Rattle at particular RPM and throttle combinations.

[Ken_P]

Ok, so I'm pulling my hair out a little bit, trying to diagnose an odd rattle. The car is a 1937 Packard 120 with 53,xxx miles.

 

Work recently done:

- In frame engine overhaul. New NOS Packard exhaust valves (replaced the incorrect Pontiac ones!!!!), honed the valves in, re-surfaced valve tappets (they weren't concentrically ground), new piston rings and rod bearings, cylinders honed. Timing chain was fine.

- Exhaust manifold heat riser valve rebuilt, manifolds planed flat.

- Distributor gone through (just visually, could NOT find anyone local with a distributor machine). [In hind sight, I should have just sent it out for rebuild] New points and cap. (ordered the wrong rotor or it would be new too!)

- Radiator rodded out and pressure tested. Re-packed water pump, verified distribution tube clean, pressure washed block and flushed with oxalic acid.

- Rebuilt fuel pump installed.

- New front motor mount.

- New throwout bearing, original was toasted. 

- Carb was rebuilt about 5 years again, fuel tank coated last year.

- Set the timing to 7 BTDC per the book. Tuned the carb.

 

The good - it runs well, pulls strong, and starts instantly, hot or cold.

 

The bad - 

 - Idle is a bit rough, especially for a Packard. Also seems to be a bit rough (engine vibration) when accelerating. For example, if I rev the engine with car parked and in neutral, it will make the steering wheel shake. I suspect ignition - with a timing light, the timing seems to fluctuate, maybe plus or minus 1/2 to 1 degree of advance. Working on getting a new distributor or mine rebuilt.

- Mechanical advance is quite a bit lower than spec - 3 at 900 RPM (good) but only 7 degrees of advance at 2200 RPM - book calls for 9 to 10 3/4.

 

The problem - I'm getting a rattle, that to my ear sounds like a heat shield or something. But, it appears to my ear to be coming from the engine (I crawled all under the chassis with my wife revving the engine, and the exhaust isn't moving). As best as I can tell, it is not the exhaust. The noise comes in when accelerating in first gear from 15-20 mph, 2nd gear at about 25 mph, and in 3rd gear between 35 and 40. I can make the noise disappear by giving it more or less throttle. Very sensitive to throttle position.

 

Temp is fine - 160 all day long. Oil pressure seems a bit low, topping out at about 30 psi. Factory mechanical gauge, haven't checked it out with a different gauge.

 

I know that's a long list, but this stupid rattle is driving me nuts. I'll get the distributor problem fixed, but I am skeptical that fixing that problem will solve this rattle. Anything else I should look at, or any thoughts?

Thanks!

Edited December 23, 2020 by Ken_P (see edit history)

[JACK M]

Check that your spark plug wires all go to the correct cylinders.

[Gary_Ash]

Let's plug in some numbers.  The 7.00-16 tires are about 30.6" diameter, 8.0 ft circumference.  The Packard 120 gear ratios were listed as about 1:1 for high ger, 1.53:1 for 2nd gear, 2.45:1 for 1st gear; rear axle ratio 4.09.  Converting your road speeds you listed when the noise occurs, here are approximate engine rpms for the speed ranges:

     15-20 in 1st = 1600-1850 rpm

     25 in 2nd = 1720 rpm  [25 mph = 2200 ft/min on road, so tire rpms = 2200/8.0 = 275 tire rpm.  4.09 axle ratio x 1.53 gearbox ratio x 275= 1720 engine rpm]

     35-40 in 3rd = 1664 rpm

So, it all comes out about 1700 rpm or ~30 revs/second.  On an 8 cylinder engine, there are 4 power strokes/rev so that's 120 pulses/second.  A frequency of 30-120 Hz is good for shaking things.  At ~1700 rpm, you are encountering the resonant frequency of something.  But, what is shaking and what is hitting?  Of course, the engine will move a bit depending on throttle position and load.  Can you follow the tailpipe all the way to the back end and look for anywhere the clearance is close?  Is anything loose inside your air cleaner?  Check all the plumbing around the engine and the horn bracket.  Look closely near the firewall to see if anything could be hitting there.  A mechanic's stethoscope is good for listening against the engine or sheet metal, but a 2 ft piece of rubber hose held up to your ear can have the other end pointed to various things and works pretty well for pinpointing noises.  Good luck with your search.

[Ken_P]

@JACK M Thanks! Checked, and again, everything is right and tight.

 

@Gary_Ash Thank you sir for the detailed reply! I appreciate your research and the technical diligence in your thoughts. I’ve inspected the exhaust system, and it is tight where it goes through the x in the frame, but it is centered. I’ll re-check!

 

I have some other thoughts as well. I’ll check it out and report back...

[wmsue]

Your logic sounds correct in thinking through the problem. I know zero about a Packard engine of that year but it sounds similar to a problem I had with my Buick.

I had the exact same vibration and running rough problem that you are having and my mistake was in the install of my flywheel. The flex plate on the Buick makes everything balanced when installed correctly.

Did you have the flywheel off when you did the rebuild and is it reinstalled correctly?

 

Good Luck

 

Bill

[Ken_P]

Bill, thanks! I didn’t pull the clutch, but I suppose the previous owner could have messed something up when a new clutch was put in... I’ll keep it in mind!

[Ronnie]

Have you considered that it might be a rod bearing rattling?  I know you said they are new but I would rule that out. Hold the RPM at about 1200-1500 and start varying the throttle up and down by a few hundred RPM. If you hear the rattle coming and going with the RPM you should check the rod bearings.

[WPVT]

You mentioned the noise sounding like a heat shield. A loose muffler baffle could sound like that, but you wouldn't see or feel anything loose. 

[Bloo]

Some thoughts...

 

Re-check valve clearance.

 

Disconnect the connection for the vacuum wipers at the intake manifold and plug the manifold side.

 

Try different spark plugs. Maybe some old ones, heck even some from another car if they are physically the right size and shape. Just try long enough to see if the roughness goes away.

 

Ohm test your plug wires. I would check from the plug end all the way to the distributor terminal in the inside. A few ohms if copper conductor, 1 or 2 k ohms if resistance wire. If resistance wire, the ohm readings should follow the length (longer = higher). If you find a bad wire, replace but wait for your new rotor to arrive before you get too excited about whether it fixed it (a bad wire will try to clobber the rotor by causing it to try and burn down toward the distributor shaft).

 

Inspect your distributor cap very closely under a bright light for cracks and carbon tracks. Also, look at the carbon button in the middle that contacts the rotor. It needs to touch the rotor. On some distributors the rotor may have a springy flat piece that reaches up to it. On most older cars like yours, the carbon button is spring loaded inside the distributor cap. Just make sure it is going to touch.

 

Look closely at your points and recheck the gap. What does the return spring look like? On many sets of points there will be a copper ribbon, but also a piece of silver or steel blue colored spring steel that actually does the springing. Sometimes the spring steel piece is separate and can get left out.

 

Check your firing order one more time. (I know that advice has to be getting old.) Which way does the distributor turn?

 

 

How do your points ground? If they are mounted on a plate that moves, for instance a plate that moves with a vacuum advance, there needs to be a ground wire from the moving part to the distributor case. It is often a special wire made of spring steel and copper to resist the constant bending. They break. If your plate is bolted directly and solidly to the distributor, disregard this.

 

Good luck. I have no idea about the noise. I am hoping unrelated is just rattling because of the rough engine.

 

 

 

 

Edited December 24, 2020 by Bloo (see edit history)

[Ken_P]

Wow guys - thanks!

 

@Ronnie - what would cause a rod bearing to rattle? Excessive side clearance or something? I did replace them all, so I was wondering about them, but it seemed odd that it was only at a specific rpm.

 

@Bloo - great list, and I’ve been through most of this already. Distributor rotates CCW. Vacuum ports are plugged, wipers aren’t hooked up. Just changed the spark plugs. Ohm checked the wires previously, non resistance, all under 2 ohms. The plate moves, and I checked the ground wire, but I’ll check it again!

 

Once I fix the distributor wobble (either bushings or a new unit), I’ll report back.

[edinmass]

Perform a cylinder power balance test, running the engine up and with the noise audible........and individually ground out one spark plug at a time. If the noise I related to any one rod or piston, without the pressure of combustion you should clearly hear the noise stop or drop off to almost nil. This is one of the most basic tests to perform an any engine of any age. Use a regular test light to ground to kill the spark. Please report back the result of the test. It doesn’t cost anything........and can be done in just a few minutes. Ed

 

PS- diagnosing a noise without actually standing in front of a machine is impossible.......I have tried watching and listening to video to try and help others remotely.........It just doesn’t seem to work........short of a rod sticking through the block. 
 

Bad bushings in the distributor would cause a running problem, especially down low......below 1500 rpm. It wouldn’t cause a timing rattle in any way that I can figure. The distributor should have been rebuilt when they did the engine.......along with the water pump, starter, and generator. Anyone who overhauls a pre war car engine and doesn’t completely go through ALL the bolt on accessories doesn’t know what they are doing. (It would make me very suspicious of the rebuild.)  I would also replace the radiator just for being old..........I know that sometimes the cost is an issue on the radiator.......but I have seen new engines fail due to poor heat exchange. 

Edited December 24, 2020 by edinmass (see edit history)

[Ronnie]

56 minutes ago, Ken_P said:

what would cause a rod bearing to rattle? Excessive side clearance or something? I did replace them all, so I was wondering about them, but it seemed odd that it was only at a specific rpm.

 

The rattle would be caused by excessive clearance in the bearings.  If that is the problem, it might start out as just a rattle and develop into a knock. Although it may not seem like it, Ed and I are having you test for the same thing. As long as combustion is putting downward pressure on the piston and rod you usually won't hear a rod rattle. Varying the throttle as I recommended or grounding the spark as Ed recommended is basically relieving the downward pressure on the rod momentarily allowing the rod journal to move inside the rod as the the rod changes direction from moving up to moving down during the rotation of the crankshaft. That change of direction is what produces the noise if there is excessive clearance between the rod bearing and the crankshaft journal.  The reason you raise the RPM to do the test is because the sound is more pronounced when the RPM is elevated.

 

I don't know what the oil pressure should be on your engine but low oil pressure could contribute the noise the rods make. Oil flowing to the rod not only lubricates the rod bearings, it also acts as a cushion between the rod journal and the bearing.

 

I hope I explained this well enough that it makes sense.

 

 

Edited December 24, 2020 by Ronnie (see edit history)

[Ken_P]

I did two tests today, both conclusively inconclusive!

 

1. Cylinder power balance test. Grounded each plug with the engine at 1800 rpm and again at 1500 rpm, equal results each cylinder, both in noise and loss of rpm.

 

2. Because the rattle is speed and throttle position dependent, I re-performed the same test at speed- pulled a plug wire, took a lap in a parking lot, noting the speed and intensity when the rattle came in. Again, unchanged for all 8 cylinders.

 

I am confident now that the rattle is some external factor. I am going to put the inner fenders on, verify the front clip is tight, and re-check the exhaust system.

 

As a side note, it’s amazing how smooth this car runs on 7 cylinders!

 

Again, thank you gentlemen for all the info, and I’ll report back once I find the culprit!

Edited December 24, 2020 by Ken_P (see edit history)

[Grimy]

The rattle MAY be occasioned by roughness (you said "rough idle").  Have you put a vacuum gauge on the vacuum wiper port yet?  Read the results--charts are on the web.  If the idle improves while the vacuum gauge is hooked up (thereby disconnecting the wipers, you might have a vacuum leak in the wiper(s) or the tubing feeding the wiper(s).  Have you run the car with the wiper vacuum plugged to see if the rattle is still there?

[Ken_P]

1 hour ago, Grimy said:

 Have you run the car with the wiper vacuum plugged to see if the rattle is still there?

Wipers are completely disconnected. Both vacuum ports on the fuel pump are plugged, as is the port on the manifold.

 

I will check engine vacuum in the next few days; I haven’t checked that since I got the engine put back together.

Edited December 25, 2020 by Ken_P (see edit history)

[Oldtech]

Vibration damper? 

[Ken_P]

1 hour ago, Oldtech said:

Vibration damper? 

I was wondering about that... any idea how to check it?

[ramair]

I have a 1938 Packard with the super 8 engine and I wanted to chime in and say that you have described the same exact issue that I have with my car.  I am down to either a vibration dampener or clutch issue and I have been reading your posts hoping for a clue that I can use.  My car idles and cruises at 50 to 55 like velvet.  The rest of the rpm range has a slight shake and a slight rattle sound, hard to describe . I talked to one of the previous owners who spent $15,000 on engine overhaul at a famous shop that does a lot of vintage Rolls Royce engines, he drove the car on a US to Canada caravan and said it was always Packard smooth .  After he sold the car to the next owner a clutch was installed , but he died and I bought the car, I am thinking that is we’re the problem is, I believe your car has the less complex vibration dampener , you could buy a used one and exchange it with yours and see if the problem goes away, if it does you can send to the dampener doctor here on the west coast great work and very reasonable . I have been trying to find another dampener for my car but no luck, the model that I have has disc and springs inside and I do not know what to do with it

[Oldtech]

On 12/25/2020 at 6:31 PM, Ken_P said:

I was wondering about that... any idea how to check it?

No! Other than a stethescope which may be difficult.   Another idea. Fuel pump??

Edited December 27, 2020 by Oldtech (see edit history)

[dictator27]

Have you tried putting the stethoscope on the transmission housing as close to the output shaft as possible while someone is running the engine at a speed that produces the noise?  If you can hear it there, do the same at the rear axle pinion housing, taking the necessary safety precautions of course.  If the noise is still there and about the same loudness, it is quite likely the clutch disc torsional dampener springs are loose in the disc.  The noise can be eliminated without having to remove the clutch.

Remove the driveshaft, and drill a hole in the yoke at one end, sized for a 1/8th pipe plug.  Rotate the driveshaft 180 degrees and drill another hole in the yoke at the other end of the shaft.  Get some flotation foam (2 part , used in small boats to keep them from sinking, and a small squeeze bottle like ketchup or mustard bottles used at hot dog stands and mix the foam ingredients in the bottle.  Put the top on the bottle quickly - the chemical action starts immediately - and push the tip of the bottle into one of the holes.  The foam expands at an incredible rate and actually causes the driveshaft to get warm to the touch as it travels down the shaft.  It will come out of the hole at the other end.  When the action stops, put the pipe plugs in and reinstall the driveshaft.

[Flivverking]

To though in more conjecture just for the hell of it.

Loose cam timing gear can make a light metalic rattle at verious speeds.

Same for wrist pins! But neither will cause rough runninng (usually.)

Sort out the engine issue first..rattle may just be an after affect as mentioned and not anything to do with the smoothness trouble.

 

Once a fellow in a model A club was going nuts trying to find a clunky single nock when slowing down or speeding up etc.

At a pick nick I leaned on his spare tire...clunk!  He hears it!  "Thats the knock"  Loose spare wheel...Ha!

[Ken_P]

Put the rest of the front clip together today, checked a million bolts on the engine, no change.

 

I won’t update this thread until I find the problem, because it’s not a project blog (that’s over on PInfo). 
 

@dictator27 - interesting idea- you’re suggesting the rattle may be torsional vibration through the drive train?

 

The problem with the rattle is that I can only recreate it at speed. I’ve got a few more things to try, and then I’ll get some chassis ears if I can’t find it.

 

Thanks again for all the help, and I’ll let you know!

[john hess]

Flat spots on cold tires.....

[Graham Man]

mechanical vibration damper? found this on our site...

 

https://forums.aaca.org/topic/201463-how-is-the-vibration-damper-removed-1927-packard/