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Discussion Starter #1
Hi all. I have a tapping sound that sounds like it's coming from a pushrod. So, the other day I went to order new pushrods, but I have a choice of three: 9.56", 9.59", or 9.62". So I ordered one of each. I round-robined them through my driver side valve train, Dykem'ing the valve ends to see what kind of wear mark each length rod had the rocker arm making on the valve end. I figured the rod with the most centered wear mark would be the correct length to use (I mistrust the rods that are in place now, not to mention they are all somewhat bent).

I also tried to put just the long rod (9.162") in various places to take the slack that may be causing the tapping. No placement made the tapping stop.

I also tried using my mechanic's stethoscope in many places to find the source of the tapping. I couldn't isolate anything.

My findings were that:
a) I cannot isolate the source of the tapping
b) I found the long rods (9.62") to cause the least centered rocker-to-valve contact point, where the other two lengths were both more centered, yet indifferentiable.

So, I don't know whats tapping, and I don't think new rods will fix it. Does anyone have any ideas?

BTW: 390ci, hydraulic lifters, non adjustable rockers. Rocker faces slightly pitted (I'm poor), I don't know much about the internals.
 

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Could be a lifter just won't pump up all the way. Does a vacuum guage show any fluxuation?
 

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You can narrow down your search by possibly putting physical pressure on the rocker arms one at a time. If the tapping tones down or goes away you have found your problem area.
 
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Discussion Starter #4
I dunno . . how would I go about employing a vacuum gauge to check for fluctuation regarding malfunctioning lifters? I have been tuning my carb via vacuum gauge, but thats going poorly as well, and I didn't notice any relation to lifter function. Is there a process I can follow here to locate the problem? Thanks, Erik.
 

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OK...

Tell us what you've established...

Where (physical location) on the engine that you believe the noise is coming from...

The nature and speed of the noise...(you said tapping but what type, how fast, eg cam speed, crank speed etc...)

The effect of the noise, if any, on performance

The cam and other valvetrain modifications made (if any)

...hmmm...oops! missed the part about bent pushrods...roll one on a flat surface and observe...if it is even slight wobbly, bye-bye...go with the checking pushrod lengths which appeared most centered...by that I mean the movement pattern line is as centered on the valve tip as possible...

Install replacement pushrods and re-check...

Get back to us... and explain to me how your pushrods got bent...*G*
 
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Discussion Starter #6
OK. The tapping appears to emanate from one of the rear 4 driver side valves. The tapping is somewhat noticeable at idle, it speeds and pronounces as revs are added. It scares me to drive hard with tapping stuff going on. I believe its a stock cam, no mods I've made. I havent messed with the valve train myself, but did port the heads a bit a while ago. I had new valve seals installed as well as hardened seats.

Yes I rolled all the rods on this side of the engine on a mirror. They were all bent to some slight degree, a few kinda wobbly.

The two shorter (of the new rods I bought to size with) rods were more centered than the long one, but not completely centered and I couldnt tell any difference between then in the average.

I don't know how they got bent, maybe as I've began autocrossing /forums/images/icons/smile.gif Maybe because the guy that put this motor together likely grabbed all my rods from a pile of crap in the corner of his old parts ridden garage.

Thing is, I figured the long rod would stop the tapping and it didnt. Then I thought maybe its not related to the rods. Should I get all new rods then work on the tapping? Thanks alot guys, E.
 

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We've established that it's possible the installed valve stem height has been changed (by installing hard seats) on the exhausts..

We've established that all of the pushrods are bent, some more so than others..

We're not sure about the pedigree of the camshaft...

The noise gets worse as rpm rises...

Question....did you find any rockers which were loose when the lobe was on its base circle? Corollary...Have you drained the oil recently? If so, any glittery specs in it?

I'm starting to have my suspicions but am not sure enough to share them...
 
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Hmm .. So far, I have not used physical force applied to the rockers to find the tapping. I also did not check to see if the rockers were loose when the lobe was down on the valve stem (I believe is what you're asking).

I drained the oil 1100 miles ago. I try to change it every 2000 miles, as when I do, it's black and foul. But the last time I changed it, I didnt notice any chips or specs in it. But I was also paying attention to other things as I did it.

Once again, as I mentioned before, there is slight pitting on the rocker arms where they contact the valve stem.

The noise gets faster and louder as RPM's increase, to a point, right off the bat. Then the noise just gets faster, not much louder.

I'll have to check these things soon and repost. Thanks for the help and ideas! Erik.
 

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Pat's got you on the right track already and I'm thinking the same suspision......

One other thing you might check before you tear into the engine is the rocker arms themselves. FE's are notorious for wearing out the rockers and the rocker shafts. With the lifter down push down hard on the pushrod end of the rocker until you have some clearence between the rocker tip and the valve stem. Then wiggle the rocker up and down at the valve end and note any play between the rocker and the shaft. If the rocker/shaft is worn you will see twice that much extra clearence because you get it at both the valve and pushrod end. If the longer pushrod didn't tighten it up then these need replaced.

The very first thing is to replace those pushrods. I'd go with the stock length - 9.59. When the rockers are OK and the cam/lifters are within spec these will fall into the middle of the lifter travel.

That is all hopeing that the cam hasn't gone flat.
 

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I just wanted to jump in with a quick question...Do Cam's go flat often? In fact how fast do they normally wear?

My 66 coupe is just a weakend driver now but it sounds like a scary subject.

Thanks, Greg.
 

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I also did not check to see if the rockers were loose when the lobe was down on the valve stem (I believe is what you're asking).

What I want to find out Erik is if you might have a cam lobe(s) going flat...

This will be evidenced by lifter preload lessening and then transitioning to lash, which will manifest as tapping...

Long shot but we're fishin' right? *G*
 

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No cam's do not go flat that often except when the engine is not taken care of properly, ie oil changes every 100,000 miles /forums/images/icons/smile.gif. Or after a rebuild worn lifters are used, wrong length push rods, etc. Basically cam wear is usually (almost always) human induced, but it does happen.
 
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