Rotax 912 Valve Stem Seal

[skippydiesel]

Rotax 912 ULS 900 hrs

 

Starts & runs very well - very smooth!

 

Oil consumption so low, no additional oil needs to be added between 50 hr changes - Oil used "Shell Sport Plus 4"

 

800 hr Cylinder compression & leak down tests indicate all cylinders well within tolerance as per previous tests.

 

Very slight exhaust staining of fuselage belly.

 

Exclusively 95-98 RON PULP used.

 

All gauges within green.

 

On my recent (about 2 weeks ago)  900 hr service, I noted the spark plugs on No 1 cylinder were considerably darker than the other cylinders. I checked back , in my Engine Log Book, to previous services and found the same note/comment for No 1, over quite a few historic services,  but may be getting darker.

 

Feel free to comment otherwise but to me it seems logical that the oil seal, on my inlet valve, for No 1, may be weeping.

 

Sooo I am wondering how hard is it to replace the oil seal ??

 

Can it be done without removing the head??

 

Am I being too picky/anall ??

 

 

[M61A1]

You might be being a bit picky IMHO. Engines that get oil through the valve guides usually do so at idle or when backing off (high vacuum in the inlet). 

 

If it really concerns you, pop the inlet manifold off and inspect the valves for evidence of oil coking on them. I reckon you probably could do it with the heads on if you tried.  Use soft rope in through the spark plug hole against the piston to hole the valves closed (leave some hanging out of course to remove it when you're done. Might be fiddly , but hardly difficult.

 

Mind you, without head gaskets to worry about it wouldn't be difficult to remove the head quite easily either.

 

 

[crashley]

rotax spark plugs get carboned up when the engine is idling  due to  two cylinders running rich at idle speeds it wont have anything to do with valve seals 

 

 

[Thruster88]

rotax spark plugs get carboned up when the engine is idling  due to  two cylinders running rich at idle speeds it wont have anything to do with valve seals 

 

Agree, lycoming's don't have valve stem seals, probably because they are not required  

 

 

[Downunder]

Front cylinders always run rich after a good idle... As in anything below flying rpm. 

 

If you have 4 egt sensors this shows up as much cooler front cyls. 

 

If you are not using oil, comps, leak down good... Go fly... 

 

You can pull both plugs and shine a torch in bottom hole. Look in top hole to see piston top.... If there's any difference to other cylinders. 

 

 

[skippydiesel]

Thank you all for your reassuring comments/observations.

 

I confess to be in the habit of an extended post sorti idle (to reduce heat soak & fuel veporistation).

 

Thanks again - unlikely to be anything to worry about.