Kriyayoga ( a compound word) - this is very complex thing to understand because this is a compound word - which can...

Kriyayoga ( a compound word) - this is very complex thing to understand because this is a compound word - which can have many splits (the split of a compound produces a sentence). Based on the context one can split the compound in multiple ways - in each way of split the meaning changes subtly to greatly and the associated purport also changes accordingly.

I. - The first type of split - "Karmadharaya" 
(1) Kriya eva yogaH - means the kriya itself is Yoga.
(2)  Kriya ca asau yogaH ca - means kriya and also yoga.
(3) Kriya iti yogaH - the yoga which is known as kriya.

In all these karmadharaya splits (where the meanings differ sometimes subtly some times greatly) - However this split doesn't differentiate greatly between Kriya and Yoga. In all these the word Kriya is synomimous with the word Karma (action). Please note the word Karma also means a cause and effect force that determines destiny of a person.

However the trick is to understand the the etymological meanings (Yogartha) of the constituents of the compound Kriyayogah. Because each one of the constituent - the word 'Kriya' and word 'Yoga' - both are themselves Kridanta compounds. Each of these compounds themselves have only Bhavaartha. Bhaava loosly means passive action or intentionality or 'kriti'.

The dhatu "kr" (from which the kridanta compound Kriya comes) has many meanings from Being (passive) to Being (active) to physically doing something to creating something to just involved in the cyclical nature of the cosmic cause-effect process to being instrumental, to being causal, to being the doer, etc. The same way "yuj" dhatu from which the kridanta compound Yoga comes has many meanings - joining, fitment, propriety, unite, merge, connect, etc.

Now both these compounds when joined together (may) lose their individual meanings and produce a new meaning or may produced an enhanced meaning from that of the constituents.

This kind of split is used in Yogasutra and even in Bhagavadgita where nishkaamya karmayoga (without the desire in the result). This is wrongly interpretted in English as the "Yoga of action" - it should be the "Yoga which is action (realised through action)"

II. - The second type of split - "Tatpurusha"
(1) Kriyayaa yogaH - means through kriya the Yoga
(2) KriyaayaaH yogaH - means the Yoga of Kriya

The second type of split is what is used by the Babaji Kriya Yoga group (Yogananda Paramahamsa) 

III. - the thrid type of split - "Bahuvrihi"
(1) Kriya Yoga yasya saH = atman (or) Kriya Yoga yamin saH - this means that which Kriya and Yoga belongs or where they reside

------------------

One thing that need to be kept in mind is that all shastras use only Yogaartha for all the technical words - means the shastras take only the etymological meanings and not the popular meanings.

Most of the translators make this mistake while translating because - for most of the words the popular meanings are only given in the dictionary as the first /second meaning. Also the context has to be taken into account before the meaning is determined. This is the reason why we have a "Bhasya" or "Vyakhyana" tradition in Sanskrit.