Strange rattle from engine - Perplexed.
 

Kinda long...

For those who have been following my AFR 185 head and Victor Jr intake install. Here's a brief refresher:

When the heads were first installed, we bent a pushrod on #6 intake. After much testing (thanks everyone, especially RT), it was determined by my friend and me to be a faulty pushrod. We installed upgraded pushrods, and to be safe, only went 1/4 turn from zero lash.

The next issue we ran into was a bad running engine. Very bad. After much testing, we found two sets of timing marks, and retimed with great success. It ran like a scalded dog. Only minor tuning issues from here. It did, however, make a funky rattling noise at about 2000-2100 RPM. It then went away until about 2700 RPM. It then rattled from 2700 RPM till about 3000. After that, I *think* it went away, but it was hard to tell with the side pipes blasting away.

I decided I'd go through the valve train and put another 1/8th turn. No help. I went another 1/4 (for a total of 5/8th turn). The rpm dependant rattle sound was still there.

At this point, I felt it *could* be an exhaust leak. I pulled the cheap Mr Gasket header gaskets that we used in lieu of Copper RTV and good felpro gaskets. No difference. Everything still the same.

I even drained the tank and put in 100 octane fuel to see if it was pinging I was hearing. Nothing changed.

I called a local performance shop and they feel it's either a jetting or a timing curve issue. I'm going there on Thursday morning and they're going to look everything over. After finding the problem, we're going to put it on the dyno and get the jetting and air fuel mixtures right. They are about 30 miles away, so I asked them what I should do about driving the car to them. They suggested I back the timing down by 2 degrees (it was then at 14 initial and 32 total). I did that last night. No difference.

I've tried to tighten everything I could get a wrench on. I'm at a loss. Anyone care to take a guess as to what's causing this mystery rattle? I'm assuming we'll find out on Thursday, but many of you are pros at this. What say you?? :)

Jake "Sincerely Puzzled" Langston

Nothing sounds obvious from your description but I'm skeptical about a "faulty pushrod". Do you think you could have damaged a lifter somehow?

That honestly did come to mind. I pulled the lifter out and inspected it closely after the bent pushrod incident, and all looked well from the outside. The roller was nice, round, and rolled smoothly. It also pumped up when I primed the oil pump. It's ability to "plunge" wasn't checked, however. Perhaps it lost it ability to retain oil?

Did you check inside the door for a Coke bottle on a string left there by an irate assembly line worker on a Monday morning? ;)

Maybe the assembly workers thought it was a Chevy engine and installed a hamster and hamster wheel. What you're hearing is the hamster coming up on cam.

I had a noise that was driving me nuts! Finally figured out that one of the rockers was just brushing the inside of valve cover where the center bolt indent is on the inside of valve cover. A little grinding....problem solved. It was a bear figuring out what the noise was.
JB ;)

I had the same thing happen with rockers hitting the inside of the valve cover, it might be the reason a pushrod bent too.

Scott S

Thanks for the ideas, fellas. I have the tall Cobra valve covers from Performance Unlimited, so that's not it, unfortunately. I did look to be sure after your suggestions, but I found no scrub marks. I was hoping I would, though. :)

I went to a local performance shop today and he felt the best explaination would probably be defective lifter(s). Especially in light of my recent bent pushrod. He checked the preloads and felt they were fine.

Wierd thing happened though... Check out my carb jetting thread.

1. Is it possible you have an exhaust manifold gasket leaking? They will sound like a tappet.

Second item:

2. Start the car and put a long screwdriver to your ear, hold it against the valve cover above a valve, then move to the next valve and listen again. Do this until you have covered all the valves. When you hear some unususal (different from the others) noises, begin your investigation at that location.

Hopefully your not rattling the pistons from running it so lean.

I chased down a "ticking" noise on my engine for some time and never found it, then one day when a buddy stopped by I cranked up the motor and he listened to it and after checking a number of things he found the source........... It was a pinhole in one of the header pipe welds right where it meets the flange.......it was on the back side and very hard to see, but when you start the motor it definetly "ticks", sounds just like a bad lifter, after a good warm up, the metal expands enough to practically seal the pinhole and sound all but goes away.........just something else to check...........

David