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what should I do?
Looking at the picture it is really hard to say. What have you done to clean it up. What is your intention for the engine. Where else did the water go.
Rebuilding those Onan engines is expensive and technical.
On an old walk behind mower I found in the dump the cylinder looked much worse than that and the valves wer stuck open. I pulled the head off. Wiped the cylinder out with emery cloth. Got it turning,sprayed WD on the valve stems, ran the piston to the bottom of its stroke and hammered the valves shut. Spun it to re open the valves and hammered them shut again. When the valves quit sticking open I gave fresh oil put the head back on and mowed the lawn. Used it for two years and gave it to a friend. I wouldn't recommend that for something you treasure but it is one of many options.
Don
 

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Discussion Starter · #4 ·
Looks like the water came in thru the carb, down the intake manifold and into the open intake valve. The other cylinder stayed dry. The valves still operate, although They are a little rusty. I can feel some roughness in the cylinder wall, but no deep pits. I ran a home in there for just a few rounds. Engine goes on an Ingersoll 4020PS that I just picked up. I intend to put it back on the Ingersoll or find another one to replace it. Don’t want to spend the $$ on parts to rebuild!
 

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Did you pull the piston to hone? That would be the best. With the piston out you can check the rings for rust and clean everything. then just put it back together and give it a try. At this point you have little to nothing to lose. If it smokes to bad to put up with and won't stop it will still be as valuable as it is now. Removing the piston also gives you the chance to inspect the rod bearing.
Don
 

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Personally I would pull the piston, hone the cylinder till clean and then measure the bore. If the bore is with in specs then install the old piston with new rings. (not a good practice to put used rings back in a cylinder) If the bore measurements are out of spec then over boring the cylinder and an over sized piston & rings will be required. Do it once, do it right & enjoy it a long time.
 

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Last year I got a Briggs opposed twin that had been sitting for like 12 years (supposededly) and I noticed one of the cylinders seemed to have really low compression. I pulled the head and found some pretty bad rusting on the cylinder. I took a small drill powered wire brush and ran it in there. Also did a lot of paper towel wiping and penetrating oil spraying. After the brushing there were some pits still but you could barely feel them. The engine smoked a bit at first, but now it runs great, and seems to litterally burn no oil. Here's a video I made of it. In part of the video (around the half way mark) you can see me do this cleaning.
 

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Had an old crusty rusty Sears SS16 with a Onan BF-MS that had Alot worse rust in it. It was actually pitted pretty deep on the bottom where the water had sat in it for many years. I wire wheeled the rust off and honed it without pulling the piston. Just enough to take the sharp edges off of the rust craters. Darn thing ran good after about 10-15 minutes of smoking. Pretty sure the oil ring was stuck in the piston.

I originally bought it for the plow and 3 point for my other Sears but I used that old rusted and busted up tractor to plow snow with for 4 years. Hood was busted off and the dash was destroyed, transmission sounded like it was about to come apart the last time I used it but the engine still ran strong. It did use a little oil but it was dependable.
 

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Discussion Starter · #9 ·
Did you pull the piston to hone? That would be the best. With the piston out you can check the rings for rust and clean everything. then just put it back together and give it a try. At this point you have little to nothing to lose. If it smokes to bad to put up with and won't stop it will still be as valuable as it is now. Removing the piston also gives you the chance to inspect the rod bearing.
Don
i did not pull the piston, but I have ordered a set of rings so I will be cracking it open and honing it properly. I do not intend to go to the expense of new pistons and proper machining, though. Thanks! Ed
 

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Discussion Starter · #10 ·
Personally I would pull the piston, hone the cylinder till clean and then measure the bore. If the bore is with in specs then install the old piston with new rings. (not a good practice to put used rings back in a cylinder) If the bore measurements are out of spec then over boring the cylinder and an over sized piston & rings will be required. Do it once, do it right & enjoy it a long time.
Thanks. Ordered rings and gaskets. Hoping to get it going without further expanse! Ed
 
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