1925 DB - Vibration Period

[TonyAus]

My 1925 roadster has now been on the road for nealy 12 months. Pussy footing around the suburbs my inate mechanical sympathy has limited top speed to around 36 mph (determined by GPS - the speedo is hopelessly slow).

At that point I hit a vibration period - vison blurs and dentures rattle!

Today, in a rash mood I put pedal to the metal and manage to drive out of the vibration period - she flew well into the forties.

My questions are whether this vibration is the breed of the brute and what damage I might do driving beyond it. While nearly keeping up with the 80 km/h traffic I had visions of rods flying through the block or a broken crankshaft.

Am I being too sensative and will the old girl take this in her stride? Should I just buy a set of earpugs?

All comments gracefully receives.

Tony

[hchris]

Bit more info needed:

Are the vibes thru the steering wheel?

or, do you get the vibes with the engine running but the car stationary?

or, do the vibes remain if you put it in neutral at that speed?

We need to establish if its unbalanced wheels,engine or drive train so answers to the above will help.

[TonyAus]

None of the above. It is an engine vibration period which I assume is a sympathetic effect of imbalance or crankshaft windup.

The engine is standard, with the exception of aluminium pistons and has not been balanced. I am assuming that the period is something that was there from new. Does anyone else have the same effect?

[platt-deutsch]

My 25 has alluminum pistons original

[franklinman]

A common source of vibration in these motors can be from an improperly adjusted starter/generator drive chain, and yes it can be periodic. Also, especially when warm, excessively high RPM's can cause damage to the S/G armature windings. They can expand and I've actually seen a couple of cases where they will lock up against the fields.

[Rusty_OToole]

I have seen the same problem on a Model A Ford that had recently been rebuilt. The problem was that the new pistons were much heavier than the originals and threw the engine out of balance.

There should be no such vibration. When they were new they did not vibrate like that or no one would have bought them.

You say you replaced the pistons but did not balance the engine. That is bad. 4 cylinder engines of that period were balanced to quite fine tolerances. They had to be, there were no rubber engine mounts and road speeds were climbing.

It is very common for modern pistons to be much heavier than the originals. If you check the weight of the original pistons and rods you may be surprised to find they are significantly lighter than the replacements and practically identical to each other. You may have to take the engine apart and have it balanced, or at least make sure the pistons are the same weight as the originals.

To drive it the way it is, is to risk rapid engine wear and possibly a catastrophic failure or in other words the rod through the block.

Edited October 26, 2010 by Rusty_OToole (see edit history)

[TonyAus]

The original cast iron pistons were replaced with aluminium ones in 1957. I am not really in a position to compare old with new but it would seem logical that the cast iron variety were considerably heavier.

I find it hard to believe that engine balancing was a high priority for cheap mass-produced cars of the era.

If the balance was that bad should not the vibration be present throught the rev range? As I said, it is periodic and I can drive through the period.

My question remains, has anyone else experienced this in their four cylinder Dodge - there must be heaps of you out there who drive their cars regularly.

BTW, I checked the starter chain some time ago and its tension appeared OK. The only other possibility is the valve train. It has considerable valve noise which I put down to worn guides. The mechanic's manual suggests that this ailment may also result in vibration. Any ideas?

Thanks

Tony

[dwollam]

My 22 Screenside has a speed where it vibrates, then goes away and really smooths out at higher speed. It is best around 48-50 mph. 40-45 vibrates. It is rebuilt with aluminum pistons replacing original cast iron ones, pistons and rods were balanced, crank and flywheel were not. New valve guides and stainless valves.

[FMF]

The engine in my '25 is original -- never rebuilt (49,000 miles). I have no vibration whatsoever but I have to admit I do not push it to 45-50 MPH. My typical driving speed is 25-40 MPH and it purrs while in this range.

[RickBrinker]

The engine in my '25 is original I have some vibration but I have to admit I do not drive it to 45-50 MPH. My driving speed is 25-40 MPH

[TonyAus]

My 22 Screenside has a speed where it vibrates, then goes away and really smooths out at higher speed. It is best around 48-50 mph. 40-45 vibrates. It is rebuilt with aluminum pistons replacing original cast iron ones, pistons and rods were balanced, crank and flywheel were not. New valve guides and stainless valves.

I would have thought that at over 45 you would be too busy holding it on the road to notice any vibration. Scary stuff!!

[dwollam]

Those speeds are by GPS too. Not too long after break-in, I had it to a top speed of 62.7 mph and yes it was a handful! Empty back road, just ever so slightly down hill. 60 the other direction. When I am running around with the Model T guys, we run 38 mph.

[oldcar]

Anyone with extensive experience with early Dodges will tell you that the factory were indeed aware and conscious of the importance of engine balance. If you look inside a set of original cast iron pistons you will see that they are all marked with the individual weight. Every original engine I have dismantled has had a set of matched pistons. The original Dodge factory iron pistons were beautifully made and relatively light. Of course I am just a beginner having rebuilt only four of five Dodges (1921-5). The last one I owned was good for 70+ mph but it was 1927 and had a five main bearing engine. It had aluminium pistons and was fully balanced.

Edited January 16, 2013 by oldcar (see edit history)

[Pete K.]

Please keep in mind, the weight of the pistons should be matched to one another. Same with the rods. It doesn't matter what they're made from. The crankshaft is balanced to "itself", not the pistons. Many of the early engines did not have a balanced crankshaft, so vibrations WILL occur. Many vibrations at speed originate from the clutch/pressure plate, pilot bearing, or the transmission input shaft bearing.

[oldcar]

Unfortunately the Dodge Brothers had no control over the ham-fisted people who maintained their cars and later rebuilt their engines. Despite all their other faults they were brilliant foundry men and engineers. This is borne out by the number of their cars still surviving despite horrific abuse suffered at the hands of their owners. Prior to building cars under their own name they did all Henry Fords iron foundry work.

[2251DB]

My 26 sedan engine was rebuilt and the engine was balanced to reduce vibration at 40 -45 mph ,one thing I did notice that after several thousand miles I thought that the gear box noise in 2nd and 1st gear could be eliminated (wrong) especially as new gears wernt purchased, when I reassembled the tail shaft and universal joint I found that there was a

vibration present at 40 and above when the car was coasting down a hill. The clutch was depressed so that the engine was at idle speed and this proved that the vibration

was in the drive train ,this vibration didnt exist proir to my intervention and when under load was smooth.

Just another thought

[oldcar]

See my Post #15.

I rest my case.

[gundog99]

I would have thought that at over 45 you would be too busy holding it on the road to notice any vibration. Scary stuff!!

And wondering if the brakes will stop the car in time!!

[billstewart]

And wondering if the brakes will stop the car in time!!

That's a easy question [ NO]

[MikeC5]

60 mph Dave! You are brave one... In regards to the question "do the vibes remain if you put it in neutral at that speed?", are you saying they do remain or not Tony? You could hook up an electric tachometer and see what rpm it is occurring at. Then see if it will repeat under no load (stationary). In more modern machines, I encountered this kind of periodicity if a wheel was bent.