Engine start without burping

[jveatch]

There are numerous threads about burping and the need for it. But I haven't seen anything specific about whether or not it is hard on the engine to start it up in the morning and not burping it before start. Are there areas of the engine that lack oil that would otherwise be lubricated due to burping?

[PilotBrent]

My understanding is that Rotax engine burping is done to force as much engine oil as possible into the external tank to measure if the level is sufficient. It has nothing do to with moving the oil around the crankcase. Many of us burp after flying when the oil is warm and most of it can be "squeezed" into the tank. If you are confident that the there is sufficient oil in a cold engine, burping is not necessary before start-up.

Warming the engine before start-up is probably a good idea in any case as many threads on here would describe.

[John-G]

In addition to what Brent said, A secondary benefit derived from turning the prop to burp the engine is insuring there is not a hydraulic lockup in one of the cylinders from either oil or, worst case, water. A hydraulic lockup can damage engine components like the starter, Sprag clutch, perhaps bend a rod, etc.

[Jim T]

Originally Posted by John-G

In addition to what Brent said, A secondary benefit derived from turning the prop to burp the engine is insuring there is not a hydraulic lockup in one of the cylinders from either oil or, worst case, water. A hydraulic lockup can damage engine components like the starter, Sprag clutch, perhaps bend a rod, etc.

I often don't burp and check the oil level each time between short flights(Rans 6-6S) . However John, what you said makes sense and I think, even if I don't burp I will, from now on, still turn the prop over a couple of times.

Jim

[RFSchaller]

I used to fly a Yak-52 that occasionally had a hydraulic lock on the bottom clylinders that needed to be cleared. I've never heard of this being an issue on horizontally opposed engines.

[DHeal]

From everything i have read and heard, hydraulic lock is not an issue on 912s installed in RV-12s. Apparently, some older 912 installations on other aircraft designs (taildragger Kitfox?) placed the oil tank higher than the engine and over time oil would seep back into the cylinders leading to potential hydraulic lock. Not a problem for us.

While not a big fan of messing with any propeller movement, I have come to peace (and hopefully not "pieces") with slowly pulling my prop through per ROTAX's standard pre-flight burping procedure. I have found that @ 12-16 cylinder compressions usually gets me a good belch. I slightly pause at every peak of compression to let the compression gases flow past the rings into the crankcase. Works well for me! YMMV

[Sink]

After Talking with a thousand Rotax users some will say they check oil every flight, others first flight of the day and others only every few flights. You should being checking your oil. A good place to see if an engine is leaking or using oil is on the bottom of the plane. I always do a pre-flight and or a post flight look on the underside. Any oil through the exhaust or from a leak goes on the bottom of the plane.

On the subject of hydraulic lock it was in fact more prevalent yeas ago with the old style filters. Kitfox used to be the number one offender for this issue because they mounted their oil tanks too high out of the Rotax spec, but there were other instances to. Now days there are still a few owners with tanks too high, but the newer filter has helped diminish the hydraulic lock issue quite a bit. The new anti drain back membrane and check valve have certainly helped. Rotax also dramatically increased the by-pass pressure. So even though it may not be as prevalent you should rotate the prop to make sure it isn't an issue. It only takes a few turns for all cylinders to reach TDC once and then you'll know for sure. If you became one of the rare cases then a start under a hydraulic lock would cause some serious damage.

In this case a few rotations is a better safe than sorry scenario since it only takes a few seconds for that peace of mind.

[RFSchaller]

I agree you must check oil level at least prior to the first flight of the day (the cap is pretty hot to be checking at each fill up on a cross country). I just didn't expect hydraulic lock to be an issue on this engine.

[WingedFrog]

I mentioned this elsewhere already but it will not hurt repeating it as we are in the right context:
There is a significant difference in the oil level between cold and hot engine. If you top the oil level in a cold engine you will overfill and guess where the extra oil will go: nice coating over the belly of your plane

[rvbuilder2002]

Originally Posted by WingedFrog

I mentioned this elsewhere already but it will not hurt repeating it as we are in the right context:
There is a significant difference in the oil level between cold and hot engine. If you top the oil level in a cold engine you will overfill and guess where the extra oil will go: nice coating over the belly of your plane

I don't think there is a difference in the actual oil level, but there is a difference in how much of it can be easily pushed back into the oil tank (where we measure it).

When the oil is cold (particularly if it is up North winter time cold) it is very viscous and doesn't flow easily. If there is quite a bit in the crank case when the engine is cold and you burp the engine for an oil level check, it can push out some oil and then burp out an air bubble, but there can still be quite a bit of oil coating the bottom of the crank case that could not easily flow to the outlet.
Test it your self. If you burp it when cold, you can do it repeatedly every few minutes and the oil level will continue to get higher each time.

Your point is valid though, that when cold (particularly very cold), the oil level is likely higher than what you are able to measure by burping it one time.
Keep in mind that when in good operating condition, the 912 engine does not use much if any oil. If you are detecting that the level has gone down rather suddenly, consider carefully before adding any (look for oil on the belly, etc). Chances are pretty good that you just haven't gotten all of the oil back to the tank for the level check.