Viscous Dampers Front Pulley
Turbo Mini Forums

as above im looking to help reduce the vibrations to prolong the life of my 1100cc with its 83mm stroke and three mains as we know they flex and work them self into a pretzel if you exceed about 5000rpm for any length of time so..

i have been told that the first thing is to get a good dampener ether rubber or viscous type witch is preferred but expensive

so what do people use i dont think ive ever read what type or brand in a build speck or such?


http://www.kentautodevelopments.com/shop/p...1-tooth-pattern

http://www.med-engineering.co.uk/catalogue...-kit-management

edit links

Edited by Turbo This.. on 19th Sep, 2013.

the Kad one will be better as its a viscous one so will work over a wide rev range.

ok the viscous dampener is the better style for a non std engine
so dose anyone know if there are any other brands kicking around?
im now considering getting one of the kad one but if there is more choice there may be different styles?

Sh engineering offer one I believe.

i spoke to the shop today regarding this topic and now im more confused than before i asked..
he went on to explain he dose not believe in them and recommends the classic rubber mounted outer mass
also said that the balance machine dose not like them due to large in balance and once balance and let to sit then re tested for balance it is off again?
perhaps the fluid need to centrifuge out over time to center the mass?

None of the machine shops I use will balance them and I believe the instructions for the fluid dampers I use say they do not recommend balancing them... This is not a mini application however

Speeding is like masturbating, everyone does it, but not all of us film it and put it on the internet

[quote=fab,8th Oct, 2010]fuck off

so how do you get the rotating assembly balanced as a whole?
what about taking the damper and spinning it in the lathe at high speed for a while to center/get the thing where it will be in operation then try balance it perhaps the "floating mass" inside gets its self off center from siting and needs to be rotating and pulsing to center?

I thought that viscous dampers we're balanced during production/assembly.

If I were using one I'd balance the rest of the assembly and leave the damper out.

If something is worth doing, it's worth doing half of.

I think there is some vizzard seminar thing on YouTube? have a search it's pretty interesting he covers materials and harmonics.

Speeding is like masturbating, everyone does it, but not all of us film it and put it on the internet

[quote=fab,8th Oct, 2010]fuck off

finally those years of doing physic's pay off, the damper is to offset the effect of simple harmonic motion.
When a frequency is applied to an object matching its natural frequency, the vibrations become larger and larger.

Here is an example of what happens when you don't take into a natural frequency of something http://www.youtube.com/watch?v=j-zczJXSxnw

so what makes the liquid material more effective over more rpm range than the rubber?

im aware that the damper is just that a device built to do just that damp out torsional vibrations and not a balance aid
my question to the best i can explain is wont you need that mass of the damper on the front end of the crank to get the true dynamic balance?

that comment regarding the bridge is how he explained the need to damp the harmonics as if you dont that can happen...

had a search on you tube and found lots of interesting vids from David but none on dampers ?

the trouble with a ruber damper is you are essentially trying to damp something with a spring... by tuning the spring to do the opposite of the "spring" you are trying to damp, the trouble is although it may workok on a standard setup, soon as you mod something the damping is then compromised... ie, lighten the flywheel increase rev range, wedge crank... ect ect.

as the fluid isn't a spring, it dosent have the same kind of peak resonance as rubber,

another thing is harmonics, you will have the main resonant freq of the crank (6100rpm for the 1275 according to DV) you will also get resonances at other frequencys albeit smaller, 2nd, 3rd harmonic ect, these all contribute to fatigue, espacially as the rubber damper will be tuned for the fundemental an do little to damp the harmonics, anyone that plays guitar should get this

i may call a company that tests and manufactures dampers and see what they say all be it probably bias to there products...
i am how ever thinking that the viscous damper is the way to go from the over all tally of things said so far
im building this engine with the goal of a longish service life conceding the power i want it to make (ill raise boost it till it feels fast enough) so i think its money well spent on a good damper all tho ill only turn it to 6000-6200 or there about keeping in mind the long 83mm stroke

If your only turning it to 6k then I would personally use a small mass rubber damper as long as you have one in good nick. It not like your spinning a 1275 to 9k rpm with no standard components left in it!

Edited by minimole23 on 24th Sep, 2013.

the 1275 is a short stroke engine compared to the 1098cc longest of all so how can a 1275 be worse?
surely the twisting stress is higher on the long stroke at low revs than short stroke at high revs due to the amount of journal over lap?

Edited by minimole23 on 24th Sep, 2013.

i see, i dont go out of my way to back chat or have the last say im just trying to get the most info on this to get the best outcome

also im not sure if you know but the internals will not be std weights (all be it std castings) witch im a where this plays a part in the point of destructive vibrations

pistons and pins will be lightened a touch and relieved for oil cooling jets then balanced
rods will be lightened to the point they almost become weak, re sized, re bushed, balanced end for end and total then shot penned
crank will be also be lightened a grate deal with out taking away from the torsional strength back drill, knife edge, turn down etc, grind, surface harden, final grind/polish
fly wheel is an ultra light job but will get a shave down on the ring gear and outer rim also the backing plate will get shaved down to further reduce weight
my goal is to make the engine rev happy also reduced mass that the engine needs to accelerate/decelerate
i do plan to install the short 3.7 diff with a good lsd for some street sprint fun but for now ill use the long 2.9 and x pin

well ive gotten side tracked talking

dose anyone know if lighting the rotating mass and internals lowers or raises the rpm at witch the torsional vibrations occur the worst?
if the mods im doing raise the nasty vibes up out of the rpm limit ill use 6k then the rubber may well be just fine for me?

Strange choices.

You say you want longevity and will only be spinning to just over 6k, yet your proposed bottom end is more suited to high revs and short lifespan.

In the 13's at last!.. Just

whats wrong with having a light weight bottom end and not turning it past 6200 ?
for me its about acceleration 0-100-0 not having an engine that turns at crazy rpm

what is the need to make an engine turn to high rpm? why not make power lower in the rpm

sorry if i am badly missing something here but i cant see the scene in revving an engine when revs kill engines?
that said my thinking is to build it to make power but at a sensible rpm

The idea with higher revs is that for a given torque, the higher the rpm the higher the power. As power is related to the torque and rpm. People generally make lighter bottom ends for higher revs due to the forces involved at high revs. These forces go up with the square of the engine speed, so if you double the rpm you quadruple the forces.
If you are not going to be revving very high then the need for a lightweight bottom end is lessened, obviously the lighter it is the better response. But the low down manners of the engine will suffer as if will seem 'too responsive'

Idle will suffer

what is the relation ship between torque and rpm is there some kind of law that says if rpm goes up 1k rpm then you will get say 10% more torque?

Edited by Rod S on 26th Sep, 2013.

Schrödinger's cat - so which one am I ???

hey turbo this, to answer your very first question,, we use to balance crankshafts and flywheel, clucth as one whole unit, without the balancer/damper bolted on, we use to do alot of deisels with V/D on them and all the info on them said dont bolt on to balance. like someone said it stops harmonics in the enigne, the std rubber ones are desgined to work "with-in" a certian rpm range, they wont stop all the harmonics in the engine, but good enough for an engine not turning to high rpm. We had a man out from ATI Dampers in the USA who explained all this to us,
we also use to get dampers for holden V8 that were netural and some that were extra weighted so you can remove all the inbalance from the damper and not the crankshaft, i dont know why people used these, but each to there own,
just tell the machine shop to balance the bottom end and then put your V/D on it,
if you lighten your bottom end it will help it rev quicker but you loose torque out of it, its only really done for race or high output motors,

i hope this helps you,

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