Advice wanted on 912ULS plugs

[Kyle Communications]

Hi All

 

I would like some advice on the plugs out of my 912ULS please.

 

I did a oil and filter change today and pulled the plugs out to have a look at them to make sure they were ok. The attached pictures show their condition. Is this normal?

 

The 2 left plugs are from the opposite rear cylinders and the 2 on the right are from the 2 front cylinders. You can see the 2 from the rear are burning quite well maybe a tad lean but I didnt expect to see the front plugs so dark. The carbys are fed each side so the rear plugs have a shorter inlet manifold length and the front plugs are furtherest away from the carbys. I am no mechanic but I did expect some difference between them but not as much as can be seen.

 

Expert advice and solutions if any needed please

 

Mark

 

 

 

 

[Guest Maj Millard]

Mark, without knowing how many hours on your engine it is hard to comment accurately . Those plugs look ok to me for a low hour engine. The 912 s will continue to pass a bit of oil past the rings until they fully seat in, which can take up to 100 hrs or so depending on how you run it. Nikasil cylinders are very hard and take a while to seat the rings. The 912 can take several hundred hours before it is fully settled in. Mine has just done 750 hrs and is now starting to really sing !...I have run those engines with 2000 hrs + and they become smooth as, like little turbines.

 

The two foward cylinder plugs will be a bit richer normally, because those front cylinders are running a bit cooler due to the direct blast of cooling air. Not much you can do about this as it doesn't seem to really worry them. Burn colour is always read on the centre- post ceramic, ensure you have the correct plugs, (DCPR8e) and gap them by the book. You could check that the idle air jet on the exterior of the carb is set at 1.5 turns out as required. (Both carbs) Last thing you want to do at this point is to fiddle or adjust anything in the carbs themselves, and do not ever try to adjust the float levels.

 

Go fly more, things will only get better !....................Maj...

 

 

[Kyle Communications]

Hi Maj

 

The engine has 75 hrs on it now. I know the front plugs would be running cooler but the difference between the colours worried me I expected to see a difference but it seemed greater than I would have thought. But if you say its normal I am happy with that. I know my engine does not run very hot at all infact it is probably too cool. Usual temps at 5000 rpm in cruise are around 92 deg for oil temp and 95 to 102 deg for water temps. Some tell me that is too cool. I do have a thermostat for the water I was going to fit at the 100 hrs but I cant remember what the insert temp was I think it may have been 85...its the thermo bob one

 

Mark

 

 

[Guest Maj Millard]

Yes thanks Mark, It's still seating the rings I would say. The 912 does tend to run too cool in most installations. Up here where it's warmish most of the year, I run with my coolant radiator half blanked off all year round, and with the oil cooler half blanked in the cooler months. Even then I still run at the bottom end of the green on both, with the standard Rotax coolers..( At cruising altitudes anyway) For plug gaps I like about .024 " which is just a light tap or two from out of the box ( factory gapped at .025".). Additionally I 'm only turning about 53-54 max RPM due my current prop and cruise pitch, however I may back it off a degree or two soon, just to liven things up a bit. Also the quality of the mogas we run now is quite variable in my opinion. If you run a touch of avgas now and then, even a mix, you'll find the plugs clean up a bit even though you do get a bit of lead deposit on them. Hope you and all are well down there .......Cheers..................Ross

 

 

[alf jessup]

Hi MajThe engine has 75 hrs on it now. I know the front plugs would be running cooler but the difference between the colours worried me I expected to see a difference but it seemed greater than I would have thought. But if you say its normal I am happy with that. I know my engine does not run very hot at all infact it is probably too cool. Usual temps at 5000 rpm in cruise are around 92 deg for oil temp and 95 to 102 deg for water temps. Some tell me that is too cool. I do have a thermostat for the water I was going to fit at the 100 hrs but I cant remember what the insert temp was I think it may have been 85...its the thermo bob one

 

Mark

Mark,

 

The temps seem to be ok, under 90 is running them too cool.

 

Are you running glycol in the radiator or the Evans NPG?

 

I got 30 deg warmer when I swapped to the Evans from the glycol in the Tecnam.

 

Alf

 

 

[cscotthendry]

Mark:

 

I have about the same number of hours on my 912uls and my plugs look the same as yours. I too was puzzled as to why the starboard side rear cylinder seemed to be running about the right color and the port front was dark and sooty. That said, I'm getting 17-18L/Hr at 5,000 RPM which I'm told is about right.

 

BTW, I'm assuming that you've done a carby balance...

 

 

[Kyle Communications]

Hi Ross

 

The book said gaps to be between .025 and .035 so I split the difference and set mine at .030. I have thought about blocking off both radiators a bit to see how much difference there is. Do you have some max and min temps you would recommend for the water and oil?

 

Interestingly I typed this message above today from the work computer but it

 

didn't come through

 

 

Mark

 

 

[Kyle Communications]

I am running 50/50 Glycol and demineralised water. Scott the plugs look exactly the same as each other both rear look the same and both front look the same. carb balance was done a while ago at the same time as I got Reg Brost to balance my prop at about 20 hrs I think it was. My fuel flow meter says at cruise at 5000 rpm at 7500 ft I am using around 13.7 litres per hour at lower levels it comes up to around 15 litres per hr I average around 16 litres per hr with climb and cruise and this holds true with the markings I did on my tank sight gauges after a long flight

 

 

[Kyle Communications]

I am running the Bolly 72 inch prop and it is set for pitch so that flat to the firewall and she gets to max I get 5600 rpm. I climb usually at 60kts and that is around 5200 and 70 knot climb comes up around 5300

 

 

[Guest Maj Millard]

Mark, Rotax book figures are: Oil temp...Min 50C (120f) Max 130C (266f)

 

Norm operating range...approx 90 - 110 C (190 - 230 F)

 

Coolant:....Max 135 C. (275 F')

 

Norm operating range...approx 75 - 110 C. (167 - 230 F)

 

Mark, your fuel consumption sounds ok, the tend to average around 16 - 18 LPH but figure on 20 LPH for Xc flight planning. Don 't let your plug gaps get too wide, it can stress your ign boxes out.................Maj...

 

 

[crashley]

how long did the engine idle for before you pulled the plugs a rotax will run very rich on two cylinders while at low power I was told by a rotax agent that the only way to check the plugs was to shut the mags off after flying at full cruise power for 30 minutes and then check the plugs

 

 

[Kyle Communications]

The aircraft was flown for about 80 mins on friday then I started the engine up sunday morning to warm it up before changing the oil so I suppose it was idling for about 5 or 6 mins while it warmed up to 50deg oil temp. I did give it a couple of 3000 rpm runs towards the end though

 

 

[Ultralights]

the 912 operators/maintenance manual has a possible cause, oil temps to low. i had the same issues coming into winter, 2 cylinders looked perfect, 2 a bit sooty. 2 pieces of tape covering about 1/3 of the oil cooler, all look perfect now. in cruise its best to keep the oil temps at 90 minium. my engine has 960 hrs on it now.

 

 

[facthunter]

Till you run your engine at high power for a while the soot will remain. Idling invalidates the "reading" Nev