It has been found that the model 18 oil tank cap retaining chain causes corrosion where the chain contacts the bottom of the oil tank.  To correct this condition, it is recommended that the retaining chains be cadmium plated.

As an alternate method of rework, it is permissible to shorten the chain, leaving only three links attached to the dipstick.  Then the retaining bar should be fastened to the end of the third link.  This will prevent the chain from contacting the bottom of the oil tank; however, it will not permit the dipstick and cap to be placed as far back outof the way when filling the oil tank.

Chains on Model 18 airplanes in production will be cadmium plated on A-466 and after, except A-469 to A-473, inclusive.