Learn me about cam lobe scratches
 

Getting ready to assemble my motor and I noticed these scratches on an exhaust cam lobe. It looks ugly, but I don't know what is severe enough to destroy a cam.

https://cimg2.ibsrv.net/gimg/www.mia...7cf1735e24.jpg

When I had similar scratches on mine, the advice I got was to replace the cam because they had gone through the surface harness of the cam lobe.

http://www.codrus.com/miata/fm2r/cam-nick3.jpg

--Ian

I personally would just send it. Worst case you need to eventually replace that lifter or shim depending on the year. Simple enough replacement in the car.

I've wiped out a ton of cams in small block chevys......every single time that metal found it's way into the oil system and bearings. If I caught it early enough it didn't spin the bearings. Yeah.....don't do that, replace the cam and think about checking the bearings.

Head came off a JDM motor. I had the head tanked, but I just happened not to send in the cams to the speed shop because I did the lifter shims myself. Existing metal FOD isn't a concern, just the scratches.

I am not so sure they are too much to be concerned with. The scratched area looks like a low contact area that doesn’t get polished from heavy friction. Are these factory cams? Could the scratching really be where coating is coming off at a slower rate?

I recall seeing something similar on my cams when they were newish. Vaguely recall I might add.

The concern is that if the scratches have gone through the hardening then the cam will wear rapidly, dumping more crap into the oiling system.

Used OEM exhaust cams are cheap, and you probably won't even have to reshim it. Now is the time.

--Ian

Ok. I'm picking up what you're putting down.

I have a junkyard motor this is replacing. Here are pictures of the cam lobes from the junker. They look better to my untrained eye.

https://cimg9.ibsrv.net/gimg/www.mia...b5f6062712.jpg
https://cimg0.ibsrv.net/gimg/www.mia...4094b32240.jpg
https://cimg2.ibsrv.net/gimg/www.mia...8e213245e0.jpg
https://cimg7.ibsrv.net/gimg/www.mia...74cf47723c.jpg

AIUI (I'm a software guy, not a "pro engine builder") the dulled wear pattern on those cam lobes is normal and not an issue. It's the bright linear scratches that are the problem.

--Ian

Thats all normal in those pics. 100% normal.

Cam swapped. Thanks all.