Scotchbrite to clean up rust spot on cam lobe

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Aug 9, 2022
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One of the new cams I purchased had a couple spots of flash rust on the heel of one lobe, so I soaked it in PB blaster penetrating oil and tried to rub it off with a towel. This was not aggressive enough to remove the rust spot, so I used the least aggressive white scotch brite pad #7445 (equivalent to 0000 steel wool per brochure) soaked in some PB blaster which mostly removed the spots other than a barely visible stain that remained after a fair bit of rubbing. I then sprayed off the entire cam well with some contact cleaner spray, then scrubbed it down with a toothbrush soaked in mineral spirits, and wiped it dry with a clean towel.

I came across some information after I had done this indicating that some OEM's put out a technical bulletin stating that scotch brite should never be used on any internal engine parts. It states that the micro abrasives which are too small to see can embed into bearing material and tear up journals in as little as a few thousand miles. I was aware of the caution not to use scotch brite pads on a grinder to clean head/block surfaces because it can generate a large amount of debris to enter the engine, but is there any risk using a scotch brite hand pad on a camshaft outside of the engine like I did considering the porous surface of the cast iron? I looked up the technical information on the white scotch brite pad, and it uses nepheline syenite as the primary abrasive which has a hardness of about 6 Mohs or 65 HRC. From a quick search it appears that cam/crank journals have hardness around 55-60 HRC on average, but could be a bit higher.

The scotch brite pad was soaked with penetrating oil so it didn't generate dust, however, it did start to shed some fibers after rubbing with it for a while. I was also reading that the proper way to clean parts after using any abrasives was submersion in hot soapy water, so should I consider removing this camshaft before installing the valve cover to clean it further since I didn't submerge it?
 
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......I came across some information after I had done this indicating that some OEM's put out a technical bulletin stating that scotch brite should never be used on any internal engine parts. It states that the micro abrasives which are too small to see can embed into bearing material and tear up journals in as little as a few thousand miles......
This is called "charging", and it is a very real possibility when using abrasives on metal. It's somewhat how a lap works. What makes it even worse is when you have the harder material charged with microscopic abrasives, (cam), and have it riding in soft bearing material.

Some abrasives are much more forgiving than others. For example, when they hone out the cylinder walls on an engine block, the abrasive material breaks down quickly on the lapping stones, and it doesn't embed itself into the cast iron cylinder sleeves, and is washed away.

In your situation perhaps a small felt polishing wheel with some Flitz Metal Polish would be a better choice than Scotch Brite. That stuff works well, but gets into everything as it breaks down.

About the only use for Scotch Brite around an automobile, would be to dress up the brushed Stainless finish on a Delorean.
 
This is called "charging", and it is a very real possibility when using abrasives on metal. It's somewhat how a lap works. What makes it even worse is when you have the harder material charged with microscopic abrasives, (cam), and have it riding in soft bearing material.

Some abrasives are much more forgiving than others. For example, when they hone out the cylinder walls on an engine block, the abrasive material breaks down quickly on the lapping stones, and it doesn't embed itself into the cast iron cylinder sleeves, and is washed away.

In your situation perhaps a small felt polishing wheel with some Flitz Metal Polish would be a better choice than Scotch Brite. That stuff works well, but gets into everything as it breaks down.

About the only use for Scotch Brite around an automobile, would be to dress up the brushed Stainless finish on a Delorean.

So am I sc%e#ed now since I already used it to clean up the rust spot on the part? Do I need to remove this cam to do a more thorough cleaning, or should I trash it and purchase a new one? I have already installed it, but haven't buttoned up the engine yet.
 
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So am I sc%e#ed now since I already used it to clean up the rust spot on the part? Do I need to remove this cam to do a more thorough cleaning, or should I trash it and purchase a new one? I have already installed it, but haven't buttoned up the engine yet.
Before you go any further, I would contact 3M, (manufacturers of Scotch Brite), and ask to talk to one of their people. Tell them exactly what you did, and how you did it. Along with whatever clean up procedure you used.

They will be able to tell you where to go from here, without causing you unnecessary labor or expense. I can't say one way or the other if the polishing compound in Scotch Brite has for certain embedded itself into the camshaft lobe.

It's certainly a possibility, depending on the Rockwell hardness of the cam, along with the exact type of abrasive 3M uses in their Scotch Brite products.

Going by their recommendation would be your best option at this point. Don't panic just yet.
 
Well I need to have the vehicle back together by Sunday night, or I am going to need to rent a car. I will try to get ahold of them today, but not sure if I will get a same day answer considering as you mentioned we would need to know they exact hardness of the rotating parts in this engine. From what I see now my options are to just button it back up and forget about it, or to put the old cam back in and button back up until I can either get a new cam or clean this one better. I would prefer to not have to put the old cam back in because I will need to completely redo the job to take it back out again, but am willing to do so if deemed necessary.
 
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I would put a new cam in it, rust however slight has damaged and weakened the surface of the lobe and that is not a good thing, for me the risk of installing it and hope the lobe does not wear badly is not worth it.

Problem is the set I have now is my second set of new OEM Mopar cams because the first set I ordered all had some minor spots of flash rust that could only be seen after cleaning off the protective grease, and a couple of the cams in the second set also have the same issue. Each set was purchased from a different vendor (both shipped from a CDJR dealership located in different states) hoping it was just a storage issue with the first dealer, but it looks like a roll of the dice as to whether I will get another rusted one or not.

The only way I was able to see these spots was to take the part out of the box and clean off the grease layer with mineral spirits, so I likely wouldn't be able to tell even if I went to the local dealer and took one out of the box to inspect it. The parts come wrapped in VCI paper and have a sparse coat of grease on the ground surfaces, but it doesn't appear to be enough protection to prevent this rust even though the boxes all have a manufacturing date between May-June of 2023.

At this point I am more concerned about whether or not the white scotch brite could embed into the camshaft and cause further issues than I am about the rust, because I already spent $2300 purchasing 8 cams and I still don't have 4 that are completely spotless (I was able to return the first set and get a refund). I only hit the worst spot with the scotch brite pad, and that is shown in the picture below.

rust_spot.jpg
 
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I would have wiped it with an oily rag and used it as it was figuring that flash rust would be removed when the engine started or returned the cam for another one.
 
Whichever course of action you decide on, I would definitely change the oil and filter every 500 miles for the first 1,500 miles or so. Just to get any of the residual crap out of the crankcase that might have been left behind.
 
some OEM's put out a technical bulletin stating that scotch brite should never be used on any internal engine parts. It states that the micro abrasives which are too small to see can embed into bearing material and tear up journals in as little as a few thousand miles.
A cam lobe is NOT a bearing. The lobe is hardened steel while a bearing is some softer material. No way it's going to have anything embedded in it from the scotch brite. On a side note, you took apart the engine of the only car you have to drive? How did you plan on getting extra parts you will inevitably need? What if that 2 day job turns into a week or two? With the money you're saving diy, why not pick up a beater 2nd car for just such cases so you don't have to work in a rush?
 
A cam lobe is NOT a bearing. The lobe is hardened steel while a bearing is some softer material. No way it's going to have anything embedded in it from the scotch brite. On a side note, you took apart the engine of the only car you have to drive? How did you plan on getting extra parts you will inevitably need? What if that 2 day job turns into a week or two? With the money you're saving diy, why not pick up a beater 2nd car for just such cases so you don't have to work in a rush?

I knew what parts I would need for this job because I inspected the area the last time I had the valve covers off to replace a leaking gasket. I had all the parts on hand before I disassembled anything, but the only wildcard was the one cam I showed in the picture above that had the worst spot of flash rust. I mentioned that I had tried ordering another set of new cams even before I started, but these also had some minor rust spots, so I figured I would just go forward with the job since couldn't get unblemished parts after two tries.

I didn't make the decision to try to clean up the rust spot with the scotch brite until I was just about ready to install it, but maybe I should have just installed it as it was. I cannot purchase another vehicle because I have no where to park it where I live. I already took this week off work to do the job, but I will have to get an Uber to the local Avis to rent a car if it ends up going past this Sunday.
 
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A cam lobe is NOT a bearing. The lobe is hardened steel while a bearing is some softer material. No way it's going to have anything embedded in it from the scotch brite. On a side note, you took apart the engine of the only car you have to drive? How did you plan on getting extra parts you will inevitably need? What if that 2 day job turns into a week or two? With the money you're saving diy, why not pick up a beater 2nd car for just such cases so you don't have to work in a rush?
This why there are so many rattletraps in my sig... One goes down, it's not an all out emergency. Unlike my younger days! (But if there's nowhere to put them...😔)
 
Problem is the set I have now is my second set of new OEM Mopar cams because the first set I ordered all had some minor spots of flash rust that could only be seen after cleaning off the protective grease, and a couple of the cams in the second set also have the same issue. Each set was purchased from a different vendor (both shipped from a CDJR dealership located in different states) hoping it was just a storage issue with the first dealer, but it looks like a roll of the dice as to whether I will get another rusted one or not.

The only way I was able to see these spots was to take the part out of the box and clean off the grease layer with mineral spirits, so I likely wouldn't be able to tell even if I went to the local dealer and took one out of the box to inspect it. The parts come wrapped in VCI paper and have a sparse coat of grease on the ground surfaces, but it doesn't appear to be enough protection to prevent this rust even though the boxes all have a manufacturing date between May-June of 2023.

At this point I am more concerned about whether or not the white scotch brite could embed into the camshaft and cause further issues than I am about the rust, because I already spent $2300 purchasing 8 cams and I still don't have 4 that are completely spotless (I was able to return the first set and get a refund). I only hit the worst spot with the scotch brite pad, and that is shown in the picture below.

View attachment 177444
If you cleaned it off the engine after you used the pad it is no problem. Is that the rust spot? I would only worry about it if it is on the top of the lobe not on the side or heel. Now I see a picture it does not look like it is on a high stress area of the lobe.
Sorry I re read you original post where you mention it is on the heel, don't worry about it.
 
If you cleaned it off the engine after you used the pad it is no problem. Is that the rust spot? I would only worry about it if it is on the top of the lobe not on the side or heel. Now I see a picture it does not look like it is on a high stress area of the lobe.
Sorry I re read you original post where you mention it is on the heel, don't worry about it.

The part was not installed in the engine when I used the white scotch brite pad. The white #7445 pad is very mild, so it took probably 5-10 minutes of agitation and there was still a slight stain left behind that was barely visible under direct white light but not natural outdoor light. It contains no aluminum oxide abrasive (Mohs hardness of 9) per the 3M website, but uses a softer nepheline syenite abrasive (Mohs harness of 6). It's still somewhat concerning though because Moh's harness of 6 seems to convert to about 65 Rockwell C. From what I can tell from a general online search is that most engine journals cam/crank are hardened to around 55-60 Rockwell C.
 
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First...as others have said the cam lobe is hardened, not soft like a bearing. I wouldn't worry.

Also, what is this cam going into? Is it a roller cam? Flat tappet? Something newer? High spring pressure? Tell us more about the application.
 
Overthinking.
More importantly: Did you check lobe taper and lifter crown profiles so you will have rotation? YES? You are good to go to a proper wear in.
cam profile.jpg
 
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First...as others have said the cam lobe is hardened, not soft like a bearing. I wouldn't worry.

Also, what is this cam going into? Is it a roller cam? Flat tappet? Something newer? High spring pressure? Tell us more about the application.

It's a roller cam from a 2015 Chrysler 3.6L Pentastar. My understanding is that this engine has higher spring pressure than many of it's peers of the same era. The reason I replaced the original cams was due to surface fatigue wear on the lobe tips.

Cam_SurfaceFatigue.jpg
 
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