High rpm vibration

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philip
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High rpm vibration

Post by philip » Wed May 15, 2019 10:07 pm

Long story so I will be brief. My 24 touring car has had a vibration since I got it.
I have new rings new valves new lifters rebuilt rear end. Coils are set on eccta
Anderson timer x plugs. Car cranks and runs good until I rev the motor I get a rough
Vibration. When I take off in low I can't build any speed because the vibration feels
Bad enough to damage something so I let the pedal out and chug into high gear.
Car runs good then up to about 30_32 mph then vibration again even with throttle up
Going down hill. Any thoughts would be great thanks philip

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John.Zibell
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Re: High rpm vibration

Post by John.Zibell » Wed May 15, 2019 10:14 pm

My guess is something is out of balance in the drive train. Unfortunately to find it will probably require a rebuild of the engine and transmission by someone that really knows what they are doing. May just be the flywheel is out of balance, but there could be more issues with the crankshaft and other parts.
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Jem
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Re: High rpm vibration

Post by Jem » Thu May 16, 2019 2:36 am

I had vibration which turned out to be loose rivets holding the brake drum to its shaft. That led to the whole trans shifting about because the tail shaft is bolted to the drum. Sorry to say, it sounds like you need to get it out and on an engine stand. I would look at Mike Bender's YouTube videos then work in reverse doing each check he does as you strip it until you find something out of true.

Thinking as I write, a bad 4th main could let the trans move around. First step is probably to pull the hogshead and inspect.


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Re: High rpm vibration

Post by Adam » Thu May 16, 2019 10:44 am

If it happens in low and high like you say, then it is definitely something internal in the engine and/or transmission. Not something in the drivetrain.

Without driving the car, it’s impossible to make much of a diagnosis. Potential vibration issues are highly subjective. Some people will pick up on a “normal” amount of vibration and consider it a catastrophic issue, while other people will have a borderline catastrophic vibration and are virtually unaware of it.

Most Model T’s that are original or rebuilt, but without any special balancing work, do have some vibration. The “usual vibration” is something that will be noticeable maybe from 30-35, seems to go away for a bit as the mph increases and then comes back again at some point in the 40’s. It's much better to drive a car like this at a speed just below where the vibration occurs instead of at the higher 35-40 speed where the vibration seems to go away again. Model T’s were on the market in a time when the national speed limit was 25. If you drive a bunch of different T’s you will generally find that on average, they seem smoothest at 25-30. Complete correct rebuilding, blueprinting, and dynamic balancing of the engine and transmission will generally produce an engine that is dead smooth from the point you shift into high gear, to past 50 mph. Even relatively small imbalances may cause noticeable vibrations at certain speeds.

The biggest potential vibration issues in my opinion are the following 2 items:

1). Magnets on flywheel of differing weights... At the factory, the flywheel was roughly balanced and the set of magnets installed on the flywheel were roughly matched by weights. If any magnets get replaced during the life of the engine, it is likely they may be higher or lower in weight than the originals. If 3 or 4 or more adjacent magnets are replaced, there can be a substantial increase in off-balance.

2). Improperly re-ground crankshafts... I have seen quite a few re-ground crankshafts where the third main bearing journal is not concentric with the flange. This causes slight off-centering of the flywheel and imbalance. It also can cause other misalignment issues, but the imbalance is the primary vibration issue.

There are a whole host of other issues, including parts that were never within spec from the very beginning, but I’ve found those two the most common.


Les Schubert
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Re: High rpm vibration

Post by Les Schubert » Thu May 16, 2019 11:40 am

Adam has pretty much nailed it!!
I will say, if you keep “chugging along “ you won’t have to worry about it very long, as that is the best way to break your crank!!
So please deal with it before it gets a LOT more expensive.


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philip
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Re: High rpm vibration

Post by philip » Thu May 16, 2019 12:23 pm

i too suspect either mains or the 4th main. i need to get in there and find it. philip


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Re: High rpm vibration

Post by Les Schubert » Thu May 16, 2019 1:03 pm

My experience is that if the rods need adjusting the centre main also needs attention


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Re: High rpm vibration

Post by rgould1910 » Thu May 16, 2019 5:32 pm

Adam hit the nail on the head as Les said. I'd like to add that crankshaft can be way out of balance as well. I had a crank that was 22 grams out balance that made an annoying vibration shifting from low to high. In addition the transmission drums can be way out of balance. Just a visual inspection of the drums will alert you to that. Anymore I balance everything that rotates in the engine and transmission. Like anything else, be careful who does the work!


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Re: High rpm vibration

Post by Mike Howell » Thu May 16, 2019 11:13 pm

It might also be that you have a mixture of heavy (early) and light (later) connecting rods. Perhaps remove the inspection cover and check before you pull the engine.
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philip
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Re: High rpm vibration

Post by philip » Fri May 17, 2019 8:16 am

rods are good i put a set of rings in it. i also put new valves springs and lifters. i dont see any thing obvious magnets look good
nothing loose that i can see. must be either mains or the 4th main. philip


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Re: High rpm vibration

Post by Adam » Fri May 17, 2019 8:43 am

FYI, Different weight magnets are not something you will be able to see. They can all look identical and be different weights.


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Re: High rpm vibration

Post by J and M Machine » Fri May 17, 2019 6:17 pm

What you are explaining is typical of old engines not being balanced.
We're so used to modern cars and forget what original cars are like.

It can be corrected by balancing the internal engine parts. Rods,pistons crank, flywheel.
Most often when the magnets come off others of random weights are re installed. For example the exchange magnet recharging service offered by some dealers.
They're not weight matching them and even still they would have to be weight matched to the flywheel.
Seeing the orginal commentor's post reminds me of a 1914 engine we rebuilt which I'm sure had been rebuilt numerous times prior to landing here.
Flywheel was so far off, I had to do some heavy metal removal to make it balance.
This particular flywheel assembly was off a total of 1000 grams. Which left unchecked would of done some damage.

If you'll notice two drilled holes removing weight which I've balanced flywheel assembly to tenth of a gram. Making it a smooth running engine.
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