By Lee Beery


When the engine mount assembly is fabricated, small holes are drilled in the 4130 chrommoly steel tubing to allow gases to escape from inside the tubing during the welding process and as a means to inject a corrosion preventative oil(usually linseed oil). Small steel plugs are then driven into these holes to close off the tubing.This maintenance item is to alert all Varga and Shinn owners to this fact.Heat from exhaust pipes can deplete the oil from the lower-most tubes in the engine mount, allowing the tubes to rust inside. This is not detectable by a visual inspection.Eventually the tubing will become so thin that even normal nose gear loading will cause the mount tube to break. One indication of a broken tube problem is when the engine will not idle down.


*Suggested Action* - Inject linseed oil or some other type of rust preventing oil, such as LPS #3, into these lower tubes by removing the upper plug rivet and pumping the tube full of oil.Reinstall the upper plug with a steel rivet held into the tube with RVT sealant.It is also suggested that any time the engine is removed, that the engine mount also be removed, seed blasted to remove all paint and inspected with a 10-power glass.Then remove all plugs and re-oil the tube interiors.Precautionary replacement of these lower tubes with a thicker wall thickness (.061) tube costs approximately $400.It is also a good idea to wrap the tubing in this area with "auto engine header wrap".If you would like some of this wrap, please contact me.


Max Bishop Note:


Boiled linseed oil installation was done on only a few of the very first airplanes. Varga was advised that hermetically sealed tubing (completely welded with no holes or gaps) provided as good or better protection so thatís what we did. If there are no drive pins visible anywhere on the tubing of your motor mount or fuselage then this Maintenance Item will not apply to your plane.