Jetranger Question...

[Rifleman]

...a lab seal(short for labrinth) ...spelling is not my best subject...could be the problem...this is a metal on metal seal inside the turbine...these have been known to give grief and usually right after a rebuld...:up:

 

Actually, a labrinth seal is not a metal-on-metal seal. It is composed of an inner and an outer ring with an air gap in between. When this very small gap becomes fouled with carbon the turbine shaft cannot rotate freely, and in the case of a 206

this can be felt be manually turning the N2 drivetrain (which is what turning the main blades backwards does).

As mentioned, if a lab seal is going to act up, it is generally shortly after overhaul.

If the seal has too small an air gap at installation, it will be susceptible to carbon fouling. If the gap is within the prescribed limits, it is somewhat self-cleaning and will likely never present a problem.

And BTW, third generation oils like Mobil 254 are substantially better in almost every way, than their predecessors (anti-coking properties included).

[vortex]

BTW, third generation oils like Mobil 254 are substantially better in almost every way, than their predecessors (anti-coking properties included).

My experience with 254 is that it is very good at getting rid of carbon but it has its drawbacks, the loadbearing characteristics are actually poor. Bell recommends not putting it in any of their gearboxes. 250 gearboxes also show more wear at teardown if they've been living on 254 and after many years of reasonably trouble free operation with splined shafting, RR is starting to have problems with that. Hmmm...maybe new oils?? 254 can be added mid life of the turbine, using the "top up" method described in one of the CSL's if you didn't want to wait for o/h time. I'm also curious about one of the other side effects of 254 which I'm not positive of but it seems like we're having more problems with carbon seals leaking when 254 is in the system. It seems to be so good at getting carbon out of the system that it even gets it off the seals. Anybody else got any thoughts?

[PerfectTrack]

the stuff stinks...literally.and one drawback to my style of maintenance is that it's a dark oil, making visual inspections for suspended debris or metal a tad bit difficult. But that's not huge issue if you have the capabilities to strain and filter the oil to look for problems.

[skywrench1]

Haven't found mag seal problems with 254, in fact I have found the incidence of leaking #5 seals an the resultant smoking on shutdown has become a nonissue. Not a big deal in a JetRanger but definitely beneficial in a 206L, 500 or Twinstar where the TOT's are normally higher. I've noticed that once you convert you may have some initial seal leaks that I've attributed to the detergent action of the oil affecting existing gearbox seals. Once a fresh one has been installed there hasn't been a noticeable difference to Jet II in terms of seal longevity (excepting starter seals where nothing lasts any length of time). As for load bearing capabilities, we have yet to experience any issues in that vein, my experience so fasr has been quite positive on all fronts except for the inability to easily see contamination as Perfect Track commented. However I firmly believe the benefits of improved turbine health outweighs the negatives. Mobil has another 3rd gen oil - 290 which is advertised as having the same coking resistance as 254 but is far less toxic - anybody out there tried it yet? Cheers