I have said this on more than one occasion, but just to drum t\it in.
Vertical shaft engines are just about exclusive to mowers and as such are made to be the cheapest engine it is possible to make that will actually run.
And when it comes to quality it is just a case of some being less cheap than others.
And this comes back from the "american Dream" that technology will deliver more at lower price every year.
So the engines just get cheaper every year till there is no profit in making them so one by one the companies that used to do it go bust or just exit the market .
The crank will clean up with a dip in cold HCl or hot NaOH followed up with a little polish with some Silvro ( 0-2 µ abrasive size )
The top bush area can be recovered by rubbing down the dags only so you do not touch the valleys, just the peaks and only just enough for the drank to spin freely in it
OR you can get it bushed , but the bush will need to be keyed into the crankcase
I use 85:5:5:5 leadded gunmetal ( you lot might call it leadded brass or leadded bronze ) which expands a poofteenth less than the aluminium so can spin when the case gets hot.
I only use a 0.0005" shrink fit as the first couple split the crankcase, although the original seizure could have started some cracks that I did not detect because I did not do proper crack testing .
Anyway about 1 in 5 top seizures will be recoverable with nothing more than a little polish on the shaft and the absolute lease work to the cases, those deep ruts will actually work as oil reservoirs to help prevent further seizures .
The big problem is in use the belts pull back on the crankshaft , the lower bush acts as a fulcrium point so if there is any excessive clearance in the top bush the crank will tilt and lock up.
So the engine you bench test will run just fine till you put it in the mower & engage the blades.
I have been caught out like this a couple of times
