Torque Cylinder Head

Hi Alejandro

Follow the sequence exactly as it is written in the heavy manual.  The 30NM is a maximum and the (-5 NM) is the minimum value, this would be then 25 NM.  Obviously you should be all the same at 30.  This step is to be sure that all the cylinder and heads are locked in place.  The last step is to just release the torque on 1 head nut at a time. (1 full turn off)  Then repeat the 10NM set torque on that stud and follow it with the 150 degree angle torque.  Then move to the next stud in sequence as shown.  

Cheers

Hi RW,

Please explain why the torque sequence needs to be so complicated/multiple step?

Thanks😈

We have a video on the Rotax Owner website, that demonstrates how to properly torque the Rotax cylinder heads. You can find the video in the link here: 

Expanded Information - SI-912-025 Cylinder Head Torque Procedure for ROTAX 912/914/912iS

https://www.rotax-owner.com/en/videos-topmenu/expanded-video-instructions/463-new-torque

Hi Sean

The issue goes back a long way.  Before 2006 the old crankcases were standard studs, they did not stretch.  In an effort to upgrade the block and try to prevent block "fretting" between the halves from vibration and allow for the possibility of longer crankcase life (TBO max at the time was 1500) they came up with a new design of the block.   The design changes the way the block holds together and this also lead to the use of the stretch bolts internally and higher torque values on them.  Only engines made after 2006 with the newer crankcases can have 2000 hour TBO.  

The cylinder studs changed in 2007 after even the new crankcases would see some issue with head nuts falling off of some engines.  Their were several changes even in the new cases.  The first "new" ones changed to a better collar nut internally, some would fracture that collar and it was a difficult fix so a better one was designed.  To be sure that correct pressure on the colleer nuts was always there the move to the all thread, stretch type,, studs started in 2007.  In the initial release they found the 195 inch lb torque was not suitable as many backed off.  Too solve this the introduction of a more high loaded head nut was introduced and originally it was a base setting and 180 degree torque.  This however failed, a number broke in the field as with prop vibrations and other aircraft influences they found again head nuts to missing.  There was a change then to reduce this to 120 degrees, again it failed.  In some cases that backed off depending on the aircraft mounts and vibration.  The final, and working solution was the base setting, then a loading to on the stud to seat all the parts with a final angle torque of 150.  This one works. There were some other improvements in the block, such as thread pitch on the bolts in the block, but not anything a user will be playing with.  Overhaul requires all the studs to be replaced.  Just like your modern motorcycle or car.  

Yes it is complicated however it is rare to see any broken head studs now or any missing head nuts.  A lot of blood and sweat and massive field testing.  Trust me, it is not worth it to shortcut the process.

Cheers