Do-It-Yourself Honda V4 Oil System Modification

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As of late 2005, Phil Rastocny may be reached at

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                    Copyright (c) 1993, Phil Rastocny

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This is the first part of a two-part article that describes one
way to slow down a known problem with upper cylinder lubrication on
Honda V-4s.


The '82-'88 Honda V-4 oiling system (700, 750, 1000, and 1100cc; all
chain and some gear-driven cams -- see complete list below [0, 1]) for 
the upper cylinder area has been a topic of this newsgroup in the past,
but I have discovered a few new things which were valuable enough to
resurrect this old topic and may prevent a few folks from incurring
the unnece$$ary expen$e of top-end rebuild$.  To begin, I will repost
an excellent summary of this problem (and suggested solutions) as once
posted by Robyn Landers (  VF750S Den0051)
for those new to this subject. Additional findings appear after this

================== begin reposting ==================================
  [ Reposting deleted --
    email to request the latest version
    of the V4 cam story. ]

======================== end reposting ==============================

Earlier, Robyn said that Honda said the oil supply bolt wasn't a problem
in the Magnas and Sabres, however, IT PROBABLY IS. What I have done is
to examine the oil supply circuit to the upper cylinder area, beginning
with one simple bolt, and study the evolution of this circuit on several
different models of the Honda V-4s.  This bolt (called a banjo bolt) is
located on the left side of the transmission roughly where the back of
your calf muscle crosses the top of the transmission case.  It has an
oil line (a.k.a. oil pipe) connected to it that runs between the front
and rear cylinder banks, splits into a ``y,'' and feeds oil to the upper
cylinder areas. This line is the ONLY source of oil for the upper
cylinder area.

As explained earlier, this source of oil is unfiltered (that is, the oil
comes directly from the pump and before it has been filtered by the oil
filter), and the available oil pressure is somewhat lower than the
53-75 psi available to the other lubricated areas. To date, I have not
confirmed these oil pressure measurements, but I have made a few
mechanical and subjective observations that are described next.

The Transmission Case Banjo Bolt:

This bolt is threaded (tapped) directly into the top-left side of the
transmission case. At the end of this tap is a hole that accesses
an oil channel (just rear of the rear cylinder bank). The diameter of
this oil channel access hole is 7/32" (.219"). Logic would assume that
to prevent significant reduction in oil volume and pressure, all
internal diameters of this oil supply circuit should be at least 7/32",
if not larger. This, however, is not the case; both the internal holes
of the banjo bolts and the internal diameter of the oil lines are in
some cases significantly smaller (and therefore quite restrictive)
which effectly reduces the volume (flow) and resulting pressure.

>From my personal examination of this bolt, here is what I found. On
the '82-'83 VF750C models, the original banjo bolt looks like this:

        | |       | | <--- 14mm head
            |   |
            | O |    <--- a single .125" exit hole
            |   |
            |   |
            |   |
            |   |
            |   |
            |   |
             |o|  <--\   aluminum insert, three drilled-through .085"
             o o  <--->- side holes plus one .085" center hole going
             |o|  <--/   up the middle of this insert
              ---------- .085" center hole through aluminum insert

On the '84-'85 VF700C models, this banjo bolt was changed by Honda and
looks like this:

        | |       | | <--- 14mm head
            |   |
            O   O    <--- two .125" exit holes (second hole is drilled
            |   |         through the first exiting on the opposite
            |   |         side)
            |   |
            |   |
            |   |
            |   |
             |o|  <--\   aluminum insert, three drilled through .085"
             o o  <--->- side holes plus one .085" center hole going
             |o|  <--/   up the middle of this insert (this insert is
             ---         identical to the one used in the '82-'83
              ^          configuration)
              ---------- .085" center hole through aluminum insert

On the '86 and later models, the banjo bolt was changed yet again and
looks like this (Honda p/n 90045-MB2-000):

         | |     | | <--- 12mm head
            O   |
            |   | <------ two exit holes (about .125") drilled through
            |   O         diagonally
            |   |
            |   |
            |   |
            |   |
            |   |
              ---------- aluminum insert is gone, center hole is
                         considerably larger (about .180")

So a quick check to see if you have the most recent design bolt is to
put a 12mm wrench on this bolt. If it fits, then you have the best
bolt Honda made, but there's on.

As stated earlier, the diameter of the hole that accesses an oil
channel is 7/32" (.219") and logic would assume that to prevent
significant reduction in oil volume, all internal diameters of this
oil supply circuit should be at least 7/32", if not larger. Since the
hole in the banjo bolts is far smaller than this, a reduction in oil
volume (and resulting loss of pressure) occurs at this bolt. To
resolve this, all holes should be enlarged so that a circular (i.e.,
cross-sectional) area of at least [[0.219"/2]e2 * pi] (i.e., 0.038")
is maintained.

What follows next are instructions on how to enlarge these holes in
any of the three transmission-case banjo bolts Honda manufactured to
maintain this desired 0.038" circular area. Read all instructions
completely and understand each step before beginning. If you have any
questions, contact the author at the address at the end of this

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
CAVEAT:  The author assumes no responsibility for any damages or
personal injury that may result from performing the following
modifications. If you feel uncomfortable about performing these
modifications, have an certified mechanic do them for you.
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

Modifying the Transmission Case Banjo Bolt:

What you will get from this modification is more oil flow, but not
significantly more pressure to the upper cylinder area. Note that this
procedure is not a cure to this problem, but it can help to extend
the life of your engine. To completely cure this problem, you must
purchase one of the aftermarket modification kits listed earlier in
this article (or also perform part 2 of this modification).

This modification can be made to any of the banjo bolts Honda produced
(a 170% improvement in flow can be achieved even in the 12mm version).
To do this, you will need:

   *  a set of metal-cutting drill bits (1/64" increments)
   *  a small electric drill
   *  a small vise bolted to a sturdy workbench
   *  a metric socket set that includes a 14mm (or 12mm for '86 and
      later models) socket
   *  a small torque wrench
   *  two new crush washers Honda p/n 90443-MB0-000 (about $4 U.S.)
   *  a clean motorcycle around the banjo bolt (degreased if necessary)
      and a clean working area
   *  clean hands and clean tools
   *  clean lint-free rags on which to place parts and tools, and
      others with which you can wipe your hands
   *  WD-40, penetrating oil, or other thin oil

*************************** W A R N I N G ! **************************
*                                                                    *
* Once you remove the banjo bolt, you have exposed the lubrication   *
* system to possible contamination. Make sure that you keep this     *
* area as clean as if you were performing open-heart surgury. Dirt,  *
* grease, and stray particles can clog the small upper cylinder      *
* lubrication ports and permanently damage your motorcycle. Just be  *
* careful and you'll have a great running scooter. Being careless or *
* casual can have absolutely disastrous results.                     *
*                                                                    *
*************************** W A R N I N G ! **************************

0.  Thoroughly clean the area around the banjo bolt making sure that
    there is no grease or dirt on or anywhere near this bolt that may
    accidentally fall into the exposed bolt hole.

1.  Remove the banjo bolt with a 14mm (12mm) socket. Keep track of the
    two compression washers. Cover the exposed hole with a clean,
    lint-free cloth to prevent anything from falling into this hole
    while you are working.

2.  Place the head of this bolt in the vise so that the shank points

3a. If there is an aluminum insert in the shank of this bolt, drill
    out this insert with several small bits, enlarging the hole slowly
    and not all at once. The original hole is about .085" in diameter.
    Start with a 3/32" (.094"), and move up in 1/64" increments until
    this hole is 15/64" in diameter (.234"). This increases the
    circular area from about 0.0057" to 0.043" (over 7.5 times larger).

3b. If there is no aluminum insert in the shank of this bolt, drill
    out the hole down the center of this bolt with several bits,
    enlarging the hole slowly and not all at once. The original hole
    is about .180" in diameter. Start with a 13/64" (.187"), and move
    up in 1/64" increments until this hole is 15/64" in diameter
    (0.234"). This increases the circular area from about 0.025" to
    0.043" (over 1.7 times larger).

4.  Place the head of this bolt in the vise, pointing sideways with
    one of the holes near the top facing upward.

5.  Drill out this hole to 11/64" (.172") in 1/64" increments as in
    step 3a or 3b above. This increases the circular area of this hole
    to about 0.023" (about half that of the hole through the center of
    this bolt).

6a. If there is another hole on the other side of the bolt, turn the
    bolt over and drill it out also to 11/64" as is step 5.

6b. If there is not another hole, use the first hole as a guide and
    keep drilling through this hole with each successively larger
    drill bit until it comes out the other side.

7.  Remove any outer burrs from the two side holes with a 1/4" or
    larger drill bit. Remove any burrs from the center hole by running
    the 15/64" bit through the center again. Remove any burrs that
    remain inside the two side holes by running the 11/64" bit through
    both of them again. Repeat deburring these holes as necessary.
    Recheck carefully to make sure that *ALL* burrs and debris have
    been removed before proceeding.

8.  Remove the bolt from the vise and clean it out thoroughly making
    sure that there are no metal filings left inside or around the
    holes. You can spray some thin oil (such as WD-40 or penetrating
    oil) into the center hole of the bolt and blow air through it to
    remove these particles. Rinse the bolt in soapy water and repeat
    the cleaning process until all debris has been removed, then spray
    one last time with some thin oil, blow out any remaining water,
    and dry with a clean, lint-free cloth.

9.  Reinstall the clean banjo bolt with the new crush washers. (I have
    been able about half of the time to make the old washers work and
    not had to buy new ones. You may have similar luck.)

10. Use a torque wrench and tighten down the banjo bolt. There is no
    torque value specified for a banjo bolt according to the 1984
    Honda shop manual[2] (or the Clymer equivalent). However, the
    torque for the 12mm drain bolt (similar threads and center hole to
    this banjo bolt) on page 1-4 of the Honda shop manual is:

               30-35 N-m
               3.0-3.5 kg-m
               20-25 foot pounds

    I have used this torque myself and have never stripped the threads
    or broken a bolt. However, if the crush washers are not new, this
    torque sometimes may not completely seal and a slow oil leak may
    result. I suggest that you replace the two crush washers and
    retorque the banjo bolt instead of risking over torquing the bolt.


As with Robyn L., I too enjoyed riding my Honda V-4 and there are
several things that I do to extend its life. They are:

1. Use a NAPA 1334 oil filter ($6.95 U.S.). This is one of the better
   oil filters on the market and can filter out smaller particles
   longer than the stock Honda or Fram filters.

2. Use a high-quality, light-weight oil. I use Improved Mobil 1 5w30
   ($3.50/quart) with one tube of B&K's Extreme Presure Concentrate
   ($5.00/tube available at most motorcycle and auto supply stores)
   all year round.

3. Change the oil often and use a blotter test to monitor the quantity
   of suspended particles[3].

This ends the banjo bolt modification portion of this posting, but
from examining the Honda microfiche, I have found that Honda also made
a change in the oil supply line late in 1987. A followup article will
be posted showing how to replace the existing oil line with larger
tubing for about $30.


[0]  Landers, Robyn "Honda V4 Cam Story",

[1]  Minton, Joe, ``VF750 Cams: Now and then a bad one.''
     MOTORCYCLIST, July 1986, Page 45, and Amirian, Armen, ``Honda V-4
     Bypass Surgury.'' MOTORCYCLIST, July 1988, Page 54-55.

[2]  1984 Honda VF700S/C and VF750S/C Shop Manual, Honda p/n
     A15508409F  (about $25 U.S.)

[3]  ``20 Questions:  Oil, Practical information about your engine's
     lifeblood.''  MOTORCYCLIST, July 1988, pp. 68-73.

    Phil Rastocny
    Now Deceased V-45 Magna (Thunder)
    DOD 4444