Chris,
I am still baffled on the knocking I get from my engine. I tried the hose deal, and no luck. I may be coming form the head, but I can't tell. It only occures on heavy exceleration, or if I floor the pedal fron a dead stop. It is faint if I put it in gear and apply the brake and stomp on the gas, not as loud as if it is running. I can drive all day and as long as I don't stomp on the gas heavy, I never hear the sound. I towed my Funny Car on a large enclosed trailer the other day and never once did I hear the sound.

The only other thing I did notice is that when I was trying to get the sound to produce in the driveway with the brake applied, was I got smoke coming from my oil dipstick opening, and if I were to remove my oil cap, it too would produce smoke while under throttle. Once the engine would idle, it would no longer smoke. I get no smoke from the exhaust, and the plugs look good.

the sound this produces sounds like a rod knocking, but why only under heavy load and not all the time? Could it be head related?


Thanks,

Justin

 

Well, you're not going to like what I have to say, so, this is your chance to hit the Back button.


The noise you described, and the times it occur, are textbook for having too much main bearing clearance at the crank. Did you use plastigage on the crank mains before bolting everything together? What was the clearance?

If you want to rule out the head, you need to use your head. I'll explain. Any noise associated with the head or valvetrain will occur half as often as a noise in the bottom end, because the cam rotates at half the speed of the crank. So, you need to use your experience and try to decide if the noise is repeating at the same rate as the rpms, or at half that many.

Take care,
~Chris

 

It's not bad news unless it can't be fixed... I believe I can fix this.

No, I was out of Plastigage and I incorrectly assumed it would be ok, after all it was "just a street engine"... Got me....

The rapid tapping I hear, sounds to fast to be top end. It also is too "strong" of a sound to be coming from such "little" parts.. It must be bottom end.

What kinda carnage am I looking at? Besides replacing the crank, are the rods gonna be ok? I have the spare crank from the first engine, I can use it, I also have the rods, if you think the rest of the engine would be OK, I can replace the crank and bearings or the rods, crank and bearings.. What do you think?

Thanks for the diagnosis. Also, why the smoke from the oil dipstick cap and oil cap?

Just what I wanted to do, pull the engine again...... YEEEEEE HAAAAA


Thanks,

Justin

 

Don't buy any parts until you've verified it. You should still pull the engine, but then pull the pan and check the mains. A new crank and bearings should be plenty. The rods should be fine, but measure their clearance as well when you take them off the crank, just for an idea of whether they were off too.

From my 1986 college engine rebuilding class required book:

"Crankshaft Noises
Excessive main bearing clearance noises are generally dull, heavy metallic knocks. The knock will increase in frequency as the speed and load on the engine is increased. Most main bearing knocks (due to excessive clearance) are not noticeable at an even idle speed. Main bearing knock is usually apparent when the engine is pulling hard, when an engine is started, during acceleration, or at speeds above 35 mph"

Sound familiar?

Take care,
~Chris

 

...."Crankshaft Noises
Excessive main bearing clearance noises are generally dull, heavy metallic knocks. The knock will increase in frequency as the speed and load on the engine is increased. Most main bearing knocks (due to excessive clearance) are not noticeable at an even idle speed. Main bearing knock is usually apparent when the engine is pulling hard, when an engine is started, during acceleration, or at speeds above 35 mph...

I don't get it at startup, regular acceleration or hear it above 35, only when I stop the gas. That is not to say it is not present at 35, I just don't hear it. I know I don't have the sound at startup, but that may be due to the Lucas oil treatment I have in the block.

Am I looking for scuffed bearing surfaces?

What about the smoke from the oil openings? Is this normal?

Justin

 

The bearing surfaces will more than likely look really shiny about a 1/2" from the top.

I don't know why your engine is s,oking under load. That's the kind of thing I would have to see and smell in person.

Take care,
~Chris

 

sorry to butt in....
could it just be your timing is off....could also explain your gas milage.

 

Thanks Chris,

I will have to schedule the engine pull. Need to get some folks over to help. As for the engine smoke, it smells like burnt oil, when I am at a stop sign, I can start to smell it, as if it is burning.
This only happens after the truck has been running for a long time. I have NO oil leaks... I can park it on a white blanket and it will be clean the next day.

I'll let you know.

Thanks!

Justin

 

The gas mileage is back to normal, I retarded the timing. I am now getting 70 miles per 1/4 tank in town....

Justin