What did you need to know? The ST series was made from 84-95. The ST120 you're looking at is probably from 86-87? Should be 12HP B&S.
If you go to www.sonnysbolens.com and click on manuals at the top of the page you will be taken to ST series and from there you can download a parts manual.
We have another member with an ST160. His name is boB. You may try emailing him for some first hand info. He posted about his tractor in the "what model do you own?" poll.
Most important questions are what is the overall condition of the tractor? Will it need any repairs before it can be used? How big is the deck? Is the 1.5 acres flat, hilly, all grass, partially wooded, etc?
Chances are the deck is 42" and should be able to handle 1.5 acres. The tractor in good condition is definately up to the task, but deck size will determine how long it will take to mow.
You haven't mentioned the price. It might be easier to offer an opinion knowing what else is available in the price range. If you have any concerns about parts, contact someone in the parts supplier thread, such as Ray's Mower and inquire.
regarding the accessories like the snow plow and rear tiller. Is the tractor heavy enough for a snow plow? quite a few of my friends tell me that these tractors are not heavy enough for this kind of work.
I think the tractor could probably handle a 6" snow on a typical driveway around 75-100 feet long with no problem. You would need to add weights and chains. I"m pretty sure that these were built pre-MTD, so are better built than the Bolens of today. I think the tiller would be no problem either, as it is only 26" wide. If you want to believe the GardenWay advertising of the time that these were made, they were touted as being very capable tractors. GardenWay had their faults, but their products were almost always able to match the claims (at least the ones I bought).
I'm not sure about larger wheels. I would hold off on any wheel size changes until you get the deck you want. There may be clearance issues with larger wheels. I know sometimes just swapping to AG's one size larger than OEM will cause the tires to rub on the edge of the deck in the raised position.
You can buy an NOS deck from [email protected] A simpler and possibly cheaper solution, (sonny's isn't giving anything away!) might be a tow behind mower set off to the side working with your 38" deck. You could increase your cutting area to 80"-90".
I suggest you try the 12HP and see how it goes. The 16HP won't necessarily mean faster speed. Most tractors operate in and around the same MPH range regardless of engine size. Like I said earlier these old engines have much more torque than the new ones.
I don't know how many upgrades you can make on this tractor. "Upgrade" assumes the options were available when new. There probably was a choice between a 38" or 42" deck, maybe AG tires instead of turf, other than that I don't you'd find too many options w/o going up the model line to an ST 140 or ST 160.
For cutting grass, your 12 HP should be fine. I can't see any problem worth swapping out a good running engine for. And the 16 twin you have will sure use more gas to do the same work. At $2 a gallon, that is something to consider.
I still don't forsee a problem with the 12 hp engine, even pulling a cart, unless you plan on hauling 2000 plus pounds up and down steep slopes, in which case, you should worry more about your brakes than HP. I think you will be surprised at the power that 12 hp will give you.
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