1958 365 light knock at idle

[54cruzer]

I have a 365 that has a real light thud sounding knock at low idle. It appears after the car has been on an extended drive here in 95 degree heat, it goes away if you raise the rpms a bit.  I tried putting under a load (in gear braking) and it goes away.  If you really raise the rpms a bit it cant be heard either.  The odometer shows 70K, I believe the motor may have been rebuilt, real clean and no oil leaks in motor or trans, but who knows.  Also, fairly hard to start when hot, cranks up and runs perfectly otherwise.

I have had several cad engines in this era and they all seem to make some mysterious noises at some point, I always fear having to rebuild, as these engines are expensive compared to chevy etc.  I had one 365 that the fuel pump rod would cause this noise,
but this doesn't seem to be coming from there?  Any one have any similar issues, or know what this might be? thanks

[Jon S]

First question - Do you have ZDDP added to your engine oil?  These engines need the added Zinc and Phosphorous.

[dplotkin]

I have a Pontiac 389 that makes a similar noise only after reaching operating temperature. I used a mechanics stethoscope and could not isolate it to the bottom end. The noise seems most prominent using the scope at the power steering pump bracket but i've yet to run it without the belt to prove it out. I've cut open oil filters and found no shavings or anything to suggest bearing or bushing failure.

You should remove your belts and run it for a very short time to rule out accessories. You can run some drained oil through a coffee filter and look for debris. If that shows nothing it could be a cracked fly wheel or a bolt touching the inspection cover. Check that. Otherwise, like myself, if it otherwise runs well, leave it be.

Dan

[54cruzer]

I added a quart of mystery oil last oil change(is that a problem?)-( because I also have an intermittent tapping lifter-separate issue).
I see zdpp on here a lot, is it readily available, is there a substitute ?(what is it?)
The noise is a VERY light thud not a tick, and not like a crack or something hitting.  It sounds like a bearing knock--eek! but it doesn't behave like one, just don't want to overreact, I always assume the worst.
Sounds just like the fuel pump noise I had a problem with before, but not from that area at all-farther back but I can;t isolate it.

[Jon S]

I added a quart of mystery oil last oil change(is that a problem?)-( because I also have an intermittent tapping lifter-separate issue).
I see zdpp on here a lot, is it readily available, is there a substitute ?(what is it?)
The noise is a VERY light thud not a tick, and not like a crack or something hitting.  It sounds like a bearing knock--eek! but it doesn't behave like one, just don't want to overreact, I always assume the worst.
Sounds just like the fuel pump noise I had a problem with before, but not from that area at all-farther back but I can;t isolate it.

Marvel Mystery Oil is great stuff, so no problem there.  ZDDP additives are readily available at most Auto Parts stores - Advanced, Pep Boys, etc.  Also Red Line's Engine Break In Oil has sufficient ZDDP (8 oz/6 Quarts).

I first discovered the ZDDP reduction 10 years ago when my son's 1990 Mercury Grand Marquis with 16,000 miles started knocking at idle after an oil change.  We first thought it was attributed to a Fram oil filter, but soon discovered the ZDDP reduction in motor oil.  We added ZDDP and the knocking stopped within 15 seconds!  Amazing!

[54cruzer]

Well! I guess the ZDDP is the first (and easiest)thing I'll try!  Any other ideas?

[Jon S]

Start with the ZDDP.  If that resolves your issue you are done.  Good Luck!

[Smedly]

Maybe check the exhaust pipe to manifold connections make sure the nuts are tight. My 72 sdv sounded like the bearings were going out of the bottom end when at operating temp. noise also went away when put under load using brakes to hold the car. the noise was actually the Y pipe moving and hitting the manifold with each opening of the exhaust valves on the right side of the engine.
Sheldon Hay

[walt chomosh #23510]

Sheldon makes a very good sugesstion,checking for exhaust manifold for leaks. I've preached this to others,and even got bitten by it myself recently! My son did a total teardown on an inline motor,only to find a crack in his exhaust manifold.....walt....tulsa,ok

[54cruzer]

Actually just replaced the Exhaust Manifold gaskets and studs on that side, and it has needed tightening up, I'll check again.
I added some rislone zinc and phosphorous additive, no help yet.  Knock doesn't increase when revving or loading, only heard at low rpms.-Does that rule out bearings/rods?

[Jon S]

The ZDDP works almost immediately, so maybe the other guys are on the right track - Good Luck!

[Tlentz]

I once had a knock in an original Mustang 289 when I was 16, Every mechanic in the area I asked told me it was a rod bearing.  Decided at the time to swap for a 302, did the swap and gave the motor to the guy who built the motor.  Only to find out it was the harmonic ballancer not torched properly, infact it was loose.  Same thing on my  1950 Chevy 235.  The ballancer is pressed on and not bolted on, so it actually jared a little lose somehow. So I made a new woodruff key and got out a piece of wood and a 10 pound sledge and boom, pow, bang...no knock.  I love the easy ones!  I have never owned a 58' so Im not sure if that is pressed on or not, but the 64' does not have a bolt, it pressed so that is something to look at.  Sorry for the long story.

[Walter Youshock]

Another consideration is the fuel pump rod making a tap.

[signart]

What you are describing is a possible main bearing wear/failure causing a loss of oil pressure at idle. This is why you don't hear a noise above idle. Check oil pressure at idle. Good Luck.


Art Woody

[Smedly]

Did we ever solve this one?
Sheldon Hay