Never before heard valve knocking started yesterday...

[Dadsun]

It was a single pinging/knocking that sped up when revving, and it occasionally was a louder knock like something was loose, so I immediately shut it down. This all happened while under the garage at cold startup.

I've taken off the valve cover and don't know where to start to diagnose. 

Here are pics. Any help on what is the most likely culprit and path to diagnose is much appreciated. Thanks.

[Dadsun]

Two more pics of the timing chain center pulley, which looks off. 

[Zed Head]

If, by pulley, you mean that off-center cam-looking thing in the middle of the chain sprocket, that's the fuel pump eccentric.  It is supposed to be off center, it pushes the fuel pump lever each time it passes by.

Can't tell how many RPM "revving' is or what ping or knocking actually mean.  But I can say that your valve lash seems tight.  On a properly adjusted valve train the base circle (the part of the cam lobe with no hump) will not be worn since that is where the lash is, and the anti-rattle springs keep the wear pad off of the base of the lobe.  The base circle is usually brown.  Yours show wear all the way around.  You might want to recheck valve lash.

You might shine a light down toward the chain tensioner and see if you can tell how far out is extended.  You can also set your damper pulley at zero and check your chain wear marks on the sprocket.  The notch and groove.  Make sure the tight side, driver's side, is tight.

Edited July 29, 2023 by Zed Head
+ not

[Dadsun]

I think I found the source of the noise. See pic. One of the rocker arms is not seated in the valve rocker guide (term from the repair manual, also pictured).

[Zed Head]

People here call that the lash pad.  That's not good, it would be holding the valve open.  Any chance the locknut came loose on the adjustment side?  Can you wiggle it by hand?

Was it mine, I'd recheck lash from scratch.  

[Dadsun]

Locknut isn't loose. 

I get what you're saying about the base circle wear. I've never adjusted the valve lash, so I'll research it. 

But in any case the valve appears to be stuck down (open). How would adjusting the lash help that?

Edited July 29, 2023 by Dadsun

[Dadsun]

I should clarify that I can move that rocker arm into place over the valve guide (lash) and push it down to seat it in place, but it springs back up. So, that tells me the valve is stuck?

[Zed Head]

Sounds like it.  Or somebody adjusted the lash too loose on that valve.  You can compare the height of the valve when it should be closed (on the base circle) to other valves that are closed.  It could be just stuck or it could be stuck because it's bent.

Rocker arms jumping their lash pads is not uncommon when revving an engine that's been sitting.  You can find stories.  Many people just put it back together and carry on and never have it happen again.

[Dadsun]

34 minutes ago, Zed Head said:

You can compare the height of the valve when it should be closed (on the base circle) to other valves that are closed.  It could be just stuck or it could be stuck because it's bent.

I just finished doing this comparison. The stuck valve when compared to fully closed valves is a little low, but not much. Nowhere near as low as ones fully pressed by the cam lobes. So, it looks stuck, but I guess there's a chance it's not bent or damaged the piston. I'm trying to avoid pulling the head because that's out of my expertise, which means getting it towed to a mechanic. Unless I can unstick it. Open to suggestions. I searched old threads and some people try penetrants and/or disassembling the valve.

[Zed Head]

Not an expert.  But, barely lower is what you'd get if the valve head was bent on the stem. 

Since everything is back together it might be worthwhile to pull the spark plugs and spin the engine by hand to see what the valve is doing.  Does it get stuck or does it move freely.  Then, if you're brave, spin it with the starter with the plugs out.  Don't forget to disconnect the coil, or use a remote starter with the key off.

You could also measure cylinder pressures if it spins freely.  If the valve is not closing completely you'll get a zero on that one.

[Dadsun]

So, the head seat on that intake valve has dropped and the head needs to be rebuilt. Not my specialty. Any suggestions on where to find another head? Just trying to compare the two options. 

[Patcon]

Depends on if you can find one in a junkyard or maybe a member might have a good candidate. Most anything you find will have to be gone through...