knocking

artic94sc

Registered User
i have a freind that just put in a motor in his sc and everything has been running good until last night. he said he was on a back road when he heard a knock of some sort. now he says in the morning he let the car warm up for like 20-30 min then took off like a bat out of hell and rev the ~~~~ out of it and heard nothing... reving the car at 2000 for like a min or two this morning and no knocking? he says its only when he drives the car for a while? and the knock comes from reving at 2000 or more...

also when the knocking starts it is not a constant knocking, its only when he is reving it at 2000 or more.
 
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motor

well looks like we are going to do a rebuild then. we are just going to do therod bearings then. anything i need to know before hand? we are going to pull the motor then drop the pan and throw in the bearings. we have bearings and some good lucas bearing oil is that good?

also there are two little knoches on the bearings do they need to be together or apart? in the picture they are in the lower right hand coners.
 

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If it's knocking then the rods need to be re-sized. The housings will be egg shaped and new bearings probably won't last long if you don't do this step.

When rod bearings start to make noise (actually the sound you hear is the pistons hitting the heads) they do it mostly in the 2000-3000rpm range and under light load only. Rods will never make noise under heavy load unless they are about to come through the side of the block.
 
rod

also should he just get a new connecting rod from rockauto? that way he dosent have to mess with bearing or rod sizing?
 
i would make absolultly sure that its rod knock before tearing that motor apart.

could it have been spark knock, or pinging. is he running premium fuel in this car.

about 90 percent of the time when I deal with rod knock it can be duplicated and then diagnosed.

yes i agree with the others that it may not happen at a load. but try this. True rod knock can be the piston hitting the head, or the side to side movement of the big side of the rod when the crank changed directions. if you remove the super charger belt does the noise come on instantly thats what mine did. the supercharger provides a sort of cushion in the cylinders that help keep the piston and rod in contact with the top of the rod. when you remove the supercharger it should get louder and be easier to duplicate.

have you checked oil pressure, fuel pressure and the basics.

when you do get the noise to be reproduced in a setting where you can get under hood and listen then you can start by carefully removing spark plug wires one by one (sounds strange but it works) the cylinder that is knocking will get very quiet. it works i have demondstrated this on a number of engines in the shop.

when I pulled down my engine and inspected it had number 2 cyl bearing was gone. it was almost welded into the rod and rotated 90 deg. i measured the crank and it had almost no damage other than light scratches and it measured good and was still round but the rod was fubared. I found a good short block to work with so I never fixed that motor so if you need a rod I have 5 great ones.

but before you condemn the motor you should have further diagnosis performed.
 
motor

yes, it has good oil pressure, fuel and prem gas only... are your rods from an 94 -95 motor?

also thanks for the awesome post^^^:D
 
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