Honda TRX 250 knock, knock knock

[Diesel Dave]

Hi there,  Dave from Dunedin New Zealand here. I help my neighbor out here and there being a mechanic. He has a farm and I only have a few acres. His TRX started knocking from the engine and was condemned by the local agent. He upgraded and asked if I wanted his old one. The engine still starts but has a death knock alright, I have not investigated yet.  I have very little experience with quads, if I were to find a replacement engine would it need to be exactly the same?  I realise the mounts will have to match but wondered if a different cc engine fits the same, I don't suppose it is viable to fix big end issues cost wise? any help appreciated!  Cheers

[Frank Angerano]

Two ways to go about this. 
1. Pull the engine and split it open and drop new crank in the engine.  Three hours to pull the engine. Prob 6 hours of engine labor and another three hours putting it back in tue frame. 
2. Find a used motor on eBay and swap out the lower end.  

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