High frequency flathead 6 engine vibration

[PT81PlymouthPickup]

Any thoughts on what might cause a high frequency vibration on acceleration in my 218 flathead engine? It runs flawlessly otherwise. Smooth idle and smooth at cruising speed with no noises. I've eliminated all other potential sources. Seems consistant at a certain rpm. All the mirrors on my truck momentarily vibrate at this frequency that you can not use them to see.   I'm toying with the idea of adding a harmonic balancer. The truck never had one, but if it would eliminate the vibration, I'm fairly sure I can adapt one to fit. My engine uses the wide belt pulleys. I'm not sure if they ever used the balancers with the wide belts? I'm thinking I could get hold of a 6 hole hub and a harmonic balancer and adapt a wide belt pulley to the hub.

Any experiences or advice on this topic and where to buy parts would be most helpful. 

[JBNeal]

I was told many moons ago that engine balancing starts with pistons, connecting rods and caps weighing practically the same, valve springs measured to within specs, and the crankshaft balanced.  The next rotational mass to balance is the driveshaft, then the tires.  Having engine and transmission mounts that are pliable enough to dampen vibrations is also required.  After that, put on some blinders and crank up the radio cuz these beasts will never be perfectly damped...a little imperfection is what many folks call "character"

[Merle Coggins]

You might want to check your engine mounts. Under acceleration the engine will flex more I the mounts than at idle or at cruising speed. If it flexes too much it could be getting your driveline a little out of phase causing your vibration. 

[NiftyFifty]

Typically high frequency equals either drive shaft or engine because their spinning so fast, tire and wheel is a slower more noticeable "wobble".  What are some details on the truck? Rebuilt engine, stock trans, stock driveshaft, and rear axle?  Might help where to direct you, but my first spot to look would be the driveshaft

[Don Coatney]

When parked in neutral revving the engine up do you get the vibration or is it just when moving? Same in all gears or just in high gear?

 

[PT81PlymouthPickup]

After restoring this truck many years ago it had this vibration. I thought then possibly the drive shaft?  I recently have made many changes. Replaced transmission with a Borg Warner T5, new differential with 3.73 gear, brand new drive shaft with a double cardan cv u joint. Runs and shifts great, but still vibrates on acceleration. So, I've pretty much narrowed it down to the engine. I can get it to vibrate a little by revving in neutral, but it seems more pronounced when driving. I rebuilt this engine about 30 years ago. We bored it and replaced pistons with new. All other components were in good condition. All new bearings and valve grind of course. It's been so long, I can't remember weighing the pistons, however I'm fairly sure I would have. This truck has not been used hardly at all over the years having racked up only a couple thousand miles. It's not bad enough to warrant a tear down, which is why I'm considering the harmonic balancer. It's a bit of a project to do correctly, but I'm  guessing it won't hurt anything? I should have been more articulate about when this happens (rpm, which gears, etc.). I'm fairly sure it does it in all gears. Right now I'm replacing the water pump so, I figured this might be a good time to install a damper?

[PT81PlymouthPickup]

Oh yeah! And engine mounts are new as well.

[BigDaddyO]

Has it done this ever since the rebuild?

The only other I can think of that hasn't been mentioned is your flywheel and clutch package alignment and balance.

[NiftyFifty]

Yep, could have a flywheel that needs a balance...and unless you were going for a balanced engine, most guys don't weigh pistons, and if you weighed them, you would remember grinding them to equal them out.  I'm not sure you will find any kind of harmonic balancer to fit that application, but I could be wrong...but if you did, likely to change your belt alignment as well

[PT81PlymouthPickup]

Yes, ever since the rebuild. I don't know if it vibrated before that, because it was not in driveable condition back then. I did change the clutch and pilot bearing when I installed the T5 but the flywheel and pressure pressure plate are the same that have been in there ever since restoration. Perhaps they could be suspect?

[PT81PlymouthPickup]

I found a hub and balancer that will fit, but it uses a narrower pulley than the original on my vehicle. I am a machinist by trade, so I can fabricate a pulley OK to match the others. Just not sure if it's worth the effort? Also the balancer I located on ebay is an NOS part.  Probably sixty year old rubber. I hear there are companies that can re vulcanize them?

[Don Coatney]

Did you use a "kit" for the T-5 install? What pilot bearing did you use? Did you correctly center the T-5 to the bell housing and flywheel? Do you get the vibration with the clutch pedal engaged and disengaged?

[Young Ed]

Time to take a look at that clutch and flywheel!

[PT81PlymouthPickup]

I did not use a kit. Bell housing was removed and machined to perfectly adapt the T5 and installed a roller pilot bearing. I don't believe the install has anything to do with the vibration. It did the same thing with the original 3 speed. Yes, I believe the vibration occurs both when clutch pedal is enagaged or disengaged. I think what I'm going to do, is go ahead with installing a harmonic balancer and if problem still exists after that I'll concentrate on flywheel and pressure plate.

[Don Coatney]

Looks great. Any photos of the pilot bearing and how it was installed?

[Jeff Balazs]

Any chance this is something simple like the balance of the front wheels and tires being out of whack?

 

Jeff

[PT81PlymouthPickup]

I wish it were simple Jeff. I've pretty much eliminated those things.  My father was a master mechanic who owned and operated a small auto repair business his entire career. He served his apprenticeship during ww2 on the carrier Midway as an aircraft mechanic. Anyhow, I grew up around this stuff and I have some skill, but I wish he were still alive to guide me like he once did. I'll never achieve that level. I'm pretty much old school and don't even have a cell phone which brings me to topic of not taking many pictures or documenting the stuff I should. I do remember installing the pilot bearing without any trouble. I did however have to change out the input shaft on the T5 for the correct length and had to have a custom clutch made to match the spline. I may have some info in my files, but no pics. God help the next guy who has to work on this truck! Lols!

 

 

 

 

 

 

 

 

 

 

 

 

 

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[PT81PlymouthPickup]

Oh yeah! Anybody knowing of a really good rebuildable mopar flathead L6 engine laying around for sale in my area I would like to know about it.  Did I mention, I'm pretty cheap too. Lols!

[Don Coatney]

I also installed a pilot bearing in my T-5 install. Did you have to enlarge the pilot hole in the crankshaft?

[Jeff Balazs]

Well I just thought I would throw it out there. Often times I think I have a tendency to over think these sorts of things......only to find a simple answer staring me in the face. Hopefully you will find a solution that isn't too difficult to implement.

Jeff

[PT81PlymouthPickup]

Yeah! I do the same thing Jeff. Too much thinking and getting too fussy is not always the best thing. One thing for sure! It takes way too long! Lols! 

As far as your question Don, I did not alter the crankshaft. It's been a while, but I'm thinking I found a 15 mm needle roller bearing that fit the T5 input shaft and I machined a bushing to adapt it to the Crank. Like I said earlier, I don't document much and my 60 year old beer pickled brain doesn't work like it used too. Lols!

[Jeff Balazs]

Yes I did it just recently. My steering had developed a fair amount of play and I had been putting off looking more deeply into it because I was under the impression I was going to have to remove the steering box to make the fix. I pulled out the manual to read up and mentally prepare for this operation when I saw that it might just be a simple adjustment from under the hood. Sure enough I had been over thinking it. A two minute under the hood adjustment and all is right with the world again. Couldn't have been any simpler!

Jeff

[Shovelhead Dave]

True high freq vibrations are caused by flywheel/clutch and driveshaft.  The vibrating mirror is the surest indicator of a high freq vibe. NOTHING else in the drivetrain

rotates fast enough to cause it. tires are low frequency only.

[PT81PlymouthPickup]

So what do you think Dave?  The harmonic damper just a waste of time? If I pull the pressure plate, clutch, and flywheel what then? I'm not sure where to take them to be dynamically balanced?

[Don Coatney]

This is how I did my pilot bearing mount. over 40,000 vibration free miles to date. I also used the Plymouth flywheel and pressure plate. with an S-10 disc, original throw out bearing, and a new driveshaft.