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Join Date: Feb 2012
Posts: 246
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Colour on camshaft
Can somebody tell what the yellow colour on this cam lobe is?
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06-24-2019, 03:52 AM
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Slippery Slope Expert
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That looks a little more serious than “discoloring” to me. I think the hardened surface of the cam lobe is worn through and you should be able to feel that with your fingernail. Not a good situation.
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“As new technologies become indistinguishable from magic, and I can no longer tinker, the magic goes away for me.” |
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06-24-2019, 05:28 AM
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Colour on camshaft
Quote:
Thanks for the reply. Forgot to mention that the "color" is a very thin layer of something that is relatively easy to polish of with 2000 grit paper. Sent from my iPhone using Tapatalk |
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06-24-2019, 05:55 AM
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Puny Bird
Join Date: Nov 2002
Location: Port Hope (near Toronto) On, Canada
Posts: 4,566
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That looks more than what will polish out, I'd at least have the cams and rocker pads reground.
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06-24-2019, 06:47 AM
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Quote:
Here's a picture after polish. Taken from another angle.  Sent from my iPad using Tapatalk |
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06-24-2019, 07:11 AM
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Under the radar
Join Date: May 2007
Location: Fortuna, CA. On the Lost Coast near the Emerald Triangle
Posts: 7,129
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I agree, looks like the hardened surface is gone. What does the rocker look like?
It will be interesting to see what that lobe looks like after you drive it.
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06-24-2019, 01:13 PM
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Just to clarify: the thin yellow layer lays on top of the cam lobe metal.
When the lobe is polished there is no groove / low area where the yellow layer was pre.polishing, the geometry of the lobe is back to what it was before the yellow stuff got on it. Sent from my iPad using Tapatalk |
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06-24-2019, 03:09 PM
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Registered
Join Date: Oct 2002
Location: Phoenix, AZ
Posts: 484
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Just a wild guess, but that might be a piece of plastic that came off a chain ramp or some other piece of plastic debris that melted onto the cam lobe and got flattened by the rocker pad.
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06-24-2019, 06:43 PM
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Join Date: May 2004
Location: Boulder, Colorado
Posts: 7,275
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I'm with Ollie (just guessing). Since it stood proud, and went away with polishing, I think it's not my (and others) first guess. Piece of plastic bag got in there? Maybe some sealant used on a valve cover? Melted onto hot cam, then smoothed? Still odd that it could withstand the pressure and rubbing by the rocker and not be worn off.
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06-25-2019, 02:20 PM
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Join Date: Oct 2002
Location: Phoenix, AZ
Posts: 484
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Looks to be on the heel of the camshaft, so if the valves were adjusted properly, it was probably .004" thick!
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06-25-2019, 06:03 PM
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Join Date: May 2003
Posts: 3,346
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Some kind of preservative on the cam. Like cosmoline.
-Andy
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06-25-2019, 09:23 PM
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Join Date: May 2004
Location: Boulder, Colorado
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Now things are looking logical. Is it on the heel (aka the base circle)? It is beginning to look like a non-issue.
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06-26-2019, 09:27 AM
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Colour on camshaft
Also forgot to mention that it is on the ramp-up and on the top of the lobe on the no. 2 exhaust
Sent from my iPad using Tapatalk |
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06-26-2019, 10:29 AM
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Location: Boulder, Colorado
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Well, that shoots a promising theory. It is something which could withstand the full pressure. But since you were able remove it, it wasn't a break through the surface hardening, which is the big worry with flaws on the surfaces.
I forget - what did the rocker for that lobe look like? Normal? Worn more on one side (where the stuff was?). The rocker is just as hard as the cam. How was the rocker bushing? That stuff seems like it would make the rocker bearing wear unevenly. If you have V blocks and a good surface, you can check to see if the rocker face is parallel with the shaft. Might be a good idea to have that rocker rebushed? How about rocker shaft wear - anything unusual there? |
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06-26-2019, 10:41 AM
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The rocker looks and is very bad. The worst area on the rocker is not what made the "yellow" stuff. If you see closely on the rocker pad right next to the bad pitting area you will see a very thin layer of some metal like something. That corresponds with the yellow stuff on the cam lobe.
I suspect worn metal particles from the rocker bearing to be the reason for the yellow stuff...but cant tell for sure. The rocker bearing is worn in the usual area but not very bad.   Sent from my iPad using Tapatalk |
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06-26-2019, 01:12 PM
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Registered
Join Date: Mar 2004
Location: Windsor, CT
Posts: 2,119
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The rocker shaft looks ugly.
If the shaft is not smooth, the oil film will breakdown and the bushing will deteriorate. I found that re-polished rocker shafts can still be too rough. I wore out the bushings and damaged both the rockers and cams in ~1000 miles because of this. Oil had a grey haze from the metal. New rocker shafts solved that source of deterioration. The rocker pad is shot. |
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06-30-2019, 03:40 PM
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My Garage
1971 Porsche 911
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