My friend has a gs-r motor and its got a knocking sound coming from the bottom end. I tried to figure this out and can not figure it out. He turned on the car for about 25 min. He drove the car around the block and then parked it. He turned it on and then turned it off just to make sure the battery charged up on its own. Then turned it on to go out and it started knocking. Its a fully built motor. I've check the valves, bearings, piston slap, crank pulley, cams, did compression test and everything checks out good. Remember the car has been driven the last 3 months perfectly fine and its been parked for two weeks. What else could it be

 

you pulled it apart to check the bearings and check for piston slap? check the flywheel bolts. if they are loose it will cause a "knocking" sound....

 

i checked for piston slap thats clear. ( no piston slap ) I'll check the flywheel. Thanks.

 

could you enlighten me on how you checked for piston slap. with out pulling the motor apart to check for piston to cylinder clearance.

 

i'm wondering the same thing

 

i GUESS I'll be the first to ask......WTF is piston slap lol

 

piston slap occurs when there is too much cylinder wall to piston clearance

 

you cant measure it exactly with bottom end together, but you can get a idea if its too much. Also piston slap normaly doesnt sound like a rod knock. Id check the flywheel and/or bolts holding clutch on see if they are hitting anything. Did the pan have bearing material in it?

 

so what does piston slap sound like?

 

piston slap occurs mostly on motors with forged pistons. the forged piston expands a lot more then the block does it self. so in order for it to run properly and have enough clearance when the motor is hot. the pistons have to be smaller then the bore to a certain clearance. so when the motor is cold you can actually hear the pistons (slapping) the cylinder wall until they get up to operating temps. then they expand from the heat and fill the clearances.