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Cylinder head "O" ring installation

by Had Robinson

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.

DO NOT REUSE CYLINDER HEAD "O" RINGS!

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 does little to seal it 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.

  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!  Now 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. Place the "O" ring in the groove.  Be certain that it 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".
  7. Torque the cylinder head nuts in a cross pattern in stages to 9 Nm.
  8. It is a good idea to check the compression of the engine to be sure the "O" ring is in place and sealing the cylinder.

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