[T3] Knock Knock

[Jim Adney]

Daniel,

Use a long screwdriver as a stethoscope to try to localize the sound a bit 
more.

You didn't mention that we had to tighten up the #3 & 4 head studs when you 
were here earlier this summer. My concern would be that they have 
loosened again. Check the compression on that side, and, if it's bad again, 
retorque the bottom 4 studs again. If they are loose, see if they will tighten 
up and if they do, check the uppers, too.

This is a new case with 8 mm head studs. Since those are set in the case 
with inserts, I don't think those ever pull out of the case, but be careful to 
only torque them to the 8 mm head stud torque, which is less than the 10 
mm torque (because the thread pitch is different.) The correct 8 mm torque is 
18 lb-ft and is NOT shown in the Brown Type 3 Bentley, since our cars never 
came from the factory with the later 8 mm head studs.

If the head had come loose, however, the valves should have loosened up, 
too. But you said the valves were fine, so I'm puzzled, unless the valves had 
loosened and you tightened them. (If you have to retorque the heads, you'll 
also need to reset the valves.)

Keep in mind that the lobes on the cam serve both sides of the engine, so 
this noise does not indicate a cam problem.

Unfortunately, I can't think of anything good that might cause this noise.

As far as the ZDDP question goes, I believe it is MUCH more important for 
breakin of a new cam. My impression is that our cams are soft when new, 
but that breakin creates a hard surface thru work hardening. This is when 
proper lubrication is most important. I've always reused my old OE cams for 
this reason, and I've never had any trouble, but let's agree that my personal 
experience proves nothing.

Maybe send your youtube link to Gary Berg for his opinion...

Jim

On 16 Sep 2017 at 18:51, Daniel Nohejl wrote:

> Over the last few weeks, we´ve been trying to diagnose a noise......
> 
> In Madison, I thought I noticed what sounded like a loose valve. A day or so later, we discovered that the connection between our heater box and muffler was loose. We tightened it and applied some muffler repair and the noise vanished. Now, we have a new louder noise that has emerged over the last few weeks. It´s been hard to diagnose as the noise is generally loudest at cold start and for the 10 or 15 seconds the engine is running before the high idle kicks in. To properly diagnose, I had to pinch off the AAR hose at the air cleaner so I could get a low idle for a longer period. I also required the assistance of Sean, whose ear has proen indispensable more than once. Anyway, here are the other general characteristics of the noise:
> 
> 1. The noise is loudest at idle
> 2. Above idle, it sounds like a loose valve.
> 3. While cruising, it can barely be heard, even when driving next to a concrete divider on the highway.
> 4. After letting off the gas, the noise doesn´t return until just above idle. It definitely doesn´t start up right after getting off the throttle.
> 5. It´s clearly coming from the 3/4 side of the motor.
> 6. All valves are correctly set, there´s no excessive side play (solid rocker shafts), the springs are fine, etc. I´ve run the motor several times with the valve cover off and everything looks right. 
> 7. After unplugging the spark plug wires at #3 and #4, it´s clear that the issue is at #3. With the #3 wire unplugged, the noise diminishes by a good 80%
> 
> Here´s a video (credit Sean) that does a great job of capturing the noise
> 
> https://youtu.be/sxs1yrFLPl0
> 
> I know what all of this suggests, but I´m curious if what I´m describing rings any other bells for anyone. Or, if we know what it is, can it be fixed without splitting the case????
> 
> Thanks, 
> 
> Daniel
> 
> 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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