M20 clunking/knocking loudly on cold startup

[thatphysicsguy]

Recently did the headgasket on my b25. I got the head cleaned and resurfaced. The machine shop also pressure tested it and it had no problems.

After I got everything back together, I did a valve adjustment and fired her up. Still pretty noisy.

Let it cool down for a while, did another valve adjustment, then turned it back on.


So my question is: does having a clean head with less gunk floating around make the clicking noisier? should I keep trying to adjust those valves till it goes away? are there other problems that might cause this? from what I've read, sometimes the eccentrics get a notch worn in them, but that isn't the case here.

Edit: after firing it up and letting it run warm a couple of times, I realized the sound isn't the usual valvetrain click, it's more of a clunking sound. It goes away once the engine warms up.

[101]

I had the exact same issue with a newly built head so I'll share my dumb-ass mistake ...

I had set the valves to 0.025 thousandths instead of 0.25mm (which is 0.010 thousandths). It sounded awful to say the least.

Just something to double check.

[Ether-D]

Timing belt a tooth off resulting in piston/valve contact? How much material did the machine shop remove? Were the depth-dimples still in the head?

Where did you place the feeler gauge? The consensus says that you should put it between the cam and the inside of the rocker. Then set it to 0.007 (I did 0.20mm) because of rocker ratio. The reason to measure it there is because the eccentrics, over time can beat a depression into the top of the valve and the feeler when placed there bridges the gap giving an incorrect setting. -----> )l) <----- That's my best shot at a drawing of this phenomenon.

I once replaced a head (w/junkyard head) and when I got it back on after rebuilding it, I had a ton of snap-snap-snaping when I would drive. I had ever so slightly bent a valve on the spring side while putting the cam (or rocker shaft) back in. So it would stick open then get forcibly shut by the piston. It was a pretty violent sound though. Probably not what's going on with you.

On another note, the pulley spacer you made for me is still performing exactly as it was intended. Thanks again.

[thatphysicsguy]

Timing belt a tooth off resulting in piston/valve contact? How much material did the machine shop remove? Were the depth-dimples still in the head?

Where did you place the feeler gauge? The consensus says that you should put it between the cam and the inside of the rocker. Then set it to 0.007 (I did 0.20mm) because of rocker ratio. The reason to measure it there is because the eccentrics, over time can beat a depression into the top of the valve and the feeler when placed there bridges the gap giving an incorrect setting. -----> )l) <----- That's my best shot at a drawing of this phenomenon.

I once replaced a head (w/junkyard head) and when I got it back on after rebuilding it, I had a ton of snap-snap-snaping when I would drive. I had ever so slightly bent a valve on the spring side while putting the cam (or rocker shaft) back in. So it would stick open then get forcibly shut by the piston. It was a pretty violent sound though. Probably not what's going on with you.

On another note, the pulley spacer you made for me is still performing exactly as it was intended. Thanks again.

Thanks, glad it's working out well for you!

The noise (more of a knocking actually now that I think about it) goes away when warm, so maybe it's no issue at all?

[dnguyen1963]

What oil are you running in your car? Incorrect oil can cause a lot noise.

[thatphysicsguy]

20w-50 castrol

Oil isn't it

Maybe it's just natural m20 noise? it is dramatic on cold startup, but goes away once warm. It's different than usual m20 valve click. A much deeper knocking sound

[my_bmw_sucks]

Having the exact same issue. Had my head rebuilt while doing a head gasket. Adjusted the valves on install; lots of noise. Adjusted again after 500 miles; still lots of noise. Going to give the cam/rocker method a try versus measuring at the eccentric.

thatphysicsguy: if you figure out what your noise issue is please let us know.

[Ether-D]

I've heard that a nice fresh top end can finish off a well used bottom end. I don't know if there's any truth to it. Could it be rod-knock?

[AwakenNoMore]

you sure your not hearing injector tick?

[Gary Yogurt]

you sure your not hearing injector tick?

Yes, this. Stethoscope it to see if it's actually coming from under the valve cover. The injectors are loud.

[thatphysicsguy]

The noise goes away once the motor is warm (which is a good sign kinda) and is more of a clunking/knocking sound rather than valvetrain/injector click.

[jeffnhiscars]

I've heard that a nice fresh top end can finish off a well used bottom end. I don't know if there's any truth to it. Could it be rod-knock?

There is some science to this the idea being that the improved compression from a valve job adds too much stress to a worn bottom end. I have to say that an engine "clunk" is never normal so I wouldn't ignore it.

[ADEN]

20w-50 castrol

Oil isn't it

Maybe it's just natural m20 noise? it is dramatic on cold startup, but goes away once warm. It's different than usual m20 valve click. A much deeper knocking sound

Exactly what i have opened head twice and the sound is there even after engine rebuilt, it is been there for more than 8 years lol.

I think it is a rod/main bearing clearance issue since i changed the bearings twice during 8 years they always came badly worn, but even after new bearings sound is still there .

[digger]

Could be piston slap if it goes away when engine warms up

[thatphysicsguy]

Hey Everyone, just checking back in for the sake of posterity on this. This was years ago that this happened and while I can't quite remember all the details, I think I eventually traced it back to either a loose pulley or the cooling fan slapping the radiator shroud. I ended up getting the motor mounts changed and rechecked the belts and everything was running smoothly from there.