Cylinder head "O" ring installation

by Had Robinson

Removing the cylinder head is straightforward.  First remove the cooling shroud.  Unfortunately, it has never been easy because the shroud sweeps around the cylinder exhaust port studs and you risk cracking the shroud if you try to force it over the studs.  Why not remove the studs?  That's not easy because, if the engine was assembled correctly, the studs were installed with red threadlock which means they won't come out without heat (a torch).  To get around this annoying factory problem, take a pair of sharp wire cutters or shears and cut the wings of the shroud off just enough so that the shroud clears the studs.  The effect on the cooling system in negligible.

Most paramotors use an "O" ring to seal the joint between the cylinder and the cylinder head.  Whenever the cylinder head is removed, the "O" ring must be replaced.


This O ring is subjected to very high pressures (over 1,000 psi) and the slightest leak will affect engine performance and possibly warp the head.  It is difficult to tell if the "O" ring is leaking because the hot gases that escape do not leave any traces.  Glopping RTV on a used "O" ring looks like it will seal the joint but will not.  This is because a used "O" ring has microscopic deformities caused by slight differences in the sealing surfaces.  It is impossible to put the "O" ring back in the exact same position it had originally.  RTV does not have the ability, by itself, to seal against 1,000+ psi pressures.  Why suffer a loss of engine performance for a few $'s?

RTV is not needed when replacing a new "O" ring nor is it used by the factory.

  1. Clean the groove that holds the "O" ring with mineral spirits and a cotton swab.  Use a toothpick to remove stuck particles.  DO NOT USE ANY METAL OBJECT TO CLEAN THE "O" RING GROOVE.
  2. Carefully examine the "O" ring groove in the cylinder head.  It must be absolutely free of particles.
  3. Gently stretch the "O" ring by pulling it around through your fingers for (30) seconds or so.  Do not be in a hurry to do this!  Place it in the groove in the cylinder head.  It should fall right in.  If not, stretch it a bit more.  If it is tight in the groove, it may later pop out of the groove as you place the head back on the cylinder.  If the head is then tightened down, the "O" ring will be ruined.
  4.  Be certain that the "O" ring stays in the groove!
  5. Put the cylinder head with the "O" ring in place on the cylinder.  As you lower the head down, keep a close eye on the "O" ring to be sure it is still in the groove.
  6. Install the fasteners.  If you are unsure of the fastener order on the Top 80, refer to the specifications page, "Torque values, Cylinder head nuts".  For other motors, check their torque specifications page.
  7. Torque the cylinder head nuts in a cross pattern in stages to 9 Nm or the correct value specified for your motor..
  8. It is a good idea to check the compression of the engine to be sure the "O" ring is in place and is completely sealing the cylinder.

Note:  When replacing the cooling shroud, put copious amounts of RTV between the large washers on the cylinder head studs and shroud.  This will help cut down the wear of the shroud at these points due to severe engine vibration. 

Turkey Vulture