Hi Gents,
After waiting for the parts to arrive and having to send one back because the wrong item was sent, I've finally managed to slave in a mechanical gauge to check the actual pump pressure. Running the engine shows around 4.5 bar after start at idle, dropping to about 3 bar at 4,000 RPM on the mechanical gauge once reasonably warmed up. The flydat shows about .5 bar less at idle and .3 bar less at 4,000 RPM. Once warmed up to around 80 degrees Celsius, idle on the mechanical gauge shows about 3 bar and 2.5 bar at 4,000 RPM. I noticed at 2,200 RPM the pressure fluctuating rapidly on both mechanical gauge and Flydat between about 3.2 and 2.2 bar at a rate of about twice per second. Increasing or decreasing the revs by a few RPM stops the rapid fluctuations.
I spoke to the UK ex-Rotax agents who are really helpful and asked about the mushroom-headed valve mod and apparently it was them that designed and submitted it to Rotax. The upshot of the discussions was to check that the valve ball and seat is not damaged and also to check whether there is already a shim under the spring. If no shim is present, try fitting a shim (actually a washer or 2 to make up the same 1.5mm thickness as the genuine shim will work) and check what difference that makes. I tried that and note the pressure is a good bit higher, but I'm now concerned it may be too high as the max pressure I've seen on the mechanical gauge was about 5.5 bar which exceeds the 5 bar limit. So, this raises the questions of what are the risks or disadvantages of too high oil pressure - sheared oil pump drive? burst seals? I've removed one of the washers and pressures are almost back to the original levels - 2.2 bar seems to be the minimum on the Flydat which is too close for my liking to the 2.0 bar limit that starts the display flashing again.
Next steps:
Probably change the pressure transmitter as it's reading low across the range according to the mechanical gauge, from 0.3 bar at best to nearly 1 bar at worst. I'm not sure about the accuracy of the mechanical gauge, but my feelings are that it is more accurate than the sensor.
A new valve spring and possibly a mushroom-headed valve to replace the ball bearing. Maybe a shim under the spring too.
I have been told there is a new bolt available to guide the spring and mushroom-headed valve better. Does anyone have any experience of this and does it work?
Thanks for any comments,
Frank.
