Fluidampr
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AFAIK they do not make a specific one for a 4bt but the 6bt ones do fit, there is someone on this board I'm sure that has one hopefully he will post up. From memory he didn't run it without it so cannot give a before and after comparison.
I'm sure if I am wrong someone will correct my recolation.
Gaza
I'm sure if I am wrong someone will correct my recolation.
Gaza
Fluidampr on a 4BT
I just put a Fluidampr, p/n 960311 for 92 to 98 12v Dodge on my 4BT. It eleminated my cold start vibrations and my engine runs smoother at full rpm.
See: www.fluidampr.com for info.
Lewis
81 J10
4BT
GM/Muncie 465
I just put a Fluidampr, p/n 960311 for 92 to 98 12v Dodge on my 4BT. It eleminated my cold start vibrations and my engine runs smoother at full rpm.
See: www.fluidampr.com for info.
Lewis
81 J10
4BT
GM/Muncie 465
I can't compare 4 and 6 cylinder vibrations. I did ask the techs at Fluidampr about putting their damper on a 4BT.
Their answere was, "they do not build a damper for the 4Bt, but some of their customers were using the 6B damper on the 4B."
But, I do not understand the lojic involved here.
Their answere was, "they do not build a damper for the 4Bt, but some of their customers were using the 6B damper on the 4B."
But, I do not understand the lojic involved here.
I brought this question up on the Engineering Forum and got a lot of feedback from the pros. A 4 cylinder has inherent vibrations that a 6 doesn't have. But, they both have some vibrations [or harmonics/frequencies] in common. The 6 cyl. damper will help to cancel out those common vibrations but won't touch the 4's design specific vibrations. It may help, and apparently does, and won't do any harm, but it's not a fix-all.
As i recall DriversWanted uses the 6BT elastometric damper with good results, and lots cheaper. Don't know if the Fluid Damper would be more or less effective.
As i recall DriversWanted uses the 6BT elastometric damper with good results, and lots cheaper. Don't know if the Fluid Damper would be more or less effective.
i have one on the shelf waiting to put into dad's dmax , from my understanding the fluid dampner has a disc inside which is suspended in a viscious fluid . the disc will spin freeley inside of the unit with the thick fluid being the only coupler. the outside of the fluid dampner is sealed against leaks. so do not dent it or it will not function. this is what i understand from what i have read and talk to. in my opionion for what it is worth i think it would be just fine on a 4bt and do a good job on dampening the twisting of the crank.
Crankshaft dampers are to help with torsional vibration which can cause a lot of problems.
Since the 4BT crankshaft is shorter, it's significantly stiffer in torsion than the 6BT one, which puts the natural frequencies much higher. I imagine they'd be so high as to be out of the rev range of the engine.
If it needed one, cummins would have fitted one.
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696 Posts
This is something that has crossed my mind aswell. How about the 4BT probably doesn't need a dampener but it benefits the passengers?bounce bounce bounce bounce
Gaza
Well for one thing it's an industrial engine. that is, it was never really intended for a passenger vehicle as such, with the closest useage to that being the stepvan delivery trucks. So Cummins did the ho-hum on dampers. Now I'm no degreed engineer, and not that bright either, but the way I understand it: There are different waveforms that develop along the along longditudinal axis of crank. Pistons transfer combustion 'hits' to crank through rods, and these are occurring in a certain order. From this waveforms develop in crank.
Next is something called sineusoidal wave harmonics, almost similar to playing a guitar chord. You may have noticed something like this at home. You have an electric fan running and it makes a rythmic humming sound. Then the refrigerator kicks on and it too makes a rythmic humming as the motor turns compressor and fan, but at a different frequency. that is, One sounds like hmmmm-hmmmm-hmmmm and the other sounds like hmm-hmm-hmm or whatever, different frequencies. Listen for a few minutes and it's amazing: the two seperate waveform frequencies will harmonize after a few minutes and assume ONE WAVEFORM! Pretty strange effect: 'Sineusoidal wave harmonics', and the sine waves harmonize.
So on the crankshaft a single waveform occurs from each cylinder's combustion, for a total of 4 waves on 4BT. Then the waves begin to harmonize, actually causing a 5th order waveform on top of the other 4. Differing engine speeds can then effect this sort of standing wave and add another, for a 6th waveform. So there's one harmonic at idle, another at running revs, and others that develop at various rpms. I've only heard the brain guys mention up to the 6th order of waveforms. It's more complicated, but I'm not going to go there.
Elastometric dampers can absorb some of the combustion hits on crank and modulate the waveforms somewhat, but they can't do much with the higher orders because of their relative frequency. Fluid Dampers are more able to abosrb the 'higher' frequencies that occur at higher rpms through that disc and fluid mentioned by FarmerO_1. So that's a function of those sineusoidal wave harmonics, as it modulates the highs and lows on the [sine] waveline to cause a harmonic, like a guitar chord, or sympathetic vibrations along the crank centerline.
Any decent engineer worth a hoot can tear what I just wrote to bits for its errors, but it may help to understand what's going on. The 4 cylinder's particular crankshaft harmonics are entirely different to the much more inherently balanced 6 cylinder waves. But at low engine speeds the elastometric [rubber membrane between steel pieces] or the fluid type harmonic dampers can help a lot to take up vibrations on either engine, up to maybe 1,000 rpm's? I don't know, maybe I should have just slept in instead....
Next is something called sineusoidal wave harmonics, almost similar to playing a guitar chord. You may have noticed something like this at home. You have an electric fan running and it makes a rythmic humming sound. Then the refrigerator kicks on and it too makes a rythmic humming as the motor turns compressor and fan, but at a different frequency. that is, One sounds like hmmmm-hmmmm-hmmmm and the other sounds like hmm-hmm-hmm or whatever, different frequencies. Listen for a few minutes and it's amazing: the two seperate waveform frequencies will harmonize after a few minutes and assume ONE WAVEFORM! Pretty strange effect: 'Sineusoidal wave harmonics', and the sine waves harmonize.
So on the crankshaft a single waveform occurs from each cylinder's combustion, for a total of 4 waves on 4BT. Then the waves begin to harmonize, actually causing a 5th order waveform on top of the other 4. Differing engine speeds can then effect this sort of standing wave and add another, for a 6th waveform. So there's one harmonic at idle, another at running revs, and others that develop at various rpms. I've only heard the brain guys mention up to the 6th order of waveforms. It's more complicated, but I'm not going to go there.
Elastometric dampers can absorb some of the combustion hits on crank and modulate the waveforms somewhat, but they can't do much with the higher orders because of their relative frequency. Fluid Dampers are more able to abosrb the 'higher' frequencies that occur at higher rpms through that disc and fluid mentioned by FarmerO_1. So that's a function of those sineusoidal wave harmonics, as it modulates the highs and lows on the [sine] waveline to cause a harmonic, like a guitar chord, or sympathetic vibrations along the crank centerline.
Any decent engineer worth a hoot can tear what I just wrote to bits for its errors, but it may help to understand what's going on. The 4 cylinder's particular crankshaft harmonics are entirely different to the much more inherently balanced 6 cylinder waves. But at low engine speeds the elastometric [rubber membrane between steel pieces] or the fluid type harmonic dampers can help a lot to take up vibrations on either engine, up to maybe 1,000 rpm's? I don't know, maybe I should have just slept in instead....
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I think the beauty of any of these dampeners is they are not tuned to a specific model, they let the fluid decide that... There is also an inexpensive rubber isolator as well. I pulled a massive metal dampener off a 24 valve that I plan to run over the stock one, simply because I damaged the stock one. If I notice even more vibes than normal I'll change. Thanks, Adnre
Do you think the passengers can notice torsional crankshaft vibration?
They are very different to the vertical and horizontal vibrations caused by the piston and conrods whipping around.
The back end of the crank has it's pulses moderated by the high inertia flywheel, this only leaves the front end to oscillate torsionally, which is why the damper is fitted there.
Fluid fillled dampers do have specific natural frequencies, just like everything else in the world. The trick (or the problem) is when the match up with other frequencies.
One of the more irritating vibrations in mine is around 1,500-2,000+ or so, just guessing as no tach. I can feel it throughout the truck, all the way up into my steering wheel! It's like one of those beds they used to have in cheap motels many moons ago, with the coin slot where you added quarters for the 'Soothing Vibro-Massage', hah!
I'd guess it's a torsional vibration and don't know if either damper would help. It may last on up in the rpms's but not sure. I built everything too rigid I think, and obviously don't have the right isolators somewhere, or everywhere. I used some tired old Dodge 400-440 mounts at engine, and the tranny tailshaft is sitting on some more tired motor mounts, maybe Dodge 360's. I'm sure new ones would help, but may need something else all together. That, and some kind of harmonic damper? Maybe...
I'd guess it's a torsional vibration and don't know if either damper would help. It may last on up in the rpms's but not sure. I built everything too rigid I think, and obviously don't have the right isolators somewhere, or everywhere. I used some tired old Dodge 400-440 mounts at engine, and the tranny tailshaft is sitting on some more tired motor mounts, maybe Dodge 360's. I'm sure new ones would help, but may need something else all together. That, and some kind of harmonic damper? Maybe...
I'd put money on it not being crankshaft torsional vibration for two reasons.
1. Those torsional vibrations are seperated from you by bearings. Being torsional you can't feel them.
2. If torsional vibrations that bad existed at that rpm, your engine would have self destructed a long time ago.
While it's true that a fluid damper will offer some damping at all frequencies, they do need tuned and matched for each application if they're going to make a difference.
Don't know, Dougal, just don't know. I've already got a harmonic damper on my trans output slipyoke, and a custom driveshaft by the top shop, Tom Wood's Custom Driveshaft in Utah, USA. Everything but adapter and bell is new Dodge 6BT CTD stuff. Happens in any gear, too. I still have to adjust my valves, hopefully this weekend, and that may contribute I guess.
My engine runs really rough when the valve clearance is out. Obviously different amounts of air getting into each cylinder and making different size bangs.
OOoohhh, now THAT's some GOOD NEWS Dougal! Sure hope that's it. Just got my new gaskets and went and picked up some paint today for the valve covers, so maybe tomorrow morning?
Don't know on your last question, Boots, but my '90 non-aftercooled Cummins from a Chevy P30 van has electric fan.
And it was good news indeed! Got the valves adjusted and the engine seems to run more smoothly, with maybe 50% less vibration!!! Only took a short run, but it also seems to have better bottom end power. I'll find out for sure next trip into town. This could certainly be part of the answer regarding harmonic dampers: first, adjust the valves.
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2,218 Posts
One thing I learned definitely no givens with these engines.. Low and behold my 4BTA came with a huge mechanical fan...
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