okay my 89 pontiac firebird is haveing engin troubel for the second time with a 2.8 liter i swaped motors and this one is now after only 2000miles is experienceing the same issuses. it has a knocking sound thats clearly audible above the sound of the engin. i tore apart the old motor wich had the same exact problem. i figured it would be a lifter or a push rod because it is a inconsitant knocking not like a regular rod knocking noise, and when i tore the old one apart i found that the lifters and the push rods are fine and it looks as if it should work perfect. so im at a loss and dont know what else it would be. someone please shed some light on this situation for me.
Thanks
Jamie

 

the sound is on the left side of the engin

 

if you push hard on the valve cover it gets quieter untill you rev it up then its hits twice as hard, i have no idea what it is

 

When you tore the old engine out, did you pull the pan? Without hearing it in person, it sounds like a rod knock to me. Either that, or your upper end has a serious oiling issue. Either way, something isn't getting oil.

Now if I could just remember if it's the #4 or #6 cylinder that's closest to the oil pump, I'd be all set. I think it's #4, but I can't swear to it. That's the one that blew out of my 2.8 when it blew up, and I assume that was the first rod bearing to be wiped when the engine overheated one too many times...

 

i thought the same thing until i realized i still had plenty of oil pressure, and i dont believe its a rod knock because of the inconceistancey in the knock sometimes its fast sometimes its slow sometimes its loud other times its quiet

 

what parts did you re-use from the old motor?

 

If you got internal balanced and external balanced engine parts mixed up or swaped around, it will knock around no matter what you do.

flywheel, crank n front balances must be all match for the right type of balance.

in 86-87 they change to internal.

 

Hi, its not something silly like rocker - valvecover clearence is it ??
is the motor running ok ?

 

i reused the whole front end, and no i dont believe it is rocker valve clearence the motor runs awesome and has been running awesome this and a new altinator are the only motor issues i have had. but when the knocking started i drove the rest of the way home and it ran as normal as ever it just knocks

 

you sure its not a loose acc. bracket on the front of the motor?

 

The question remains: What year is the replacement engine from, or was it a rebuilt engine from another year? Does it vibrate like mad when it's running?

If the engine was unbalanced due to not having the right flexplate or flywheel, you would KNOW. That feeling tells you something isn't right with the engine. When I had to redo the crank bearings in a Chrysler 2.5, I screwed up and mistimed the balance carrier. I thought the car was going to shake itself apart! And I was only about 5 chain links off on the balance carrier's timing chain...

 

yea she shakes like it has a torn motor mount but thats what i figured it was a torn mount

 

If you reused your flexplate or flywheel from the old engine and it had the balance weight at one time (and possibly threw it or somehow became unbalanced), then the same thing was guaranteed to happen. Meaning, if you reused the wheel from the old engine and the engine you currently run NEEDS a balance weight and the wheel doesn't have it, you need to get one that does. Or, if you have an internally balanced engine and the wheel is externally balanced, you need to either replace the wheel or grind off the weight.

The only way to tell for sure whether the wheel is balanced or neutral is to look at the crank side towards the crank surface. The weight will be there or there will be a bare spot if it got up and left, or the weight will never have been there at all and the wheel will look the same all the way around.

Still need to know the year of the engine to know how it's balanced before you do any more damage.

 

Do know if this is common knowledge but a rod doesn't have to sound the same all the time. I have seen bearings spin around and stop knocking