Kohler 321c

I have a 1983 Allis Chalmers 914H tractor that has been a trooper for years. When mowing deep grass when the outside temp is hot the enging makes a rapping noise and suddenly binds. It has done this for 2 years now and after 10 minutes cooling down she will fire up and run again like new. My Kohler manual makes no mention of usage of synthetic oils. Would synthetic oil help it run cooler?It sounds like the connecting rod is giving up on me. I want to run it till it dies for good then replace the engine with a new short block. I have always kept the mower serviced well. She is just an old horse. I don't want a new one. What viscosity synthetic should I try if I do? Outside temp when mowing is usually between 75 and 90 degrees.
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I run Mobil 10W-40 Synthetic in mine, however from what you are describing it sounds as though you have problems beyond which a change of oil type will address. It's really not that much trouble to open up the engine and replace the connecting rod. How long do you run between oil changes?
Steve wrote:

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Oil is changed twice per summer. It does not happen often, just when really heading through deep grass. May only happen twice a summer but it is a hellacious noise. Just thought synthetic might help it run cooler.

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I'd say go for it with the synthetic Mobil 10W-40. You certainly aren't going to hurt anything and at worst you are out a $3-$4 quart of oil. Like the other poster said, make sure that you don't have any blocked cooling fins around the cylinder head. Also make sure any shrouding around the cylinder head that directs air flow is in place. You can hose it down to clean any grass and crud out if it is not clean. Then crank the engine and let it run to dry every thing out and get the oil good and hot. Draining hot oil from a recently run engine is more likely to get any junk that will tend to fall out of suspension while the motor sits. I'd be really curious what your results are. After you have done this drop us a line and let us know what happened.
BTW, sounds like you are changing the oil often enough, unless you are cutting grass for a living. Two changes a year for a residential user should be more than enough. Does your engine have a spin on oil filter? I'd make sure I change that as well.
As I said, I'm curious to know what your results are.
Joe
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Steve wrote:

Make sure the cooling fins aren't blocked (maybe with grass?), the timing is correct and the mixture is not too lean. These are among the things which can cause overheating.
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