Viscous coupling - operation

[Mark Serj]

Hi all,

Can I ask what the correct amount of rotational play I should expect in a viscous coupling is please?

I can turn it by hand quite freely (with no for & aft bearing play), and if I were to flick it hard, it would probably manage 1/2 - 2/3rds of a turn.

I'm wondering how effectively it will operate the fan up to it's rev limit, if it is relatively easy to turn by hand?

This is on a motor I have yet to run up after a rebuild so I can't comment on it when running.

Regards

Mark

[mole42]

That doesn't sound right Mark, a couple of blades spin is all I get and I think that's correct. Russ or Ian or Dave will confirm or otherwise.

Richard

[SGN]

Hi Mark

1/2 to 2/3 turn is about right, if it spins freely when you flick the blades, you need to get it changed.

Cheers
Steve

[DJT]

It shouldn't spin more than a couple of blades width when spun by hand. This ensures it will rotate at engine speed up to approx 2600-2800 rpm, then the viscous fluid inside will 'shear' so that it free wheels at higher revs.

[Mark Serj]

I think that seems about right then, I probably over estimated the free spin amount having had a tinker again last night.

Thanks chaps

Mark

[Andrew S]

Sorry to hijack this thread but I need educating as I thought the there was fluid inside the viscous that was thin when cold as the fan doesn't really need to spin and in fact you can hold the fan by hand, but as it gets warmer, the viscous grips and therefore spins the fan at a higher speed but up to a set number of revs.
I say this as mine runs cool but the fan spins very easily and also if I really grip the fan close the viscous, I can feel and hear movement.

[mole42]

Hi Andrew, you're nearly right but not quite.
The viscous coupling is nearly solid at low revs, transmitting most of the engine speed to the fan. At higher revs the coupling slips, so that the fan runs at a slower speed.

It has nothing at all to do with temperature.

There are some engines that use a temperature controlled fan coupling that may look similar to the Stag one, but they are not the same and do not work in a similar way.
Richard

[Andrew S]

Thanks Richard
So, is there any kind of play allowance from cold if I twist the fan near to viscous? Would this play tighten up at higher revs or possibly cause an imbalance? This what I am trying to cure, not an over heating problem as she runs at a 1/4 most of the time.

[new to this]

Sorry to hijack this thread but I need educating as I thought the there was fluid inside the viscous that was thin when cold as the fan doesn't really need to spin and in fact you can hold the fan by hand, but as it gets warmer, the viscous grips and therefore spins the fan at a higher speed but up to a set number of revs.
I say this as mine runs cool but the fan spins very easily and also if I really grip the fan close the viscous, I can feel and hear movement.

if you have any side ways movement in the viscous unit,its on its way out

Dave

[mjheathcote]

Yes only a couple of blades basically as soon as you remove your finger it pretty much should stop.
Over the years the amount of cars that I have flicked the blades and they spin much more with shot couplings, is greater than good ones for sure.

[Andrew S]

Thanks Mike and Dave

[DJT]

Thanks Mike and Dave

You're welcome Andrew (post #4)

[Arbman Al]

Has anyone taken a vc apart to see if its serviceable?

I have a vc on my Mitsubishi pajero that works the other way around, it spins freely when cool and as the engine heats up, starts to lock up. Someone dissected one and found It can be taken apart and new oil put inside, some remote control car silicon oil.

[Bob Heritage]

Has anyone taken a vc apart to see if its serviceable?

I have a vc on my Mitsubishi pajero that works the other way around, it spins freely when cool and as the engine heats up, starts to lock up. Someone dissected one and found It can be taken apart and new oil put inside, some remote control car silicon oil.

Perhaps it's been fitted back to front Al