Jake,

When to rebuild can sometimes be a difficult question.

Usually, R/C car engines get rebuilt when the compression starts to go and the engine's not developing proper power.

If it's been damaged in a crash, it may need work sooner.

If the crank is difficult to turn over when it's the only thing in the crankcase, then you likely need new bearings. If the crank is damaged because the bearing seized and the crank kept going, then you'll need a new crank.

To check the connecting rod, you need to inspect it carefully. If you can only see oil squeeze, then it's OK. If you can see it actually move, then it's shot. Usually, if the rod-crank clearance gets much over .006"-.007" you might want to start thinking about a new rod. While it can work with as much as .010" clearance, power may start to suffer.

Basically, you determine what needs to be replaced, add up the costs of the needed parts and then compare to a new engine. You have to decide where you stop buying parts and buy a new engine, based upon the prices.

If you have us repair the engine, a new one will come sooner because of the labor charges.