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Wisconsin Model S-12D Heavy Duty Air Cooled Engine - Value?


I have a Wisconsin S-12D engine with electric start and charging system. I have been completely through this engine and replaced everything that needed to be replaced to bring it back to original specifications. The engine is all original except color and it is painted Chevrolet orange and black. And the exhaust pipe nipple between block and muffler has been replaced with steel couplings I assume to lower exhaust exit. Other than color and pipe it is completely stock. Wisconsin Model S-12D, Spec. No. 298798, Serial No. 5008932. Can anyone tell me the year of manufacture? Also I would like to sell this engine and I would appreciate any help with determining the value before I post it for sale. I just cleaned carburetor and installed carburetor kit, set valve clearances, cleaned and set points and timing. I also cleaned gas tank. It starts right up with push of starter button and runs smooth as silk. Charging system works as it should also, including ampere meter.



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Asking value is always a loaded question. What a collector says it's worth (if they were to sell theirs), is often more than they'd be willing to pay to buy one. In the SoCal market, your engine would probably would bring you $50-100 unless you found the right person, needing that particular engine to replace one on a machine that was built around it. While it looks to be in very nice shape, it is an orphan, what parts are left are usually quite pricey and the "S" series wasn't Wisconsin's best offering. By Zira's SN list, your engine was built sometime after April1958 but before April1981. If I had to take a guess, I'd put it in the late 60s to mid 70s. I have one of these on an 1800rpm Winco gen set. It runs well, but finding something as stupid set of points is near impossible.
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Colin O

I agree with JF671. I would narrow done the date of manufacture based on engines in my possession to around 1971-1972. It is a nice engine. If you were near me I would offer you about $150.00. That being send I don't think the S series would classify as collectible to most. I myself would rather have a TFD which is essentially the same hp.
If you are serious about selling you need to get as much exposure as possible. There are old tractor collectors that would value this unit as I believe they were on a few older model riding mowers. Try listing on Ebay, Craigslist, etc.

Colin O


Your engine was built in May of 1971. Although I have an S-12D in my collection, I do not value it highly. I paid $50 for mine with a Lindsay compressor hanging off the end of the crankshaft. It turns out the coil in mine was butchered, and that a replacement cost more than the whole engine. Quite a few Bolens tractors used the S-12D, or at least the TRA-12D, which is essentially the same engine. The S-series was designed to be a cheap, lightweight high rpm engine (3600rpm) to compete with the Kohler K series in the garden tractor market. Although they are built nearly as well as their equivalent Kohlers, they are a far cry from any of the earlier cast iron single cylinder Wisconsin engines. If you compare the 630cc 12hp AGND to the 472cc 12hp S-12D, the AGND develops 50% more torque on the same amount of fuel. Alot of people like and belive the S-12D is the greatest thing since sliced bread, and I am sure you could sell it easily to anyone needing an engine for their garden tractor. If it runs as good as it looks, $200-300 would be a good buy on that engine to the right guy. That number is based on the fuel tank, starter generator, a working stator, air intake and correct carburetor. I know several people who have paid $200 for just that carburetor alone.



Zira lives in Apex NC, he is a moderator on this site. He would know values, etc for your area. You would get more money locally because of the cost of shipping any distance.



The S-12D & TRA-12D are far from the same engine. Basically the S-series can be split into two separate families. The S-12D shares many parts with the S-10D & S-14D. The TRA-12D has parts commonality with the S-8D, TR-10D & TRA-10D and to a lesser extent the S-7D.

Earlier Bolens large frame tractors used the former, whilst Bolens tube frame tractors used the latter throughout their production run.



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I actually work in Sanford (at least for now). JF671 pretty well nailed it (in my opinion). As far as Ktron's quote "The S-series was designed to be a cheap, lightweight high rpm engine (3600rpm) to compete with the Kohler K series in the garden tractor market.", I would have said cheaper, lighterweight, but otherwise he too nailed it. Basically, unless you have equipment that uses this engine, there's not much demand. Good user, not real collectable.


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I have an S-8D that I picked up a couple decades ago at a swap meet for $35. It’s been a great engine, and, after my friend and I carried it out of there, I would say it is by no means light! ;)