They are not a friction fit. Remove the retracts, Look on the side in the pivot axle area and you will see an allen set screw inside. Loosen it, remove the strut and grind a flat on it where the set screw will contact the strut (it probably already has one) Reinstall and tighten the set screw using some Locktite. If you want extra security, add a second setscrew on the other side since both sides are threaded. It's easy to jump on the H9 lousy gear bandwagon, but on this model they work just fine.

After a while flying with mechanical retracts you get used to checking and tightening screws that loosen from vibration and every now and then replacing struts with 3/16 piano wire units. H9 is a bad offender for using flimsy struts on planes like their P-51 and that particular model definatelly needs the heavier struts. My T-34 has many flights off very rough grass with no problems due to the short strut lengths, but I am still considering installing the thicker wire.

quint