Chattering noise from head after a track day

[JGood]

Car is an 87 325is. Stock m20b25, with a chip and long tube headers. I put this motor in last year (pulled the stock motor because it had 270k miles), and have approximately 6 track days on it. It has about 140k miles. It pulls hard, feels great. Dyno'd 145whp & trq, and has a smooth powerband.

I was at NJMP last weekend, and after one of the sessions, went to go get gas. I noticed some additional valvetrain noise at 2100-2200 on up, along with a higher idle (900-1000). The car still ran great and pulled fine. I took it out another session and ran my FTD with it. But it's still making the noise. Right at 2100 or so, it starts making a loud chattering noise, and it sounds like it's coming from the front of the motor, possibly the head. It's similar to valve tap, but a little different.

I pulled the valve cover and checked all valve clearances. One was a little loose, so I got it back into spec, and ran the motor. It's still doing it. It does NOT seem to do it when cold though.

The water pump does appear to be making some noise at idle, although that, the belt, and tensioner are new from when I put the motor in the car (~1 year and 2k miles / 6 track days).


Any ideas?

[nando]

are any of the clips that hold the rockers in place loose/worn? I had some that were actually so worn I could move the rockers side to side 1/4". it was pretty noisy!

[JGood]

are any of the clips that hold the rockers in place loose/worn? I had some that were actually so worn I could move the rockers side to side 1/4". it was pretty noisy!

I actually didn't check for that. But when I was moving the rockers around to measure the valve gaps, I would think I'd notice some side to side play, if it was bad. I'll take a look if/when I pull the valve cover again though.

[JGood]

Bump. Going to do a leak down test this weekend, any ideas of anything else to check?

[briansjacobs]

The car still ran great and pulled fine. I took it out another session and ran my FTD with it.
Any ideas?

well you know they say the motor makes the most power just before it blows up because everything is nice and loose.

Good luck

[jlevie]

Since this could have serious consequences, I'd treat it accordingly and not drive the car until the cause has been found and fixed. A mechanic's stethoscope may help identify the source of the noise. A bad timing belt tensioner or water pump are possibilities. But it is possible that the noise is coming from the head. If so the head and if there's nothing obviously wrong, the head will probably have to come off and be torn down to find the problem. I'm thinking worn cam journals/bearings, rockers, or valve guides.

[Sagaris]

Danger to the manifold?

[nando]

try taking the belt of the waterpump, start the car and see if it goes away. Another guy just had a 2500 mile Graf water pump fail on him, made some awful noises. Just because it's new doesn't mean it's good!

[JGood]

try taking the belt of the waterpump, start the car and see if it goes away. Another guy just had a 2500 mile Graf water pump fail on him, made some awful noises. Just because it's new doesn't mean it's good!

Never thought of that. Will do that before I fork over the cash for the leakdown tester and/or a new water pump. Thanks!

[JGood]

Pulled all the belts off and started the car - still tapping at 2k RPM's. It's like an on/off switch for the tapping, as I rev it up it starts, and as I rev it down it stops at the same RPM. It doesn't gradually start... it goes from not tapping, to tapping, at the same exact RPM. It also only does it when warmed up.

I pulled the timing covers off, and checked for tension on the belt and to make sure nothing looked unusual. The cam sprocket nut is tight, the belt is rubbing anywhere, nothing unusual at all. The water pump was smooth and didn't make any noise when I spun it.

I pulled the valve cover, again. All rockers were fine, no loose eccentric nuts, the spring clips were all in good shape, valve adjustments were perfect.

Finally got a leak down tester at Harbor Freight (for $30!) after coming up with nothing at Autozone, Pep Boys, Advance Auto, CarQuest, etc. So, I'll do that test this week. If it tests OK, I'm just going to ignore the noise. There's no point in tearing down an m20 to rebuild it, it would be much cheaper to just get another used m20. And I'll need to do that anyway if anything happens to this engine.

[jlevie]

Use a stethoscope to find out if the noise is from the head, or the block. The noise you've just described could be from a rod.

[JGood]

Will do. I actually just bought one from Harbor Freight yesterday, when I got the leak down tester. Whether it's from the head or block though, it will still need torn down, which I won't do.

[JGood]

What a piece of shit. The harbor freight leak down tester is a dual gauge setup. The second gauge is not identical to the 1st gauge. The 1st gauge reads 0-100 PSI. The second gauge reads 100-0% (for % leakdown). The process is to hook up the air supply, use the built in regulator to zero the second gauge, connect the cylinder hose, and wherever the needle on the second gauge goes, is your percent leakdown. The interesting thing is, the first gauge serves no purpose other then to tell you what the inlet pressure to the second gauge is. And that's a whopping 15psi. Which is not enough to accurately test an m20 IMO. I did some research, this is a known issue with these HF units, and it has been verified by HF tech support that it's a 15psi tester.

I did run it on all 6 cylinders and got about 15%.

I also used my stethoscope to try to track down the noise. I can't hear it through the head, block, valve cover, timing cover, injectors, anything. It happens at exactly 2k RPM's now, it's exact every time, and starts and stops instantly, not a gradual onset.

I'm out of ideas. I'm pulling the motor and putting in my spare m20.

[Jaxx_]

stupid question, but how's oil pressure?

[JGood]

stupid question, but how's oil pressure?

Hmmm... didn't check it.