Replacing Rod Bearings... should I polish the crank? - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

nissandrift · 03-21-2011, 09:47 AM

I've got rod knock on #3, and the cars been parked for a few weeks now. I've already decided to just get a standard set of ACL bearings, and replace all 4 while I'm at it. Right now I'm hoping that the crank doesn't have any scarring, and that at most it will only need a polish. I'm pulling the motor out next weekend, and I'll know for sure then. Does anyone have a suggestion on a technique to polish the crank without pulling the crank out, or taking it to a machine shop? My reasoning behind that is that I haven't ordered any main bearings, and I'd rather not have to mess with them. I've heard of the 2000 grit emery paper wrapped around the journal, and using a shoe string to keep even pressure, but that's mainly on classic domestic motors with looser tolerances. I've also heard of scuffing the crank with a scotch brite pad. Would either of those be good choices, or would I be better off slapping the new bearings on as-is if I don't see any scarring?

Andrew@9K · 03-21-2011, 10:19 AM

If you had rod knock I assure you that the crank will be out of spec. The damage will be obvious when you take apart the motor, but you can have the crank re-ground and saved but you will need to speak with the machinist on the sizes of bearings you will be needing depending on the damage(.010/.020/.040). Main journals will also need to be machined and bearings ordered accordingly, so with that said order rod/main bearings and consider a OIL PUMP!

Andrew

p.s. you should order bearings after you have crank ground.

nissandrift · 03-21-2011, 10:22 AM

Yeah, I figured if I saw any damage I'd have to pull the crank. If that's the case I'll talk to the machinist, and order rod/main bearings with the specs he suggests. As soon as I heard rod knock the car was shut down, and I'm hoping it'll be ok... we'll see once it's apart. The car had been sitting for a month or previous, and the rod knock appeared first time I got on the throttle at about 3.5k which I hoped would minimize damage. I don't have the money for a new OEM pump, but I do have an oil pressure gauge to keep an eye on.

WholeGrainS13 · 03-21-2011, 10:34 AM

Quote:

Originally Posted by Andrew@9K

If you had rod knock I assure you that the crank will be out of spec. The damage will be obvious when you take apart the motor, but you can have the crank re-ground and saved but you will need to speak with the machinist on the sizes of bearings you will be needing depending on the damage(.010/.020/.040). Main journals will also need to be machined and bearings ordered accordingly, so with that said order rod/main bearings and consider a OIL PUMP!

Andrew

p.s. you should order bearings after you have crank ground.

This is true. You should have searched before ordering anything

nissandrift · 03-21-2011, 10:39 AM

A few of the local guys here have had luck with just throwing in a standard set after light knocking, and that's the main reason I've ordered a set to have on hand when I get the motor out. My main concern is whether or not I should try to hand polish the crank or just throw the bearings in if I don't see scarring. Right now it sounds as if no one goes about rod bearings without first going to the machine shop.

Andrew@9K · 03-21-2011, 10:47 AM

Quote:

Originally Posted by nissandrift

A few of the local guys here have had luck with just throwing in a standard set after light knocking, and that's the main reason I've ordered a set to have on hand when I get the motor out. My main concern is whether or not I should try to hand polish the crank or just throw the bearings in if I don't see scarring. Right now it sounds as if no one goes about rod bearings without first going to the machine shop.

I am sure that worked, But the question is. For how long?

nissandrift · 03-21-2011, 10:54 AM

My one buddy has put 115k on the S13 since he put the bearing in back in 03' which is the longest I know of. He only replaced the one bearing making noise though with an OEM bearing. The other guys have different makes an models, but most of them have a few years on the rod bearing replacements. I'm not against taking my crank to a machine shop, but I'm hoping to be able to have the motor back in the car Sunday. Otherwise I won't have another free weekend to put the car together until mid-late summer. Generally this car is only driven maybe 50 miles a week with an occasional autocross thrown in for good measure.

Forge_55b · 03-21-2011, 11:05 AM

screw it, just do it and see if it solves the prob. could have just been as simple as a split second of oil starvation that caused it

03-21-2011, 09:47 AM	#1
nissandrift Leaky Injector Join Date: Oct 2003 Location: Raleigh, NC Age: 41 Posts: 103 Trader Rating: (0) Feedback Score: 0 reviews	Replacing Rod Bearings... should I polish the crank? I've got rod knock on #3, and the cars been parked for a few weeks now. I've already decided to just get a standard set of ACL bearings, and replace all 4 while I'm at it. Right now I'm hoping that the crank doesn't have any scarring, and that at most it will only need a polish. I'm pulling the motor out next weekend, and I'll know for sure then. Does anyone have a suggestion on a technique to polish the crank without pulling the crank out, or taking it to a machine shop? My reasoning behind that is that I haven't ordered any main bearings, and I'd rather not have to mess with them. I've heard of the 2000 grit emery paper wrapped around the journal, and using a shoe string to keep even pressure, but that's mainly on classic domestic motors with looser tolerances. I've also heard of scuffing the crank with a scotch brite pad. Would either of those be good choices, or would I be better off slapping the new bearings on as-is if I don't see any scarring?

03-21-2011, 10:54 AM	#7
nissandrift Leaky Injector Join Date: Oct 2003 Location: Raleigh, NC Age: 41 Posts: 103 Trader Rating: (0) Feedback Score: 0 reviews	My one buddy has put 115k on the S13 since he put the bearing in back in 03' which is the longest I know of. He only replaced the one bearing making noise though with an OEM bearing. The other guys have different makes an models, but most of them have a few years on the rod bearing replacements. I'm not against taking my crank to a machine shop, but I'm hoping to be able to have the motor back in the car Sunday. Otherwise I won't have another free weekend to put the car together until mid-late summer. Generally this car is only driven maybe 50 miles a week with an occasional autocross thrown in for good measure. Last edited by nissandrift; 03-21-2011 at 12:25 PM..

03-21-2011, 10:19 AM	#2
Andrew@9K Join Date: Feb 2011 Location: Chino Hills Posts: 38 Trader Rating: (0) Feedback Score: 0 reviews	If you had rod knock I assure you that the crank will be out of spec. The damage will be obvious when you take apart the motor, but you can have the crank re-ground and saved but you will need to speak with the machinist on the sizes of bearings you will be needing depending on the damage(.010/.020/.040). Main journals will also need to be machined and bearings ordered accordingly, so with that said order rod/main bearings and consider a OIL PUMP! Andrew p.s. you should order bearings after you have crank ground.

03-21-2011, 10:22 AM	#3
nissandrift Leaky Injector Join Date: Oct 2003 Location: Raleigh, NC Age: 41 Posts: 103 Trader Rating: (0) Feedback Score: 0 reviews	Yeah, I figured if I saw any damage I'd have to pull the crank. If that's the case I'll talk to the machinist, and order rod/main bearings with the specs he suggests. As soon as I heard rod knock the car was shut down, and I'm hoping it'll be ok... we'll see once it's apart. The car had been sitting for a month or previous, and the rod knock appeared first time I got on the throttle at about 3.5k which I hoped would minimize damage. I don't have the money for a new OEM pump, but I do have an oil pressure gauge to keep an eye on.

03-21-2011, 10:39 AM	#5
nissandrift Leaky Injector Join Date: Oct 2003 Location: Raleigh, NC Age: 41 Posts: 103 Trader Rating: (0) Feedback Score: 0 reviews	A few of the local guys here have had luck with just throwing in a standard set after light knocking, and that's the main reason I've ordered a set to have on hand when I get the motor out. My main concern is whether or not I should try to hand polish the crank or just throw the bearings in if I don't see scarring. Right now it sounds as if no one goes about rod bearings without first going to the machine shop.

03-21-2011, 11:05 AM	#8
Forge_55b Zilvia Junkie Join Date: Jun 2007 Location: OC Age: 43 Posts: 414 Trader Rating: (2) Feedback Score: 2 reviews	screw it, just do it and see if it solves the prob. could have just been as simple as a split second of oil starvation that caused it