Most A-4s can be rebuilt the 1st time around without even so much as an over-bore. The low compression is gentle on the cylinders. Marvel Mystery Oil removes carbon deposits and insures the comrpession stays nice and low. Because it is an old "L" head design the valves run cooler than in overhead designs and there is no long valve train to wear. There were more than 40,000 A-4s put into MOST of the small production sailboats. They have outlived MANY of the diesel options available at the time as well. One notable Canadian diesel manufacturer stopped supplying parts to the engines they provided as options leaving many with nothing to do but get rid of their engines for fear that the next breakdown would leave them stranded needing an entire engine replacement. That corporation was the most prevalent supplier of options diesels at the time as well. So those who ordered their boats with A-4s avoided that issue. Many parts are still available for the A-4. The increase in re-sale value a diesel replacement provides is never anywhere NEAR the cost of the replacement and about the best one can hope for is a 40% price recovery at resale with most taking far less. The only real place anyone is going to see any cost benefit from a diesel is in fuel economy. You have to do a LOT of motoring to get that as well to actaully offset a substantial portion of replacement costs. With the arrival of bullet proof solid state ignition systems, converting an A-4 to one of those ends a huge part of the dependability issues inherent with gasoline engines. As far refreshing an A-4 goes one owner was quoted a price of 8,000 dollars from the yard. He took his out and back home and spent 800 dollars under the guidance of Moyer Marine. That spring he installed the engine and it ran like new. A BARE, rebuilt, short block with pistons, crank, valves and bearings all spec'ed out runs 3,500 dollars from Moyer Marine. Needless to say, a completely NEW A-4 costs every bit what a replacement diesel can cost and then some in many instances. The A-4 is rated at 30HP at 3000 RPM. One matched to a proper prop will never spin over 2500. Many of the stock props were horridly over pop for tehe A-4. Indiego sells one specifically designed for the A-4 that simply can not be beat. The A-4 is EASY to rebuild with simple hand tools and a low speed drill and cylinder hone are that is needed even if the rings do need to be replaced. Considering the age of most of the boats these engines were offered in, getting any real value out of a diesel this late in the game for them is simply never going to happen in most cases for various reasons. This is why so many A-4s will probably live on for another 45 years. Increasing the compression for performance is an A-4 killer. There are no center crank bearings in the A-4. Increasing cylinder pressures is a very stupid thing to do with one. Speaking of crank shafts though. So many were stockpiled because the only way to really break one is to flood the cylinders by over cranking, that those can be had for a scrap price. I have never heard of one needing to be replaced or ground unless somebody ran without oil.