Belt tensioner knock in (98 astro)

My (98) astro has a knock sound when motor is first started
coming from the belt tensioner, I have replaced the tensioner
with a new one, but It didn't help. Has anyone had this problem?
the knock goes away as engine warms. Thanks for reading.

Dont think ive herd a tensioner make that kind of noise before, but before going any further pull off the belt & see if the noise is still there. You wont like this but I think it will be! Internal engine problem if its loud & if not very loud could be piston
slap from a tight wrist pin, main brgs on the loose side, or as simple as a cheap oil filter that dosnt have an antidrain back valve in it, buy an AC/DELCO its a PF52 or PF47.
If you pulled the belt & its quiet, depending on options you might also have an idler pulley with a bearing failure. Also check alt, w/p, a/c comp, there
is a failed brg on one of these.

I have a 96 Astro, which is the first year of the newer 4.3Vortec and is exactly the same as the 98's. My belt tensioer is bad, the spring in it is loose, so it knocks at all times. The way I can tell it is my tensioner is because while its knocking, you can look down and see the tensioner, shaking like crazy. Look down towards the tensior and see if it is shaking while it knocks. If it is shaking like crazy to where it just looks like its going off, than the tensioner is bad and need replacing, or the tensioner is postioned on the engine block(has a small peg that goes in to a hole on the block to keep it in place) or the one bolt holding it on is loose. Hope this helps you out.

My (98) astro has a knock sound when motor is first started
coming from the belt tensioner, I have replaced the tensioner
with a new one, but It didn't help. Has anyone had this problem?
the knock goes away as engine warms. Thanks for reading.


I have an '89 Astro, since I changed the belt, started to have sounds, my mechanic toldme that now it was the belt tensioner and the Generator's roller bearing, I decided to check by miself,
With my Mechanics Sthetoscope, I checked the sound periods and found: one sound per 2 motor turns, I got scare thinking it was the cam or minimun the timing chain, but the sound could be heard only in the belt tensioner, but it turns 3 times per motor revolution and 6 times per belt or timing chain revolution so, it could not be,
so it could only be the belt, but I Could not put the Mechanics Sthetoscope on the belt with motor running, so,
I Analyzed the belt and found that, it was a ruber brand sticker attached to the new belt that in hot used to expand itself and when pasing by the belt tensioner was doing noises. The noises lasted 4 months until they desapeared as sticker got flat.

Wow!! That is some good detective work there pesime!

Good job!