Scratch on Rod Journal - Need Advice
11-19-2006, 12:48 PM
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Scratch on Rod Journal - Need Advice I have a new stock LS6 motor and I decided to tear it down and swap the rings out. I've been re-ringing each piston one by one and noticed a light scratch on one of the rod journals. It looks like the assembling GM tech did not make sure the journal and bearing were perfectly clean. The scratch is all the way around the journal and I can barely hang a fingernail on it. The bearing has a slight marking and maybe a tiny piece embedded. This motor has never been run before, only turned over by hand. Does this crank need to come out and be polished? I guess the GM techs really don't give a **** about making sure everything is clean. This could be the reason so many of us spin bearings. Good thing I dug into this thing. How perfectly smooth do these journals have to be?
I loaned out my camera. Otherwise I'd post a pic. Thanks
I loaned out my camera. Otherwise I'd post a pic. Thanks
11-19-2006, 05:21 PM
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If you can feel it at all with a finger nail, it needs to be polished, at minimum. I'd also replace that bearing if it looks like it has anything embedded in it.
You're lucky to have found it now, rather than trying to start it/run it like that though.
Mike
You're lucky to have found it now, rather than trying to start it/run it like that though.
Mike
11-19-2006, 05:33 PM
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It seems to be a little raised and you can definitely hang your fingernail on it. I'm thinking I'll polish as it sits on the engine stand. As a matter of fact, I'm probably going to lightly polish all the journals and get all new bearings. Pretty crazy that I'm having to do this to a brand new engine
11-19-2006, 05:36 PM
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Yeah, I'm glad I decided to install better rings. There's no telling how long the bearing would have lasted.
Originally Posted by Mikey 97Z M6
If you can feel it at all with a finger nail, it needs to be polished, at minimum. I'd also replace that bearing if it looks like it has anything embedded in it.
You're lucky to have found it now, rather than trying to start it/run it like that though.
Mike
You're lucky to have found it now, rather than trying to start it/run it like that though.
Mike
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11-19-2006, 10:22 PM
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Thanks man. I guess I'll be pulling the crank out and find someone that can polish it for me. I was going to try and do it myself, but I don't think it's a good idea. My buddy was thinking we could probably do it with some 600 grit and a leather strap. It's just too critical to risk screwing up something. Lunati is here in town, but I don't think they would even touch a stock crank off the street. I'll give them a call.
11-20-2006, 08:24 AM
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Will be pulling crank out tonight and taking it to the machine shop in the morning. If they can't polish the scratch out by hand, they will be taking it to Lunati for polishing. I am not looking foward to breaking the crank pulley bolt loose while the engine is on the stand. I'm sure it will be damn near impossible. Any suggestions?
11-20-2006, 11:03 AM
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I would go with Federal Mogul bearings (I'm a little biased since I work at FM as a bearing engineer). Go with the high performance copper-lead bearings (rod set = 7100CH, main set = 152M) if you are going forced induction or NA over 500 hp. If you are keeping it a fairly mild street car you can go with the OE aluminum bearings (rod set = 2555A, main set = 7298M).
Don't be too concerned with seeing some debris embedded in a new bearing. Granted this is not a desireable condition, but there is no such thing as a perfectly clean (high volume) engine as just about every engine has some minor contamination somewhere in the system.
I would ask the machine shop to target a surface finish of 0.1 Ra (obviously smoother is better), but not to go over 0.15. Make sure he is polishing it in the direction of crank rotation. This should be obvious but I've seen cases where they were polished in the oposite direction which lead to severe bearing wear.
Don't be too concerned with seeing some debris embedded in a new bearing. Granted this is not a desireable condition, but there is no such thing as a perfectly clean (high volume) engine as just about every engine has some minor contamination somewhere in the system.
I would ask the machine shop to target a surface finish of 0.1 Ra (obviously smoother is better), but not to go over 0.15. Make sure he is polishing it in the direction of crank rotation. This should be obvious but I've seen cases where they were polished in the oposite direction which lead to severe bearing wear.
11-20-2006, 11:57 AM
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Thanks for the detailed info. Would the high performance bearing set be the best for any setup? Also, I thought that the journals need to be polished in the opposite direction of engine rotation.
11-20-2006, 12:15 PM
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Some shops will do a grind in the opposite direction to get the ferritic caps to stick up and then follow up with a polish in the direction of rotation to knock them down. However, I think most common method is to grind and polish in the direction of rotation.
The performance bearings can be used in all cases, however they are more sensitive to crankshaft surface finish and debris. The performance bearings have a soft electroplate that can wear excessively if the crank is too rough. The OE aluminum bearings contain silicon in the alloy which can condition the crankshaft if the surface finish is a little high. The OE bearings do everything very well but their load capacity is limited. I typically recommend the performance bearings for high cylinder pressure / high horsepower applications or if a steel crank is used, and the OE aluminum bearings if power is kept under ~500 and the iron crank is used. Some builders use our aluminum bearings in 600+ hp Grand Nationals w/ the stock iron crank without any issues.
The performance bearings can be used in all cases, however they are more sensitive to crankshaft surface finish and debris. The performance bearings have a soft electroplate that can wear excessively if the crank is too rough. The OE aluminum bearings contain silicon in the alloy which can condition the crankshaft if the surface finish is a little high. The OE bearings do everything very well but their load capacity is limited. I typically recommend the performance bearings for high cylinder pressure / high horsepower applications or if a steel crank is used, and the OE aluminum bearings if power is kept under ~500 and the iron crank is used. Some builders use our aluminum bearings in 600+ hp Grand Nationals w/ the stock iron crank without any issues.
