anti wet sump valve

[Derek996]

Do all of you park with your engine at TDC?

I do if I'm laying it up for a few weeks or longer but what's that got to do with wet sumping? It won't prevent it.

[cdsdorset]

Do all of you park with your engine at TDC?

I do if I'm laying it up for a few weeks or longer but what's that got to do with wet sumping? It won't prevent it.

Why would it not?
Why do you park it at TDC?

[rhyatt]

There is a school of thought that it used to save valve springs from unequal compression

[Derek996]

Do all of you park with your engine at TDC?

I do if I'm laying it up for a few weeks or longer but what's that got to do with wet sumping? It won't prevent it.

Why would it not?
Why do you park it at TDC?

Wet sumping is caused by oil seeping past the oil pump gears. It will do that whether the valves are closed or not.
If I am parking the bike up for an extended time I turn the kickstart until it is against compression so both valves are closed. My thinking is simply to keep the combustion chamber and barrel sealed against atmospheric changes, i.e. condensation and dampness. It will also keep our spiders and earwigs. 
I can see the point of rhyatt's comment as the valve springs won't be left with a load on them for an extended period.

[DAVE BRADY]

Hi,

With the big end at BDC there will be a greater draining affect through the crank with oil even being drawn through the pump. With the big end at TDC this affect is greatly reduced as the oil has, to some extent, to go up to seep out. I suppose that there is a slight possibility of the reverse affect of oil from the big end/sludge trap draining down so that there is not enough oil for cold starting.
A few turns of the engine before firing it up will overcome this.
Best solution is to ride or at least run the engine regularly up to temperature thus keeping everything oiled and reducing internal condensation.

Dave.

[Derek996]

It may make a little difference on the twins but I doubt if parking with the big end at TDC will make much difference to a single. The spigot feeding the crank from the timing cover on the singles is hardly an interference fit.