Has anyone, ever went to the extent of replacing the piston connecting rod, to get rid of knocking in engine? I am debating doing it, more to prove to myself I can do it.
EVERYTHING else on ATV is great, of course the plastics, are faded, but, everything works as it should, and it has plenty of power for me.
From what I can glean from from pictures it seems the connecting rod and crankshaft are sold and replaced as a pair. Any info would be greatly appreciated.
Happy Thanksgiving

 

Very rare to have a big end knocking on a bike. I have only had two in nearly 20 years of fixing them for a living. Piston slap on air cooled engines is common, usually the result of a slight piston seizure which has scored the piston skirt but done little other damage. They knock quite loudly at idle but go quiet once revving. Also, looks like there is a harmonic balancer from your picture, possible that has a fault, either not timed correctly, or some have spring loaded dampers built in, which could have deteriorated.

Regarding "built up" crankshafts, the big end journal is pressed into the crankshaft halves with rod already on it. Regarded as a specialist job, as the two halves of the crank have to be aligned afterwards.

 

I have found early on, your input is value added, from your years of experience working on these engines, so please do not take this the wrong way, as I have several questions, please see below. Also, this Bayou 250 engine, had experienced significant damage, bent valves, broken timing gear, severely damaged rocker arms, etc...
1. As the harmonic balancer appears to be molded, and "keyed" how could it get out of time?
2. Maybe the damage caused when timing timing gear broke could have caused damage to harmonic balancer, and/or balancer drive gear, and springs, or maybe, just from age, the springs have become weakened, I suppose I should have replaced it.
3. I have replaced the piston and rings, and honed the cylinder before placing it in service, so I don't know how much piston slap could be happening.
4. I think this ATV was severely mistreated, by previous owners, but I have narrowed the knock down to the right side, have you ever seen a harmonic balancer drive gear cause a knocking, and would it hurt the engine?
I am sorry for so many questions, but I really want to make this ATV as good as it can be for personal use, NOT re-sale.

 

If the timing marks on the harmonic balancer and crank are lined up, it should be OK. Never had a Kawasaki balancer apart but Yamaha balancers can be assembled up wrongly which throws them out of time.
With a new piston, there shouldn't be any slap, provided bore was within size tolerance.
I have not had balancer problems, though have an Eiger in at the moment which may, it has a similar knock to yours. Others asking my advice here about Yamaha 350s, have rebuilt their balancers wrongly, resulting in it being out of time. If the balancer hits the crank once a rev, it isn't going to do the engine any good.