knock knock... what's that?

[Tom D]

i'm a little late to the party, but a rod knock (common name for a spun rod bearing) is a sound that you will never forget. it sounds like no other noises from the engine.

there was mention of not over revving or racing the car. fact; you are more likely to spin a rod bearing from a high G corner then from high revolutions.

over revving will take out the valve train. this happens because the valves can't close fast enough and the piston slams into them.

spun bearings (rod) are usually the result of oil cavitation, but not limited to only this. lack of oil pressure will trash the bearings as well.

i'm surprised that the mechanic thought it was a rod bearing. like i said, once you hear it you will forever know what it sounds like.

[cpatstone]

Originally Posted by Tom D

... spun bearings (rod) are usually the result of oil cavitation, but not limited to only this. lack of oil pressure will trash the bearings as well...

PO autocrossed the car plenty. Enough high-g, long, sweeping turns could possibly have contributed?

Here's something that I should have known. Obvious in hindsight. I could have taken a dowel, maybe 1/4" diameter, and put it through the spark plug holes on each cylinder. I already had the belts off and could spin the motor by the crank pulley. With the block all naked, I can spin the crank and at the top or bottom of the stroke, feel the slop between the rod and the piston. Could have done that with the motor all together too. oh well.

Guess I know that for next time?

[Tom D]

Originally Posted by cpatstone

……..PO autocrossed the car plenty. Enough high-g, long, sweeping turns could possibly have contributed?

absolutly, turn 14 at the ex-riverside raceway in southern calif. was known for eating rod bearings.

[cpatstone]

edit/update, one more:

The issue was actually on the bottom end of the #2 cylinder connecting rod. Bearings spun in the rod. Some visible galling/wear on the rod and outside bearing surfaces, but inside / crank look fine.

So, in retrospect, I could have actually pulled the oil pan, and not knowing what was going on, tried to rattle each rod at the crank end. I would have found the problem and it would have been a $30 repair using ebay bearings (assuming rod isn't significantly damaged, and I haven't measured).

But, the Dinan-ized M50 is pretty cool and by now this M44's head has (hopefully) given new life to a Z3.

Anyone need a good block/crank/etc?

[Tom D]

the rod's big end could have been refurbished as well.

[gimp]

Originally Posted by cpatstone

edit/update, one more:

The issue was actually on the bottom end of the #2 cylinder connecting rod. Bearings spun in the rod. Some visible galling/wear on the rod and outside bearing surfaces, but inside / crank look fine.

So, in retrospect, I could have actually pulled the oil pan, and not knowing what was going on, tried to rattle each rod at the crank end. I would have found the problem and it would have been a $30 repair using ebay bearings (assuming rod isn't significantly damaged, and I haven't measured).

But, the Dinan-ized M50 is pretty cool and by now this M44's head has (hopefully) given new life to a Z3.

Anyone need a good block/crank/etc?

In other words, what I should have done before I sold the car.

[cpatstone]

Originally Posted by gimp

In other words, what I should have done before I sold the car.

Hindsight is always 20/20... Besides, if the bottom of that rod is worn / oversized now, sure, it could be ground even and an oversize bearing put in, but then you'd need to pull the piston to get the rod fully out, IE pull the head. You were itchin' for a faster/newer ride anyway.