Help - Rod knock?

G50911 · 03-24-2014, 12:27 PM

Posted this in the engine rebuild forum but also want to post here for more coverage.

Help with knock noise

Ronnie's.930 · 03-24-2014, 12:33 PM

That's definitely not rod knock - rod knock is a much deeper, "thunk" sound, does not go away with heat, and gets much worse very quickly. It's obviously difficult to diagnose engine noises on these cars, particularly over the internet, but that sounds like an exhaust leak to me (maybe at one of the header flanges?), or a compression leak due to a broken head stud.

Reiver · 03-24-2014, 01:12 PM

Sounds like piston slap...if you have forged pistons (Nikasils) you can get that sound. It will quiet down when warm. V8's with FP's really sound off when cold.
Rod Knock does not go away when warm.

OldSpool87 · 03-24-2014, 01:43 PM

No clue on the sound. BUT sweet engine bay!!

Rich Gas · 03-24-2014, 01:55 PM

Lot of times it's just the fan hitting the housing, because of over tightening of the strap. Take the fan belt off and give it a try.

Reiver · 03-24-2014, 02:09 PM

Too slow to be the fan, my euro 3.0 with Nikies makes a very similar noise and has for thousands of miles.
Louder when cold, quieter when warm...goes away under acceleration and can be heard warm at idle...piston slap.
Hope that's the issue as it's really not an issue.

pors1968 · pors1968's Garage

I would recheck valve ajustement

G50911 · 03-24-2014, 05:48 PM

i just heard back from the shop and looks like cylinder #2's compression is super low (~70). going to check the valves in that bank tomorrow and see what could be going on. i hope it's nothing more than stuck valves...

Trackrash · Trackrash's Garage

You can isolate where the noise is coming from using a stethoscope. They are inexpensive at HF.

Put the car on some secure jack stands or a lift, and get under the motor when it is running using the stethoscope to pinpoint where the noise is coming from.

Ronnie's.930 · 03-24-2014, 06:11 PM

Quote:

Originally Posted by G50911

i just heard back from the shop and looks like cylinder #2's compression is super low (~70). going to check the valves in that bank tomorrow and see what could be going on. i hope it's nothing more than stuck valves...

Not to be Mr. Negative, but with that noise, and now the poor compression number, I bet they will find two or more broken head studs on that cylinder.

G50911 · 03-24-2014, 06:19 PM

Quote:

Not to be Mr. Negative, but with that noise, and now the poor compression number, I bet they will find two or more broken head studs on that cylinder.

don't jinx me now!

man i hope not. i just dropped the motor less than 3 weeks ago. i'd hate to have to do it again.

G50911 · 03-25-2014, 03:42 PM

so quick update... no broken studs. just tight valves. i just got this valve job done less than a month ago so pretty disappointed with the other wrench but glad i found a new one.

re-adjusted and now getting 150lbs!

other valves in same bank are off too. going to do the other side now just in case.

Reiver · 03-25-2014, 03:48 PM

that also cleared the noise issue?

pors1968 · pors1968's Garage

It happen to me with2.4 new valve guide ajust valve and after 10minutes poor running and same knock 50 psi had bent valve but your came back 150psi add some oil aditif and let run idle because next time temp goes up you wont be lucky.That why i said recheck valve ajustement.