So after removing my foot from my mouth I went to the parts catalogue to check as I was sure there were O/S B &S pistons listed.
I was right, they were listed , in the 2009-2011 catalogue from one of the local aftermarket suppliers.
Not in any of the subsequent ones & the O/S rings vanished in the 2017-2019 catalogue .
A long time ago I was having a chat to the Tecumseh storeman before Stens closed down the Sydney warehouse.
He showed the spot where the concrete was damaged where the containers full of push mower engines used to stand.
Apparently even back then when labour was cheap most mower shops would simply swap your blower housing & pull start onto a brand new engine, and charge the customer 1 or 2 hours labour for "fixing " your push mower engine rather than trying to actually diagnose & repair the faulty one .
So no surprise that there are no O/S pistons available any more
Now you CAN do anything mechanical if your wallet is thick enough .
For an O/S rebore
You need to find a piston of the correct dimensions & WEIGHT or take your old pistons to a specialist and have it expanded , but I have not heard of this service being available here for the last 30 years .
A new custom piston will have about 1 hour of machining by a 1st class machinist so there is $ 100 to $ 200
Then you need to have the cylinder bored
Now these engine do not have a bolt on cylinder block so you have to find some one who can mount the crankcases & bore the cylinder which will most likely add the price of fabricating a mounting plate .
A standard bore here is $ 60 ( Aus ) , a custom bore can go several hundred dollars if you can find some one to do it .
I had some blind cylinders (no head ) bored a while back and they cost $ 350 a hit because the machinist had to make up mounting plates and customise a boring bar
Even worse he could not hone it so we had to use a bottle brush hone .
And finally you will need to find some piston rings to fit .
You might get lucky but ring catalogues no longer list rings by size, they list them by application so you will have to ask one of the custom ring makers to make a set.
Even if it is a stock size you will be charged the custom ring price because you can not look up bore stroke & radial depth any more .
So a rebore & oversized piston will probably run to twice the retail price of a new engine.
Now fitting a sleeve has the same boring problems as the O/S piston
Next problem is finding a cast iron / steel sleeve in the right size
These are not just a piece of pipe turned down to fit, they are spun cast to achieve the right grain structure .
Down here I have never gotten a liner for small engines ( 250 cc or less ) any cheaper than $ 150 ( Aus ) which is more than the wholesale price of a replacement short block .
Then there is the problem of the head which will not be designed to clamp onto & hold the sleeve in place so it might fail
Then there is the problem of wall thickness in the actual cylinder which may split
IT will now be 3 seasons latter
Your grass will be 10' tall
And the rebuilt engine will have cost you about the same as a brand new Honda Commercial walk behind .
Now if you know a teached in a trade school you could get the whole shooting match done for a case of beer but it will take a full seimester
