Any chance the white puff of smoke may be from a partial compressor stall? Power was low then bumping it up a bit rather then raising it slowly. If you watch the video you can hear a slight pop as the smoke puffs out.
Not noticed in the cabin though.

I found this youtube video of a BK117 helicopters engine doing something similar.
[https://www.youtube.com/watch?v=H7DIAnz40dc]

A compressor stall, even a partial stall in a single engine helicopter like the 206 Series, will produce a slight-to-noticeable torsional oscillation (yawing of the entire airframe about the mast) as the engine power to the transmission fluctuates. Also, the instrumentation will similarly fluctuate to indicate the event, particularly the N1 Indicator and Torquemeter - did you feel and/or observe anything like this? If not, it was probably your imagination.
A few questions at this point, a) Are the rotors being turned backwards for three revolutions after each shut-down as I described earlier? b) Are you and all others flying this helicopter observing the two-minute dwell time between rolling back to flight idle and shut-down?
I'd like to revisited the "FCU settings" for a moment. with the twist grip full open, does the lever on the FCU make FIRM contact with the full open stop? This is very important and is the reason why you see that very powerful-looking spring around the lever spindle. Get a piece of very thin paper and place it on the full open stop, then gently roll the twist grip to full open to trap the paper. Without touching the twist grip or the FCU arm, gently try to pull the paper away, if it tears everything is OK, if it pulls away the N1 controls need re-rigging.
Finally, can you say that all engine maintenance requirements have been perform conscientiously, I'm thinking of the No. 6 and 7 oil jet inspection, the No. 6 and 7 scavenge strut cleaning and fuel nozzle cleaning plus a spray pattern check, etc.

@hyperflyboy
I think you are one puff away from a much larger issue - your smoke issues are not normal and certainly not with such regularity. The black puff on start up is the cold ejection and the white is the same problem when hot, what you don't know is how often its doing the same en-route, I would put money on this doing it every "x" minutes, which is systematic of a tiny problem, that will eventually turn into a much bigger problem. Hangar time me thinks and be on your toes for auto at the whiff of a problem till you get it under cover and the cowlings off!

Interesting what Saint Jack said. I had never seen any helicopter oil in NZ for at least 30 years other than Jet II. now there is the new 256 or what ever it is, and other people go and buy some other different oil, probably cheaper...

But there must be a reason why, right through the 80s and 90s most people, that were running JRs and 500s, all had Jet II. it certainly wasn't the cheapest, but all i got told was the other stuff was ****!

I used Aeroshell 560 from the late 1990's on, in both my 206s and my BK: third generation low coking and met the specs for the JetRangers. Coking issues on the LTS101 led me to that choice with expert advice, it improved the oil galleries in the LTS 101s and was far cleaner at oil changes in the 206s than Jet II ever was.

The 'puff' of smoke in one of the photos is far more than a puff, IMO, and is white not black. Agree that is could be indicative of something more serious.

I had this issue on my 206A/B C20: on shutdown it would puff out a plume of smoke.

In the early 80's Hughes 500D's were delivered with Mobil Jet II. In the UK AS 500 was much used and easy to obtain. We noticed that aircraft that were changed to AS500 had much higher levels of carbon forming in the oil. One of the aircraft had a turbine seize due to blocked oilways and all owners were advised to change back to Jet II.
The levels of carbon soon reduced to normal.

Around this time we also had AS555 which may have had better coking characteristics
but ate helicopter gearbox seals for breakfast.

Bond helicopters had massive coking problems with the Allison C30 in the S76. The problem was so bad that Sikorsky brought out a mod to armour plate the tail rotor drive shaft (20 kilos of steel) just in case the turbine bearings seized and the turbines departed. Bond were stripping and cleaning out a pair of turbines every weekend, in effect a six week cycle as they had six aircraft, in an attempt to alleviate the problem.
They ran a comparison test with each aircraft on a different engine oil, AS 500 was junked and Mobil 254 was found to give the best results. This was still the standard UK engine oil (used in the Arriel) for the company now CHC more than thirty years later.
Replaced with BP2380 for the PT6.

I'm the only one flying this machine at this time and it flies once every week or two for about an hour. The blades are rotated 2.5 turns counter-clockwise every start and shutdown with a 2 minute cool down every shutdown as well. Annual inspection was done about 20 hours ago with a compressor wash and the usual engine and airframe maintenance all done by a reputable maintenance shop with 30+ years experience with 206's.. The engine has a monitoring system that prevents hot starts and records all exceedances and maximum engine and air frame parameters all of which appear normal.

I just checked the FCU lever position to see if it contacts the stop at full open and it does not. There is about a 0.100" gap.

hyper
Surely they should be rotated CLOCKWISE,(Backwards) in order to rotate the power turbine and crack any congealed oil on the bearings etc?

My mistake, it is clockwise looking down from above. I turn the blades backwards so the free wheeling clutch is engaged.

The carbon is built up on the labrynth seals in the turbine , extreme buildup can cause damage to the turbine and lockup.

hyperflyboy,

Just looked at your photo - not good.

Reasons why -

1/ The full throttle stop determines your MAX N1 speed. Possibly not an issue at the altitudes you are flying at.
At higher density altitudes you will not achieve MAX N1 and the engine will TOP and the RRPM will decrease before you reach TO power.
If it was a multi-engine install - an even bigger issue as your remaining engine will not achieve OEI power.

2/ The lever will possibly be under the 30? degree point when at IDLE and too close to ICO (idle cut off). The downside of this is that should you do a practice power failure there is every chance it might flame out and make it a little more interesting than it needs to be!!

With the engine shut down - Fuel OFF - BP off - Check the throttle as follows -

CLOSED it should be preloaded against the stop on the FCU - if not you can have afterfires.

Open the throttle slowly until the stop just clicks out on the twist grip - pointer on FCU should NOT be under the IDLE marking.

Open the throttle fully and it should be preloaded against the MAX N1 stop.

Close the throttle slowly to the twist grip idle stop - again the pointer should be above the idle mark.
If the difference between opening and closing is significant your throttle linkages are worn out.

The IDLE position of the lever does not relate to the IDLE speed - that is set within the FCU although can be cheated with bad rigging.

To check the actual IDLE speed within the FCU - on shutdown - slowly decrease the throttle after pushing the IDLE stop and watch the N1 tach. Note the RPM where the fuel shuts off.
If lower than the recommended IDLE RPM get it adjusted.

Frankly I am surprised that your shop has let this slip as it is pretty important yet basic stuff. I would be a little apprehensive as to the rest of your problems when you have an obvious issue such as this!

Amazing isn't it, I went to see the doctor with a cough and a runny nose and spent the next four and a half days in hospital! Anyway, back to the matter in hand, RVDT has essentially put in writing what I was thinking. the final paragraph of his post above (#32) is the conclusion I was coming too also. I'm sorry hyperflyboy, but your statement in Post #28 that "engine and airframe maintenance all done by a reputable maintenance shop with 30+ years experience with 206's" is not supported by what you're experiencing which, quite frankly, are relatively straightforward problems for an experienced 206/250 mechanic/engineer to diagnose and rectify. Do you have any alternatives for maintenance support?

Not the papal copter is it?