I'm installing a used engine in my 03 MCS .The engine has 144k . Before I install it im pulling the front cover to change the front cover gasket and the crank seal . Also the timing chain guides and tensioner .

Would it be a good idea to also change the timing chain as long as im in there ?
I've read that when replacing the chain you should replace the crank and cam gear. Is that really necessary ?

 

While not an "absolute" requirement..!
YES, it is a very good idea to change both sprockets / gears, along with a new chain. When I changed a chain on any of my motorcycles over the years, I always changed the sprockets, at the same time. Even if the old sprockets "looked" ok, I know that they aren't...ok.

Why you ask!!?

Because as the old chain side plates start to stretch and the pin to pin dimension starts to get longer (despite some saying no...YES...this happens), that wears the sprockets / gear tooth tooth root location from the original, as designed dimension.
So...when you put a new chain onto old / used sprockets / gears, that "worn" sprocket / gear still has had it tooth root dimension permanently changed, which WILL cause an early demise to your new chain.

Hope that helps.

Mike

 

Thanks Mike it does help except now I'm thinking it's better to just leave the chain alone