Rod Knock

[mrnickleye]

I too have seen a loose crank pulley sound like a rod knock, on a couple of cars.
Rod knock develops due to the bearing(s) on the rod that attach it to the crankshaft, getting too much clearance (gap, play).

It can happen when the oil LEVEL gets too low, and you go around a corner and the pump doesn't pick up oil for a moment. Lack of oil at the bearing is the cause.

Oil quality plays a role. If the oil level NEVER got low, but has not been changed for too long, it won't lubricate very well.

Repeated high RPMs stress the bearings.

I change my oil every 2k, just to be safe. Oil is still cheap enough, and cheaper than engine work.

[kewlcoconut]

Yea, I always keep an eye on my oil and get it changed a lot. I'm scheduled for a tune up as well. I never let the oil get low, I'm always paranoid about it. I always have bottles of oil on hand in case I need to top up.

I will check my crank pulley and see if it is loose. This morning when I started up my car, it was still there, I drove it to work and came out 5hrs later, and I couldn't really hear it. Odd...

As for the previous owner, it was my uncle, and he babied this thing. So I think that rules out lack of care on his part haha.

[mrnickleye]

Go ahead and put a 19mm socket on that crank bolt to see if its loose.

[Bullz_EyE]

Originally Posted by mrnickleye

I change my oil every 2k, just to be safe. Oil is still cheap enough, and cheaper than engine work.

WoWzerz! Drive your car much? Just a note (not to you, just being general), the recommended interval for oil changes is every 3000 miles or 3 months, which ever comes 1st. It's been studied before that changing every 3000 may be a bit excessive, although I religiously change it at that interval.

[rnoswal]

If you start it up in the mornings and it rattles pretty good then quietens down a lot when the oil light goes out then it is in irrepairable rod bearing. There can be loose torque converter bolts and bad harmonic balancers and very loose valve settings but anyone that has heard the rod knock before know what it is almost immediately and sighs because it means pulling the engine.


All it takes is one time for the oil level to get to low to be picked up and the damage has been done, from slight to major. Putting thick oil in will help, like STP or others like these, but..........

Let us know.

Russ

[mrnickleye]

If it is a very light knock, you can prolong a rebuild by using 20-50w oil with one bottle of STP. It will be a little thicker and fill in the clearances more.

[*c-town*]

you can get a rod knock and have the PERFECT amount of oil

i use to have a 69' plymouth sport statelite w/ a fully built 383 rv cams dual quads .30 over and a high volume oil pump then one day while racing on highway 80 i got the car to sideways and i sucked the pan dry of oil when i looked at the oil press gauge and saw it drop so did my heart

good luck and i hope its not a knock

[stumpjumper]

You may try retarding the timing a few degrees to see if that helps.

[*c-town*]

Originally Posted by stumpjumper

You may try retarding the timing a few degrees to see if that helps.

how would that help? i think that would hurt it causing, detonation early?

[TONY!]

Originally Posted by kewlcoconut

... Is it possible to get a rod knock with the oil levels being fine?? ...

Actually, a friend of mine (Shaeff) and I were talking about this. He said that he got it without the oil being low.

Another guy I chatted with got it also and his oil was also not low but from a bad build.
I have heard of many cases of rod knock where there was plenty of oil in the crankcase, but the results were still the same.

Originally Posted by Bullz_EyE

WoWzerz! Drive your car much? Just a note (not to you, just being general), the recommended interval for oil changes is every 3000 miles or 3 months, which ever comes 1st. It's been studied before that changing every 3000 may be a bit excessive, although I religiously change it at that interval.

You know I somehow got it in my head when I first got a car that when the oil gets dark to a certain point, that is a good time to change it. I guess I thought of the very dark characteristic as being carbon.
I guess I always assumed that the degree of how dark the oil is would determine how much carbon and blowby got into the oil.
So I just try to keep it from getting dark, more or less.
Usually on older cars, the oil change interval would be less (according to my logic) because of the sealing of the combustion chamber and allowing for more carbon to get to the oil.

Well either way, I like to keep it from getting too dark, and sometimes 3000 miles would be too long because the oil would be too black for me.



As far as knowing if it is rod knock:
I have not done extensive testing by any means on this, but only reciting what I have heard:
If you remove the spark plug wire to the cylinder that has the knock, it would quiet the knock down. So if you go through the wires and can find that removing one of them quiets things, you have a major operation on your hands.

Having rod knock means that you need to replace the rod because the indentation for the bearings’ tangs would be damaged. And I sell rods by the piece dirt cheap for folks in need due to knocking.
When people use the same damaged rod....that is a huge no no.