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Old 01-08-2015, 05:01 PM
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Walt Walt is offline
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 7,023

Some builders have chosen to go with a taper pin for some improved load margin up-front, but we recommend that the taper pin installation should be viewed as an optional enhancement; not a requirement. Below is some info on taper pin installation.

Alternate method for Nose Gear Leg retainer bolt:

Alternative: If you have not installed the engine mount or can easily remove the engine mount for working access, you can elect to replace the AN5-20A bolt with an AN386-4-13 taper pin. Many RV-A builders have done this and this alternative seems to be working fine. However, it should be noted that installing a taper pin is not a method approved by Van’s Aircraft.

There are currently two taper pin installation methods:

a. Manual Taper Pin Install (manually ream and taper the gear leg and engine mount simultaneously) by Jim Ellis and posted on Matronics as follows:
Note: ACS now stocks the AN386-4-13 taper pin without a separate part number, and there are other online sources for this taper pin as well.

Taper Tools:

Procedure: Manually reaming the nose gear leg and engine mount combination is a three-step process which requires considerable patience and force.

(1) The nose gear leg and engine mount must be properly aligned and clamped in-place to prevent movement. Temporarily installing the AN5-20A bolt or a 5/16-inch hardware bolt (undersized) helps. Both the gear leg and the engine mount are then simultaneously (2) match-drilled and (3) reamed:

(2) Measure the diameter of the taper pin with calipers at the point where the small end will exit the engine mount. Make sure the tapered pin provides enough threads protruding for the castle nut and taper pin washer. You can set up the taper pin with the nut and washer on the threads, then line up the caliper next to the washer. For the initial match-drilling of the hole prior to reaming, use a drill bit slightly under this measurement as your initial drill size. The Matronics instructions say to use an “S” sized bit or 11/32-inch. It is always good to verify this size before you start cutting and drilling. For example, a 21/64-inch drill bit might be better.

For the initial, match-drilled hole, go slowly with the drill RPM’s and use a lot of cutting oil or Boelube frequently to get the factory gear leg and engine mount holes aligned and enlarged (matched) before you begin reaming with the tapered reamer.

(3) Put the tapered reamer into a tap handle. Using generous amounts of cutting oil, begin turning the reamer in the cutting direction only. Do the reaming slowly by hand. You will need to push hard and turn at the same time, so it helps to have another person help with the reaming. Do not turn the reamer in the non-cutting direction, or you will dull the cutting edges. Always turn in the cutting direction only. Remove the reamer frequently and clean off the cutting edges and reapply the cutting oil generously.

Once the reamer starts producing chips, make sure to frequently measure the length of the reamer or taper pin protruding from the hole. The taper pin’s grip shoulder must not protrude more than 1/16-inch beyond the engine mount, because the taper pin washer is actually a collar with a depth between 3/32 and 1/8-inch. Once the reaming process gets started, it will approach the proper taper pin depth very quickly so be observant. A few turns goes a long way to increase the cone depth of the tapered hole, so don’t get too aggressive and go too fast once you are reaming the entire length of the hole or you will overshoot and go too far.

Considerable axial pressure must be continually applied to the reamer to keep the ream process going. Above all, take it slow and do not hurt yourself!

Notes: Some builders have had difficulty keeping the reamer sharp and have resorted to purchasing an additional reamer or two to complete the process. If the reamer is not making chips and has dulled, you can try lightly running a fine sharpening stone along the cutting flute interior edges to get them sharpened up again. One or two strokes of the sharpening stone is plenty. You just want to revive the cutting edge, not take any material off in the process. Also, using a drill for the reaming step is not recommended, because it will spin too fast; quickly dulling the reamer and thus burnishing (surface-hardening) the hole. Slow, manual reaming works best with plenty of cutting oil and steady pressure being used.

There are some good pictures of the process in this thread on VAF:

b. Wire-EDM-Assisted Taper Pin Install (machine-ream the nose gear leg first and then manually ream the engine mount to match).

For those who have had difficulty with the manual reaming process or for those who feel more comfortable with professional tapering of the relatively hard nose gear leg, here is the drawing developed by Bill Pendergrass for Wire-EDM-machining (taper-reaming) of the nose gear leg hole:

Pros: Manually reaming the engine mount to match an already-machined (tapered) nose gear leg is relatively easy. The engine mount steel is soft in comparison. Also, the nose gear leg is relatively easy to vertically align at the machine shop.

Cons: Finding a reasonable Wire EDM machining shop nearby may not be easy or even possible. The machining cost is probably at least $250 for tapering one gear leg including the set-up cost. Finding several builders to spread the set-up cost over multiple gear legs might be a good idea.
Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
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Last edited by Walt : 01-06-2019 at 06:41 AM.
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