Excessive Engine Backlash
We’ve just started supporting a new marine operator, and the other day they were getting some concerning noises following the overhaul of their Caterpillar 3406 engine by another firm.
As it turned out, a fundamental setting had been missed.
Once on the vessel, we checked the backlash of the timing gears and found them to be out of tolerance, and the result was this damage to the teeth on the gears:
The engine arrived in our workshop, where we began our investigations including:
- Changing their oil pump gear for one we had in stock to see if there were any gear issues – none were found
- Removing their shaft from the case and swapping for a genuine one we had in stock – on testing, the backlash reduced from 0.025” to 0.010”!!
On further inspection we discovered that the 3rd party crankshaft was incorrectly made, with the teeth on the crankshaft gears being cut too deeply, causing the excessive backlash.
As part of the overhaul, we also measure all conrods – all were oval.
One way of rectifying this could be to machine them, like the repair shared here, but because they were 3rd party, with no markings denoting manufacturer or conformity, we cannot recommend this process.
It is vital to ensure your maintenance provider is using quality parts when carrying out any work on your engines, and you should always get backlash readings from anyone overhauling your engine.