The lifespan of an Atomic 4 is not measured in hours run but in how much of the internals of the block have corroded away.
How to measure how much 'meat' is left: Drain the engine if fresh water
cooled, then remove one of the exhaust
manifold bolts; with a dental pick, etc. reach into the bore of the bolt hole and count how many threads are left - if 4 or more threads than you have enough/sufficient casting thickness for quite a few hours. Less than 3-4 threads, the engine has corroded away internally and isnt even a candidate for a 'rebuild'.
(Reseal the end of the manifold bolt with aircraft grade 'Permatex' when replacing to seal the bolt/threads.)
An Atomic-4 that would be a 'keeper' or a 'good find': Has freshwater cooling
(heat exchanger) ... meaning that the boat was stored with the engine ***never drained / dried-out**** but had antifreeze
with rust inhibitor in all the cooling
jackets and exhaust
manifold ... prevents the formation of internal 'slab rust' and protects the 'good' / blue or black rust and prevents the change to bad: 'red' rust.
One that was run often and hard; not, one that 'sat around'.
One that had 'hardened valve seats' installed ... to handle the 'hammering' caused by unleaded gasoline ... this engine was designed for leaded gasoline and unless the PO used a 're-lead' compound you can expect the valves and seats to be quite 'hammered' no matter how many hours on it.
If the current compression
is good and the internals arent showing much corrosion
, then ~4000+ hours is a fair amount of time. They dont 'wear out' as much as they 'corrode away' from the inside out.
A top-of-the-line, precisioin rebuilt A-4 would run about $4500; $3500 for a 'short block' .... the install labor is extra but its easy to do yourself. go to www.moyermarine.com
for prices and options ...this is the website of probably the world's recognized 'guru' of Atomic-4s.
If it doesnt already have these then consider to add: electonic ignition with compatible ignition coil, electric fuel pump
, PCV valve, heat exchanger
, new external thermostat housing.
conversion: $9-11000 engine, $1-2000 bed rebuild
, $300 new shaft and prop, $??? new tank and fuel delivery
system ... add labor ... probably about $14000 when you're done. And the boat will SQUAT on its stern with all that extra added weight of a diesel.
***** Make SURE that this boat does NOT have a fiberglass fuel tank
. As the USA changes over from MTBE to Ethanolated gasoline severe problems are showing up in marine
engines, etc. 1. most old (pre mid 1980s) fiberglass
fuel tanks are INCOMPATIBLE with ethanolated gasolines ... will dissolve the resin and the tank WILL leak ..... BOOOOOM!. 2. MTBE fuel co-mixed with Ethanolated gasoline forms strange 'gums', etc. and these can destroy the engine .... just like adding sugar to the gasoline. 3. The rubber components (float needle valve, gaskets, etc.) of the carburator are NOT compatible with Gasoline with Ethanol - need to be changed. Be aware that the 3/4-1 gallon per hour was leaded or MTBE added gasolines; you can expect 10-15% LESS fuel economy with gasoline formulated with ethanol.
Hope this helps.