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My M30B28 has around 185K on it. I'm the second owner, and the PO (allegedly) had the valve train refreshed at around 90K. I don't know what that work involved, so I have to assume every component is original.

I've adjusted the valve clearance before and just did so again. There is a loud tick that seems to come from a single valve, but I have not yet identified which one. I'm going to use a stethoscope and ballpark it before opening the valve cover again.

When adjusting the valve clearance, I adjust each individual valve with the rocker pad on the heel of the cam rather than at TDC. I don't think that matters, but maybe I'm wrong.

I read that the valve stem can dimple over time so that using the feeler gauge at the eccentric can give a false reading (i.e., the true clearance is larger than what's measured). It was suggested that the feeler gauge be used between the cam heel and the rocker pad. That sounds plausible in theory so I though I'd try it to see if there's any obviously wide clearances and if so readjust.

Any reason not to do this?

I'm also looking for tips on how to isolate the tick. Some places mention that the rocker pad can become loose, but I thought the rocker was a single part (with a bearing pressed into it for the rocker shaft). Is there a technique for determining is the pad or bearing are loose without disassembly? I've read that an experienced mechanic can "feel" a wobble if the bearing is worn.

There is faint scoring on one cam lobe. I would assume that's a good place to start, but I don't want to fixate on it if it's not the source of the tick.

I'm thinking my next move will be to replace eccentrics, but I'm open to suggestions.

I know that removing the head for a full refresh is where I might be headed, but if I can avoid that for awhile that would be great.

I would suggest going thru and doing it again. Be very careful about the position of the cam lobe, the ramp starts before you think and it can be just a tiny bit onto the opening or closing ramp causing you to misadjust a valve.

On the rocker arm. There is a separate steel or cast iron or whatever piece cast into the rocker at the time of manufacture. I've never seen one come loose, but I'm sure it's happened in rare cases. The aluminum of the rocker arm is much too soft to ride directly on the cam. Even hardened I've seen many a rocker arm pad with a scalloped wear pattern on it, typically due to a loose/missing banjo oiler bolt.

If it were ME, . . .
I’d pop the cover off again and recheck the clearances. I was taught to check the valves in firing order sequence, starting with cylinder 1 at TDC. Remove all spark plugs. Cool that your car is manual transmission, have it in top gear (4th, 5th). It gives you mechanical leverage to turn the engine. (Obviously, neutral, brake off and CHOCK THE WHEELS!)

As the rocker is at dwell (back side of the cam) you can get a feel if it’s loose by pull-push to get a feel of how loose it is.

Feeler gauge .025 - .030 mm (.010-.012 inch). Coat it with light oil. Check between the rocker and cam, or rocker and valve stem. Don’t force it, lest ye wind up with a tighter gap.

Personally, I shoot for .010” for the intake and .012” for exhaust. The little extra helps assure heat transfer from the valve to the seat.

I readjusted the valve clearances and checked them twice. The engine sounds like it should ... except for one loud tick. This occurs at all RPMs. It gets a little quieter after warmup. It makes me want it gone even more.

There is no obvious wear to any rocker arm or shaft, but a problem can of course be in hiding. But no pitting or scoring or other obvious damage to the rockers, the shafts or the cam. The timing chain looks fine. Oil delivery looks to be uniform and good.

If I don't want to live with this, what's my next best move? I keep landing on pulling the head and rebuilding it. It looks like removing the rocker shafts is a major pain with the head still on the engine. My car has about 185K miles, with the last valve train overhaul at about 90K (according to the PO).

are you sure you don`t have an exhaust manifold leak?

Fuel injectors have been known to tick.

dutch wrote: Thu May 01, 2025 1:45 am are you sure you don`t have an exhaust manifold leak?

I wasn't until yesterday. It's an exhaust manifold leak at number 6. Once the manifold is off I can see if it needs resurfacing or if it's just the gasket. I gotta say, that beats knocking rocker shafts off any day.

agreed. much better...

My car is back on the road after machining the exhaust manifolds and new gaskets. It sounds better than I could have hoped for. I can't tell you what a relief this is - the clicking was a constant irritant and a constant reminder of something unsolved, and now it's gone. But it's also generally way quieter, and with all the exhaust going out the tailpipe it doesn't smell at all. Now it's just the M30 sewing machine that revs up like a turbine. The manifold mating surfaces were far from flat. Hat tip again to Dutch for pointing me in the right direction.

glad you got it solved.