912 engine inspection after oil supply disruption

I had a suboptimal day yesterday.
I had done an oil change followed by a 1hr test flight all good,followed by a trip out to a satellite field when things went bad.
My engine sounded off? Gauges showed nothing abnormal so I headed back to base.

My engine was sounding like it had split an exhaust,then the oil pressure and revs began to drop.30 psi rather than 55psi,4800 at 27inches where I would expect to see 5500rpm.
on reaching my home base after 10 min? Shutdown saw a lot of smoke pour out the cowling:eek:

The problem was traced to a braided hose on the tank to pump circuit had failed internally and was sucking air which I believe let the lifters bleed down?

On shutdown a small amount of oil flowed out and onto the exhaust causing the smoke,the pipe was replaced an extended ground run was done with all appearing normal,another flight of approximately 1 hour failed to show anything different to normal operation.

I plan to get to the hanger to investigate further tomorrow.
I will remove the rocker covers and inspect the retainers and valve stem to head length in case the valves have stretched.I can't find online an acceptable length to use as a baseline,the engine is an early ul with dual valve springs.

Is there a published valve length,and procedure for checkling after this sort of problem?
Cheers
Dusty

Your best bet is to reference the Heavy Maintenance Manual available on line from Rotax. They have step-by-step procedures for inspection after this this contingency.

I understand that Ops are normal after replacing the hose. How come you believe valves may be stretched? Would it not being running differently if that were the case?

How much oil in the tank after this occurred?

I'll have another look online but I could only find reference to air entering via the oil pump seals.
No oil was lost other than the tee spoon amount dropped on shutdown.
I was worried about valve stretch after an aircraft from our field flew for a while with an air leak,the valves stretched to the point of low compression making starting difficult.
I used the rocker cover face as a reference on mine and another engine ,they were the same,the collets and springs visually liked ok.
I flew or a couple of hours today with pressure and performance as before,
Maybe i've dodged a bullet.
Time will tell.

Oil starvation will first impact the camshaft and lifters with extreme wear. I've seen lifters destroyed by starting an engine after an oil change without bringing up oil pressure first. I don't know how the valves would be "stretched".


I also believe you have most likely dodged a bullet, but careful inspection of the valve train and an oil change with a thorough filter inspection for metal is defiantly warranted.

www.rotax-owner.com has all the engine manuals for free, click support and your engine and you will be able to download all the manuals, operators, line maintenance, Heavy maintenance.