cyn cael cinio	before having dinner
cyn cyrraedd	before arriving

But i must be used with a person:

cyn i fi gael cinio	before I have dinner
cyn iddi hi gyrraedd	before she arrives

Remember to use the correct suffix with i. You can find the conjugation of the preposition i and other prepositions by clicking here.

There are other words which are used in this way with i, e.g.

nes, ar ôl, rhag ofn, erbyn, e.g.

erbyn i ti gyrraedd	by the time you arrive
ar ôl i chi adael	after you left

Don't forget that the preposition i causes a soft mutation.  A table of mutations can be found by clicking here.