High frequency flathead 6 engine vibration

[William Davey]

On 9/25/2016 at 8:42 PM, PT81PlymouthPickup said:

Well, I crawled up in the attic and yep, the original disc was definitely a 10 inch diameter. Sounds like a 9 inch disc S10 disc would have worked OK with a 10 inch pressure plate. I guess I was too fussy? I had a custom 10 inch disc made with a splline that matched the T5. Well, if I live long enough to replace it, I'll go with a 9" off the shelf disc. All this brings me back to my original dilemma. The harmonic balancer! I just ordered a hub and a balancer I found on ebay. (for almost $200.) Geez! I must be nuts, but hell or high water, I'm going to adapt it to my wide belt pulley. If it does not improve the vibration, the transmission comes out and I'll see if I can get the flywheel  and pressure plate checked out for balance.

 

PT - I'm new to this discussion, so please forgive me if this has already been considered. You're planning to put a harmonic balancer on the engine but why not disassemble the clutch/pressure plate first? Replace with stock S10 disc and have the pressure plate rebuilt/rebalanced?  I replaced the clutch and pressure plate in a Ford truck back in the day and had immediate vibration problems like yours. Swapped the pressure plate for another rebuilt (properly balanced) unit and the vibration was gone. IMO, you could eliminate possible causes with simple nut and bolt replacements and possibly avoid the much more involved balancer project.

[Shovelhead Dave]

Sorry for not getting back sooner. I don't think a harmonic balancer is the answer, Chrysler had competent engineers and they

didn't think it needed one. I would lean toward the driveshaft after reading all posts. As stated if no vibration in neutral that most

likely rules out the clutch/press plate/flywheel.

[NiftyFifty]

He did say it vibrated in neutral, just not as bad...that needs to be addressed before the DS

[Plymouthy Adams]

again...there are many factors in the upgrade that could be suspect...review of this documentation of the build may reveal a suspect component or process...in the absence of this documentation (the process of blueprinting) only a tear down and re-accomplishment can rule items in or out..

[PT81PlymouthPickup]

Thank you all for your inputs! It is most appreciated. I'm new to this site and very glad to have found it. Quite amazing to find so many still have interest in vintage Mopars. I agree there are several factors that could be suspect in my vibration issue. At this point, it is a process of elimination. The fact that it is not a serious vibration, I'm fairly certain I could run this truck for years without any major issues, but being fussy, I would like to get rid of the vibration. My harmonic balancer plan has come to a complete halt. I have discovered that the outside diameter of the mopar harmonic balancer made for these engines is just too large to work on the truck. It barely clears the cross member which does not allow enough room to get a belt on. So, I'll focus on flywheel and pressure plate. And! Yes, I know, I might still have a problem after that which could be in the engine. If that's the case, I'll attempt to locate a rebuildable core and put together an engine more precisely than I was capable of 30+ years ago.

I began this post hoping to find someone that may have installed a balancer to L6 mopar in the 39-47 trucks.  I'm not sure why, but Chrysler's engineers certainly installed them on some of their car engines. One thing for sure! The vintage mopar balancer will not work on the pickups.

[Jeff Balazs]

Just looking at your photo......sure looks like the rubber front mount has either collapsed or is missing? Maybe it is the angle of the photo? Should be about 3/4" between the engine plate and the mount.

Jeff

[PT81PlymouthPickup]

Yeah, It's the angle of photo. The rubber is amazingly perfect. I bought this NOS balancer and other than some light surface rust it looks like it was made yesterday. Too bad I can't use it.

[Jeff Balazs]

Hmmm.....how much bigger in diameter is the balancer. One thing that comes to mind is the height of the rear mounts. There are at least 2 or 3 different height rear mounts available........and if they were too high that would make the front end of the engine lower to the cross member. Just a thought.

Jeff

[Jerry Roberts]

5 hours ago, PT81PlymouthPickup said:

I have discovered that the outside diameter of the mopar harmonic balancer made for these engines is just too large to work on the truck. It barely clears the cross member which does not allow enough room to get a belt on. 

Are you aware that some of the mopar harmonic balancers were made with a flat spot that was used as a space for belt installation ?

[Don Coatney]

I had clearance issues when I built my car due to the fact I installed a Desoto engine that is 2 inches longer than the original engine. I had to modify my front cross member  as well as shorten up the harmonic balancer as pictured below.

[PT81PlymouthPickup]

At the full diameter there is only about 1/32 inch clearance. Even with a flat positioned downward the belt will not fit.

Wow! Don, you really did some serious work there. I had to modify one cross member to get the T5 to fit, but at this point, I'm not willing to modify the front cross member for a harmonic balancer that might not fix my vibration problem anyhow. I'm disappointed there was not enough clearance. It would have been a simple job for me to adapt or turn a pulley. I'm surprised that you were able to weld a flange to your balancer without melting the rubber or throwing it out of balance? Did you have it re vulcanized after welding?

[Jerry Roberts]

Is there enough room to install the belt on the damper pulley , then bolt the damper onto the engine , then put the belt on the upper parts , then test drive ? 

[PT81PlymouthPickup]

Yes, but I have to adapt an old, or make a new pulley first. The balancer would be spinning too close for comfort to the cross member and when a belt change was needed it would be a royal pain. Not a practical solution, but you are correct, it could be done.

[Jeff Balazs]

That is what link belts are for. On a side note I have rotating stationary equipment in my shop that I have fitted link belts on. Reason for this.....elimination of vibration....and boy do they run smoother than a conventional belt. I can remember a time when lots of old cars either had one fitted or one in the trunk as a spare.

Jeff

[Jerry Roberts]

1 hour ago, PT81PlymouthPickup said:

Yes, but I have to adapt an old, or make a new pulley first. The balancer would be spinning too close for comfort to the cross member and when a belt change was needed it would be a royal pain. Not a practical solution, but you are correct, it could be done.

 My thinking wasn't intended as a complete solution to the problem , only to help find the cause of the vibration . You could then eliminate the lack of a damper as a  cause .   

[PT81PlymouthPickup]

 

Hey Jeff! You must be older than I am if you remember linked belts on old cars. Lols! Your comment got me to thinking. I just read that the reason they used the wide belts on early vehicles was to dampen vibrations. Not sure if that's a fact or how that works? I have been using a cogged belt on my truck. I'm wondering if perhaps a solid belt would be a better choice?

You're definitely right Jerry! I'm just too lazy to make the pulley if I can't keep it on there.

[Jeff Balazs]

Hey what can I say........I just hung out with a lot of old school people And I had an Uncle who swore by link belts.....and swore at everything else.

Bottom line is you actually can eliminate a lot of vibration using them. A lot of conventional belts are not made all that well and will cause vibration right out of the box. This is probably harder to notice in an automotive application than on stationary equipment....but trust me it still applies.

Jeff

[Jerry Roberts]

PT81 1939 Plymouth truck , Are you sure that it is a 218 ?  Could it be a 218 from a later model car that came with a damper ? Perhaps the damper was removed and the old stuff from the original engine was placed on the front because the damper wouldn't fit . For example : a 1939 Dodge truck model TC came with a 201 engine . Have you researched the number on the side of the engine to verify what it was made for ? If the engine came originally with a damper , for sure you would want to put a damper on it again .  If you want to post your engine number  someone can look it up . 

[PT81PlymouthPickup]

Jerry, I was afraid someone would ask that question. Lols!  At this point, I'm not sure of anything! It's been 37 years (1979) since I rebuilt this engine. I think you're correct that orignally it would have come with a 201? I'm completely sure it was not the original engine that came with the truck when I got it. There was a engine replacement tag on the firewall and there were / are no numbers on the block where they should be? I'm fairly certain at the time we rebuilt the engine we were able to deterimine it was a 218. I cannot remember how. Perhaps casting numbers? Anyhow, Yes, this engine could have come from a later model car that had a harmonic balancer? I've heard by some that it would make a difference and others say not? Some say they were added only for extra smooth running on the higher end cars? I really don't know what the facts are?

[Jerry Roberts]

Here is some general information on dampers printed in Motors Auto Engines & Electrical Systems  ;  Printed in 1976  

[PT81PlymouthPickup]

Thanks Jerry for the information! It reads just like what my engine is doing. I have read other articles that led me to believe a damper might solve my issue. What is confusing me, is that if undesireable harmonics was an issue, why didn't Chrysler Corp. install them on all the inline flatheads? It sounds like there were more L6 flatheads without them than with them? Engine balancing and harmonics are evedently two separate issues. An engine could be balanced to perfection and still produce undesireable harmonics. It's more of a Physics anomoly of the engine designs. Some engine designs are more prone than others. I was thinking I could possibly adapt a smaller diameter damper which would allow me to get a belt off and on, but I also have read that these dampers are specifically designed to counteract known harmonics of different engine designs. So, not being an automotive engineer, it might be a waste of time? The high frequency vibration I have is minimal and only occurs shortly on acceleration. I think a lot of people might not even notice it? Overall, my truck runs really well. There is also a possiblity that something else in my driveline could be causing or exasberating this vibration. Perhaps, as one responder to my posting indicated I'm just being too fussy? Using anecdotal evidence only, I surmise that all of the mopar L6's may have had this issue. Chrysler Corp. may have installed the dampers on the higher end Chryslers and Plymouths? I'm thinking my best course of action is to reinstall the original crank pulley and get back on the road. I'll pay closer attention to details of how and when the vibration occurs which might lead to solving this mystery? Does this sound logical?

[Jeff Balazs]

Well it sure would be interesting to know if adding a dampener assembly made any noticeable difference on your truck. I have not really felt this in my truck.......but then my 3/4 ton has a fluid drive and might behave a bit differently as it is probably quite a bit longer and heavier than yours.

Jeff

[Jerry Roberts]

PT 81 , When I was a kid in a family with 5 children and we were noisy , my dad would say  " put a damper on it ! "     Perhaps that is what they did at mopar when a new engine was developed that was noisy with vibration .  My 1939 Dodge car engine doesn't have a damper and doesn't have a vibration . I can see by your photos that you took great care to make your truck nice and it is understandable that you don't want that vibration. 

[PT81PlymouthPickup]

Now that's funny Jerry!  I remember that phrase too. Has the engine in your Dodge ever been bored for oversized pistons?  I just read where that could contribute to harmonics? I can't remember exactly how much, but I know my engine is at least .030 over.

Thanks for the compliment! I tend to over do things, and it's bugging me I can't get a handle on this.

[JBNeal]

Chrysler had a different view on cost back then, with 3 examples:  oil filtration was an option, as ppl who did not rack up a lot of miles could get by with changing their oil when it got dirty (or once a season or maybe once a year, like how we service push mowers nowadays); PCV systems, designed for military applications, were not implemented on any vehicles (or stationary engines) but instead used the draft tube setup, giving us "the drip" and smoke puffing from the engine compartment, so we could motivate Nixon to sign us up for the EPA decades later; and harmonic balancers were used on finer automobiles as they were the only ones that "needed it"...everyone thought a buzzing car was normal back then