Volvo Penta sterndrive - Vacuum Test Dilemma

[moresparks]

Hi.. Should I worry...
Volvo Penta sterndrives -290 SP-A’s about 30 years old.
I have them both at home for general cleaning and painting.
When I drained the oil from both, it was as good as it went in – no hint of water contamination.
Pressure and Vacuum tested – one is spot on according to the Workshop Manual. The other – not quite!
It will hold correct pressure for hours – but the vacuum is slightly down. Looking back on my notes it doesn’t appear to have changed since the last time I checked.
I can evacuate to around 12 / 13 ins HGa then it very slowly leaks to around 9ins HGa and then holds for hours. I believe it’s in specification; but different to the other drive.
I have replaced the Gear Shift (Eccentric Piston) seal and O ring but only a slight improvement.
I could replace the shaft seal but wondered if I was wasting my time, on top of that my pressure / vacuum tool‘s handle just broke! The shaft seal has been replaced but a couple of seasons ago.
So decisions decisions .... I was kind of hoping this would be my last time in taking them off and putting them back on... I am getting too old and they are heavy!!

 

[DavidJ]

If it’s within specification then it’s ok
That’s what a specification is.
The specification will take into account all the variabilities and an allowance for acceptable wear

 

[moresparks]

I guess so... That’s why I accepted the previous test.
As I am at home in “Lockdown” I thought I may try to get it similar to the other Drive which is rock steady for the Vacuum test for hours.
The Manual states not to lose more than approx 1” (25mm) HGa during 3 minutes and it is better than that.

 

[DavidJ]

I admire what you are trying to do. The problem with a specification or a tolerance is that it implies that it’s good if within (and bad if not) There is a “best” which we should try and achieve (in life) by reducing variables
I wish you well in your quest

There is another argument “If it ain't broke don’t fix it”