I bought a couple of used engines off that auction site recently and amin the process of slowlyrefurbishing them.

One of the engines had a lot of crud and caster residue inside and even a 6 hour soak in a warm anti-freeze bath followed by some vigourous scrubbing with a toothbrush couldn't get the crud off.

The rear bearing was stuck pretty well to the crank and in an effort to remove the bearing i sprayed some WD-40 onto it in the hope that it would penetrate and allow the bearing to slip free.

Much to my surprise, when i was handling the crank and bearing a lot of the crud just started to wipe off.
So then Isprayed the inside of the crankcase with a liberal dose of WD-40 and all of the crud in there wiped clean too. Anything that didn't wipe off with a rag came away with a scrapeof the fingernail.It seems to work really well when cleaning aluminium.

Iwas impressed.

I'm not advocating the use of WD-40 as an after-run but it now has a permanent place in my toolbox as a cleaner.

WD40 is fair, but there are better lubes out threre,...ill be honest i didnt haveanything else last ttime i reassembled and engine and used wd40 to coat everything....3 in one is good too, .....youll need to heat the engine in an oven or use a heat gun(personal fave) Youll need to remove cylinder head, and back plate, remove piston liner, then piston...then take the prop hub off which will require atleast 250 degrees, same thing to pop out shaft....Im sure by the morning someone way more qualified than me will give you a better answere. Ive only changed bearing three times.

WD40 works pretty good as a cleaner and to free up things. It will also was out the contaminated oil from a engine