Moisture in Breva/Griso Clocks

[tris]

Following on from Motos well argued thread (http://wildguzzi.com/forum/index.php?topic=84968.0) I wondered what the members of this forum believe is the route cause of the moisture inside the Breva/Griso group of bikes.

Hopefully this wont turn in to an "OIL THREAD" 

[pete roper]

I have no idea of a definitive cause which is why I've been following Moto's investigations with interest. I've got nothing to offer though as I've only ever seen two failed dashes, probably because of where I live. It's generally very dry in the Canberra region.

Pete

[tris]

And that's the problem Pete

I've ridden mine in the pouring rain - no misting

Ride it in dry cold weather and stop for a coffee break - misting at the bottom of the clocks

This is why (at least on my bike) I lean towards the condensation caused by poor ventilation

[lucky phil]

And that's the problem Pete

I've ridden mine in the pouring rain - no misting

Ride it in dry cold weather and stop for a coffee break - misting at the bottom of the clocks

This is why (at least on my bike) I lean towards the condensation caused by poor ventilation

I posted in the other thread the causes and cures given to me by and instrument maker that Pete would probably remember
(Dennis Quinlan, the guy that visited VDO in Germany to show them their corroded circuit boards) and the mods I did on a BMW and Triumph that were successful, but if you must keep wondering, go right ahead. 

Ciao 

[pete roper]

Phil, I'm on holiday mate. I have been following it, not reading every word of every post. Gimme a break!

[lucky phil]

Phil, I'm on holiday mate. I have been following it, not reading every word of every post. Gimme a break!

Reply was for tris Pete, and whats this holiday stuff
USA one year, old blighty the next, bloody hell.
Ciao

[Moto]

 [  ] Water ingress from the outside due poorly designed sealing
 [  ] Condensation from moist air drawn into the clocks via the heat rising from the instruments
 [  ] Both
 [  ] The faries put it there
 [X] None of the above

I don't know if there is really a single answer. Sometimes there might be a leak through the seal at the top, but I don't think ingress of liquid water is likely through the bottom vents. I don't think the heat of the instruments is drawing moist air into the case.

I believe it is just statistical mechanics, that is, the mixing action of the atoms in the atmosphere slowly causes an equalization of the proportion (or partial pressure) of water vapor (gas molecules) in the air inside the dash with that in the surrounding air. This can occur through those small vents, and engineers are familiar with the fact that it can occur right through the solid plastic walls of the case. If there is more venting it will occur faster, on both dry and humid days.

Once humid air is inside the case is when the fun begins. I think of the dash as a little terrarium, a sealed environment with a clear top (but hopefully without the moss and turtles). When the terrarium cools down, water condenses from the air -- in our terrariums, right onto the PCB. When it heats up, the water will evaporate, returning to the gaseous state. The next night, or other cool period, will see the condensation occur again. And on and on, the evaporation-condensation cycle continues, each night wetting a surface that has more accumulating damage than the night before.

Sometimes the air in the terrarium/dash is warm enough to contain a lot of moisture while the clear top is cooler. This causes the condensation on the instrument cover that we see. This phenomenon is harmless in itself, since that water is evidently not on the PCB at such times. Heating of the air inside the case commonly occurs in bright sunlight, which does not directly affect the temperature of the transparent instrument cover (since it is transparent), but warms the black instrument panel directly and the air by conduction from the panel. The transparent case is left cool enough to cause condensation from the warmed air that contacts it on its lower surface. This is a kind of greenhouse effect which can be observed in greenhouses and terrariums everywhere. Another possible cause of this effect is the heat generated from the instruments, which similarly heats the air, causing it to hold more moisture, while not directly or effectively heating the transparent cover, which remains cooled by contact with outside air (assuming the outside is cooler). This can also lead to condensation on the inside of the clear cover.

So sunlight and instrument heat are not causes of the problem, as I understand it, but are causes of a telltale symptom of water in the dash -- condensation on the lower surface of the instrument cover. Without the presence of sunlight or instrument heat, the destruction of the PCB by condensed water can go on quite nicely, with ever-increasing levels of contamination being picked up in each evening's re-condensing water.

Temperature changes of the air above and around the PCB are the fundamental problem. If the temperature could be held steady, no condensation from the air would occur, so long as only water vapor and not a mist, had been admitted. (The droplets in a fog or mist can collect on surfaces through surface tension.) When the temperature of the air inside the dash drops below the dew point, condensation will begin.

It doesn't matter whether the dash is well vented if the surrounding air is as moist as the air inside the dash when condensation has begun. All of us have found that riding faster through the fog that condensation brings does not keep us dry.

The trick is to keep humid air out of the dash when the temperature is going to drop, or to keep the temperature inside the dash above the dew point. Sometimes the climate can save us, and sometimes it works against us.

I am immune to appeals to the authority of an instrument maker in Germany because I have spent enough time researching and thinking about this to have confidence in my own understanding. In fact, most of the fun I have had in pursuing my project has been in the learning that went with it.

Moto

[Moto]

And that's the problem Pete

I've ridden mine in the pouring rain - no misting

Ride it in dry cold weather and stop for a coffee break - misting at the bottom of the clocks

This is why (at least on my bike) I lean towards the condensation caused by poor ventilation

Sounds right to me. And let me venture another prediction -- those rides in dry cold weather followed by a stop for coffee were on sunny days. (Else you have very hot PCB components!) This would be consistent with my terrarium model, just described.

[Moto]

And that's the problem Pete

I've ridden mine in the pouring rain - no misting

Ride it in dry cold weather and stop for a coffee break - misting at the bottom of the clocks

This is why (at least on my bike) I lean towards the condensation caused by poor ventilation

Looking at your post again, I suggest that your symptoms are not inconsistent with water leaking in during the pouring rain. It could be pooling in your dash unseen, with later evaporation and condensation in bright sunlit conditions providing the evidence of your problem. That is, condensation on the clear instrument cover is not diagnostic of the source of the water! (See my terrarium discussion above.)

M.