need advice on my 81 natique engine rebuild

I recently purchased an 81 natique from a friends family, they basically gave it to me as it was the extra boat they had not used in two years. this is my first real boat so i am very excited and already in love with it. i knew it had some engine issues and was warned that it had overheated last time it was out. i picked the boat up and drove it home and when my dad and i pulled the engine apart we were very dissapointed to see that there had been water sitting in the cylinders for two years. needless to say the cylinders were not in good condition. all but two had spot rust on the cylinder walls.                          

my dad and i rented a cylinder hone and honed the rust out of the cylinders with the pistons at bottom dead center (not the best technique i know)

after honing all the damaged cylinders there are still small spots in each cylinder that are rough to the touch. they do not look or feel too bad but they are definitely not perfect. i am not too familiar with this kind of work and i am now wondering if i need to get a new block.   

   (after hone)

realistically i have about two months of boating season left in the sierra nevada region and i would get an engine replacement this winter. however i know the cylinders could allow extra oil to be deposited in the rough spots and then burned which may pollute quite a bit?

i am considering running it like it is, having it bored to 60 over (40 over now), or getting an engine replacement. any advice or help is much appreciated. thanks!

You probably should try and figure out how the water got in there before repairing it. Bad manifold, head, or whatever.

You need to do some research and find out if that block can be safely bored to .060 over. Maybe someone here knows for sure. Some manufacturers in the 70's and 80's only provided enough meat in the cylinder walls to go .030 over. I'm not sure what Ford did. My 81 is out to .040 but that was only because the machine shop was unhappy with how some of the walls looked at .030. Its been fine at .040 over.

Since your new at this, you need to know that engine is a reverse rotation. So the crank, cam, and crank seals are different and not interchangeable with a lefty which what a typical car or truck engine is. A block should be the same.

I think I would try and figure out how the water got in there. If not a cracked block or head, put it back together and run it for the rest of the season. Then figure out what you want to do. Rebuild or replace with rebuilt shorblock. Finding a reputable machine shop that knows how to properly work on marine engines especially a right had rotation can be a PITA!

thanks mark, the heads are in good enough condition to be refurbished and put back on. ill be looking for a new engine in the mean time.

I just got my engine to turn over, on a hunch that i already have an auto replacement engine. the belts turn clockwise which to me seems to mean that this is not a marine engine? any thoughts?

here's my prop. I'm almost positive that this boat ran with this prop, engine/starter combo right before it blew a gasket etc. should this shed some light on the issue?

Gary S wrote: The 351 block is all you need,the newer the better,but don't go older,rear seals will be different. The crank is made for right hand rotation,you would be best to have yours remachined since RR cranks are hard to come by,you remachine yours you know it will be right.Reuse your flywheel,dampner,rods,timing cover etc. RR cams you can get from places like Cam Research,everything else,ie gaskets,bearings,cam chain you can use quality automotive parts. Brass core plugs are needed too. The only part I understand thats hard to get is the rear main seal.

Careful Gary. If he does in fact have a newer 1-piece rear main seal style block, then the crank will not be rotation specific- only the seal. I agree that he has to be careful not to try and interchange parts (cranks/blocks) between the 2 styles. Stick with the newer 1-piece stuff, especially now that we suspect that it was rebuilt incorrectly as a Lefty somewhere along the way. Rebuild it properly as a Righty, as that will make the boat perform much better.