than the engine can handle. In this case, most mechanical distributors can be tuned using a pair of tiny springs inside. Install stiffer springs and the advance is delayed until a slightly higher RPM. This allows you to keep the optimal high speed advance yet reduce the pinging at lower engine speeds.

Magicrat,

Thanks for the input. I had somemore time today, so I retarded the timing. I do not have a light, so kinda went by feel. Took the vacuum line off and plugged it and then retarded it to a point where it was stuttering, and then advanced a degree or 2. I started there and kept advancing it a degree or 2 at a time back to original point, and got no difference in the knock sound.
I have one other question also..... could it be possible that my oil pump is not worthy of this high performance engine, and at a sudden increase in RPMs cannot produce the lubrcant needed to quiet the rockers?? Cause like I said, the only time I get the noise is when I floor it with a dramatic increase in RPMs.

I guess I should add this.....

We have learned that it does not get any better or worse by advancing or retarding the timing.

try holding it at redline for 1-2 minuntes. If it seizes, then you know it's the oil pump.

Hey 350, if you're trying to impress the ladies with your sociopathic behaviors- here really isn't the place. Thanks.

I was joking

Well, ragtop, I'm sorry that there haven't been any expert break-throughs uncovered here for ya. it sounds like you're still troubleshooting, yes?

It also sounds like it could be a rocker arm with too much clearance against the valve stem. This could be due to a partially malfunctioning hydraulic lifter, or an improperly torqued rocker arm nut. Also, your car may have press-fit rocker arm studs, in which case, one could possibly be starting to ease its way loose. None of these are horrible, really- except maybe the lifter, and it's by farthest the least likely to be a problem.
What is most likely is that someone did a good job of rebuilding your motor, but did what basically everyone does- install a performance cam & lifters with an otherwise entirely stock valvetrain. This means only that it's possibly become your job to finish "de-bugging" the hi performance motor that you bought with your car.
It may be time for a set of screw in studs and roller bearing rocker arms-
OK, that's a bit much, but if rocker arm clearance is indeed the issue (You can find out by removing the valve cover and checking each rocker arm against the valve with a feeler guage- you'll need to crank the motor incrementally, checking each valve/rocker arm in its most "relaxed" position- this should be where you'll find the "slop". You'll need some reference for this concerning tolerances. Then agin, maybe it will be fairly obvious when you pull the vave cover and test each one by feel. You can also run the motor with the valve cover removed- it's slightly messy for short periods of time- and just listen for the slapping ) and all of the studs are seated firmly against the head, you may want to start with Nylon-locking rocker arm nuts.

All in all, it seems strange that you don't hear the ticking at idle- Sometimes RPMS will eliminate the ticking (as you described)- as the valvetrain moves so fast that the rocker arm doesn't have a chance to slap. But that doesn't explain why you can't hear it at idle.

I hope that it's not a wrist pin, or something in the bottom end.
Again, good luck.

How well does it run when its rattling? Is it stumbling, running rough, etc? If its just got a bit of a rattle but no power loss/stumbling, that is probably the valvetrain. The way the 351c's oil system is set up, the driver's side lifter oil galley is the last in line to get oil, so they tend to make a bit of noise. Mine does. Doesn't really hurt the motor, just a bit noisey. There are ways to "fix" it, the two popular ones are to run oil restrictors or an external oil line.
Cleveland rocker studs are not press fit. Actually there are no rocker studs. They are sled type rockers that bolt in. I'd check those first - if you have stock rockers, they tend to bend out of shape after a while, especially with a bigger than stock cam.
If you need any cleveland specific advice, I can direct you towards a great cleveland forum.