Crank pulley damper ring came off...

[wrwtexan]

While changing a filter on my JD 790E hoe with the JD 6068 engine, I found the rubber mounted damper ring from the crank pulley had spun off at some point. I haven't noticed any vibration and I have many farm tractors that don't have this ring. Not to be cheap, but as this is going to be a major teardown and expense to replace, how necessary is the ring and will I run the risk of engine damage if I don't replace the pulley/damper assembly soon or at all?

 

[kshansen]

Not familiar with the JD 6068 engine but I would think that John Deere had a reason for putting it on there, doubt they just did it for fun.

If you want to do some reading on the subject: https://www.google.com/url?sa=t&rct...A9qIEDAwsyYHT-LjQ&sig2=IgMTTwd7hPsj7yguiTPTww

Most of the ones I have seen with the rubber ring between the two steel parts have a couple chisel mark to indicate if the outer ring has moved in relation to the inner hub.

 

[Delmer]

• Tuned absorber type of "dampers" often referred to as a harmonic dampers or harmonic balancers (even though it technically does not dampen or balance the crankshaft). This damper uses a spring element (often rubber in automobile engines) and an inertia ring that is typically tuned to the first torsional natural frequency of the crankshaft. This type of damper reduces the vibration at specific engine speeds when an excitation torque excites the first natural frequency of the crankshaft, but not at other speeds. This type of damper is analogous to the tuned mass dampers used in skyscrapers to reduce the building motion during an earthquake. from the wikipedia link

Fascinating. It sounds like you want to be real careful not to run the engine speed at the "first natural frequency of the crankshaft" whatever that is. I'd just be careful to run the engine wherever it's smooth. That was my thought before reading the article, and more so after reading it.

I'm not familiar with a harmonic balancer that can lose the rubber and not lose the pulley also, is yours just missing the outer rubber ring that's visible?

There are 4045 engines with no harmonic balancer either, and a six is inherently much smoother than a four cylinder.

 

[kshansen]

There are 4045 engines with no harmonic balancer either, and a six is inherently much smoother than a four cylinder.

I think that the longer length of the inline 6 cylinder crank is one of the reasons they may need the dampers more than the four cylinder engines. I'm not sure one can tell just by the "feel" of the engine's smoothness or lack of it how much flex is being put into the crankshaft. And the term "balancer" is somewhat of a misnomer when used in this regard. A more accurate term is "damper". Many engines, such as 3304 Cat four cylinder engines had weighted shafts or gear that are used to make the engine run smoother but this is much different than the purpose of the viscous or rubber dampers used on the crankshaft.

 

[Shimmy1]

My uncle ran an ISX for about a year with a damper that was suspect. Put a new one on, and less than a year later the nose of the crank broke off. I would get it replaced as soon as possible.

 

[kshansen]

My uncle ran an ISX for about a year with a damper that was suspect. Put a new one on, and less than a year later the nose of the crank broke off. I would get it replaced as soon as possible.

Yep a crankshaft is no different than a cheap paper clip, bend it a bit for long enough and SNAP!

 

[wrwtexan]

outer ring is pressed on over a rubber band and is separate from the driving pulley.


Thanks to all who have replied. I have heard of crank snouts on Chevy 350's breaking off and this is my worry. The 4 bangers have gear driven balancers or in JD's design, balance shafts. As I haven't noticed any vibrations while operating or doing a running engine inspection, I had hoped it might not be too big of a problem as the radiator will have to come out and I'm sure they don't give theses pulleys away. I know they didn't put it on for no reason but wasn't sure if this might be one of those things that can be done without and not hurt anything. From the replies, I had better break out the wrenches before I start the big job I bought it for.

 

[Delmer]

"damper reduces the vibration at specific engine speeds when an excitation torque excites the first natural frequency of the crankshaft, but not at other speeds"

That's the part of the quote I was talking about, I'd bet without a harmonic balancer you would know where that speed is because it would be loader and harsher, bring out all the rattles. The crankshaft is "resonating" at that speed if I understand it right. The damper is tuned for that speed specifically, like a shock absorber will dampen the suspension, but not keep the suspension from moving. A six is smoother because the torque from each cylinder overlaps slightly instead of going full torque to zero and back again twice each revolution, that's the source of the harmonics.

 

[kshansen]

From the replies, I had better break out the wrenches before I start the big job I bought it for.

I know for myself I would sleep better knowing I had replaced that damper, every little rattle or buzz would be haunting me while running it. Besides, probably find a few things that need replacing while it's apart, belts, hoses and a loose motor mount or two. Don't you love people who are so eager to spend your money?

 

[Delmer]

Heck yeah, Don't even think of NOT replacing the front crankshaft seal if you're that far.

Especially since this was bought for "one big project", fix it before it breaks halfway through if at all possible.

 

[56wrench]

The damper is to absorb torisional vibration of the crankshaft. I would replace it. It will be a lot cheaper to replace it than have to change a broken crank and/or the engine. Hopefully there is no damage (cracks) . It depends how long it was running with the damper separated. Just my 2cents

 

[GregsHD]

outer ring is pressed on over a rubber band and is separate from the driving pulley.


Thanks to all who have replied. I have heard of crank snouts on Chevy 350's breaking off and this is my worry. The 4 bangers have gear driven balancers or in JD's design, balance shafts. As I haven't noticed any vibrations while operating or doing a running engine inspection, I had hoped it might not be too big of a problem as the radiator will have to come out and I'm sure they don't give theses pulleys away. I know they didn't put it on for no reason but wasn't sure if this might be one of those things that can be done without and not hurt anything. From the replies, I had better break out the wrenches before I start the big job I bought it for.

When you replace the damper / front seal, I'd replace the centre bolt in the crank snout, blue loctite, and proper torque.

Worked on a 624G that the bolt came loose, destroyed the crank snout, I pulled and rebuilt the engine with a new crank, the mains were way out, had to be line bored as the vibration distorted the block. I'm still supprised the crank didn't break!

I've always liked Deere engines but they seem to be held together with the bare minimum of fastener size/strength
compared to other brands IMO...

 

[wrwtexan]

Dang. Working on my own stuff doesn't pay worth a crap as who do I submit my bill to when I get done??? Oh well, I need the practice. Thanks for all the replies!

One more bit of info. The damper was clean enough that it didn't appear to have been off for very long. Maybe a few hours so likely no damage done. Thankfully it is near my shop so I won't be working in the field if I had found it after moving back to the worksite.

 

[StanRUS]

Keep running without the damper and the crankshaft will break @ #1 or #6 throw-arm! Cummins 855s with viscous dampers would break if the viscous fluid leaked out.

 

[wrwtexan]

I finally started on what I thought was going to be a project but to my pleasant surprise found that the damper is mounted on a plate held onto the front pulley with four 3/8'" bolts! I had it out in just a few minutes. Evan though it isn't the whole pulley, my research still shows it to be over $300. Likely nowhere near as expensive as it could have been.