Hi,

I have recently purchased a 1989 Honda Prelude 2.0 EX Auto with a B20A4 12 valve engine with only 22000 miles. However this car has been stood in a garage next to a river for 28 years. Within this time it had suffered two floods and at one point been completely submerged. I’m now in the process of trying to recommission the car . The Body, trim and paint have cleaned up well. However I’m really struggling to find or obtain mechanical parts including exhaust ‘“currently making’’ and internal  engine parts including , valves, piston rings and gasket sets. 

Even though I’m experiencing some significant headaches. I have to say I’m really impressed with car and Hondas quality engineering. 
Regards 

Michael Hargreaves 

Hi Michael....welcome to the Club

Sounds an interesting project and story to tell of its tragic history.
The exhaust I can understand as open to corrosion with standing in water but the engine, if not turned over should be fine as wouldn't necessarily ingest water to the cylinders.
I would be tempted to remove as much of the anciliary items from the top of the engine and take the plugs out and fill with WD40, etc to turn over to clean the bores.
Obviously,  the cambelt would need changing along with water pump, etc and I reckon it will clean up nicely internally. I believe the pistons have ceramic coating and wouldn't require replacing or even cleaning.

Let us know how you get on and photos of the condition as it would be great to see