The Mechanicus work for everyone, in all layers of Imperial society,

from the lowliest garbage recycling plant; up to the loftiest spire of a wealthy noble house;

from the most mundane cargo freighter; and out to the most gigantic battlecruiser.

They maintain the machinery of most all Imperial organizations.

(All names are random, insert your campaign notes at will)

So they might see all kinds of things, good and bad,

as they make their rounds and maintain or fix machinery that is everywhere.

Because everyone everywhere needs water, air, power, sanitation, vox, etc.

Not to mention more complex needs such as gravity, force domes, terraforming, etc.

They see the heresy of House Avendorf, they see the hard work of House Bendix.

They notice the hoarding of the Mining Guilds, they see the graft of the Arbites Prefect.

They see the true faith of Cardinal Champlain, and the despair of Colonel Destromp.

They observe xeno-tech in the hands of RT Exidine,

and they see the stirrings of chaos in the faculty of a schola,

or observe the sheltering of xenos in the outskirts of a hive.

---------------------

Now having said all that, my topic for debate is this: How often do they blab ?

Can the Inquisition expect the Ad-Mech's cooperation ?

Do the mechanicus ever expose 5th columnists ?

Do the machines of criminals get maintained as well as good citizens ?

The Mechanicus work for everyone, in all layers of Imperial society,

First of all, the AdMech work for themselves accumulating scientific knowledge as part of the Quest for Knowledge. Than they fulfill their obligations to Imperium proper as outlined in the Treaty of Mars (however that treaty most likely concernes providing the machines and services for imperial Adepta, including the Imperial Navy (seems as much part of the Mechanicum, that of the Imperium), Imperial Guard, Adeptus Astartes, Inquisition and etc.) and their obligation towards individual Imperial planets and men like rogue traders as part of the respective treaties signed with them (for me, it's likely in both case they have to strike pacts with the Mechanicum to get their machines and services).

Is it generally in the interest of the Mechanicus to expose a criminal or a heretic ?

One could argue there primary concern is machinery, but a lawful society would seem to benefit all.

If I was an enginseer, I'd rather have the contract working for Jonquin Saul than Haderak Fell.

Is it generally in the interest of the Mechanicus to expose a criminal or a heretic ?

Good question, perhaps. As far as it is stated in canon, there is both similarities and differencies in what consitute crimes/heresiy according to Dictates Imperialis and what constiute tech-heresy for the Adeptus Mechanicus. For example while things like Warp Sorcery or creating Sylica Animus is both grave heresy by the Lex Imperialis and grave tech-heresy by AdMech, in other things at may vary - for example, creating oblivion volitors is a grave crime by Dictates Imperialis but only minor tech-heresy for AdMech, while introducing individual (non-approved by the standard AdMech processes for approving and testing such things) innovations to STC designs may be a tech-heresy for some (not for all) of the AdMech brass (the incident with the Space Wolves and Predator Annihilator proves that), while this is most likely perfectly legal under Imperium's Lex Imperialis.

As for AdMech and criminals - space pirates and privateers most likely employ the services of tech-priests to have their ships running.

Right, it could be argued that the Ad-Mech would wear blinders to everything but tech-heresy.

Aside, but related: In Thomas Covenant, he realizes the immortal Blood-Guard had been beside all the Lore-Masters for over 2000 years, so one of them had witnessed the old rituals and the old despair. So Thomas tries to pressure them into revealing what they saw as it pertains to the current troubles.

But what about common sense? If House Adreskin is going to ruin the entire hive with their cult activities,

isn't it foolish for the technicians fixing their appliances to keep quiet about it ?

Of course the house will just bribe the techs like they bribe the arbites....

Surely its a grey area, not black and white. I can't be the only person ever to think of this . . .

I see where you are coming from, but it can screw up, at least for me, so many areas of things where you need Tech-Priests (or Navigators, or Astropaths). If you are a pirate fleet, where are you getting these, except maybe from Chaos Cult sources? I sometimes like to read about the other places in the Expanse, where the various associations of the Adeptus Terra haven't been in ages, or never, and wonder how they all keep their technology going (such as the Engine-Order of Zayth, or whatever Imhotep-themed guys might be maintaining the bizarre tech of Vaporius). There seem so many areas where, if you break with the Imperium, the losses in specialists should just cripple you. I like how, in Only War, at least for a good run of it, Duke Severus isn't just another cultist to Chaos. He might be eventually, and he might even unknowingly be being manipulated by them, all along, but it's not officially stated. However, I still don't get how he maintains technology (AdMech), or long-range communications (astrotelepathy), if he has broken away from the Imperium, an organization with which these two institutions at least somewhat answer to. Has EVERY Tech-Priest among the Separatists flipped the aquila to the Lathes? To Mars? They have some ability to communicate with the rest of the Adeptus Mechanicus, and could cripple Severus's forces, if they wanted to, from leaving his tanks broken to disabling the void shields on his palace, or setting the plasma reactor under it to blow, the same way one can in No Surrender, aboard the star fort. As for the Atropaths, they are all somewhat connected to the Emperor, and that should make them not want to shy away from His Imperium, in my mind (the religion says it is the Imperium He envisioned, lie that that is), yet Severus's forces aren't just a thousand little islands, cut off from one another.

The same can be said in Rogue Trader. Once your ship starts to collect a few too many xenos things, or you start to, as a crew, slip into piracy, sedition, possibly secessionist activities, or full-on heresy, and worshiping the Ruinous Powers, whole segments of it should start to be a problem, and beyond mere crew revolts. If your Explorators won't keep the bits working, even the weird, xenos bits they don't like you to have, or the Astropaths refuse to keep you in contact with your other assets, or the people around you, where you might find warnings, opportunities, or whatever, or if the Navigators say "what do I look like? A Nostromo? Guide this benighted craft yourself, if this is the path you seek to follow", choosing to go to the dark side would seem suicidal, even more so than by alienating yourself from the Imperium beyond your ship. Yet, nothing convinces me that every instance of these results in every specialist saying "I follow your lead, Master, wherever it might go", or wiping out 90% of each, and then somehow surviving to replenish those with other traitors, and heretics, yet there are plenty of terrible people, and they must all have at least some support, of at least several of these organizations. Certain things might remain compartmentalized, aboard your ship, but we all know that secrets can be very hard to maintain.

I don't know if I'm supposed to see some "supreme loyalty to Master and Commander" that doesn't really make sense in the rest of things, or if you are just so fabulously rich, or likely to run into old tech, that you can just bribe various of these to ignore their own sensibilities. Oh well, whatever, as long as the game, and the party, are having fun, right?

Well, there's a sizeable underground, so to speak, of those who are technically "hereteks". There's a lot of them who probably aren't actually Dark Mechanicus (Chaos AdMech), and are just not regular adherents/members of the Cult Mechanicus, but would still get turned into servitors if the AdMech caught them, because they're practicing technologists and not part of the AdMech. The technologists of non-Imperium worlds might be given the chance to convert to the Cult Mechanicus instead, depending. Or they were members of the AdMech who are on the run for committing techno-heresy, but not Chaos-related techno-heresy, say a Magos who got a little too friendly with Eldar or Tau technology or biology.

If you can't get enough astropaths to follow when you go rogue, then, yeah, you need rogue psykers or sorcerers of your own for 'pathic communications. Which, while a very useful asset, is not, strictly speaking, a vital one.

If you can't get your Navigators to go with you, then you're left with calculated jumps, possibly with archeo/xeno-tech or illegal warp-tech aid, or rogue psykers/sorcerers of your own or figuring out a way to get rogue Navigators.

There's a reason why many who go rogue end up sliding into it and sliding into full-on Chaos following forms of Heresy. Because that's where most of the available support infrastructure and vital capabilities exist outside of Imperium control.

but would still get turned into servitors if the AdMech caught them, because they're practicing technologists and not part of the AdMech. The technologists of non-Imperium worlds might be given the chance to convert to the Cult Mechanicus instead, depending

Well, there are pretty much many local technologists and scientists throutght the Imperium who are not part of the Adeptus Mechanicus. Unless they dabble into clearly forbidden (like the unrestricted AI creation or Chaos tech) or mostly forbidden (like xeno-technology) the Machine Cult simply ignores them - they are free to maintain their own level of technology or even do (if they have the capacity) some improvements upon it, but in turn no assistance would be given or knowledge shared with such people by the AdMech.

Such people are not Hereteks per se. There are several ways a person could become one, actually:

1) To be inducted into the Mechanicum cult, shared some of it's sacred knowledge and then betraying the AdMech.

2) To dabble into something clearly forbidden by the Treaty of Mars or to dabble in xenotech.

For example: If a local engeneer conceives a new pattern of an airplane that's legal to the Imperium and of little (if any concern) to the AdMech, however if someone binds daemons to the machines or strive to recreate the Silica Animus - that's another story...

and are just not regular adherents/members of the Cult Mechanicus, but would still get turned into servitors if the AdMech caught them, because they're practicing technologists and not part of the AdMech

Whats more, in practice, maximum sanction from the AdMech for just "practicing tech-science outside the Mechanicum" (if no grave matters like the AIs, warp-sorcery or xenos-tech involved) is called "excommunication from the Omnissiah blessing". That's basically an embargo - the AdMech would cease all trade with and all services for the sanctioned world. The real "pain" from such depends on the planet - if the planet in question is a feudal world with steam power as pinnacle of engeneering - planetary lord wouldn't even notice such measure, however in case of hive world or a world, dependant upon spaceflight effects could be more drastic.

but for heresy or crime other than tech . . . . .

but for heresy or crime other than tech . . . . .

Well, the AdMech sometimes view actions differently from how it is viewed by Lex Imperialis. For example, creating Oblivion Volitors (devices, erasing personality of its victim and instatransfroming a victim into a combat servitor, loyal to Volitors' creator every whim) is a grave crime according to Lex Imperialis but only a minor tech-heresy for the AdMech with techpriests reluctant to take any action at all.

Can the Inquisition expect the Ad-Mech's cooperation ?

There is a specific Ordo with responsibility for oversight of the Mechanicus.

As to how often they 'blab' - bear in mind that the Adeptus Mechancius is no more a homogenous organisation than the Ecclesiarchy or the Inquisition - you can find tech-priests who have xenophile leanings, or else source out-land born renegades (either formal dark mechanicus or people trained on Zayth or on any number of independent worlds).

Acquiring tech-lore sufficient to maintain complex technology without going through the mechanicus is dangerous, but no more or less so, and certainly no more or less difficult, than acquiring xenotech or daemonological lore. One who wants to maintain a secret facility aimed at the latter would probably also manage the former.

Can the Inquisition expect the Ad-Mech's cooperation ?

Depends entirely on the circumstances. If an inquisitor tells a lowly enginseer on an imperial world to jump the most likely answer he will get is "how high".

If he tries the same thing with the Fabricator General of a major forgeworld (let alone of Mars itself) if he gets a reply at all it will most likely be a question regarding how far he would like it shoved up his own arse.

Do the machines of criminals get maintained as well as good citizens ?

They say crime doesn't pay, but since that is a lie, they might be.

Can the Inquisition expect the Ad-Mech's cooperation ?

Adeptus Mechanicus are in fact more of an allied empire, than a standard Imperial Adepta. However, since the Treaty of Mars suggest cooperation between Mechanicus and Imperium proper, an Inquisitor could ask (but not give an order to) for AdMech help.

Then it would boil down to 3 criterias:

1) As Bankinus already stated, the place of the techpriest, whose assistance is requested in the AdMech hierarchy.

2) The asking Inquisitor's renown and place in the Inquisition hierarchy (a novice, inherited his teacher's Inquisitorial Rosette just some time age would command less respect than a famous inquisitor lord from Ordo Malleus)

3) The compatibility between Inquisitor's aims and that of the Adeptus Mechanicus.

Just one curious question - what about the relations between AdMech and the Ecclesiarchy? With the latter actively working towards introducing tech-heresy among the forge worlds' population their relationships might not be that easy...

The AdMech and the Ecclesiarchy do not get along. At all.

There's a small amount of necessary/required cooperation, but unless there's a clear and present outside threat to both or they're being forced to work together by someone higher up, expect that each will try to backstab the other, or at minimum, sabotage their efforts or undercut their position. And even when they're forced to work together, each will jockey for position so as to benefit more, or put most of the losses/damage onto the other.

If the AdMech could, they'd see the Ecclesiarchy destroyed ... unfortunately, the AdMech isn't in a position to replace the Ecclesiarchy as a whole, and so Chaos would likely end up replacing it, which the AdMech doesn't want. The Ecclesiarchy is actively, if discretely, attempting to undermine the AdMech entirely, or at least, elements within the Ecclesiarchy are. When the AdMech identifies those responsible, the AdMech seeks to assassinate or otherwise eliminate those responsible.

Opinion, certainly, but I like to think that many Inquisitors would have little trouble; like so many organizations, the AdMech is fractured, compartmentalized, and internally competitive, and an Inquisitor could, possibly more easily than the reverse, use those who the Tech-Priest in question doesn't like, or must listen to, to compel them. Otherwise, the AdMech might be willing to cut losses, and let the Inquisitor have one, if it spares the rest of the organization, or they'll pressure their underling to appease the big =][= and remember it for later, when they can avenge his arrogance against the Omnissiah's chosen. In many lights, the AdMech attempts to appear as if they support the Emperor's Imperium, whether they they actually believe Him to be a manifestation of the Omnissiah, or just because it is easier to play along, and in this case, Inquisitors are to be heeded. If it isn't convenient, they fake it, and things "fall short" later, when he can't as easily retaliate.

More than likely, I'm just giving the lesser than you greatest Inquisitors a bit more respect than they might actually deserve, but many Inquisitors are, in fact, experts in the art of getting the myriad components of the Imperium to work together, as a single agency, and they have numerous friends, contacts, and moles in almost every group, so I imagine if the Inquisitor is playing to his strengths, and not just flouting his authority for the luls, he'll probably get what he wants, and with people like the AdMech, he'll see to it that it was worth their while, too, so they will go along.