What to look for in a motor?

[KenRas]

I will be building the Olympian in the next or so and am considering an I/O or possibly twin OB's. The price of twins has me a little concerned unless I go used. I would like to have in the neighborhood of 300HP with either the OB or I/O. When looking at used motors what should I be looking for? Is there any way, other than prop damage, to tell if a motor has been abused? Being new to boat building I do not want to get into a position where overhaul costs would be more than a new motor.

[fergal butler]

A good starting point would be to have good compression with around a 10% difference between each cylinder also check the gear oil for any sings of water.

[darthplywood]

i've been burnt on more then one used outboard over the years. The only circumstances i would buy used again is it would have to fit certain conditions:

1. i wouldn't buy unless i was buying from an authorized dealer for that make of outboard who was willing to provide some sort of warranty (not much of a warranty....just enough to know i could take it out and run it some and bring it back if it had any problems in the few months to follow the purchase)

2. good compression test (everyone would agree to that)

3. i personally (and i know many will disagree) would NEVER buy a used outboard that was used in salt water (UNLESS...i personally knew the person selling the outboard and it fit the above 2 conditions).