New noise developing...

[CajunKenny]

I may be a little paranoid here because I've already been through a rod knock and just went through a BHG; but, tonight there is a new engine noise.

I can only hear it once the car is at operating temp. Not at first start up. It is evident during 'in-gear' decels; but, not so much during acceleration. It sounds like a knock while in the car; but, with the hood up, it sounds like valvetrain.

The car has 6k on a full rebuild. The HG was supposed to be an MHG; but, wasn't and I found that out at 135 mph, around 5200 rpm @ 16psi.

I've heard some REALLY loud MK3 valvetrains.

I know this is probably a tough question; but, could this just be valves/shims starting to loosen up a bit? Maybe starting to break in...??

Does anyone have suggestions on how to diagnose a rod knock?

Thanks...

 

[dumbo]

Notice a change(a drop more importantly) in oil pressure? Cut open your oil filter next time you change your oil, squeeze the oil out of a few pleats, and shiny=bad. Good Luck...

 

[CajunKenny]

Haven't noticed a drop in oil pressure. I watch it like a hawk too!

I like the oil filter idea! Thanks!

 

[mattsplat72]

there is a real good FAQ on rod knock in Supracentrals sig

 

[strippedsup87]

Notice a change(a drop more importantly) in oil pressure? Cut open your oil filter next time you change your oil, squeeze the oil out of a few pleats, and shiny=bad. Good Luck...

Dumbo pretty much covered it here...Drop in oil pressure indicates a spun bearing, metal in the oil means bearing is spinning. Might try using a stethoscope on the oil pan or a long screw driver while its running to see if the moise is coming from there also...

 

[dumbo]

Dumbo pretty much covered it here...Drop in oil pressure indicates a spun bearing, metal in the oil means bearing is spinning. Might try using a stethoscope on the oil pan or a long screw driver while its running to see if the moise is coming from there also...

I didn't say spun, he'd know if it did. You'll still get a bit metal in the filter if knock is developing.

I totally missed you said it might be the valve train CajunKenny, you could pull the valve covers and check you cam caps/valve lash ect.

 

[CajunKenny]

Thanks Matt! I'll try one of SupraCentral suggestions today after work.

Dumbo: I'll try that too depending on what I find today.

I wouldn't be surprised if it is a rod knock especially after repairing a BHG. It's been about 2k miles since the BHG...

Thanks guys!

 

[Supracentral]

Another thing you can do.

Get a test kit here:

http://www.blackstone-labs.com/free_test_kit.html

Send your oil in for an analysis. It's cheap and it's not subjective. I do this on every oil change. It's how I developed my 8,000 mile change interval with Royal Purple on the MKIV. Anytime you suspect anything physical going wrong in the motor, send in a sample.

They will send you the results showing how many parts per millionth of contaminants there are in your oil. They have an engineer on staff who will give you a writeup with his conclusions/suggestions. For example you might see something in the comments section like "I'm seeing a lot of lead in your oil, you're likely experiencing bearing wear."

Once you've done it a few times, they can develop some "trending" and what the norms are for your car. Sudden jumps in certain contaminants indicate problems, and they will point them out to you.

You want to catch this stuff at the parts per millionth level, not when there's enough to see in an oil filter. If you can SEE metal in your oil, the whole motor needs a rebuild at that point.

Just about every component in the motor puts a different metal into the oil.

Contaminant|Source
Aluminum|Pistons, bearings, cases (heads & blocks).
Chromium|Rings, a trace element in steel.
Iron|Cylinders, rotating shafts, the valve train, and any steel part sharing the oil.
Copper|Brass or bronze parts, copper bushings, bearings, oil coolers, also an additive in some gasoline engine oils.
Lead|Bearings.
Tin|Bearings, bronze parts, piston coatings.
Molybdenum|Anti-wear additive, coating on some new rings (washes off as break-in occurs).
Nickel|Trace element in steel.
Manganese|Trace element, additive in gasoline.
Silver|Trace element.
Titanium|Trace element.
Potassium|Antifreeze inhibitor, additive in some oil types.
Boron| Detergent/dispersant additive, antifreeze inhibitors.
Silicon|Airborne dirt, sealers, gaskets, antifreeze inhibitors.
Sodium|Antifreeze inhibitors, additive in some gasoline engine oils.
Calcium|Detergent/dispersant additive.
Magnesium|Detergent/dispersant additive.
Phosphorus|Anti-wear additive.
Zinc|Anti-wear additive.
Barium|Detergent/dispersant additive.

 

[dumbo]

Supracentral, guess what I just ordered. We send out oil analyisis all the time for equipment at work, but didn't know the general public could get it done for so cheap. THANKS!!

As for my suggestion to cut open a filter, usaully by the time you hear knock there's a good chance you'll see a glitter in the right light.

Anyways much apperciated this could be fun or just an upset, very similar to my dyno coming up.:biglaugh::biglaugh::biglaugh::biglaugh::biglaugh::biglaugh:

 

[mk3tattoos]

supracentral.... breaking it down! very nice, i like the chart alot. cant wait to send in my oil sample, now that the motor is all broke in.

 

[Supracentral]

Here's what you get back from the lab. This is the analysis for my MKIV hardtop from April of last year:

This one let me know about a small intake leak that was sucking dirt through the motor.

Later analysis improved, and in the end I've been changing oil at 8,000 miles with good results.

So even though I'm buying expensive oil, I'm getting more than twice the life that I would get out of cheap oil. In the end it's actually saving money.

 

[CajunKenny]

Yeah, thanks Supracentral!

I ordered two kits. One for my PowerStroke Diesel and one for my Supra!

What I'll try to go outside and do here in the next little bit is short each plug wire at the coil pack and see if the sound goes away. I'm hoping that it won't!!!

 

[mattsplat72]

Hey SC I got one as well. In the how did you hear about us drop down menu it has NASIOC.com how can we get supramania in there as well.

 

[CajunKenny]

Ok everyone. I went out and shorted each plug to ground using a 12v tester and the sound did not go away. Two of them caused a different sound; but, the main noise in question never did go away.

So, with that info, what is the general guess. Valve train or rod knock?

 

[Supracentral]

Hey SC I got one as well. In the how did you hear about us drop down menu it has NASIOC.com how can we get supramania in there as well.

I emailed them about it - we'll see.

Ok everyone. I went out and shorted each plug to ground using a 12v tester and the sound did not go away. Two of them caused a different sound; but, the main noise in question never did go away.

So, with that info, what is the general guess. Valve train or rod knock?

I don't like guesses with engine noises. Pull the valve covers and check the clearances on your cams. It's easy, quick and it will eliminate them as a source. Check the torque on your cam gears. I've had more "top end rattles" that came from those than I care to remember. Also check your CPS, they've been known to make some annoying sounds too.

Start with the stuff that is easy to get to (like above) before you worry about the bottom end. Look at it this way, if it is the bottom end, you need a rebuild. If not, you'll likely find it up here first.

 

[CajunKenny]

I didn't think about the CPS...

I think I'll check valve clearances and cam gear caps first. I need to replace the valve cover gaskets anyway.

I'm sure I'll have more quesitons when I have more findings.

Thanks again everyone!