Oil level in a 1971 OIL Lightning

[BorisX]

When I brought my Lightning it did not have a dip stick so I purchased one using the part number in the spares book. This has two marks on it but they are far apart (3 1/2" inches). The stick is 4 1/2" from the bottom of the "loop" to the end. There is a mark 1" from the bottom. I think I have over filled the tank which has caused oil to spill out of the breather but I'm not sure which mark to use but don't want to put too little oil in the engine? Is the bottom mark minimum oil level and the top one maximum (hot)?

[A10 JWO]

I think I used the lower level when it was cold, that is quite a big tank in the OIF, mine was 1972.

[Allan G]

A picture of your dipstick will help but there's usually a minimum and maximum mark. I resorted to the triumph dipstick on mine as the other type has a reputation of being dropped down the frame tube.

[Ian C]

Breather is on the top tube near headstock, so I can't see how overfilling would cause that.. Rule of thumb without dipstick is to fill to just below the return tube outlet.. I bought the later Triumph T140 dipstick which is fastened into the oil tank cap, but I don't bother too much with what it reads as I use my 'Rule of thumb' as mentioned earlier.. HTH

[ChrisG]

There is a cross piece below the filler cap where the dipstick fits and stops it dropping down to the bottom - provided you put it in the right way round (dont ask me how I know that).
Yes, the breather is at the front but if the tank is full to climbing into the front top tube then on heavy braking/ fork dip/ downwards on a steep hill, the oil can rush forward and possibly reach the breather.
Re the original question, I used it more as a 'see how far down the tank the level is'. If no oil shows I used to top it up until it did, up to about 1/2". Problem is, if it's not showing, its difficult to tell just how empty the tank may be.