Montgomery Wards lawn tractor

It is likely a Briggs and Stratton. The numbers are stamped into a shroud and should be visible unless the tin work has been replaced, thrown away or painted over with a roller.

thank you for the piston size that was helpful, but I think I need to clarify. I am going to be rebuilding this engines top end so I will need gaskets seals and anything else I see wrong.
I have no tins or anything that is stamped.
there must be a way to reverse engineer the engine to find out what it is, such as " this is different in each engine'.

robbrujohn
yes, I know it is a b&s but there must be a way to identify it another way to get gaskets, seals, and pistons

It would take a lot of research of your part.
 
The first digit of the model is displacement. In the case of an opposed engine would be 40 or 42 cu in.
The first digit/character after displacement is the basic design series which can be code from 0-9, A-Z
The second digit after displacement is the crankshaft style, carburetor, and governor design.
The third digit after displacement is the PTO bearing, gear reduction, auxiliary gear, and lubrication system.  

And four digit after displacement is the starter type. 
 
Here is the chart of the variables. Now the chart that is the 271172 service would the details about the carburetors and governors. that is more specific the opposed engines.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwi8hoaaiazmAhWTvZ4KHRUzCKYQFjAAegQIBRAC&url=https%3A%2F%2Fwww.briggsandstratton.com%2Fcontent%2Fdam%2Fbriggsandstratton%2Fna%2Fen_us%2FFiles%2FNumerical_Designation_System.pdf&usg=AOvVaw2NvmXLlio9cta-uK9S3-F0
 
Once you get a possible model code then you need go thru the various model and type numbers IPL comparing all the possible variants.
 
A copy of the Briggs 271172 Twin L-Head service manual would be useful too so you can compare various specs.



        


    




Okay now due to being a pre 1981 model (1978, Sept 12) format the model number as 401417-0128-99 then you can look-up the parts on most sites that have illustrated parts lookup (IPL). THe reason for the slight change the model number is that Briggs has combined all of the trim codes for pre 1981 under 99.
 
Note complete gasket set is PN 394501. Also you have the 3 bolt fuel pump carburetor which uses carburetor repair kit PN 694056.