Incorrect compression ratioimage

Incorrect compression ratio



This week we are working on a Mercedes Benz 400 series engine which is used in a crane on an oil platform.

The engine had been experiencing problems resulting in cracked manifolds and turbocharger housings which is why it’s in our workshop, but during our inspection of the supplied spares set, we’ve been able to prevent another problem.

Originally the engine had been taken out of service by another company who had ordered a set of spares for the engine, though couldn’t source the replacement manifolds or turbochargers.

With our MTU dealership, we also support Mercedes off-highway engines, so we’re able to utilise this experience to source the missing parts and have the competency to carry out the engine overhaul.

Beginning with a thorough inspection, our engineers found the main bearings and pistons that had been purchased by the previous company, were incorrect.

Piston compression ratio differences

Comparing these pistons, you can see the pistons are different, with the compression chamber on the new piston smaller and shallower.

Piston compression ratio differences

Using the MTU portal codes, we were able to confirm that although the purchased bearings and pistons were for an OM400 series engine, they were for a different specification.

The pistons supplied were from a model with a different compression ratio, meaning there would be an increase in the horsepower output from the 800hp required for this application.

It’s vital to bear in mind that not all engines are built the same – any parts you order must be correct for the engine you have. It is not enough to know that it is from the same type.

If you need help with sourcing difficult parts or any other aspect of engine maintenance, get in touch.

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