Some of you guys know I work on big junk. Great big junk, for over 30 years and I've gone all over the world making the junk perform as advertized. And it all uses viscous fluid filled units from Siberia to Saudi. A massive flywheel on one end with a free floating weight on the other end to constrain torsionals between the 2 is the way the theory works as my feeble mind grasps the concept.
The drivers on My Junk are very similar to auto engines but there are differences in my junk and automotive that sometimes I have to learn the hard way. Normally this is constrained to stuff like "no Tim, do NOT make the bracket out of 1/2" steel plate".
Which I did one time to get a PS pump back on something where a bracket got lost so I just grabbed the torch and made one out of 3/4 or 1/2" plate. Nobody liked it but me for some reason. Talk about calming down some belts.
I used to propound the fluid unit, but have learned that is one of the differences. I have theories as to why but nothing real. I theorize there is no massive weight at the rear. I theorize guys who have had fluid unit failures hadn't a clue as to maintainance(shoot the temperature of the shell, replace every 40,000 hours) and may have even possibly damaged their unit by prying or beating on it and unintentionally locking up the "free" inertia weight. The viscous fluid will reflect the amount of work it is doing in the temp of the shell, and believe it or not there are monster engines that have drilled passages to run cooling oil into the damper.
I reckon there's been problems with the viscous units or else there wouldn't be stories.
Beats me. Whatever.
I know I am not risking my junk though, even though I know viscous is good medicine.
I use ATI on good engines and Pioneer on stockerish stuff. Call ATI for a diameter recommendation and they will tell you it is based on cid. And they can use different shore hardness elastomers to make the smaller unit work for larger engines. I know this because I had a 7" unit and called them when I went from 412" to 421" and they said they could either install 70 shore orings in my small one or sell me an 8". I bought a new one even though it is a pita getting them fitted(ATI builds them with the ID on the small side) because I like having lots of extra junk.
Ron, in extreme cold you are supposed to let the damper shell reach x° before loading. I am sorry I do not remember the definition of X. I do remember you risk destruction if you don't wait for it. I don't like waiting for it, I survived a wfew winters in the mountains of West Virginia and I know it gets colder where you are but -36 effing degrees is pretty cold and I can attest to a buttload of viscous units survivng that.
Ev, yup they still recommend 10 years. But viscous units on industrial engines are supposed to be heaved and replaced at overhaul(which very few actually do because they can cost $2000 on my junk). Some engine mfgrs also recommend periodic fluid replacement iirc.
If you run a viscous unit, shoot the shell temp after you make a hard run is what I would do. I would expect the temp to be at or slightly below engine water pump suction hose temp as the cold water temp is an indicator of the air temp that was hitting the face of the damper. The water temp will be above the air temp(this is called "approach" if you give a hoot about heat exchange terminolgy).
An engine with a good air cooled viscous damper that has been running at 100% load for several hundred hours will have a shell temp just slightly above ambient if the shell is NOT exposed to air that crossed a radiator. If it is an engine with a radiator(and I don't work on may of those) from memory it will be right at cold water temp or slightly below. Definitely never above engine hot water temp on the most heavily loaded engines I've ever seen. This again is a sizing deal where the mass of the inertia ring has to mate with whatever it is absorbing. And you have to remember that as the heavy fluid gets hotter it becomes less effective.
Hope this helps, and I am not recommending or dis-recommending anything OK? Just trying to pass on my hard won knowledge as I know it.