camshaft lobe discoloration ??

[Alumarine]

Hi there. On the back outside edge of my cam lobes I have small discolored spots on either side of the lobe.<br />Anyone know if this is a problem?<br />The rest of the cam surface looks great and the lifters look like new with no wear at all.<br />Thanks hope you can see it in the picture.<br />1974 mercruiser 140<br /><br />

 

[Buttanic]

Re: camshaft lobe discoloration ??

Looks to me like it is a area on the lobe that does not touch the lifter so it is the original finish along with baked on oil film. Flat tappet cam lobes are ground at slight angle to cause the lifter to rotate to distribute ware over a larger surface. That is probably the low side of the lobe. I don't see it as a problem. The angle also causes thrust toward the back of the block to keep the cam from walking forward out of the block.

 

[rodbolt]

Re: camshaft lobe discoloration ??

usually if the lobe is shiney all the way across it indicates ecsessive lobe wear. the lobe is ground on an angle to promote lifter rotation while its running. keeps the wear from being in one spot. check the lifter for flatness or concavity on the lifter foot with a straight edge and a good light. should not be flat nor concave it should be slightly convex.

 

[Alumarine]

Re: camshaft lobe discoloration ??

Hey guys thanks for the great info.<br />I'll check the lifters tomorrow.

 

[Alumarine]

Re: camshaft lobe discoloration ??

DHP, I don't really have a big problem. I'm down a bit on compression on the back 2 cylinders and just checking out the motor to see if it's in spec.<br /><br />Rodbolt, actually the picture is deceiving. All the lobes are nice and shiny except where I've circled it. It must have been the flash or something making the lobe look rusted.<br /><br />I just had the head decked and am going to install new rings.

 

[DHPMARINE]

Re: camshaft lobe discoloration ??

Looks to me like a normal Mercruiser (1974) cam.Has to have some wear.What is your problem ? ?<br />I mean this well,what isn't working on your engine ?<br /><br />DHP

 

[rodbolt]

Re: camshaft lobe discoloration ??

only thing I saw was the rust spots on the lobe that did not look good. the cam is only surfaced hardened and rustspots can penetrate the surface.<br /> the small spots circiled are normal. the light g;are may be sufficient to hide the marks but normally the cam is not shiney all the way across at the lobe tip. by wear I am not saying worn out. about .003 of wear and your into soft iron.