CAS O-Ring Change
by Jim Creer
Note: This article includes photos of a 1.6l engine. Additional photos of a 1.8 provided by Phil Ethier
The
objective here is to change the Cam Angle Sensor (CAS) O ring in about 10
minutes without removing the cam cover. A timing light is not
needed. Have done 5 like this and
found it works just as easily on both the 1.6 and 1.8 NA Miatas. Only variation is the CAS is on the back of
the intake cam on the 1.6, and on the back of the
exhaust cam on the 1.8. Both are just
as easy to do. Started doing this around
Y2K, after doing several others using by the book. If not comfortable trying it this way then please
follow instructions in your manuals.
Have
a spare CAS, so we can look at one to see what we are trying to do. The arrow points to the O Ring we will be replacing.
The area in the box is the tip that rotates inside the rear of the
cam. The elongated hole is for the
bolt that holds the CAS in place. This bolt is loosened for the CAS to rotate
when changing the ignition timing.
A different view shows the two little “tangs” at the end of the rotating tip. They are slightly off center. There is only one way it will fit, so no chance of it being 180’ out of phase after installation. Also note one end has a little groove running down the end, which is a bit clearer in the previous picture. The opposing tang has a little dot stamped near the end and no groove. Found some that did not have this dot and just a flat end.
The
size of O Ring needed is 1/8” – 1 ˝” x 1 3/4”.
They run around 59 cents each at about any local auto parts store,
or can get this little pack of 4 each for $1.79.
As far as I can tell it is made from the same material as the Dealership
replacement units. BUNA-N. If you are not sure of this, go ahead and get
one from the Dealership. Expect to
pay at least $6, even with some sort of discount.
Another option is a Viton ring, rated for higher temperatures.
To prep for removal, have unplugged the O2 sensor (1.6) and both plugs.
I tucked them back out of the way so have some working space.
Used a soft lead pencil to mark position of the CAS. When finished, will align
the marks again so the ignition timing will not change. Will probably be some grime and oil on the unit,
but the pencil will mark through it.
As a side note for those that frequently prefer to change ignition timing, scribe a timing gauge here for different ignition settings. Will only take a moment to change it later and no need for a timing light or engine to warm up. Just remember as the timing belt stretches with age, or belt is replaced, this extra gauge will probably not be accurate.
Remove the 12 mm bolt. Does
not matter if the CAS gets rotated slightly since you have the ignition timing
marked. Just need to be careful
we don’t slide the CAS out of the back of the head during this stage. If the CAS was leaking oil, it will probably
be flat, hard, and well lubricated. Will need both hands and the pencil again for the next step.
Dave let me use this picture of his 1.8 CAS bolt. Little different shape and has a longer bolt head. May not be able to get some ratchets behind the head, but a 12 mm box wrench works very well on either the 1.6 or 1.8.
Now
for a bit of dexterity! Slide the CAS
straight back toward the firewall. Do
not twist it during removal and try to avoid hitting the tip on anything. When clear, lower the back and rotate the front
upward. I made a second pencil mark
to show orientation where the little tang fits inside the cam. If you disturb the end slightly, make your best
correction guess and mark it anyway. At
best will only be a few degrees off, but may take a few extra light pokes
when installing it back together. Will be a bit clearer as we progress. In this instance, the position marked was not
the tang with the groove. That should
be easy to remember!
Used
pocketknife to cut the old ring off, or when you pry up on it a little, it
may shatter and fall behind the engine. Have
a new ring handy to fumble in place. The
barrel should have enough oil remaining for lubrication. If you need a little more oil to smear, just
poke finger inside back of cam. Does
not matter if the tip was rotated, since will need to orient it again prior
to installing the CAS.
Caution is needed at these stages that pencil marks are not erased. For the next step will line up our pencil marks,
starting with the little tang on the tip, orient it with the cam and ignition
timing pencil mark and slide it in back in place.
Note. Many instances it is difficult to remove the CAS from behind the head, but still easy enough to replace ring as shown.
If
you see this little space on the barrel between the new O ring and yoke, that means the little tangs are not properly aligned
with the cam. Back the CAS out slightly
and rotate a hair. Try another poke.
Repeat if needed until it slides in.
If you try rotating the unit with pressure on the cam, will just be
twisting the nose out of position and be at it for a long time!
I have only hit one exactly with the first poke, but could expect about
3 to 5 little jabs. Most will be pending on how well you eyeballed
both pencil marks.
In
this position the new O ring is flush against the yoke. That means it is properly aligned inside the
cam. The fatter new O ring will be
a little harder to squeeze inside the yoke.
It should have some oil on it, can push harder on it and twist the
CAS around a bit until it snaps back in place.
Brings us back to this picture. Replace the bolt and ensure your first pencil mark is aligned prior to tightening. Now the ignition timing is back in the same setting before the CAS was removed. Plug the 3 plugs back in and go for a drive! Can also pat your self on the back for saving a $100 from having a Dealership do the job. Should also be able to do the job in about 10 minutes rather than dropping the Miata off somewhere for a day.
Why do it like this? For other reasons than stated above, the O ring
and the cam gasket may not fail at the same time. Many owners are unaware of this ring when replacing
the cam gasket. The 1.8 can leak oil
down and ruin the heater hose.. The 1.6 can leak oil down on the small unused
water cap nipple. Not sure if this
will hurt the cap but will guess it does not do it much good! We could pull the cam cover to do it, but will
probably be spending at least 5 times longer. Even if the cam gasket is still serviceable,
no need to move the coil bracket or clean the old gasket sealer from the 6
points and apply fresh sealant.