Q: Vortec 5700 rocker loose? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-28-2009, 11:48 AM
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Q: Vortec 5700 rocker loose?

I've got a '99 Yukon with 100k miles. It's got the original Vortec 5700.

One morning the other week it started making this noise, like valve problem. Unfortunately I went abroad for a holiday and got back only yesterday.

So, this morning I took the right valve cover off to have a look and sure enough, cyl.2 intake rocker was loose. That was clearly the source of the rattle it made. But now the question is why is it loose?

The rattle started just one morning, with only warning on prior day, when my wife told that the car didn't run smoothly for a while. But when driving home, she had no issues.

So, only thing that comes to my mind is a "collapsed" (hydraulic) lifter.

Anybody had a similar issue? Any other ideas?

Also what would be the best way to set the lash cold when putting this together? - Turn the nut "finger tight" and then 3/4 turn more. That's what I've heard. (Engine is stock.)

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Old 08-28-2009, 12:21 PM
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Take a good look at the stud that the loose rocker is on. You want to be sure that it hasn't pulled out of the head (it is a tight press-fit). Usually, this can be seen as the stud being higher than the others, a simple straight edge placed atop the row of studs will expose it, if it has pulled.

Next, look to see if there's an equal amount of threads showing above the tops of all the nuts. This might not be exact, but should be very close. If the loose rocker's nut has backed off for some reason, it should be evident.

Next you want to see if the valve spring has broken. It might be broken in such a way that the ends are back in alignment w/each other, so you will have to manipulate the spring to see if it's broken. Push down hard on the end of the rocker, as if to push the valve open. You might need to do some levering w/a screwdriver, etc., if you don't have a valve spring compressor handy- just don't get carried away and don't nick or score the spring, or damage the valve stem seal while doing this.

There is also the chance that the rocker arm has failed. A close inspection of it will show if the pushrod seat had punched through, or if the valve tip or rocker arm tip has excessive wear. Usually the ball pivot doesn't cause trouble like this on a stock engine, but you can check it anyway, while you are in there.

Before you relash that valve, remove and check the pushrod for straightness by rolling it across a piece of flat glass. If it's bent you will hear the tell-tail ticking of it as it rolls.

If the lifter won't hold pressure, you may need to remove it, take it apart and clean it, reassemble and see if that does it. A lot of work. You can try some of the chemical remedies, like Seafoam, Marvel Mystery Oil, etc. to see if that'll unstick it.

If all looks to be OK, you might have a cam lobe going bad. About all you can do, is adjust the valve and run it to see if it gets loose again.

If you do a search for "adjust valves" you will get any number of hits on how to do it. Basically, you want to remove all lash, with the lifter on the base circle of the cam. Then turn the adjusting nut one turn more.

Last edited by cobalt327; 08-28-2009 at 12:26 PM.
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Old 08-28-2009, 03:39 PM
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Unfortunately it seems to be a "collapsed" / stuck lifter...

On closer inspection I can clearly see the pushrod end of the rocker is much lower than other rockers (at rest). This doesn't seem to leave many possibile causes in my mind...

I did take the rocker off already, so no hope with getting the lifter unstuck with oil additives. Even if they would work, I couldn't set the rocker to correct lash without lifter fully open anyway... =(

Seems like I need to get a new set of lifters...
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Old 08-28-2009, 06:34 PM
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Quote:
Originally Posted by tug3
Seems like I need to get a new set of lifters...
At least you can replace the lifter/lifters w/o the worry of wiping out the cam, like w/a flat tappet cam and lifters. Providing the cam's OK, which it prolly is.
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