51 8n side mount converted to 12v..We picked up this tractor awhile ago, it had been sitting in a quonset for an unknown amount of time as the owner had passed. It appeared to have been serviced and then parked as the oil was like new. Anyhow first thing we did was put some atf in the cylinders. We were able to turn it over using a round metal bar on the nut. Did a carb rebuild, fixed the 12v conversion, rewired and so on. First bumped the starter button a few times with the key off. Everything sounded ok. No oil pressure while doing this. So we turned key on and she fired right up. Only ran it a few seconds as we got smoked out by the atf!! Started it again and thought we heard a noise so we shut it right back off. 3rd time we started it oil pressure came right up and let it run oh probably 45 seconds and realized we have a problem. Something somewhere in the engine was hammering. Any idea on what it would be. Sounded like from the lower side of the engine. Possibly towards the rear. Do things go bad just sitting for years? Am i looking at a whole rebuild?