1931 Buick 60 series engine vibration

[Str8-8-Dave]

I wonder if other owners of 1931 Buick 60 series cars could share their experience with engine vibration.  I'm in the process of sorting my 1931 model 8-66S special coupe and, while not obnoxious, the engine does vibrate. I isolated the vibration to the engine, versus driveline or wheel vibration by simple experiment.  I observed vibration sets up at about the same engine rpm in any gear, it's not road speed dependent, it's engine rpm dependent.

 

Someone else did a pretty nice job of overhauling and restoring the engine, it fires on all cylinders, starts easily, has good oil pressure and does not smoke.  I very carefully overhauled the distributor and ignition is timed correctly at both 11 degrees BTDC and SYN-6 timing marks.  The carburetor has been completely rebuilt and works well.  That all said, I found via borescope inspection that original iron pistons were replaced by aluminum items and I have no idea if the rotating assembly was balanced, and I suspect it has not.

 

If you own a good running drivable 31 Buick 60 series car could you tell me the following:

Does your engine still have original pistons or were they replaced with aluminum?

Do you have some engine vibration or is it dead smooth?

 

Thanks in advance!

 

Dave

[DonMicheletti]

While it has been years since I owned my '31 8-67 Buick, it had replacement aluminum pistons and you couldnt tell when it was running it was so vibration free. I do not remember the piston manufacturer.

[Str8-8-Dave]

Thanks Don...

[Str8-8-Dave]

4 minutes ago, DonMicheletti said:

While it has been years since I owned my '31 8-67 Buick, it had replacement aluminum pistons and you couldn't tell when it was running it was so vibration free. I do not remember the piston manufacturer.

Were pistons replaced during a restoration you did or did someone else do that before you got the car?  Any idea if there was an effort to balance the rotating assembly?

Edited February 13, 2023 by Str8-8-Dave (see edit history)

[DonMicheletti]

I  rebuilt the engine when I restored the car. The pistons were replaced then.  Yes, the engine was balanced.  There is a ton of rotating mass.

[Robert Engle]

In the 1932 Specs and adjustments manual, there is a whole section  on vibration and the adjustment  of the torsion balancer.  I believe this is similar to the 1931 straight 8 engines.

 

Bob Engle 

[Str8-8-Dave]

2 hours ago, Robert Engle said:

In the 1932 Specs and adjustments manual, there is a whole section  on vibration and the adjustment  of the torsion balancer.  I believe this is similar to the 1931 straight 8 engines.

Hi Bob and thanks for this.  The torsion balancer, as described in the 31 specs and adjustments manual, is balanced statically and dynamically separate from the crankshaft.   It's purpose is stated as to counteract vibration set up by piston impulses which I interpret to mean vibration caused by sudden rise in cylinder pressure when fuel/air is ignited at the start of the power stroke.  The 8 crank journals are counterweighted to prevent deflection due to centrifugal forces.  I interpret that to mean the counterweights at each rod journal are responsible for cancelling vibration due to the reciprocating weight of piston and rod assemblies.  The 31 manual tells how to remove the torsion balancer by separating the halves and letting each half drop out as the crank is rotated to allow service of first and second connecting rods and pistons in the chassis with crank in place.  It warns against disassembling the weight stacks of the torsion balancer.    In my mind, to correct rotating centrifugal balance the crank and rods all have to come out of the engine.   The rebuilder probably skipped re-balancing and now it is off by the difference in weight of the piston/rod assemblies with iron slugs VS weight of piston and rod assemblies with lighter aluminum slugs.  To correct it the weight of each rod and piston assembly should first be determined and equalized, then the crankshaft needs to be run in a strain-gauged balance rig to find out how much weight should be removed from each crank throw counterweight to correctly offset the weight of the balanced piston/rod assemblies.  

 

Dave

Edited February 13, 2023 by Str8-8-Dave (see edit history)

[nat]

    

     Is the compression uniform?  Does the exhaust flow sound and feel smooth?

[Str8-8-Dave]

Exhaust sounds very even.  I haven't actually run a compression test but a cylinder short test verifies each cylinder is producing at least roughly same output.  There is no exhaust popping or intake side backfire when the speed of the engine is increased under load.   The car takes throttle willingly and has good power.

[nat]

     It's a handsome looking car.  

[ramair]

Dave, you have a great looking Buick, of course I might add that I have a earlier version of your car.

   I think I know how frustrated you are with the vibration, as I have a similar issue with one of my 8 cylinder cars.  I have a 1938 Packard super 8 that I bought 7 years ago.  I have receipts from a complete engine overhaul from a well know Southern California shop that specializes in Rolls Royce restoration, the work was done a couple of years before I bought it. I can’t believe that they might of forgot something like check the balance. 
so I checked as many things that I thought would cause the problem , short of total engine disassembly.  We started with compression check, distributor test, oscilloscope, carburetor rebuild, fan balance and vacuum leaks.  None of this helped.  On this car it idles fairly smoothly, vibration increases noticeable from 800 to 2000 rpm , above 2000 not noticeable.  I recently was able to talk to the owner that commissioned the engine overhaul and he said he took the car on a 2,000 mile tour from Southern California up to Canada and back and he felt it was Packard smooth.  So now I have it narrowed down to a possible imbalanced clutch that was installed after the owner above sold the car or the fairly complex multidisc harmonic balancer issue . I  understand that some people have gutted out the individual fiber disc and have rubber poured in them, hope I don’t have to go there. I am hoping it is something simple, the only thing that lurks in my mind is the crankshaft has counterweights that must be remover to reground what if one of those came off after rebuild! No, no , no!!!!!!! , off comes the pan

Edited February 14, 2023 by ramair
Misspell (see edit history)

[Grimy]

A tractor mechanic / lazy man's way of addressing the issue short of a tear-down:  Put a washer under a clutch bolt.  Worse or better or no change?  Then all the way around the clutch mounting bolts.

[nat]

5 hours ago, ramair said:

the crankshaft has counterweights that must be remover to reground what if one of those came off after rebuild!

    I remember the need to remove the counterweights on my 47' seven passenger.  Three bolts in each weight then ground off flush. That's a Packard thing.  I think the Buick crank is all one piece.

      A, or the weights haven't come off.  You would know it if they had.

      I think I remember that the Packard had some sort of witness mark on the flywheel to orient it with the crank.  It's been almost 50 years since I worked on the Packard.  I might have that mixed up with some other engine.

[Johan Boltendal]

Hello Dave, perhaps I can give  an idea , you know I'm into '30's Cads, have several cars repaired and know what you are exp. Have searched for a long time, for a cause, because I own one now,  that has this vibration. 

The original cast iron piston equiped engines run without a question, vibration free. The one I'm talking about now, had that one apart 3 times btw , still has the engine vibration from about just above idle and from there on it is present, to a degree where the inside rear mirror vibrates as well. 

It's irritating to say the least. Having this exp. now is an advantage when overhauling an engine now, where ever possible reline and keep the old piston's . I know this isn't science , but from what I have exp, this is the only conclusion I can come up with. Have talked to a few , it has been exp more then once, I learned.

Balancing moving parts will help and lessen the trouble, done that,  it will never run as good and more quit ,as with cast irons in place, my exp. Have never tried having alu pistons made to a comparable weight , might be a solution, gladly hear if soem one has been there.

Hope you will solve this isue one way or another, it takes part of the fun out of driving, it does with me.   Johan

[Mark Shaw]

On 2/13/2023 at 8:23 AM, Str8-8-Dave said:

Does your engine still have original pistons or were they replaced with aluminum?

Do you have some engine vibration or is it dead smooth?

Dave,

    My 1931 Buick Model 67 does have aluminum pistons and it runs very smooth. 

I suggest you make sure the distributor advance & dual points are properly adjusted & lubricated.  

[ramair]

Grimy, I thought about tying the clutch weight trick, but Packard thought otherwise, there is no access to those bolts unless you pull the transmission.  Which would solve the mystery.

 Johan I know exactly what you are saying about taking the fun out of driving, of course my wife says that when I hear the slightest noise when driving her car I go on a “witch hunt”, looking for loose change in the ashtray ect.  so I guess it’s normal for me to react or (overreact)

[Buick35]

If you've replaced the motor mounts maby the rubber is too stiff .I read on an MG forum that their car experienced a vibration due to new motor mounts. Just a thought.

[Brian_Heil]

A couple of comments on engine balance 

 

The balance being addressed is the balance of the rotating and reciprocating masses not the firing impulses.  Firing impulse imbalance is when a cylinder does not fire.  That we have all felt and is something entirely different.  A miss.

 

So back to things going round and round and others going up and down.

 

Let's start with the up and down masses or as they are called reciprocating masses.  Piston, rings, wrist pin, pin retention device (If so equipped) and the small end of the rod.  Small end of the rod mass?  What?

 

The rod is laid on its side and weighed on two knife edges at the center line of the large crank bore and at center line of the small wrist pin bore.  The weight of the small end of the rod is considered to be a reciprocating mass (the other, large end, is a rotating mass we will discuss in a bit).

 

Ever wonder why there are eight cylinders in a row or 8 in a 90 degree V8?  (Or 6 in a row?)  There are certain cylinder layouts of an engine where the reciprocating mass of each cylinder cancels that of another.  So in a straight 8, assuming you got the total reciprocating mass of each cylinder equal to all the others, they cancel out.  You just balanced the second order imbalance.  Second order?  Fancy engineer talk for a shake twice per engine rev which makes sense since the piston makes two movements (one up one down) per rev.

 

Now to rotating.  Ever wonder where the position and shapes of all those crankshaft counterweights came from?  They are there to cancel or 'balance' the mass of the large end of each rod and the bearing shell (if equipped).  The rotating mass.  They also balance the mass of each the crank journals and to get picky, some of the crankshaft mass/structure to get out to that journal.  But, if we do in this case 8 in a row, and do it right, the whole thing rotates balanced like it was just a simple bar of round steel.  No shake.  So how do you do that?  On a straight 8 it’s done with just the counter weight design, no ring/bob weights to balance.
 

On a V8, that large end of the rod mass you weighed above, you make 8 ring weights that match that mass plus 1/2 the mass of the reciprocating mass and bolt them to each of the eight journals.  Think of it as a two half shell ring bolted together onto the journal.  You put the crankshaft with these 8 equal ring/bob weights installed and spin it on a crankshaft balancing machine.   Think of it like the tire balance machine at the tire store where it spins and tells the tech where to add weight to balance.  Except typically on a crankshaft we make two opposing counterweights just a little bit too big so you drill away some mass to bring it in to balance.  Why drill and not add mass?  It's easier to drill in a production line and things attached to a crankshaft could loosen and fly off.  Never seen a drilled hole fly off.  Assuming you got all the large end of the rods to match and weigh the same, made 8 ring weights to match that mass and knew what you were doing on the crankshaft balance machine, you have now balanced the engine's primary balance, or first order balance or rotating balance.  Congratulations.

 

A further word on crankshaft design.  The location of those counterweights on more modern engines that run at higher RPMs contribute to some nasty bending and torsional stresses of the crankshaft.  You have to check for those after you figure out where and how big the counterweights are for balance and you may have to do some trade off to reduce stress in the crankshaft.

 

Torsional stresses (think of the crank as a towel you are winding up to wring out the water) are important in a long straight 8 crank and the torsional damper keeps the crank from setting up a torsional 'ringing' by dampening these.  Think of placing your hand on a tuning fork to calm it down.

 

So where does all this go wrong?  Most machine shops will weigh and match parts, (some don't even do that).  Most machine shops do not own a rather expensive piece of equipment called a crankshaft balancer.  They 'assume' the crankshaft was balanced once and if you use the correct rod large end mass (which they may or may not know what that should be), the crankshaft will still be in balance.  Sort of like guessing where to put the weights on your new tires and not running them on the tire balance machine.  

 

Some good news though.  If you upgrade to aluminum pistons, and they all weigh the same (the total reciprocating mass of each cylinder is equal), and you don't touch the lower end of the rod or the crankshaft, the engine will remain in balance or as balanced as it was before the piston change.  If it’s a straight 8 or 6.

 

And for the engineers out there I'm aware that these are rotating and reciprocating dynamic couples but I'm not going to teach a class in Dynamics of Solids.

And more good news for straight 6 and 8 engines, if all the parts are matched for weights, everything cancels out.  Also a straight 6 or 8 crank does not require bob/ring weights to balance the crank.  You balance spin a straight 6 / 8 bare. 

 

Edited April 8, 2023 by Brian_Heil (see edit history)

[Str8-8-Dave]

5 minutes ago, Brian_Heil said:

 

The balance being addressed is the balance of the rotating and reciprocating masses not the firing impulses.

Hi Brian, agree 100%, My best guess is the reciprocating mass IS the source of vibration, I just needed to hear from others that 60 series engines are capable of running perfectly smoothly at speed.  There is no doubt pistons were replaced, and my theory is whoever did the engine work did not balance the rotating assembly, pistons, rings, rods and crank.  The balance is off by the difference in weight of original iron pistons VS weight of replacement aluminum pistons.  At engine idle there is virtually no vibration.  As engine speed increases regardless of gear selected, the engine does vibrate. 

[Brian_Heil]

Dave, read the second to last paragraph I wrote again.

 

So, I think my rebuilt engine is in dynamic balance or close to being so, why is it now shaking?

 

Engine mounts.  Either they are side loaded because I'm not lined up on them the same as before.  Or the elastimor (rubber) has separated from the metal or cracked or hardened or gone altogether missing or the new replacement is not of the correct dampening rate (hardness).

 

Same goes for the torsional damper if it has an elastimor.  A failure here is also a concern for torsional failure of the crankshaft if you run it hard and long enough.  And even if correct, that piston mass change you made makes this damper tuned to the wrong frequency.  But this is a high speed dynamic issue if the tuning is off.  Most of us don't run the engine hard enough to worry.  But a torsional dampener with a missing or failed elastimor can shake and even make a terrible rattle noise.

 

 

[Brian_Heil]

Just so it's clear.

 

If you go to aluminum pistons which are what ~30% lighter.  As long as each cylinder's new lighter mass is matched and equal, they will continue to cancel out.

 

In simplified terms, two fat kids on a teeter totter that weigh the same balance.  Two lighter kids that weigh the same also balance. 

[Brian_Heil]

 The reason you feel the vibration force as speed goes up is because there is is an X²  term in the unbalance force equation.

 

The unbalance force you feel increases as a square of the engine speed.  IF you have an unbalance.

[Str8-8-Dave]

12 minutes ago, Brian_Heil said:

Dave, read the second to last paragraph I wrote again.

This is a revelation to me, I always thought if piston weight changed, you needed to balance.  I was around for the engine rebuild, someone else did that.  I'm sure they bought and installed a set of new pistons.  Engine mounts are very hard to evaluate in this car, you can hardly see them with all the splash pans in place.  They certainly could be the culprit.  The torsional balancer would require removal of the pan to inspect.  I can't tell from limited description of the balancer, whether it has rubber or not.  I would think if it has rubber it would be prone to fail after 90yrs in hot oil.  I do have engine drawings, I will see what I can learn from them.

[Oldtech]

I'm not familiar with the torsion damper on a 31 but I doubt highly that there is any rubber involved as it is inside the engine. If it is like the late sixes, they just had a weight on a pivot with a spring under each end.  If it was my car I would be looking at the clutch assembly as the prime suspect . 

[Brian_Heil]

I had to go run an errand but Oldtech hit on my next comment.

 

The clutch and pressure plate can be a source.

 

They are rather heavy and have a large diameter both are factors in the equation and can be big unbalance numbers.

 

I've seen where the Flywheel, clutch and pressure plate are bolted up to the crankshaft in the balance machine and they are then balanced and left alone and the engine is then assembled with them in place.

 

I once put a new clutch in a small block Chevy.  Got a new bad shake.  I rotated the pressure plate on the flywheel 180 degrees and it did wonders in reducing the shake.

Edited February 15, 2023 by Brian_Heil (see edit history)

[Brian_Heil]

So the next question is, did Buick bolt ring weights onto every crank and balance each?

 

No.  A master crank was built with ring weights and run on a balance machine.  Easy.

 

That same crank then has the ring weights removed and placed in the production balance machine.  The production machine has built in internal balance weights that can be adjusted to make up for the missing ring weights.  These internal weights are zeroed out on the bare (ring weights not installed) master crank.

 

This production balance machine also has two built in drill presses with a 3/4 in drill bit.  The skilled operator reads the angle an amount of unbalance and knows how much to drill and where on either of the end counter weights.  In modern times this drilling became all automated but several parts a day that were balanced had ring weights installed and the balance checked on the manual balance machine.

 

 

Edited February 15, 2023 by Brian_Heil (see edit history)

[Brian_Heil]

I've heard Buick used an internal torsional damper on the straight 8s but I've never studied one to know how that design was executed.

 

I've spent most of my time on earlier 1920's Buick engines  (and 8 years as one of the original engineers on the 3800 and its variants).  I still have people track me down and ask questions like how do I balance my modified 3800 supercharged race engine that I pulled the balance shaft out of?  That one's easy, you can't.

[Str8-8-Dave]

3 minutes ago, Brian_Heil said:

I still have people track me down and ask questions like how do I balance my modified 3800 supercharged race engine that I pulled the balance shaft out of?  That one's easy, you can't.

Yeah- believe it or not, they put that balance shaft in there for a reason...  Briggs & Stratton used a gear driven balance shaft in the "Synchro Balance" cast iron air cooled single cylinder industrial engines.  Some motorcycle engines and other car engines use them to great effect.

[Rock10]

@Brian_Heil,

Thank you for the lecture, Professor.

So much useful info. Engine balance can be confusing. You made it simple.

 

[Robert Engle]

To the best of my knowledge, there is no rubber in the internals of the engines for 1932 and earlier.  there is a balancer on the crankshaft that has flat leaf springs inside.  The manual has instructions on how to tighten the springs if they come loose.  The front mounts are rubber, but both of my 32 Buicks were running with original rubber in the mounts.  

 

Bob Engle

[Brian_Heil]

52 minutes ago, Rock10 said:

@Brian_Heil,

Thank you for the lecture, Professor.

So much useful info. Engine balance can be confusing. You made it simple.

 

I had a great teacher and boss. Richard A. Miller out of Purdue Class of ‘62.  He was an engine design expert at Buick.  Most of us went home at night and worked on old cars or hot rods or race cars or something.  His vice was golf.  We joked he didn’t own a pair of plyers. Wonderful man.  Memory like a vault. 

Edited February 15, 2023 by Brian_Heil (see edit history)

[Str8-8-Dave]

52 minutes ago, Robert Engle said:

The front mounts are rubber, but both of my 32 Buicks were running with original rubber in the mounts. 

Agree on torsion balancer inside the crankcase, no rubber there.  Both front and rear engine mounts do have rubber, rears are likely vulcanized to steel plates. 

 

 

[EmTee]

Did the engine builder convert the big end of the rod bearings to accept insert-type bearings?  Seems to me that would potentially upset the crankshaft balance unless the weight of the modified rods with inserts is the same as the original rod 'big end' with the babbit.

[EmTee]

9 hours ago, Brian_Heil said:

Some good news though.  If you upgrade to aluminum pistons, and they all weigh the same (the total reciprocating mass of each cylinder is equal), and you don't touch the lower end of the rod or the crankshaft, the engine will remain in balance or as balanced as it was before the piston change

Thanks for putting into words the thoughts I had been wrestling with in my head since this thread began.  It seemed that as long as all pistons were equal weight, the engine would remain balanced.  I didn't know the balancing process, however, once you explained it the concept makes sense.

[32buick67]

Sorry to hear about the struggles @Str8-8-Dave.

Dropping the pan, albeit not fun, might be needed before driving season to avoid harming anything.

Our engines are nearly identical, here are some pics, red arrows show the metal shims in the balancer ahead of cylinder#1, and the circle shows the drilled counterweight on the crank as @Brian_Heil mentioned, I think its a 3/4" production line hole as he also mentioned.

As @Bob Engle mentioned, there is no rubber anywhere in the balancer, its all metal.

Sorry I don't have better quality pics.

 

My engine has original motor mounts, which I have to admit seem worthless as squashed reinforced 91yo rubber, and I was going to replace them, but they seem to work fine.

With the original cast iron pistons and original engine setup (no rebuild) at 53kmi, it is as rotationally smooth at idle as it is over 60mph, so there is hope for your setup.

And...I replaced the old worn clutch with a newly lined clutch and rebuilt the transmission this winter, and spent a lot of time adjusting the pressure plate and making sure the rotating side of the driveline were correct, then I road tested the car to 60mph and all is good, except its too cold for me this time of year, brrrr.

For what its worth, as others have mentioned, I wouldn't rule out non-engine rotating components.

What if your engine is fine?!....I would still drop the pan to put eyes on the underside if you haven't seen it or don't have pics of it to your satisfaction...

 

@Brian_Heil the 60 series cast iron pistons weigh approx 26oz (pin not included), and Egge said on their best day they could only get a new aluminum piston to 11-12oz max for our 3.0625" standard bore.

Your estimate of 30% weight reduction is headed in the right direction, but its more like 60% weight reduction, but...with a rotating and reciprocating mass of about 180lbs in our straight 8s, who is counting, ha.

Thanks for the ME 101 distraction after a long day of EE work...thinking about rotating inertia calcs, jerk and jounce bring back memories with the 6 axis robots...and can be more interesting at times than NEC...

 

Mario

[Str8-8-Dave]

Thanks to all who responded to this thread.  I'm armed with several new ideas as a result of expert input from you.  Now al I have to do is get this 73yr old bod of mine back under the car...

 

Thanks!

[Oldtech]

Thanks for the pics 32. I figured it was "mechanical".  and yes, we know about the 7x body under the car.

[32buick67]

Dave, sorry if I missed it, but according to KISS principles I have to ask if you pushed the clutch in and/or shifted to neutral when at speed to see if the vibration changed?

 

[Str8-8-Dave]

5 minutes ago, 32buick67 said:

Dave, sorry if I missed it, but according to KISS principles I have to ask if you pushed the clutch in and/or shifted to neutral when at speed to see if the vibration changed?

 

The vibration WILL change if I push the clutch in UNLESS I hold engine RPM steady.  At engine idle, there is little or no vibration detectable.  Now, I had thought about just running the revs up in the garage in neutral and pushing the clutch while holding engine rpm to see if that affects vibration or stopping the car on the street and with clutch depressed in low gear revving the engine up to see what I get.  If by any stretch of the imagination doing so resulted in vibration going away that would mean clutch driven plate, IE friction plate splined to the input shaft of the trans, has an issue.  Clutch housing and pressure plate would still rotate flywheel speed and assuming no difference in vibration, housing and pressure plate or even the flywheel, could be the culprit I suppose.  The pressure plate would be least likely to cause vibration unless it was missing a shock dampening spring or a sizeable chunk of lining material.  Clutch housing and pressure plate are always at engine rpm and are much heavier components, more likely to cause noticeable vibration.

[Gene Brink]

On 2/15/2023 at 8:36 AM, Brian_Heil said:

But a torsional dampener with a missing or failed elastimor can shake and even make a terrible rattle noise.

 

 

Amen to that, Brian! Especially the awful noise...