High frequency flathead 6 engine vibration

[Jerry Roberts]

13 hours ago, PT81PlymouthPickup said:

... Has the engine in your Dodge ever been bored for oversized pistons?  I just read where that could contribute to harmonics? ...

   I ran my engine with oversized pistons for two years and it was then sleeved back to standard size . No vibration ether way . 

[Jerry Roberts]

15 hours ago, PT81PlymouthPickup said:

 

   One of the members once said that you can use a narrow V belt in a wide pulley . If this is possible then you can do a test for vibration without modifying your new damper pulley . Just a test - not permanent . 

[Dave72dt]

I'd consider a narrow v belt a "maybe" at best.  V belts pull on the sides and if the wide pulley is too wide at the bottom for the narrow belt to contact the sides properly and runs on the bottom of the pulleys, it may complicate the issue.  It'll be a lot shorter belt than the wide belt as well so some trial and error of getting one to fit  may be in order.

[Plymouthy Adams]

on the narrow belt on the wide pulley...odds are the very bottom of the belt will bottom-out and leave you no ability to have the necessary friction to pull the components under load at speed without slipping...a belt riding on the very bottom of the vee has a tendency to roll

Edited October 8, 2016 by Plymouthy Adams

[Don Coatney]

5 hours ago, Jerry Roberts said:

   One of the members once said that you can use a narrow V belt in a wide pulley . If this is possible then you can do a test for vibration without modifying your new damper pulley . Just a test - not permanent . 

I do not know who said that but I disagree. Not a good practice.I would not advice it.

[Brent B3B]

2 hours ago, Plymouthy Adams said:

on the narrow belt on the wide pulley...odds are the very bottom of the belt will bottom-out and leave you no ability to have the necessary friction to pull the components under load at speed without slipping...a belt riding on the very bottom of the vee has a tendency to roll

Flip the belt inside out 

[PT81Jan]

Hi, I just got aware of that topic.
I think every possible source was considered in the comments, so it actually needs no further idea ... but I have a possibilty that at least might be worth to try out.
I also have an PT81 and I also had that kind of vibration. Idles very smooth and runs smooth up to about 85 km/h - 53 mph. (Whatever smooth means with that old trucks ). The vibrations that occured deterred me to go 1 mph faster!
In the meantime I had to remove and reinstall my transmission. I did not change something on the transmission that should have an effect on vibrations. But after I had reinstalled eveything, the vibrations where gone! Of course I was very surprised!

I could have left it as it is, but now I was noisy. Screwed off the propeller shaft flange at the transmission side, turned it by 90 ° and .... had some vibrations. Did the same by another 90° ... vibrations. I tested every possibility (another 90°, turned the shaft from front to back, ...). Found back to a installation that doesn`t cause vibrations.

In order to make it short: although my shaft and flanges seemed to fit without noticeable play, it must have had an slight effect on the unbalance oft the propeller shaft. Maybe not the perfect technical solution but very easy and cheap to test Best regards, Jan

Edited October 21, 2016 by PT81Jan
wrong description

[_shel_ny]

Had a 1973 Dodge B-100 van with a slant 6.

Swapped the engine out one winter. (outside)  I don't remember why. It had a sometime vibration before the swap. Not the reason for the swap. Still had it after the swap. Annoying vibration, but not horrible, any not all the time.

Years down the road. Spun a bearing, or maybe more than one. Replaced some bearings out in the yard. Ran it more miles.

More time passed. While returning from NY to Michigan from leave after leaving a Thruway stop while getting back up to speed the oil pressure light came on. I was able to make it to a friends house to leave the van. Rented a car to return to Michigan, and looked for an engine.

Found a Plymouth Duster with a frame that was giving up as a donor vehicle. Had grand visions of driving it back to NY to swap out the engine.  That plan fell through as the rust out proved to be to much for the front suspension to keep the tires from rubbing in places where they should not.

Borrowed a Toyota Landrover, and towed the van back to Michigan. Did the engine swap on base at the auto hobby shop.  No more vibration.  Difference was that this time I swapped the car engine flywheel, clutch disk, and pressure plate along with the engine. I was going to keep the larger clutch and pressure plate that was in the van, but just did the straight swap even though it was smaller.

 

[Don Coatney]

Interesting post Shel. I once had a Dodge van late 60's. About 73 or so I swapped the engine in a tiny one car garage by jacking up the van and dropping the engine on the ground and dragging it out from underneath. Installed the replacement through the side doors with a cherry picker.