How To Modify the Distributor Cap And Apply Copper Contacts
From: "Marc L. Summers-SysAdmin" (marcs@tdd.hbo.nec.com)
Date: Fri, 13 Feb 1998 7:43:30 PST
Detailed Instructions On How To
Modify the OEM Distributor Cap
And Apply Copper Contacts
To 1991, 1992, and 1993 MKII MR2 Turbos
Mk1 SC caps, and many others.
FOR THOSE THAT WANT TO:
For those that want to up front the $200 bucks that it takes
to get all of the materials together to do this mod, then
here is the proceedure that I follow to do it.
TOOLS REQUIRED:
RCBS Grain Scale (this is a scale that is used in reloading
bullets. It can be found at most any gun smith shop and many
hardware stores that carry firearms reloading equipment.
Cost is about $55
Rounded blade Xacto knife or some type of small scoop
that can be used to scoop out a small portion of the epoxy
and put it in the scale pan.
Small jewelers screw driver, or some small implement that
can be used to press on the copper pads after they have been
put in place, used to manipulate the copper pads and press
them down and move them into precise position.
Metal sheers, used to cut the copper sheet into strips and
then small .250 X .250 pads.
Dial caliper, used to measure and mark the copper sheet and
mark the size for the copper pads.
Rounded end Xacto knife blade and handle holder, used to clean
up any extra silver epoxy that might get on the face of the
copper pad. NOTE: same as above.
Plastic or glass plate flat surface used to mix the epoxy
and work it. NOTE: the surface that you mix the epoxy on
needs to be a non-porous surface, like plastic or glass so that
none of the epoxy hardner is absorbed into the surface as you
are mixing it together.
Plastic handled Q-tips. I used these to mix the epoxy and
to apply it to the contacts. It works very well because it is
round and can be used to manipulate the epoxy easily.
Sharp end triangular blade Xacto knife, used to score one side
of the copper pads.
Small pair of needle nose pliers, that have a flat area
down towards the bottom of the jaws. I use this flat area
to press and straighten the copper pads after they have been
cut into .250 X .250 pieces.
Small pair of tweezers, used to pick up the copper pads and
place them into position.
Small artist paint brush, measures about .200 X .200 thousands
in size, used to brush the 3M surface prep cleaner over the
contacts, and also clean the surface of the aluminum contacts
in the cap.
Dremel tool with wire brush, used in the case that this is
a used cap, and the aluminum contacts are even a tiny bit
oxidized. If the cap has been used then the aluminum contacts
will have to be cleaned with a Dremel tool wire brush.
Pair of inside measuring calipers, used to check spacing distance
on the copper contacts ONLY AFTER they have 24 hour cured.
PARTS PURCHASED:
Duralco 120 Conductive Silver Epoxy from
Cotronics
3379 Shore Parkway
Brooklyn NY 11235
PH# 1-718-646-7996
cost 2oz $59.95
plus S&H $10.00
---------------
Total $69.95
Copper Sheet purchased From K&S Engineering Co.
Chicago Ill. 60638
I have no additional information on this company
I purchased this copper sheet at a local Faulk Hardware
store.
Copper sheet #259 .025 thick by 4 inches by 10 inches
Cost for one sheet was $4, sufficient to make hundreds of
.250 X .250 copper contacts.
3M adhesive surface cleaner, this is a 3M product that is
specifically for the purpose of surface prep and cleaning
so as to remove any hand oils or surface contaminants that
may be on the copper or cap aluminum contacts.
I would not suggest using alcohol, even 99% as it can leave
a surface film that can cause the epoxy to lose adhesion.
PROCEEDURES:
Cutting Contacts:
Using your dial calipers, set them to .250 inch or 250 thousandths
inch and lock them in place, mine has a little screw knob lock
that allows them to be locked in place so that the specific measurment
set in will not move.
Once this is done, then using the new sheet of copper, and using the
ends of the dial caliper mark a line down the width of the copper
sheet using the dial caliper to mark the line in the soft surface
of the copper. This method may take a little practice as it is
a little difficult to hold the dial caliper jaws just right so that
one rides along the edge of the copper sheet, while the other jaw
actually marks the line on the copper.
After this .250 line is marked into the copper then using the
metal sheers, cut carefully down the line as straight as you can
and slowly cut the .250 strip of copper off.
Of course as you cut, the strip will curl up, it would be
nice to have a metal sheer brake, but not many have enough money
to purchase such a piece of equipment.
After cutting the .250 strip of copper off, then straighten it out
as much as possible.
Now using the dial calipers, and the metal sheers, mark and cut
.250 X .250 pieces of copper. One 4 inch wide strip can make
16 pads.
After the .250 X .250 pads have been cut, then using the small
pair of needle nose pliers with the flat area towards the rear
of the jaws, place each pad in the jaws of the pliers and apply
force so as to flatten the pad. Turn the pad as you squeeze down
on the pliers, meaning, turn-squeeze-turn-squeeze-turn... and
so on until the pad is flat as possible. Don't squeeze to hard
and distort the pad.
Scoring The Contacts:
Your now ready to score a cross-hatch pattern on one of the surfaces
of the copper pads. NOTE: only one surface is to be scored.
Using the needle nose pliers pick one of the copper pads, and hold
it in place using the pliers on the edges of the copper pad.
Then using the trianguler sharp blade Xacto knife, score a cross
hatch pattern onto one side of the copper pad.
I do this in a specific way so as to increase the grip of the pad
when the epoxy is cured. The way to do this is to hold the Xacto
knife blade at an angle when scoring a line onto the copper pad.
Be careful not to score a line too deep, but it needs to be sufficient
to allow the epoxy to grab onto the copper contact.
I score three lines, and then turn the pad and score three more lines
for a total of six lines in one direction to make the first part of
the cross hatch. Then score at least six more lines to make the
cross hatch pattern on the copper pad, in the same manner, three lines
and then turn the pad and score three more in the same direction.
This completes the cross hatch pattern.
What is nice about this method is that if you look at it under a
microscope, the edges of the crosshatch form a tooth like lip that
gives the epoxy some place to grab onto when it cures. This greatly
increases the holding force of the contact to the aluminum.
NOTE: this scoring proceedure does not need to be done to the aluminum.
Surface Prep:
Surface prep is very important so that it will allow the epoxy
maximum holding force on the contact. Using the small artist brush
and the sharp blade Xacto knife, on a clean surface, use the Xacto
knife to hold one of the contacts down with the cross hatch pattern
facing up. Dip the small brush into some of the 3M surface prep
cleaner, and then brush the face of each of the contacts.
Making sure NOT TO TOUCH them with your fingers after you have
cleaned them. Use only tools to manipulate the contacts after they
have been cleaned.
After cleaning the copper pads, then also clean the aluminum contact
surface of the cap. If this is a new cap, then no additional prep is
necessary. If this is a used cap then you will first need to
clean the aluminum contacts using a dremel tool, fitted with a wire
brush attachment. NOTE: take eye protection precautions using this
tool, these wire brushes can throw out very sharp pieces of the brush
wire and lodge one in your eye, BE CAREFUL.
So, using the dremel tool with a small wire brush, clean off the
aluminum contacts in the cap, be careful not to remove much material
meaning don't grind on the contact and wear the surface down.
After all four contacts are clean, then using the small brush
and the 3M surface prep cleaner, clean up the surface of the
aluminum contacts. Make sure not to touch them again with your
fingers after cleaning.
ZEROING OUT THE GRAIN SCALE
This is an important step, to ensure that you are properly
weighing out the epoxy. What I do is position the scale on
as level as surface as you can possibly get, and then move
all three of the small slide adjusting weights over to 0.
After doing that then get yourself level with the front of
the scale so you are not suffering from parallax and look dead
on at the balance marker, while doing this then adjust the
adjustable foot to make the marker exactly even on the line
mark which means that the scale is not exactly zeroed.
NOTE: DON'T MOVE THE SCALE UNTIL AFTER you have weighted
out the silver epoxy, or you will upset the zero reading.
MIXING THE EPOXY AND PLACING THE CONTACTS
You are now ready to mix up the silver epoxy and epoxy the copper
contacts in place in the cap.
NOTE: I normally mix enough epoxy for two caps, ie.(8 contacts)
since it is a ratio mix, then the same ratio should work
for just four contacts, by cutting the mixture in half.
But one cap can be done with 9.1 grains of epoxy
and two drops of hardner.
The mixture for 8 contacts is 18.3 grains of silver epoxy
to 3 or 3.5 drops of hardner. The hardner is in the
syringe. So following this same ratio then 9.1 grains
of silver epoxy to 1.5 to 2 drops of hardner. I would use
two drops of hardner, as it will allow just a touch more time
to manipulate the epoxy. Also it is a little tricky getting
a half drop out of the syringe, but it can be done.
NOTE: before actually mixing the epoxy make sure you have
the following things in easy reach, as you do not have
very much time to mess around with the epoxy once it is
mixed.
Have the following ready:
tweezers
cut off end of a plastic shaft Q-tip
small jewelers screw driver, or you could use the sharp
bladed Xacto knife I suppose.
A small rag or paper towel to wipe the silver epoxy on.
NOTE: once the epoxy is mixed you need to work quickly and carefully
to apply the epoxy to each contact, place the contact on the
contact in the cap, and then position the contact properly.
So to summarize the steps:
1. dab epoxy on scored side of copper contact
2. dab epoxy on aluminum contact in cap
3. pickup copper contact with tweezers and position it on the
aluminum contact in the cap
4. using the jewelers screwdriver or a small Xacto knife blade
do the final positioning of the contact.
Of course this is always easier said than done, and in this case
it might be difficult to say exactly how to do this.
So here goes.
After you have zeroed out the grain scale, then using the sliding
weights on the cross bar, slide the weights over for the amount
of epoxy that you are going to use. If you are doing one cap
and of course only 4 contacts, then leave the large weight at zero
and slide over the middle weight to 9 and the smallest weight to
1 (one). This is the smallest grain increment that this scale can
handle.
Then using a small round bladed Xacto knife, or something to
scoop up a small portion of the silver epoxy, scoop up a small amount and
place it in the scale pan. You will probably not hit the exact weight
on the first try, so either subtract a small amount, or add a small
amount of epoxy until the scale zeros out again.
Make sure that you look dead on at the scale so that parallax is not
messing up the reading. Once you have the silver epoxy measured out
then remove it, as much as you can, from the scale pan, there will
probably be some small residue left in the pan which you can clean up
later, remember without the hardner, it will stay soft.
Now position the measured silver epoxy on the flat plastic or glass
surface and have your end cut off the plastic shaft Q-Tip ready.
Carefully remove the tip of the syringe hardener and VERY carefully
press down and measure out 1.5 to 2 drops.
I hold the syringe in my right hand so that the plunger part is
partly held in place by the upper part of my hand, and the lower part
is held in place by the bottom part of my hand. This gives the
plunger part more friction with my hand and keeps me from accidently
pushing on it too hard.
If you are very careful you can get 1.5 to 2 drops out of the syringe
and no more. After that is done then put the tip back on the syringe
and using the cut off plastic shaft Q-Tip, start to mix the epoxy
together. Make sure that you mix it thouroughly
Once it is mixed you need to work quickly and carefully to dab the
epoxy on the contacts, and then place them.
First move one of the copper contacts over with the scored cross hatch
face up, get a small dab of the silver epoxy on the plastic end of the
Q-Tip, and dab it on to the scored surface of the copper contact.
Use almost a rubbing motion, so that you dig the epoxy into the scoring
on the surface of the copper. Cover the entire contact then let it set
there while you dab some epoxy on the first aluminum contact you are
going to do. Try not to use too much, and at the same time don't use
to little epoxy.
Now using the tweezers, pick up the copper contact and at the same
time turn your hand to flip it over and lay it onto the aluminum
contact that has the epoxy on it.
Now set the Q-Tip down and pick up the jewelers screw driver or
a sharp bladed Xacto knife and push the copper contact into position.
You want to do a little back and forth motion to settle the copper contact
into position. Move it around so that it is square with the aluminum
contact, not cocked over at an angle. Push down gently on the top center
of the copper contact so that it squishes the epoxy out just a little.
Center the contact on the aluminum contact, and given the rotation of
the rotor, and the upside down orientation of the cap now, you can
slide the copper contact over to the left just a touch if you want.
This will allow that last microsecond of conduction before the rotor
spins past and goes on to the next contact.
After doing this to the first copper contact then proceed with the
other three contact in basically the same manner.
Using the cut off plastic shaft Q-Tip pick up a small dab of epoxy and
dab it onto the scored side of the copper contact. Then dab a bit more
onto the aluminum contact in the cap, then using the tweezers pick up
the contact, and flip it so that the scored side is down onto the
surface of the aluminum contact, then using either a small jewelers
screw driver or an Xacto knife position the copper contact and
move it so that it is squared up with the aluminum contact.
Look at the contacts and see that they are square, and not cocked over
at an angle, and that the face is also level, meaning that one side
of the contact is not higher than the other.
Believe it or not, I have done enough of these now, that I can place the
contacts within .003 inch plus or minus. But it does take some practice.
Do the remaining contacts in the same manner, and when you have finished
then set the cap bottom up, on a level surface and put something on
the rubber vents to hold the cap level while the epoxy cures.
Also make sure that you clean up any left over epoxy very quickly as
once it is setup, it is very hard to remove. So if you want to use the
mixing surface that you used to mix up the epoxy again, then clean it
now.
EPOXY CURING
There are two curing cycles for this epoxy, the first one is a full
and that is a FULL 24 hours RT (Room Temperture) curing.
It also means that the copper contacts are not to be touched or
manipulated in any way during this first 24 hour curing cycle.
The second cycle can be done anytime after the 24 hour curing cycle
is complete. The second cycle is as the book explains, 250 degrees
for one hour. I turn my oven on to 250 degrees, (on bake), and
let it heat up. Then when it is at 250, it beeps that it is up to
temp. I then put the cap or caps, into the oven on a plate and
let them set for one hour. My oven has a bake timer, that I set
and when the hour is over, it shuts the oven off.
CONTACT MEASURMENT, AND CLEARANCE
One aspect of this mod is that you need to make sure that there is now
sufficient clearance from the tip of the rotor to the contact.
This is where the inside calipers come into play. After the FULL 24
hour room temperture cure, you then use the inside calipers to measure
across from face to face of opposite contacts to measure the distance.
This gives you a total distance but of course does not give you
offset from center.
Typically what I have found, and after having done so many caps, I can
place the contacts very closely so that the center to contact differential
is with in .005 inch.
There is really no practical way to measure the center to contact face
measurement so you will have to rely on the overall measurement.
And it is nice to know that there is sufficient slop in the stock
size so that even being as much as .010 off would still be inside the
margin.
So the way I measure the clearance is like this. Using the inside caliper
set it so that the end tangs are just touching the surface of opposite
contact faces. You will have to feel this, meaning that as you move
the caliper ends across the face of the contact you will feel a slight
drag on the caliper. That means you are within about .002 to .003 of
the proper measurement. After you are satisfied with the measurement
then using the dial calipers, measure across the inside caliper end
tangs, with the same amount of drag as across the copper contact faces.
Check the reading on the dial caliper. Remember the smaller the reading
the closer the contact is to the rotor face. The reading will need to
be larger than 2.540 inch, if it is 2.540 or smaller then the
contacts are sticking out to far and will have to be removed and
re-applied because the rotor will hit the contact.
My readings typically come in at 2.600 or slightly below that.
Also after having measured several rotors, I have found that the
typical rotor center to rotor tip distance is 1.270
So simply take the inside caliper reading and divide it by two
and subtract either 1.270 or take an exact measurement of the rotor
that you will be using with this cap, and measure the center
carbon spot where the carbon contact of the cap touches the rotor
out to the tip of the center of the rotor.
Most of the ones I measured were within .005 thousandths of each other.
If you do suspect that one of the contacts is more than .010 off then
it would probably be best to either redo all of the contacts or just
the one you suspect.
Of course the acid test is to install the cap and rotor and start
the engine.
PROPER CAP SCREW HOLD DOWN TORQUE
After having moded several users, used caps I have found that some
have obviously been over torqued.
Given that the specific clearance has now been reduced from a stock
of .060 to around .025 thousandths, then making sure that the cap
sets down on the distributor properly and squarely is very important.
I have found that 40 inch pounds of torque, works out just about fine
on the cap hold down screws. Even though the BGB (Big Green Book)
doesn't have any specific torque spec for these specific screws.
You need to make sure that the cap is setting square on the lip of
the distributor, and that the rubber gasket has not been damaged
due to over torquing, and also that the cap has not been mashed
around the screw holes due to over torquing.
If any of these are out of alignment, then it is very easy for that
remaining .025 thousandths to be eaten up, and have the rotor
hit one of the contacts.
So make sure that you have a good rubber seal, a square cap
and torque the hold down screws to 40 inch pounds and you will
have thousands of miles of trouble free sparks getting to the
spark plugs.
--
Email: marcs@tdd.hbo.nec.com