[07nnbs4x4]

So, I am doing my cam swap on my 2007.5 Silverado NNBS with a Gen 4, 5.3 LMG. I am also removing the AFM hardware. So I pulled out my old cam and inspected my cam bearings and noticed they had these odd marks on every bearing and only on the top portion (above the oiling holes), they do not appear to be worn and there is no visible copper. They do not really appear to be marks from damage but more machine marks but I could be wrong. The old cam is smooth as can be and has no visible marks on it. I had no plans to swap the bearings since the motor has a tad over 100k miles, it made no noises and had great oil pressure (45-50psi above 2k rpm and 25psi at hot idle). The marks all seem to be uniform and cover the full width of the bearings and do not differ. I talked to a motor tech at my local dealership and he said those are normal to aid in oiling. Are these marks normal or should I change them out?

 

[GR2017]

......had these odd marks on every bearing.....

I think the fact that every bearing has them would indicate it is intentional and normal.

 

[Gozzie]

I'm no expert but I'm sure that's there to help spread the oil film across the whole surface of the bearing

 

[redtherocket]

I would imagine it has something to do with when the block was being manufactured..

It looks to me like a correction was made to the bore

 

[MIKE91B]

I believe the Cam journals are not alignbored in the block. From what I understand the cam bearings are pressed in and then the bearings are alignbored when produced at the factory. This is true of all the LS family of engines. That's why bad cam bearings = new engine while under factory warranty. If you can't feel the marks with your finger it's good to go. I have replaced two cams in 5.3s in the last month. Both were products of lifter failure.

 

[WhiteBoyZ71]

Saw your post and got curious about it. Sent your pic to a well known private mechanic here in the 405 that does a lot of work with LS based engines. He also recently did the AFM/DOD delete to mine and it runs great.

Here's his response, "Looks to have a little wear. The lines are what look strange. I wonder if that's just visual or if you can feel ridges?"

 

[apcnc]

Looks like a wear pattern to me. Even though it looks to be straight and basically is each time a valve is opened the pressure misaligns the cam. Basically it is tetering up and down. If you notice the wear is aligned with the lifters. Depending on the angle of the cam which valve is opened etc. it will press down more in a specific spot. More wear could indicate dirty broken down oil.. carbon etc.

 

[apcnc]

I believe the Cam journals are not alignbored in the block. From what I understand the cam bearings are pressed in and then the bearings are alignbored when produced at the factory. This is true of all the LS family of engines. That's why bad cam bearings = new engine while under factory warranty. If you can't feel the marks with your finger it's good to go. I have replaced two cams in 5.3s in the last month. Both were products of lifter failure.

Why would they not align bore the block? Time? So how did your cams line up with new bearings?

 

[apcnc]

One more thing.. Great pic btw. If you zoom in on the cam. You can see very faint parallel marks on it. Its much harder so not much wear. The bearings will probably be fine but... I would replace them just in case but would find out about this boring issue. If new bearing will not be aligned properly that will cause wear also. So you may be just as well to use the old if you don't machine the block.

 

[07nnbs4x4]

I believe the Cam journals are not alignbored in the block. From what I understand the cam bearings are pressed in and then the bearings are alignbored when produced at the factory. This is true of all the LS family of engines. That's why bad cam bearings = new engine while under factory warranty. If you can't feel the marks with your finger it's good to go. I have replaced two cams in 5.3s in the last month. Both were products of lifter failure.

Well the thing is you can fell the marks in a sense. It has a different texture, more like a rougher surface compared to smooth. It does look like machine marks but I have never seen something like this before and I have messed with LS engine a few times. If it is wear its odd that the wear is on the top portion of the bearings. Every other part of the valvetrain is fine, no wear that is not normal. I am almost tempted to have some Durabond Coated bearings put in to be on the safe side. I just did not want to remove the crank and rods and have to replace those bearings and bolts/studs as well. The good thing is I have the engine out on a stand and it is stripped down to the block/rods/crank/pistons.

 

[MIKE91B]

If you can feel anything it's time to replace bearings or get another block. GM has polymer coated bearings as a warranty repair. My thought is with the polymer bearings the cam is more likely to center its self. Once again that's a warranty repair not a fix if you will. At this point I'm stepping out of the suggestion circle. This requires a engine machinest or builder with more experience than I can provide. As to the question regarding new bearings with the old cam. You don't nor do dealer technicians want to install cam bearings. I have never seen cam bearings replaced in a dealership nor do I want to. Some things are best left to specialists. Some of us can do it but most should not. Please keep in mind warranty repairs don't equal race engine precision. Modern engines can hide all types of issues. With no outward signs of failure.

 

[WhiteBoyZ71]

I believe the Cam journals are not alignbored in the block. From what I understand the cam bearings are pressed in and then the bearings are alignbored when produced at the factory. This is true of all the LS family of engines. That's why bad cam bearings = new engine while under factory warranty. If you can't feel the marks with your finger it's good to go. I have replaced two cams in 5.3s in the last month. Both were products of lifter failure.

Well the thing is you can fell the marks in a sense. It has a different texture, more like a rougher surface compared to smooth. It does look like machine marks but I have never seen something like this before and I have messed with LS engine a few times. If it is wear its odd that the wear is on the top portion of the bearings. Every other part of the valvetrain is fine, no wear that is not normal. I am almost tempted to have some Durabond Coated bearings put in to be on the safe side. I just did not want to remove the crank and rods and have to replace those bearings and bolts/studs as well. The good thing is I have the engine out on a stand and it is stripped down to the block/rods/crank/pistons.

I would rebuild the entire thing if it were me since your that far into it already.

 

[07nnbs4x4]

There is no need to rebuild the entire engine. The engine specs are perfect and there is absolutely no wear on the entire engine. The Cylinder wall specs are way within spec and can see the factory hone marks. I have measured all aspects of the engine and everything is within specs, even the cam bearings. I talked to another LS engine tech and he said the bearings are normal and they do that for oil purposes, but I should not feel a texture difference. But I may change them since I have the engine torn down. So looks like a will probably end up getting some Durabond Coated bearings. CHP-25T, along with Clevite Coated Rod and main bearings with stock bolts. I was thinking about going with ARP but I really didn't want to spend the extra cash for them plus have them line bored due to the extra clamping force. I was not planning on this and will mess up my budget I had. But better be safe than sorry. The engine was supposed to be in the truck and running since I had already scheduled my vacation and was going to tow my TT.

 

[07nnbs4x4]

If you can feel anything it's time to replace bearings or get another block. GM has polymer coated bearings as a warranty repair. My thought is with the polymer bearings the cam is more likely to center its self. Once again that's a warranty repair not a fix if you will. At this point I'm stepping out of the suggestion circle. This requires a engine machinest or builder with more experience than I can provide. As to the question regarding new bearings with the old cam. You don't nor do dealer technicians want to install cam bearings. I have never seen cam bearings replaced in a dealership nor do I want to. Some things are best left to specialists. Some of us can do it but most should not. Please keep in mind warranty repairs don't equal race engine precision. Modern engines can hide all types of issues. With no outward signs of failure.

I see no reason to replace the block. The stock GM bearings are fine for stock but I have modified my engine and will boost it later on so Durabond Coated bearings are my best option. I do not know what you mean by warranty since my truck is almost 10 years old and has a tad over 100k miles on it. I have changed numerous cam bearings on LS engines before and it is something I an not worried about, I did work as an engine tech for a GM dealer about 7 years ago. I will have it done by a machine shop to make sure everything is trued up tho. I just have never seen any machined or worn bearings like I have tho, it is a first for me, and the 3 LS engine Techs I talked to all say it is normal.

 

[07nnbs4x4]

Now don't get me wrong here, when I say texture difference I do not mean its a rough surface or anything, it is as smooth as can be and there is no grooves what-so-ever. It just feels a tad different than the bottom portion of the bearing. I also did some measurements with a micrometer and a dial gauge and their is no deviation and the inner diameter is perfectly round. After hearing from the 3 techs and them all saying it is for oil purposes and after doing measurements I may run it as is. My thought is, if it was some sort of wear, there would be some sort of indication on the cam journals themselves or the bearings would be showing some copper. I am 99% sure the marks are machined marks which would be from the factory. I wish I had some used Gen 4 5.3 LMG cam bearings to compare it to.

 

[GMT604]

The deviations may be too small to measure with just a micrometer, and inside measurements are not easy at the best of times. :roll: A difference in diameter of tens or even hundreds of thousands of an inch could leave those marks. They are also at the top of the bearing where there is no cam load, all the load is at the bottom of the bearing.

I would mic the old cam and the new one to see if there is any appreciable difference, and closely inspect the bottom of the cam bearing for wear.

 

[07nnbs4x4]

Well, I did Mic the cam and it is right in the middle of the recommend measurements. I have an entire GM spec and setup guide for the 2007-2013 LMG 5.3. I mic'd the Cam and bearings and everything is well within the factory specs. I also found some pics on another forum of another Gen 4 5.3 LMG that he was doing a cam swap and the bearings look, for the most part, identical with those machine marks. So It may be a gen 4 thing or a LMG 5.3 thing but from what I was told and the pics I seen it is normal and not wear. So this research has really eased my mind and now know, at least on the Gen 4 LMG 5.3, have odd machine marks on the cam bearings.

There is no marks or grooves on the bottom of the cam bearings, the front bearings does have a ever so slight foggy look to it on one small portion of it but nothing out of the norm for a used cam bearing. All the other 4 bearings and smooth as glass and look like new.

 

[07nnbs4x4]

Great news guys! I had a GM Engine Tech at my local dealership look at it today to install new bearings, someone I know pretty well. He said the markings are from the Machine process they do after they are installed, similar to doing a Line Bore, and also aids in oiling. He showed me pictures from there engine build/spec program or whatever they call it, that shows the markings on the bearings. The marks are very smooth to the touch but do have a different texture to it. He also measured them out and said they are well within spec, and there was really no wear on them at all as well as the factory coating was still in great shape. He said there is no need to change them at all and are good to run as is, but.....did say that GM recommends to change cam bearings when swapping a cam. I think he also said it is something they are doing on the Gen 4 and newer Truck engines from the factory. It is a big relief because I really did not want to change them out and remove the crank, rods, pistons and then have to swap out those bearings and get new Main and rod bolts. So in case anyone here runs into those kind of markings, they are completely normal and no need to worry.

Thanks guys.