Purging Engine - What Oil Pressure Should I See?

Doing the Rotax S/B purge with the compressor set 10 PSI, the max I seem to get is around 20-21 PSI on the engine page in Skyview after about 30 prop spins....is that right?

Top plugs are removed only...thought I saw someone somewhere saying I should get around 40 PSI.

It 's OK

You have pressure. That's what counts.

Vic

The purge pressure will depend on the speed that you rotate the prop. For new engines I do the purge twice just to make sure. I have never had a soft lifter or air in the system problem. I rotate at a prop speed of 60 rotations per minute and I do 90-100 rotations. I will see 50 psi on the gauge at that speed. I wear a long leather welders glove to protect my hand from the prop.

If you want to see some real pressure then take the bottom spark plug wires off and then clear the area and with the ignitions off engage the starter for 30 seconds!

I guess min oil press is listed as 12 PSI in the the operating manual so 20 is fine?

John,

I just did enough rotation to get a positive indication. The rise shows the system is purged..

Rich

Just because the oil pump has oil in it doesn't mean the tappets have oil behind them. This is why you are suppose to check each tappet by removing the valve cover and pressing down hard to see if there is air behind a lifter. I would not use the engine to do the purge. If a tappet has too much air behind it and the others don't then you can cause damage by the force and speed of the starter. If this was an acceptable method Rotax would teach it in schools and have it in a manual. This is why on the Rotax-Owner website they show it being done by hand in the video.

Remember that even though you may get away with somethings at the beginning it can cause enough hidden damage that won't show up for 100 hrs. and then you'll say it was Rotax's fault and it was a faulty engine or part.
Follow the manuals as they are your Bible for your engine. I can't stress enough that tens or even hundreds of thousands of dollars worldwide is wasted on owner caused engine damage.

Don't be afraid to do several purges if needed

I've followed Roger's and Lockwood's advice on this and ended up purging my engine several times in order to get one soft rocker arm to firm up. While I did the initial purge and got fairly good and steady indicated oil pressure when rotating the propeller by hand, I had one subborn tappet that ended up needing several purges to meet the spec. Roger pointed out that multiple purges can't hurt, and that he routinely does a more robust purge than even the manual and video (Rotax-owner.com) illustrate. Good advise.

roger lee said:

I would not use the engine to do the purge. If a tappet has too much air behind it and the others don't then you can cause damage by the force and speed of the starter.

Click to expand...

Not that I am advocating using the starter to turn the engine during a purge (even though, with plugs removed, the load on the starter is very low and it is highly unlikely to get over heated... even if done for 30 seconds as some have suggested), but there is no way this could cause any damage just because some hyd. tappets were not fully purged of air. This only causes excessive clearance which prevents the valve from being opened fully. There is nothing related to that that could be damaged just because the cam was turning a bit faster. In fact, if memory serves me right, a procedure of using a short engine run and rechecking a stubborn lifter as described as a standard procedure. If the engine turning fast for a short time could cause damage, Rotax, and the class instructors, would never recommend that procedure.

True, it is not the way Rotax documents to do it, but as you have pointed out many times Roger, just because a manufacturer says to do it a particular way, that doesn't mean it is the only way... or the best way.

My only "but" here is that unless you truly fully understand the system you are working on the Rotax manual way is the safest way and won't void the warranty since that is the period that many do odd or un-authorised types of maintenance.
Doing things that are done to Cont., Lycomings and listening to John Doe next door is what keeps Rotax in the parts business and keeps Rotax service centers in business. It's at least 30% of my business.

Roger,

It's been a while since I set up my engine, but I seem to recall that the engine gets run for a short period before the tappet check. That seems counter intuitive if running them dry damages them.

Rich

You purge (terrible term LOL) then check the lifter softness. If there isn't any a run is okay, then it never hurts to check the lifters one more time. This is the beginning of your engine's life. Might as well get it off on a good foot.

RFSchaller said:

Roger,

It's been a while since I set up my engine, but I seem to recall that the engine gets run for a short period before the tappet check. That seems counter intuitive if running them dry damages them.

Rich

Click to expand...

I did it again twice by hand and got it to rise from around 1-2 PSI to 18-19 psi, at least that is what I saw when I got back over to Skyview - of course it was falling as I arrived.

Now - that tappet check - re-re-re-reading the Rotax SI, I assume you then start the engine, observing normal oil pressure, then after shut down, check the tappets for play?

Hi John,

You're on the right path. Your doing a good job, keep it up. An engine start is is your near future.
If tappets are firm and all other engine first start items are good to go then start away.

When I rotate the prop fairly fast I usually have another person watching in the cockpit. My bet is your pressure was also much higher because when you slow the prop rotation pressure drops quite fast.