Topic: Engine Knock

[95 Lowbuck]

I have a 95 Rio Grande with a 2.5L and it has about
120K on the odometer.
I am not too good identifing engine knocks but this is what I have.
In the mourning when I start it there is no knock.
After about 15-20 seconds I start to hear a slight knock and
it lasts for about a minute or two then then goes away when warm.
This is not a lifter noise, I know what they sound like.
Other than that it runs fine with good oil pressure.
Any Ideas?

[low output 2.5]

sounds like mine............ its been that way for about 2 years

[Jeffy]

You will want to locate the noise.  An automotive stethoscope would be best byt you can use a long screwdriver or rod and hold it up to the block and try to listen for it.

Are you sure it's a knock and not a tap?  A knock is a heavy low fewquency sound you can feel.  A tap is much lighter but higher pitch.  You can't usually feel it.

If it's low in the block it could be crank or rod bearings,  Top end it would be valves, rockers, lifters or pushrods.  It could also be a small exhaust leak which only appears when things heat up and expand a bit.

[jwrape]

My Tahoe does that at first crank. Been doing it forever.. Takes a few minutes for the oil to get from the bottom of the oil pan to the top of the motor and back again.

A lot of cars and trucks do that at first start up, that's why all the oil commercials say that start up is one of the hardest times on your motor because all the oil has drained back down into the pan and there is only a small film of oil protecting your engines insides.

This is the exact reason why I don't use Quaker state is because it doesn't stick to the parts as well as other oils. It;s more like water. But that's another thread.

[Brad McKay HVACMAN]

I had that same problem when I bought my rig. One tech using a computer diagnostic machine said it was the lower crank bearing?
Another using a long screwdriver and his ear said it was a hole in the rear piston, that guy was right. Took the whole damn thing out and bored it, sleaved it, line bored it and redecked it. Had to sleave that one piston because of wall damage from the hole being so close to the wall. The thing roars now (like a kitten). Hey it's a 4 banger with a 2 1/2 " exhust.
Good luck  :roll:

[95 Lowbuck]

I don't think I have a hole in my piston.
I have good compression in all cylinders,
very little blowbye out of the oil fill, and the
plugs run fairly clean.
But thanks for the info.
I did take previous advise and took a rubber hose
to locate the source of the Knock.
It sounds like it is coming from the top end,
but I never heard this type of noise from there.
Maybe a bad rocker, I don't know.