high idle speed issue

[Zed Head]

The hole position varies.  They just drill in a straight line for some, then another straight line for the others, I think.

Those lobes would be for the same cylinder.  That looks like a very wide lobe separation angle if that chip is at the top of the lobe.

I'd keep an ear on it, then an eye.

http://datnissparts.com/new-oe-l6-camshaft-datsun-240z-260z-280z-l24-l26-l28-13001-e4182/

[Jeff Berk]

Here's a closer look at the chip from a different angle. Yes, it is on the lobe.

[Zed Head]

Or not on the base circle.  Not sure which cylinder it is.  p.s. just saw Jeff Berks reply...  Question answered.

 

[Zed Head]

L

2 minutes ago, Jeff Berk said:

Here's a closer look at the chip from a different angle. Yes, it is on the lobe.

Looks scary.  Interesting experiment.

[Jeff Berk]

I pulled the valve cover off this morning to get a closer look at the rocker arm. I see something that worries me but what do I know. Keep in mind that the chip in the lobe is to the rear of the car when inspecting the photos. That would be the side marked "S" on the rocker.

[Jeff G 78]

Were the rockers resurfaced because they don't look new.  That little spot doesn't scare me as much as the one on the lobe, though if they were not resurfaced, they shouldn't be paired with a new cam.

[Jeff Berk]

Jeff G 78, 

I looked at the Aug 2020 receipt and the rockers were shown as being replaced. That was 400 miles ago. (I need to get this out on the road more)

The fractures on the "S" side of the rocker running parallel with the face don't bother you?

Jeff

[Jeff G 78]

51 minutes ago, Jeff Berk said:

Jeff G 78, 

I looked at the Aug 2020 receipt and the rockers were shown as being replaced. That was 400 miles ago. (I need to get this out on the road more)

The fractures on the "S" side of the rocker running parallel with the face don't bother you?

Jeff

Those sure don't look new to me.  I could be wrong, but they look like they have old oil residue on them.  What do the lash pad ends look like?

As for the S side, I can't tell what's going on there.  I have never seen a pad split, so I assumed it was just a debris line.  I thought you were referring to the chip in the edge which I've also never seen.  I'd probably have a machine shop magnaflux that and see if it's really a crack.  You might even be able to tap on a good rocker and then tap on that and listen for a different tone.  It should thud if it's cracked.

Was the shop that did this work reputable?  I would not be comfortable with what I'm seeing.

[Zed Head]

Do you know how the cam lobe got chipped?  How many miles or minutes have you put on it so far?

[Jeff G 78]

3 minutes ago, Zed Head said:

Do you know how the cam lobe got chipped?  How many miles or minutes have you put on it so far?

What if it chucked a rocker?  The chip on the rocker and the chip on the lobe could have been done together?  I've chucked rockers on the track with no damage, but I guess it could happen.

[Jeff Berk]

Jeff G, what does it mean to chuck a rocker. The lash pads look ok to my untrained eye. I'll clean the rocker in an ultrasonic cleaner, stain it with ink, and see if the apparent cracks are still there.

ZH, There's 395 miles on it. I'm assuming the chip on the lobe occurred during the machining as it's not very noticeable. I'm not familiar with (or know) the machine shop and relied on the mechanic to select one he was familiar with. 

What I think might be happening is the lobe got chipped possibly due to a defect during machining. The rocker was chattering due to the uneven surface and created the cracks.

Possible solution? I was thinking that I'd replace the rocker (they are inexpensive) and grind away just enough on the trailing edge to miss the chipped area of the lobe. Then I'd protect the area around the cam shaft with rags and smooth out the lobe chip with a small grinder to lessen the potential for propagation of the damage.

I'm waiting for the mechanic to get back to me with his suggestion(s).

This is my third shaft in 2 years. 

Jeff

Edited June 18, 2021 by Jeff Berk

[Jeff G 78]

Chucking a rocker refers to a rocker coming dislodged from it's position.  This can happen due to it being adjusted too loose, over-rev, or weak springs.  If it partially dislodged, it could have caught the edge of the lobe.  In your case, the rocker could have pivoted rearward.  By the time the cam rotated back around, it was BARELY over the lobe.  With the rocker pivoted, I'll bet that the chip in the rocker lines up with the chip in the lobe.  The other possibility for the lobe damage is that it's in the rear of the lobe which could get damaged during assembly in the head.  The cam is slid through the towers and if it wasn't carefully lined up, I suppose it could have caught a tower just right to chip it.

As for the rocker, I'd sure verify that the pad isn't split.  If it sheers, it will destroy the cam and then send metal throughout the engine.