lifter check procedure

Assuming you have a 912, 912ULS or 914 engine, The Rotax Line Maintenance (LMM) manual section 05-50-00 page 23 states the following:

NOTICE: Any exceeding of the max. admissible engine RPM must be entered by the pilot into the engine logbook stating duration extent of over speeding and pertinent detail.

• 5800 rpm up to max. 6200 rpm - If the limit was exceeded for max. 1 minute up to 6200 rpm – No action required

• 5800 rpm up to max. 6200 rpm - If the limit was exceeded for more than 1 minute up to 6200 rpm. - Check that the pushrods are straight. See current Maintenance Manual Heavy (MMH), Chapter 72- 00-00.

• 6200 rpm up to max. 6500 rpm - If the limit was exceeded for max. 3 seconds up to 6500 rpm - No action is required.

• 6200 rpm up to max. 6500 rpm - If the limit was exceeded for more than 3 seconds and max. 1 minute up to 6500 rpm. - Check that the push-rods are straight. See current Maintenance Manual Heavy (MMH), Chapter 72- 00-00.

• 6200 rpm up to max. 6500 rpm - If the limit was exceeded for more than 1 minute up to 6500 rpm:

1. The whole engine must be inspected, repaired or overhauled in accordance with the BRP-Rotax instructions for continued airworthiness.
2. Check that the push-rods are straight. See current Maintenance Manual Heavy (MMH), Chapter 72- 00-00.
3. Inspect the crankshaft for out-of-roundness and distortion. See current Maintenance Manual Heavy (MMH), Chapter 72- 00-00.
4. Inspect all systems for correct functioning.
5. Detailed inspection of affected engine components.

• If the speed of 6500 rpm was exceeded.

1. The whole engine must be inspected, repaired or overhauled in accordance with the BRP-Rotax instructions for continued airworthiness.
2. Check cylinder differential pressure. See Chapter 12-20-00, section Differential pressure check.
3. Check that the push-rods are straight. See current Maintenance Manual Heavy (MMH), Chapter 72- 00-00.
4. Check if piston had contact with valve. See current Maintenance Manual Heavy (MMH), Chapter 72- 00-00.
5.  Check for out of roundness of valves. See current Maintenance Manual Heavy (MMH), Chapter 72- 00-00.
6.  Replace the crankshaft. The crankshaft has to be inspected in according to the current Overhaul Manual (OHM) for the respective engine type. Overhaul Manual (OHM) and its appendix is available for any appropriately rated person or entity on request and by following the standards of the original manufacturer.
7. Inspect all systems for correct functioning.
8.  Detailed inspection of affected engine components.

Here are the links to the where you can find LMM and the HMM for the 912ULS and 912UL engines. https://www.rotax-owner.com/en/support-topmenu/engine-manuals#current-engines

Thanks, i know this info.

Problem is that there was a governor malfunction (bad air speed sensor) in a short period of time and during that period there was a sudden decrease in max power (you can note during take off - climb in cruise is dificult to note less power).

In addtion to power loss engine became more rought and unbalanced and min rpm drop by 200 rpm.

I do not know if these sympoms are due to an overspeed . It was an rational guess because power loss started  in the same 1-2 hours of governor malfuncion  . but i have no data if and how much max rpm was exceeded.

Compression and leak down test were ok and borescope inspection also ok. so i think i can exclude a valve problem. 

i asked for a rapid lifter test because not rational to dismantle an engine withoud max rpm data to follow correct procedure.

last thing:  1350 Eur plus tax for lifters set is OUT OF THIS WORLD.  

Overspeed on a Rotax 912/914 can only result in two types of mechanical damage:

• A twisted crankshaft, or
• A valve strike (piston-to-valve contact)

The hydraulic lifters are not affected by overspeed, and an overspeed cannot trap air inside a lifter. For that reason, the lifter air-bleed test you referenced does not serve as an overspeed diagnostic and does not help determine whether an overspeed event occurred.

A flat (failed) lifter would cause:

• hard starting
• minor roughness
• light ticking noise (often too faint to hear)
• hammering on the valve train, which can sometimes be seen as wear on the spring washer

But a flat lifter is not caused by overspeed, and an overspeed will not damage the lifters.

Your symptoms, “rough running, imbalance, and a 200 RPM drop,” are consistent with:

• An incorrect carb balance
• propeller out of balance
• governor malfunction
• or general tuning issues

They are not consistent with lifter damage from overspeed.

Since compression, leakdown, and borescope inspections were all normal, you can reasonably exclude a valve strike. If the crankshaft were twisted, the vibration would be severe and unmistakable.

My recommendation is to return to the basics:

• perform a full carb balance and synchronization
• balance the propeller
• Verify governor function and prop tracking

Lifter replacement is not required.

And yes, if any part of the oil circuit was opened (especially an oil pressure gallery), the oil purge procedure must be performed.