Need other perspectives on my engine noise

[dice2012]

Hi all, I've been trying to hunt down a ticking/knocking noise in my m20 for a while now.
When I start the car from cold, there's a knocking/ticking noise coming from the bottom end. Got the proper spring tool to make sure I was properly adjusting the valves, the valve noise sounds much better, but the knocking sound persisted(I'll link an old video I took but it was before I properly adjusted the valves so keep that in mind).

Ended up pulling the spark plug wire on individual cylinders, and I found that when I disconnected the spark plug on cylinder 1, the sound pretty much went completely away, even when the engine was completely cold.
Do the symptoms I'm describing sound more like a piston slap, or rod knock, or something else?
Also, where do I go from here to repair the engine? Or will I most likely have to replace the whole bottom end. Should I take my car to a mechanic or machining shop?

[e30davie]

Does the sound go away when it warms up?

Certainly doesn't sound good thats for sure. based purely on the video and your description id be inclined to check that #1 rod bearing.

[dice2012]

yeah it goes away almost completely when warm, thought I included this originally but I guess I forgot. Once it warms up, can't hear it when it's idling, though sometimes changing revs between 1k-2k rpm it happens.

[ADEN]

If it goes away when warmed up then probably you crank is still good just need new bearings. don't drive it till you sort it out.

It may be a piston pin knock since it goes away if plug wire removed.

Pop the oil pan off and the oil pump then grap the conrod with your hand wiggle it upside down and listen.

[dice2012]

If it goes away when warmed up then probably you crank is still good just need new bearings. don't drive it till you sort it out.

It may be a piston pin knock since it goes away if plug wire removed.

Pop the oil pan off and the oil pump then grap the conrod with your hand wiggle it upside down and listen.

Reviving this thread. Haven't been able to check the bearings yet bc of school but after getting greedy and thrashing the car for an hour (got a free bottom end so thought if it exploded that I'd have a backup plan anyways) I found that the knock completely went away, even at idle, revving between 1-2k rpm, all of that. Gonna start it up this weekend and see how it sounds, and if the knocking is the same or worse then I'll drop the pan and check the rods. Maybe it just needed to hit redline a few times :P

[e30vert]

Lack of oil pressure in one of the galleys? Perhaps an obstruction in one of the oil passages was cleared as you built up additional oil pressure. Just spitballing here.

[ADEN]

A sound like this indicates a major problem in the bottom end even if the noise has gone for now after listening to it again i think it might be a piston slap, mine was doing this only in the first 2 mins in cold mornings for more the 3 years i never revved it till the noise stopped, when engine removed for rebuild i found that the piston to bore clearance was way off.

If your engine loses oil between oil changes that might confirm the piston slap.

[dice2012]

Started it up again yesterday, noise was back and same thing happened with the noise pretty much going fully away after warm.
I don't think I've lost too much oil, I changed it back in April IIRC, and when I checked yesterday, the oil level was just between half and the low mark on the dipstick, compared to when it was just under the full mark after changing. Is that a lot of oil loss for driving maybe 2k miles since I changed it last? Honestly still relatively new to e30s (and old cars in general) so not sure what to expect. For context, I have to put a quart into my daily driver (2011 subaru outback) nearly every 1-2k miles to keep it above the low mark on the dipstick.
Also I don't rev it until it's warmed up and noise goes away.
Definitely pulling the m20 and doing a rebuild once winter hits to put an end to this problem. Should I send it to a machinist or is this all something I could/should do myself? I'm 100% willing to get the supplies, tools, and literature to rebuild a motor, just wanna make sure that there aren't steps that I should leave to professionals.

[ADEN]

On m20s try to keep it on full always these engines have problems with oil pressure go low on hard left turns due to oil pan design and low oil capacity causing bearings to wear much faster, Some tends to fill it above full to minimize damage when left hard cornering check das beast thread for more knowledge on the subject.

M20s are very easy, simple and fun to rebuild DIY (search the fourm and YouTube for info) if you go stock no strokers foucs on maintaining precise clearances and you are good to go.

[jbontke]

Its a lifter. Rod and Main bearings get louder as oil thins and gets hot. Pop the valve cover. Plug any vacuum ports from the valve cover. Start the engine and use a stethoscope. Put it on the cam caps between the lifters and you will find the one. I had the same issue and spent a while tracking it.