I have a good 150,000 block that i'm about to build into a low compression stock sleeve 2.4 with inline pro rods mahle pistons and a k24 crank. Is it a must to replace the oil pump and water pump even i know these are good and working? These thing arent things there wear down is it?

 

Its not a must, but it saves a lot of time and labor if you do it while the engine is already out. They're also relatively inexpensive parts. It would suck to have your oil pump fail only a few months after putting the block back in

 

I would definitely do a new oil pump, I put one in my F20 when it went south. I went with a new ap2 oil pump, I heard that the ap2 pump is an upgrade, but I saw no visual differences and I can't confirm that it is or isn't.

The water pump is easy enough to do later down the road within the engine bay if needed, but given the low cost of a new pump it might be a good idea to do it now as well. Particularly with that amount of miles on the old one.

 

Where is that thread that claimed replacing oil pump does not require removing cylinder head like the Honda service manual said?

I remember reading that all you need to remove is the front cover of the engine.

But how do I loosen the timing chain wrapped around the oil pump pulley?

Will loosening the timing chain tensioner be enough to let the timing chain slip loose from the oil pump pulley?

 

Oil pump always, for sure. Water pump, depending on miles/condition.