I'm looking to purchase an engine with a bottom end knock, with the assumption that I will be able to rebuild it with no previous experience, fitting aftermarket forged parts.

These are my assumptions based on the info on the advert and what I've been told by the seller:

  • The engine has a bottom end knock, probably a spun journal bearing
  • Replacing the journal bearings, conrods and pistons (+pins etc) will solve the problem.
  • There is hopefully nothing else wrong with the engine.

Is this likely to be sufficient? What else can I look for if not?


  • If it has a knock the crankshaft will need machining for sure. – Moab Sep 12 '18 at 22:22

It very much depends on how bad the knock is and how long it was ran whilst knocking.

I'd be factoring a crank regrind into the engineering work you'll need. I'd also personally consider at minimum honing the bores but there is a slight chance that you'll need an overbore in which case, if you've already changing the pistons, go oversize. You won't know until you have the engine stripped and get the DTI on the crank though.

Unless the engine is scrap price or is incredibly rare, I'd personally be looking for an engine I could hear running and has no known issues as a better candidate for a rebuild. Engineering work has a habit of spiralling, especially when you're starting with an engine you don't personally know but are told already has a known issue.

  • Thanks, I will send both off for machining as I have just got a quote and it is very reasonable. Edit: the price of running engines is 3-5x the price of faulty engines and I will be replacing the broken parts anyway. I just dont want to spend the extra and i'm willing to learn – MIL-SPEC Sep 12 '18 at 11:15

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