RV Nose Gear Strut

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Jim Ellis

Nose Gear Strut Attachment

Over the years some builders have reported problems with the nose gear strut becoming loose in the engine mount socket.

The problem is created when the bolt moves slightly in the socket due to twisting loads created by the movement of the strut from side to side. This causes the hole to oval and as a result the strut becomes loose. Nose wheel shimmy can lead to very fast elongation of the hole. No matter how closely the bolt fits the hole unless the bolt is a press fit this movement can occur.

 Lower engine mount and strut assembly.
Lower engine mount and strut assembly.
A way to repair this problem or, better yet, prevent it from happening in the first place is to replace the AN5-20A bolt that holds the strut in the socket with a taper pin. A taper pin by design provides zero clearance between the hole in the strut and the hole in the socket making any movement impossible.
 Taper reamer and taper pins with washer and nuts.
Taper reamer and taper pins with washer and nuts.

If you decide to do this you will need a #3 Brown and Sharpe taper reamer. Aircraft Spruce sells these, P/N 12-04711.

You will also need the following hardware:

  • (1) AN386-4-13 Taper Pin
  • (1) AN975-5 Taper Pin Washer
  • (1) AN310-5 Castle Nut (or AN320-5 Shear Castle Nut)
  • (1) AN380-2-3 Cotter Pin

Finding AN386-4-13 taper pins can be difficult. One place you might try is Jay-Tex Aviation Inc., (903) 572-3688. They do have a minimum order amount so you might want to combine this with your other hardware needs.

Reaming the hole for the pin must be done with the engine mount removed from the firewall. Insert the nose gear strut and align the hole in the strut with the hole in the engine mount socket. Drill the assembly with a letter size "S" or 11/32" drill. Ream the hole starting from the aft and working forward. This will place the attachment nut on the upper forward side of the weldment. Go slow and use lots of cutting fluid. A socket that fits the shank of the reamer and a rachet wrench will make driving the cutter easier. Remove and clean the reamer frequently and go very slowly as you reach the correct depth. Insert the taper pin to check the fit. The pin shoulder should not protrude through the hole more than 1/16" when fully inserted.

 Assembled strut and mount with taper pin installed.
Assembled strut and mount with taper pin installed.
Clean the hole and install the nut, washer and cotter pin to retain the taper pin.

If you need to insert the taper pin after the engine mount is bolted to the firewall there is a trick that makes this easy. Loop a 12" piece of thin safety wire through the cotter pin hole in the taper pin. Insert the two ends of the wire into and through the aft side of the tapered hole. Push the large end of the taper pin into the hole in the firewall that is provided in the plans for bolt insertion. Grasp the wire and pull the taper pin up and forward through the tapered hole. Remove the wire and install the washer and nut.

The following information comes from Bill Palmer:

For those interested in purchasing the AN386-4-13 taper pin to mod their nose gear attachment per Jim Ellis' instructions.

I just finished working with Aircraft Spruce (West) to set-up a part number for ordering an individual AN386-4-13 taper pin. The new ACS part number is 04-01939. The price is $10.50. ACS has placed an initial stocking order with their supplier. If enough orders are received, ACS will continue to stock this particular taper pin and retain the individual part number 04-01939.

Bottom Line: No more special orders or minimum quantity.

Please place your AN386-4-13 order with Aircraft Spruce.

Best Regards,

Bill Palmer Chino Hills, CA

P.S. ACS already stocks for individual order the other hardware listed by Jim Ellis as follows: AN975-5 Taper Pin Washer, AN310-5 Castle Nut, and AN380-2-3 Cotter Pin. Personally, I substituted the slightly more expensive MS17825-5 Self-Locking Castle Nut for the AN310-5.