Seeking help in identifying a "vibration" that occurs on the 26 Star Coach Continental Red Star 6 Cylinder (14L) engine. While reving up the engine in neutral, standing still, it reaches a point of vibration evident in the shaking of front fenders. It has a similar vibration while driving about 25 mph. Wheels and tires have been eliminated because of its performance standing still. Something is out of balance it seems. Any clues?

Don't mean to sound personal but wonder if the balls in your U-joint need to be replaced.

Mac: Thanks for the suggestion, but yes, new hard rubber balls were installed in the U joint with no change in the vibration. Have exhausted many suggestions, hence the plea to find someone who may provide another clue.

How are your rubber engine mounts?
These rubber mounts if stock are usually rock hard and crumble like dry bread. The other thing could be you fan beeing bent or worn out. Are all the engine mounting bolts tight?

Franz Fraitzl

Where Are You From? Vancouverdurantstarcarconnection.ca

Ron I don't know how your distributor is set up but on my W5 if I don't advance the dist. right it will give a vibration and since yours is when reving and at 25mph it might be something to look into.

Franz and Mike: Thanks for the possible "diagnosis" -- will report back soon!

Ron:
Unfortunately, with most any engine there is a great many things which could cause a car to vibrate at a specific RPM. The good part is it’s easily reproducible at idle conditions.

My first question for you is, how long have you owned the car and has it always vibrated like this or is this something new that just started. The reason I ask this is it was a common practice in the ‘30s and ‘40s to repair just one cylinder as needed with an oversize piston. The result being a vibration at specific RPMs. I have found this condition with cars as late as the ‘50s. My dad came across a ’35 Ford once that had 4 different piston sizes in it!

Also, I have seen badly worn cam bearings and broken valve springs create RPM specific issues. However, these usually require the engine to be under a load before the vibration becomes apparent – seldom revving in idle conditions.

External to the engine, partially fouled spark plugs or bad plug wires can cause similar problems. However, again, these usually require the engine to be under a load before the vibration becomes apparent – though I did once encounter a spark plug cable that would arc to the block at a specific RPM. You could audibly hear the snap-snap as it did so.

Fan belts too can cause vibrations – especially ones making a long to an accessory like AC. Loosening or tightening the belt in question should help in eliminating this as the source.

I have driven vehicles with both motor-mounts completely broken and cars that had half of their clutch disc missing and encountered no discernable vibrations and so I’m inclined to look elsewhere for the source. However, I have installed flywheels (which were balanced to the crank shaft) at the wrong position and induced a vibration similar to yours. Also, if the front pulley is loose, it could cause a vibration.

I hope I haven’t obfuscated things too badly for you. Good luck.

Curt Smith.

Ron:
I agree with Curt. First question, has this condition developed after you have completed some repairs to the engine? Or has this just developed without any major repairs being done.
The reason I say this, is because I had my 22A engine rebuilt (1932 Frontenac) and after the rebuild it ran rougher than ever before. Vibrated, and seemed as if everything was fighting inside. Went to another machine shop and this machinest found the problem. When the crank was originnaly reground, the crankshaft journals were not all on the same plane, the distance from the centre line of the journal to the top of the cylinder block varied from journal to journal. The second machinest was able to regrind the crankshaft, making sure the centre line of each journal had the same measurement to the top of the cylinder block. This made all the difference in the world. ( Hope you can understand this)
This condition would only occur if you have had the crank reground. It would develop by itself.
It is always wise to get everything that spins, balanced as a unit. You would not believe just how much this affects the smooth running of the engine.
Hope all of our suggestions haven't overwhelmed you.
Best of luck, and smooth running.
Gord.

Now you have all got my curiosity up, does the (14-L)have a counterweighted crankshaft? Could this vibration be part of its inharent design?...Bill

Bill. All the Durant engines I have run usually run real smooth and almost vibration free. They all have the nice heavy large vibration damper on the front of the crank shaft. And no there is no counter balances in these engines. There is one of our motors that are a real vibrator and that are the 1930 Durant 4 cylinder 407 car W8 200 cubic inch engine. It is a large 4 banger and has no vibration damper in it. Course that was built for the Mason Durant built trucks. The dampers rubber can rot and be causing problems and the clutch mechanism can be out of balance as well. So there are lots of things to check. Even a simple thing like a bad spark plug or spark plug wire with one hole not firing right can cause vibrations. Doctor doctor. Later Lance

Colleague Advisors:

We bought the 26 Star Coach last December and believe that the vibrations were there when we got the car.

Prior to purchase it was driven occasionally for about 10 years (less than 300 miles) after a complete detailed frame off restoration, including interior.

At some point the head was off but what was done to the engine is unknown; we’re now in the process of finding out from the original owner.

All pistons are firing.

We varied the distributor settings which makes no difference.

The Spicer Joint balls have been replaced by us recently with no change.

The vibration exists from idle to speed and under load and not.

We have loosened and tightened the fan belt and there is no change, and no visual damage to the fan itself.

The engine appears to be bolted (4 bolts) directly to the frame, front and rear, without any gaskets or bushings between. Did the 14L and Star have rubber or vibration dampening mounts? Does anyone have a good picture or knowledge of how they are supposed to look? There is no indication in the 1926 Star repair manual of any engine mounts.

Ron did you do a compression check to see if you have a dead cylinder or not ?

Ron I was talking to a good friend of mine also a car guy he tells me a broken crankshaft will do the same , depending on were it brakes you will have all cylinders working, good compression, all cylinders firing but alot of vibration and shaking going on ?

Ron,
If you haven't already done so, you might check your flywheel for any unusual or free movement both in a rotational direction and by flexing with a small bar, you may be able to determine if your flywheel bolts have came loose and or if you may have a broked crank as Steve just mentioned....Just a thought, Bill

Colleagues: Wow! Thanks for the response and clues to pursue the vibration mystery. Will update the report on findings soon. Ron