Help Please - 912ULS Low differential pressure on Cyls 1 & 4

If you resolve your compression and oil consumption problem I would be interested in the solution as I've still got a rebuilt engine in a crate that I would like to get working again.

The piston is pretty obvious. The cylinder looks like it has low spots on it so I wouldn’t use it. I’ve got better ones sitting on the bench.

The cylinder head looks to be blowing is the first thing that jumps out, Lapping them together would help cure that, are you sure the piston rings were installed the correct way up? I have seen that a few times. I personally think what Sam thinks are low spots are just a reflection of the deposits on the piston crown. 

I may be absolutely wrong but this sounds to me like an engine run at low RPM (below optimum) for an extended time (over a 400 hr period).

I put it to you - low hrs, increased oil consumption, evidence of possible failure of piston ring/cylinder wall bedding in (low compression)  - all suggest incorrect engine management.

A Rotax 9 run within the recommended rpm 5200-5500 (over 400 hrs) would be unlikely to show these sort of symptoms.

Cheapest way out is to work the engine hard (5500rpm) over an extended period (s) - if it doesn't work what has the owner lost?

I've only owned it for the last 100 hrs but wouldn't see why the operating parameters I use would have been any different from new.

It has a CSP and is set at 5700 for takeoff, 5300 for climb and 5100-5250 for cruise.