Hey all I have a 1991 blazer auto 4x4 4.3 that is driving me nuts. When you
start the engine cold and drive off it has a mid range rattle. stop the
truck and the rattle goes away. It only rattles while you drive and its
consistant with the rpms. Im thinking it could be the rockers hammering but
if it was the rockers then wouldnt they hammer at idle while the trucks in
What is confusing me is the fact that it only rattles when the engine is
cold and in gear.
So far I have gave it a tune up, changed the oil (the sound changed its tone
after the oil change, which leads me to think that it may be the rocker
arms) and replaced the TPS (thinking maybe timing/fuel issue)
ANY AND ALL Ideas would be greatly appreciated
its not the gas ( I have tried several different brands and ratings)
Tonite I took off the valve cover and loosened up a rocker and started te
engine. the sound is Definitly a rocker. now my question is Why would the
rockers make noise only when they are cold and at mid range. this weekend I
plan on getting new rockers installed and hopefully that will cure the
collapsed lifter -duh didnt even think of that, that would make the most
sense. Valve spring pressure would keep the rocker from ratlling at idle.
bump up the rpm, valve pressure cant hold it still anymore. the engine warms
up the check valve in the lifter lets some oil thru and the sound goes away.
now how the hell do I figure out wich one is the culprit?????????????????
You get to get dirty, pull the valve covers off one side at a time, fire the
beast up and use your thumb on the rocker arm over the push rod moving from
one to the next. You'll now when you find the right one, assuming it is a
collapsed lifter. also that particular one might not have as much oil
squirting as the rest. Usually a collapsed lifter is quieter when the oil
is cold and thick, then when its hot and thinner. You might be able to
narrow which side down before pulling the valve covers with a stethoscope,
or a long extension one end against the valve cover, one against your ear.
A collapsed lifter makes noise because there is gap between the rocker and
valve because the lifter and push rod aren't keeping pressure on it, the
same basic noise you get with solid lifters if they aren't adjusted
correctly, ie too loose, or the noise you get when you back the valve
adjustment off on hydraulics before cranking them back down to zero lash and
a 1/2 turn more.
One thing you might try first, is a quart of Marvel Mystery Oil in the
crankcase for a little while and then another oil change and filter. It
could just be gummed up, everyone gets lucky once in a while. Drive easy
while the Marvel is in there, it will thin the oil out.
Another question comes to mind, does this rig have an oil pressure gauge,
what's the oil pressure hot and cold.
Too much Work
Simpler to Take a Broom stick...
Cup your hand around the handle at one end
put your Ear to your hand.
Now put the other end on the Valve cover
Move it around and when The ticking sound gets the loudest , you are
Right over top of the Noisy tappet
No need to even get dirty , Nor remove the valve cover
Works as if u were using a Stethoscope
Be care not to touch moving parts..
if it is not a tappet, Then move the stick around the engine till u here
the noise Via the BROOM STICK
also that particular one might not have as much oil
forget the broom handle, get a mechanic's stethoscope, about 20 bucks
from Snap-On or Mac (or borrow one from a neighbor) much more precise
Besides you can use it later to decide which belt pulley to replace
when one goes South
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.