I've been chasing down valvetrain noise for the last month or two on my 240Z (stock block, E31 head), and I think I've found the culprit: #3 intake valve is sticking.

I noticed it this way: I was (again) checking valve clearances, because of clacking, and once I had everything set, I cranked the motor over, and it sounded like a box of rocks. I pulled the valve cover again, and saw that #3 intake valve was stuck at about half-mast, the rocker arm quite askew.

I was able to free the valve with a quick tap with a soft-faced hammer (it popped right back up).

There is definitely some damage to the cam lobe at the edges (it threw a lash pad once before). There is no damage to the retainer, the lash pad, the valve spring, or the rocker. The valve still seats fine, too (good compression, so no bend and no piston lovin').

What's my way forward from here?

On the "I wish I may, I wish I might" front, I could probably swing new guides, rockers, seals, lash pads, and the 274/274 Schneider cam plus whatever machining costs I incur to get the bare head built up with the new stuff.

On the "my wife won't divorce me" front, I could probably swing a new stock cam, and a new rocker, but if the guide or the valve is damaged, I'm still in the "I've gotta pull the head and take it to the machine shop anyway" pickle, and I could possibly have damaged the new cam.

On a related note, how are the Beck Arnley replacement rockers? They're about all I can find, but if they're not adequate, what's going to be my best option?

Is there any varnish in the engine? Varnish can cause your valves to stick. Flushing your engine with Gunk Motor Flush will resolve that problem. It can take a few flushes, and the first flush can actually cause the problem to worsen slightly, as it swells the varnish. Chemtool B12 added to the gas tank can also help dissolve varnish off the lower ends of the valve stems. Unfortunately valve stems are the hardest part of the engine to get clean, hence the multiple flushes.

A more gradual approach can be running Chevron Delo motor oil, which is very high detergent (a diesel formulation). Alternatively, you can add Rislone (detergent additive) to your motor oil.

I don't believe there's any varnish aboard. I re-ringed, bearing-ed, and gasketed the motor in '09, and I think I did a pretty good job cleaning at that point (I soaked the valvetrain in B-12 chemtool, and knocked all the crap off of the valves).

I will consider moving to a higher detergent oil, since this issue seemed to start right after changing the oil. I didn't swap to any different oil, though, which puzzles me (it's always seen Mobil1 10W30).

I ran some seafoam through my crankcase for about 250 miles, it cleaned everything right up.

Are you supposed to run SeaFoam that long? With the Gunk flush (probably not that different from the SeaFoam), you're supposed to idle the engine 5 min and then change the oil.

Are you supposed to run SeaFoam that long? With the Gunk flush (probably not that different from the SeaFoam), you're supposed to idle the engine 5 min and then change the oil.

I read up on it for a while before i tried it, a lot of people do it for about 250-500 miles before the next oil change. Its basically a "deep cleaning" of the engine.

It had no ill effects on my motor, when i inspected some parts after the cleaning all of the varnish was removed, and it looked superclean.

After that did an oil change, drove for 500 miles and then i changed the oil again just to get all of the solvent out of the motor.

its been about 1300 miles now and i haven't had any issues

Interesting. I think the main hazard is that you liberate so much sludge (with a very dirty engine) that you clog up the filter, blow the bypass, and then clog up the oil passages. I think the rationale behind the Gunk flush instructions is that there's not too much agitation, flow, or pressure at an idle, and the gunk dissolves about all it can hold in 5 min. Whenever I do a flush, I keep my eye trained on both the oil pressure and temp gauges. If oil pressure were even to flinch (which it never has), my immediate response would be to shut down the motor. I've done maybe a couple dozen flushes in my life, with no incident.

I know the Magic Mystery Oil recommendations are to run the stuff long-ish-term, like you do with the SeaFoam. Supposedly the high volatiles dissolve out the crud and suspend it in the oil, and then they eventually burn off, leaving just the motor oil. Maybe that's what happens with the SeaFoam.

Another treatment, popular with the Miata crowd, is to run a quart of ATF in the motor oil for about 100 mi. Apparently ATF is super-high in detergent.

We use ATF in rotary engines to un seize them when carbon breaks free form the apex seal and binds inside the housing. That stuff is incredibly strong against carbon

Bastard bucked and threw a lash pad again today.

I'm going to swap a different head on for a few weeks and rebuild this one.

I've got an extra N47 if you're interested, 62k miles

Oh, I'm going over to a friend with a barn full of Zs tomorrow morning. Thanks for the offer, though!

It's purely a short-term thing, I intend to put the original E-31 back on as soon as it's better.

You might find that your valve guides are coming loose causing the valve to get in a bind-and there's only one fix for that. I had the same thing happen to my early z.

The E31 on the engine, with the intake attached

Without the intake

L24 minus head:

Stripping the head (cam towers are gone, I've started pulling the rockers and adjusters)

As soon as I swap the greaseball E88 head onto the motor, I'm going to drop the E31 down at the machine shop. The #3 intake valve was sticking badly enough to introduce itself to a piston. While there was no damage to the piston beyond a small scar, I'm sure the valve is bent.

Plans:

MSA stage 2 cam

new rockers

new valve springs

new keepers

new guides

valve seats cut

valves lapped

#3 intake valve (and any others beyond serviceability) replaced