Parked-up two stroke conrod bearing issue

[David Lahey]

I was tidying up at home today and found this TY250 conrod kit that had been removed from a working motor a few years ago.
I was rebuilding the motor at the time and had a decision to make about the job. Should I fit a new conrod kit or leave the existing one in there?
I knew that the bike had been sitting parked up in a shed for 10-15 years before I worked on it. I test rode the bike before pulling it apart to test for things that might need doing while the motor was apart. There were a few things but this story is just about the conrod big end bearing.
The big end side clearance and rod-rocking play were well within spec. However knowing the bike had been parked up for so long, I was concerned that there may have been corrosion pitting on the big end pin or on the big end rollers that was not visible with the crankshaft assembled. Because of the risk of there being hidden corrosion damage, a new (Hot Rods) conrod kit was ordered.
The old crank pin did have corrosion pitting which can be seen in the photo, so fitting a new conrod kit turned out to be a very good decision. Pitting like what can be seen on this pin will soon cause the big end bearing to fail catastrophically. This releases metal particles which then destroy the bore, piston and rings as they make their way towards the exhaust pipe.

There's a few things that can be done to minimise the possibility of corrosion damage to two stroke engine bearings.

If your bike runs on premix and you know you are going to be parking the bike for a while, run the motor with the starting device engaged for a while before stopping the motor. This puts additional oil inside the motor. It's also a quick way to empty out the float bowl, which is also important for a stored bike.
Run, or at the very least, turn over the motor every couple of months. This redistributes the oil around the bearings. When it is stopped, the oil works its way downhill (into the bottoms of the bearings). Running a two stroke is far superior for this than just turning it over.
If you normally run full synthetic two stroke oil in your premix, run it on some premix that has some mineral oil in it before you store it. Mineral oil provides much better corrosion resistance for the bearings. It's why I use semi synthetic premix oil.

The photos show two sides of the same big end pin. The lower photo shows the pitting. The side with the pits was probably facing upwards while the bike was stored (and has the least residual oil coating it).