Originally Posted by
PDR1
As far as I'm aware you can't "shim" the pressure transmitter (it's a hydraulic transducer that responds to pressure) - the thing you shim is the oil pressure release valve spring. Adding more shims puts more pressure on the release valve piston and thus increases the pressure at which it opens. I can see the logic of putting a lot of shims in for the first run to ensure a healthy oil pressure for those important first few minutes of running, but as it's the actual oil pressure which is excessive (not just the gauge reading) it should be reduced to the specified range as soon as practicable because running in that condition will have all the consequences previously described.
But I am confused - if this was a "new" engine then the oil pressure should have been set at the factory because engines have to be bench run in a dyno (actually several bench runs at a range of power settings and durations) before being released for sale. If it was an overhauled engine it should also have had a number of bench runs before release - these are certification requirements. If a new or overhauled engine was installed without a correctly set oil pressure relief valve then the company who made/overhauled it seem to have been playing fast and loose with release certificates...
PDR
Hi
PDR, TBH, I'm not sure exactly which bit had the extra shims fitted (this was 20+ years ago now and I have difficulty remembering anything at all these days) so I'd not use my post ILO the Maintenance Manual.
Point was, the engine came with a full set of shims fitted (shims I do recall being mentioned) to the
oil widger-thingy-ma-jig which were then removed once the donk was on the aircraft to "calibrate it" to the aircraft using a calibrated pressure gauge and that was all part of the install - hence why it was such a quick fix. But I guess my real point is, if it's wrong, don't take people's word for it being "OK" etc, etc, etc - just make a bit of a fuss and just get it sorted – or walk away! I've had a few cases where things have been plain wrong, often straight out of maint, but have taken very little time to sort. But I often have found pilots have accepted the issue without snagging them for a while until I ended up flying them!
Now, as to whether that was just the gauge system, or to take into account the effects of oil coolers etc in the system and to what the shims were fitted to etc, etc I know not – the transmitter is what my memory tells me I was told but I could be wrong. It’s the “If not right, get it fixed!” message which is important and I wanted to highlight. Sorry I can't add more to the Techie detail but, being of the LEC/AV "persuasion", I've always left the messy stuff to the Riggers/Sooties/Grubbers who appear to enjoy being up to their armpits in gunk! What’s the saying, “If there are dogs around, why bark yourself?”!!!!!
And on that last bomb-shell - hat, coat and exit sharp Left before the nasty old Riggers/Sooties/Grubbers catch up with me!!!!!!
Cheers,
H 'n' H