M35A2 Continental Multi Fuel - Harmonic Balancer cracked - why?

[Mayor Joe]

Front seal on my 1971 M35A2 began leaking for the second time in 4 years.
In both cases, we found the hub of the harmonic balancer cracked along the key way slot. This part of the hub rides inside the front seal. I'm trying to understand what conditions could lead to the this type of failure? Have any of you seen this before? A good friend made the first repair. I'm currently doing the second one. I used a puller to remove the balancer (per TM) and had no issues removing it. The front seal came off with it and was holding the broken piece in place. I posted a thread in the classifieds looking for a new balancer, but I'd sure like to understand the cause.

Help greatly appreciated!

Thanks.

Joe W.

 

[Jeepsinker]

I would have to suggest metal fatigue over time has something to do with it. Everything has a service life and these engines being unbalanced and vibrating like a junkie stranded in Antarctica is hard on balancers.

 

[oddshot]

I would have to suggest metal fatigue over time has something to do with it. Everything has a service life and these engines being unbalanced and vibrating like a junkie stranded in Antarctica is hard on balancers.

The exact same failure ... on the same engine ... over a 4 year time span?

That isn't normal service life ... something ain't right.

How many miles did you cover in four years?

Is the key worn ... even a little bit?

Did you put on a NOS part or a used one during the last repair?

When you took it apart this time, did you happen to check the torque?

When you put it back together, you might want to check to see if the crankshaft is bent.


I had a good used one from andy3's engine. I'd have been happy to share it with you, but I dropped the dang thing and broke off a hunk. Fortunately, I missed my foot.

Sorry for your trouble.

Please keep us posted.

 

[rustystud]

When you installed the first one, did you use an installer or did you just take a hammer and pound it one ? You really need to install all balancers with the proper tools.

 

[Mayor Joe]

The exact same failure ... on the same engine ... over a 4 year time span?

That isn't normal service life ... something ain't right.

How many miles did you cover in four years?

Is the key worn ... even a little bit?

Did you put on a NOS part or a used one during the last repair?

When you took it apart this time, did you happen to check the torque?

When you put it back together, you might want to check to see if the crankshaft is bent.


I had a good used one from andy3's engine. I'd have been happy to share it with you, but I dropped the dang thing and broke off a hunk. Fortunately, I missed my foot.

Sorry for your trouble.

Please keep us posted.

Ok- good questions and thoughts -

I agree about the fact that two in four years would not seem to be from service. I only drive the truck in the summer months for shows, parades and events. I do drive it a lot, but not daily. I would say about 700 to 1000 miles a year (that would be high). I am often pulling a trailer with another vehicle - either a WC53 or an M37 (6 or 7k plus 3k trailer). In both situations when the seal failed, I was towing earlier that day. I didn't notice any unusual vibration.

The key may be worn, it does have a small grove in the side. I plan to replace it. I'll also look closer at the crank and key way.

The he first replacement was used. I did not check the torque. I noticed that it was VERY difficult to remove the retaining volt for the first two or three turns. I'm trying to find the torque spec in the TM.

i purchased a replacement yesterday from a gentleman who removed it from a crate motor so we're not sure if it's new or not.

When I called suppliers, I was surprised to learn that two separate suppliers indicated that they sell A LOT of balances, but we're not aware of a specific reason or the condition I'm experiencing.

i appreciate your thoughts and questions, I would certainly like to understand the cause. I'm going to take photos of the parts this morning and will post them here later today.

THANKS AGAIN !!

Joe

 

[Mayor Joe]

The first one was installed by a good friend (very knowledgeable regarding deuces - he has two). HOWEVER, while installing the first replacement, he tapped it with a hammer and broke the edge of the pulley.

He replaced that one and installed it using a tool like a reverse puller. I don't know much else about that install, because I wasn't there.

Another good friend and full time diesel mechanic has the install tool and will be there when I install this one. He's also researching possible causes.

I'll be posting photos later today and keep updating this thread.

i appreciate everyone's thoughts and suggestions!

Thanks

Joe

 

[gringeltaube]

....................I'm trying to find the torque spec in the TM.
....................

150 pound feet.



G.

 

[Keith_J]

The harmonic damper isn't there to correct imbalance, although many have this provision. The purpose is to damp crankshaft torsional vibrations. Diesels need this far more than gasoline engines due to higher compression ratios and sharper ignition conditions (diesel clatter).

prolonged idling and aged rubber rings are two of the greatest contributors to failure points on standard dampers. Vibrations are energy, when the damper absorbs this energy in the rubber ring, it gets hot. Rubber is cured by heat so eventually, the rubber over cures or gets hard. Also dry rot and fatigue set in.

 

[Mayor Joe]

150 pound feet.



G.

GREAT Thanks!!

 

[Mayor Joe]

The harmonic damper isn't there to correct imbalance, although many have this provision. The purpose is to damp crankshaft torsional vibrations. Diesels need this far more than gasoline engines due to higher compression ratios and sharper ignition conditions (diesel clatter).

prolonged idling and aged rubber rings are two of the greatest contributors to failure points on standard dampers. Vibrations are energy, when the damper absorbs this energy in the rubber ring, it gets hot. Rubber is cured by heat so eventually, the rubber over cures or gets hard. Also dry rot and fatigue set in.

VERY interesting. So... If it's old / dry rotted or hardened, the vibration isn't absorbed which could cause the balancer itself to fail (crack)?

Can the rubber be inspected?

 

[Jeepsinker]

150 pound feet.



G.

If my feet weighed that much I'd be going nowhere fast.

 

[Keith_J]

VERY interesting. So... If it's old / dry rotted or hardened, the vibration isn't absorbed which could cause the balancer itself to fail (crack)?

Can the rubber be inspected?

yes, the rubber should be visible, at least where it is injected in between the hub and weight ring. I believe the hub material is gray cast iron so it is brittle, even more so on the key way as that is a huge stress riser. Most are cut with a key way broach that has sharp corners.

 

[DavidB]

Can the rubber be inspected?[/QUOTE]

 

[DavidB]

Was the package torn ?
Good luck with repairs.

 

[gringeltaube]

150 pound feet.

If my feet weighed that much I'd be going nowhere fast.

Haha, very true...
I sure had some fun too when I found that term on page 305 in TM 9-2815-204-35 (1964)
It's an old- but good book, BTW.



G.

 

[Mayor Joe]

Below are some photos I took yesterday. QUESTION - while going through the TM's regarding removal and replacement of the damper and seal(s), it mentions TWO front seals - an 'inner' and 'outer' seal. When searching for front seals on line, I only find one - and none of the vendors mention that TWO are required. Anyone know if it's a matter of installing two of the same seals? I'm checking this morning to see if there's enough room in the timing cover to fit two. If so, the fact that there was only ONE installed previously - could be a contributing factor??? Also, the TM mentions a 'Key seal' , but I'm not sure how to identify this part / part number.

I sure hope we find out the answers so this will benefit others.

Thanks again to all who have replied - I really enjoy learning more and more about these vehicles / engines.

Here's some photos I took of the Damper (now that I know it's not a balancer)
Damper with broken piece - the crack on the right is along the keyway

Side View of the Key (same wear appears on BOTH sides)
A closer look inside the Damper hub
A close look at the timing cover where the seal(s) sit
Side view of the crankshaft looking into the timing cover

 

[Jeepsinker]

Joe, looking at that key and the way that damper hub broke, I would say that is your cause of failure. You need not worry about a second seal, and you can apply silicone sealant to the key way to help seal it.
see how it has worn the key way slot by the crankshaft too? That is no good.

 

[R Racing]

That key is flat worn out !! So I would say there is your problem. Also the center hub looks removable from the horamonic balancer. So perhaps that piece could be had by itself. Is the crank worn any from the key beating it up?

 

[DanMac]

Since this is a tapered shaft, my guess would be over tightening, which would "stretch" the hub on the damper causing it to stress crack, or the damper has been run too loose, allowing it to work back and forth on the shaft. There has been a lot of galling on the shaft, which just isn't good. I would replace the damper and the key, torque it correctly, cross my fingers and see what happens.

 

[R Racing]

Since this is a tapered shaft, my guess would be over tightening, which would "stretch" the hub on the damper causing it to stress crack, or the damper has been run too loose, allowing it to work back and forth on the shaft. There has been a lot of galling on the shaft, which just isn't good. I would replace the damper and the key, torque it correctly, cross my fingers and see what happens.

Crank isn't a taper shaft. Its a .001 press fit on the hub. After looking at the pictures on my computer and not my phone . That crank is beat up a bit. Buy a new key and use green locktite might work.