Who's there? I don't know, but I'm starting to get worried. The engine ('95 4.0) in my van has developed a knock that is only heard after startup after sitting for some time. It can only be heard at a certain speed (high idle) and goes away when the engine is warm. It's a heavier sounding noise sort of like a rivet gun, not a ticking like valve train noise, so I'm fearing the worst - main or con rod bearing - but I've never heard what a bad bearing sounds like. It's not getting any worse, but I think my days are numbered. I'm having a hard time trying to pinpoint the location. The engine is way too young to have bearing problems, it's only got 106K on the clock (I said the same thing when I had to replace the heads at 70K). Anybody got any other ideas?

 

i dunno, but id stick my ear in a garden hose, and find outwhere the noise is really coming from on the block or heads.

cut a hose bout 3 feet long and plug one ear, and listen through the hose as you point it around the engine to locate the noise.

my aerostar has never knocked like that, but my truck did, and it was a rod. the truck knocked louder at idle, and the noise died down at hiway speeds. when finally it went bang! and the engine was seriously unbalanced and hella louder, and oil was gushing out the side of the block. no fun.

so, get it figured out before it breaks!

 

i would say that you may have piston slap. i have seen over the years. this happens when the engine gets overheated and collappses a piston. when the engine warms up the piston exspands and the knock goes away. good news is it will not hurt anything and will last a long time like that if ya can live with the knock. i know i did.

 

Could also be a worn wrist pin - had a fairly new 3.0L engine do that once, just on one piston. Sounded like a heavy knock but was up high on the engine, not low like you would expect with a main bearing. One of those inexpensive sound amplifiers helped to pinpoint the correct piston and location of the noise. This was a battery powered 'wand' with a pair of earphones. Can't remember where I found it - Sears possibly.

 

Lasher, I have a RV with a V10, and I believe it has piston slap.. cold day start up it "knocks" for about full minute, and then justs gets more quiet as it warms up, until the noise is fully gone after a couple of minutes or so.. So, you say you had this and your motor lasted a good while?.. I am not currently planning to do anything about it and hoping you are right... It really doesn't burn much oil and other than that ugly sound at cold start up everything is fine..

 

i always learn alot reading these threads.!my 4.0 is approaching 200 thou. miles. it too has similiar knocks. at start up they seem to be from many sources. after 10 min it seems to be lifters...after 20 or 30 min it purrs except for a low knock...still has power. not burning oil.so i'll just keep driving.. i bought some rislone to add to the oil, not sure if it will help the engine, or just me ,by thinking i'm doing something good for my aging road warrior.so we can continue going on down the road!!! rick

 

if that is what your knock is it should last a long time like that. piston noise does not really hurt anything. a deisel engine is a good example of that. make sure you have good oil pressure when cold.