56 engine knock with hot engine only

[James Landi]

I think the white accumulation on that plug is a "good" clue. That's USUALLY an indication of excessive heat... and that could be causing pre-ignition.  Another data point---- I owed a '56 and had the engine re-built... ran great for around a year.  One day, with the a/c ( a very hot day), and the temp gauge a little over that magical 1/4 mark, it started to run poorly.  The issue--- a burnt exhaust valve--- one of the mid cylinders (this occurred back in 1975 when I commuted 90 miles a day) .  So, perhaps the infrared temperature gun is a good investment.  Also, the comment from the guy who rebuilt my engine way back when the car was only 20 years old, "You really needed a new radiator." UGH!  Hope this helps,   James

[Jay Friedman]

What I'm going to say may raise some eyebrows, but here goes.  When my '49 has a vacuum leak from a leaking hose, a knocking sound occurs which closely mimics a bearing knock.  The sound is created in the vacuum pump side of the fuel pump.  I have been scared silly more than once by this. 

[DaveO]

The RISLONE worked fantastic for me.

[Hillbillycat]

Hey Jay, I can feel your scare.
Fuel pump on the 56 is single action, not double action anymore. That can be ruled out. I could however cap all vac lines with the engine hot and hear if the knock goes away.

James, that "white" spark plug had not a white accumulation but was just plain clean on the ceramic. Like a totally new spark plug, except for the grey oxidation on the electrode. All the others had this haze of light brown on one side of the ceramic.
Too bad I didn´t take my camera to picture them.
But it would all make sense. Carbon buildup (at least some one the piston face, but if present there then present in the cylinder head, too), causing pre-ignition when real hot, leading to the white spark plug and causing excessive heat around this cylinder. And that could´ve caused the manifold to warp some and the new gasket to fail this soon.
Makes sense or is this just sugarcoating?

I definitely will run my Seafoam mixture through the engine. I mixed up a can yesterday and tested it in my lawnmowers first.

[Roger Zimmermann]

Years ago, I had a crack at one cylinder head from my '56 Sedan de Ville. If I remember well, the spark plug was also very clean compared to the other ones! However, the engine had no knock, but the exhaust noise was different left/right.

[Hillbillycat]

Hi Roger,

aha, a crack in the cylinder head itself or the manifold?

Did some reading and looked at spark plug pics online and it appears that my engine could also be running slightly lean. That, combined with the already very hot running engine on the 1956 models and an old radiator could very likely cause a pre-ignition on hot engine.  But why is that knock only heard at idle then? Not during acceleration?

CO-metering the exhaust should reveal a lean mixture and could be corrected and dialed in then with the CO-Meter.

Ignition timing s set at "A" mark and I´m running E5 95 ROZ gasoline with 1:200 2-stroke oil. I had tried to set ignition timing with a vacuum gauge once. Got up to 22Hg vacuum then and had much more zest, but engine got a lot hotter and was almost a no start. My engine reads around 14in Hg at "A" mark, but from what I learned that´s correct for the 56 with the change in the camshaft during production run (as noted in the SB).
I could try to set timing to the "C" mark for regular gas and see if the knock disappears.

I also listened to various engine knock videos on youtube and the only one that really nails my noise down is the one from the link in my initial post.

[Roger Zimmermann]

It was a crack at the cylinder head, between both valve seats.
The knock I heard from your video is not a pre-ignition knock.
Do you have maybe an electrical fuel pump in parallel to the mechanical one? I have such an installation on my '56 Biarritz and, at idle, there is a knock coming from the mechanical fuel pump when the engine is idling.

[James Landi]

Roger may be on to another issue I had with my '56 SDV from the early 1970's.  THe damn fuel pump is located well above the "oiling" surfaces below the oil filler.  What I learned is that before installing a new pump, one needed to pack the fuel pump cavity with grease!, so that the pump fulghum  and pivot shaft stay lubed--- so perhaps that's the noise--- a loose fulghum....   and yes, as he noted, mine,too, had a cracked head between the valves in one cylinder, but that contributed to low compression in the cylinder.  Hope this helps in your search.    James 

[Hillbillycat]

I indeed have an electric aux pump but in series, not parallel. It is located right at the fuel tank.
That video is not my engine, but it sounds exactly the same. I just found that video on youtube and used for reference.

Wouldn´t a lubricant loss on the stock mechanical pump make noise all the time?

Pump got changed by PO, so I don´t know if they repacked with grease. It´s only two bolts in a handy location, so at least that can be checked and repacked with ease just to rule this out.

Anyway, it´s so much speculations now. I plan to do the following:

Run the engine till knock appears, then I will pull spark wires and vacuum advance hose to see if they affect the knock.

Then I´ll do the oil system flush, new oil and carb adjustment. I´ll also check if TDC is matching my C marker on the balancer and re-set timing if necessary. While in there I´ll give the vacuum advance a look.

Since cooling system got mentioned I´ll flush that out, too. Maybe it´s time for a new radiator insert. We have a shop around that does this using your old radiator shells.

[Roger Zimmermann]

Put your finders on the fuel pump without engine knock and again with the knock. You will notice a difference. Or, as suggested, take a bit of a rubber hose and put it on the pump and at your ear.

[Daddio]

I would think narrowing down the source of the noise would be the first step. If you don't have a proper stethoscope, stick a length of heater hose onto an oil funnel, then put funnel to ear and move the end of the hose around.

[Hillbillycat]

Hi Roger,

what pump are you refering to? The electirc auxiliary one or the mechanical one?

I have a stethoscope for medical use. The car ones seem to have a long tube on the membrane. Will duct taping a vacuum hose line work? If not I can use the funnel hose device.
And yes, good idea to try and locate the knock at first.

Oh well, so much input for now and so little time. Besides we have so much rain this summer the car hadn´t seen much road and a lot of things to do get stuck on hold.

[Roger Zimmermann]

Sorry if I was not clear enough: the mechanical pump is doing a nock on my own car. Depending at its location, putting finger(s) on the electrical one is not easy!

[Hillbillycat]

Ok thank you Roger.

[The Tassie Devil(le)]

I have a stethoscope for medical use. The car ones seem to have a long tube on the membrane. Will duct taping a vacuum hose line work? If not I can use the funnel hose device.   

I have found that the Medical Stethoscope is not sufficiently sensitive enough to use in an engine bay, where there is a lot of noise.

Plus, the Mechanics one has the extended probe to get down and into the innards whilst keeping fingers well clear.   And don't press the probe too hard on the parts, as you need the internal metal spring diaphragm to vibrate.   Press too hard, and you lose sensitivity.

As for using the garden hose method, I find that a 6 foot length of 1/2" plastic hose works well, placing the one end up against the ear, and the other end, roving around the various parts of the engine, and actually placing the end up against the parts being tested.

Bruce.

[Caddieman53]

In regards to the video, that sounds like a wrist pin knock to me.

[savemy67]

Hello Hillbillycat (and all),

I have found that a solid "stethoscope" works well, as opposed to a hose.  The reason is that sound travels better through a solid than air.  One is not trying to amplify the sound, but to pinpoint it.

I use a broomstick without the broom bristles.  One end of the stick contacts the surface of a suspect area, and the other end contacts my ear.  Of course one needs to know what one is listening for, so I suggest listening to the various assemblies on a good engine so you have an idea of what they normally sound like.

A stick placed on an alternator will reveal the whirring of the bearing in the end frame.  A stick placed on a fuel injector will reveal the staccato of the injector pulses.  A stick placed at the base of an engine block will hopefully reveal normal (no knock) rotation of the crankshaft.  Iron and aluminum will sound different due to the difference in the density of the metals.

I listened to the video of the Buick, and there is definitely something to investigate.  It might help to use a process of elimination.  Remove the belts to rule out any of the belt driven accessories.  Disconnect the spark plug wires one at a time to see if the knock goes away at a particular cylinder.  While a stethoscope can help rule out, or narrow down a fault, you will have to take something apart to verify the trouble.

Respectfully submitted,

Christopher Winter

[Hillbillycat]

Hey, Caddieman53,

looks like you´re on the right track. This youtube video with confirmed damaged wrist pin sounds alike:
https://www.youtube.com/watch?v=1ZexzYxaldo

[Hillbillycat]

Well, I did some testing and documentation yesterday.

First of all:
The knock can be traced down to coming from the head at Cyl #3. This is the cyl with more carbon deposit inside and the spark plug insulator plain white inside, with no trace of a tan haze.
The knock, when present, is intermittant. Not constant. Same beat but different lengt of pauses. Like: tock......tock,tock...tock,tock,tock,tock.......tock...tock,tock...............tock,tock,tock.
Knock is louder on Dr, quieter on N or P. Still at idle only.


Here´s my diagnostics from yesterday´s evening:

Cold engine:
1. Confirmed TDC is on par with the C mark on the crankshaft pulley.
2. Tested each piston for movement via the spark plug hole with piston set short after TDC. Not a single movement to be felt, hence not any knock to be heard.

After startup:
3. valves are audible right after startup but no clattering. The valve noise does not disappear when at idle for a few minutes after startup and is also heard inside the car when driving the cold car.
4. Broomstick stethoscoped the valve covers, heads besides each spark plug, intake mainfold, distruibutor shaft, valley pan, oil pan, fuel pump.
Results:
No knock to be heard except for the fuel pump making a sound similar to the knock plus some sort of grinding sound.
Valves clicking uniformly on each bank/cyl.
5. Finger tested the fuel pump: You feel the movement inside but only very lightly.

Hot engine with dull knock audible.
5. Broomstick stethoscope again:
Fuel pump still makes the same noise not much more to be felt with the finger on top.
Knock can be heard around Cyl#3 in the head.

Spark plugs appear to be running lean.

Car hesitates on full throttle when hot.

[James Landi]

That fuel pump clatter is likely caused by lack of lube creating wear on the fulgham pivot (suggest you use bearing grease in the pump cavity).  Another simple suggestion:  Change the spark plug wire on the offending cylinder as well as the spark plug (and the rotor cap as a final attempt.  An internal electrical break in the plug wire or spark plug tower conductor or spark arcing  on the cap will create a RETARDED SPARK on that cylinder...  Had this happen with a marine generator  (drove me NUTS)---James