Complete Vented Optispark Replacement Guide
Optispark is the distributor that was installed on all late model LT1’s
and LT4’s. This distributor was installed on :
1992 – 1996
LT1/LT4 Corvettes (Y-Body)
1993 – 1997 LT1/LT4 Camaro’s, Trans Ams
1994 – 1996 Fleetwood (D-Body)
1994 – 1996 Impala, Caprice,
The concept of the Optispark was a great idea.
It allowed for very accurate control of the spark to each plug. The cap
and rotor were pretty basic in design, however the heart of the Optispark
was the LED/disc setup. There were 2 LED’s that controlled the spark and
timing of the engine. Additionally, it was mounted to the CAM which
greatly assisted in giving an accurate position of TDC/BDC.
problem however was just that. The location of the Optispark. It allowed
road dirt, grime and water to attack the Optispark. Because of its
location, it had to be mounted behind the water pump and the balancer
making removal very time consuming. Dealers can charge upwards of $1200
to simple change a distributor. Additionally, water pumps as we know
fail. When they go, more times than not the pump starts with a small
leak. Because the water pump is located directly above the Optispark,
guess what? Another source of damage. This is by far the worst. Water
from the road MIGHT dry out. Antifreeze won’t, and will instantly damage
Finally, from 1992 – 1994 the Optispark was what is known in
the gearhead world as “unvented”. The reason it is called this is
because it does not have the vacuum hoses connected like the newer 1995+
LT1/LT4 engines have. What the vacuum hoses do, is they pull the moisture
out of the Optispark.
What a lot of people don’t realize is the
unvented Optisparks are actually vented!! Yes, they have 3 weep holes at
the base of the Optispark to allow moisture to escape. Well, all this
does is pull moisture back in. Put cold water on a hot Optispark, it’s
going to suck the water in! This is the BIGGEST problem with the design.
Before you go out and buy a brand new 1995+ Optispark, be
forewarned. You CANNOT bolt a 1995+ Optispark up to a 1992-1994 LT1. The
CAM is different. You could change the CAM, timing cover, CAM gear, etc
but this gets expensive, and is very labor intensive.
So, what is
You can do 1 of 2 things :
1. Change the
Optispark out and be up and running again. However you risk damaging it
again. There have been people who have had to replace a brand new
Optispark because they got them wet.
2. Change the Optispark out
with a modified unit.
The conversion process is
Buy a older style Optispark (the one you’re supposed to
buy), and simply change the cap! Of course you will need to do a few
Here is a listing of parts you will need
before you begin :
GM Parts :
Optispark for 1992-1994
LT1’s PN – 10457702
Cap and Rotor kit PN – 10457735 or
Distr. rebuild kit (Pep Boys or NAPA)
1996 Vacuum Hose Kit PN –
1995 Vacuum Hose Kit PN – 12555323
parts from http://www.gmpartsdirect.com/ or from your local GM dealer
Inverse Torx Bit – E4, deep well!!
SnapOn part number STLE40 – I stopped a truck, or you can order online at
2-claw puller – Autozone
2 water pump
Vacuum T or a brass T that will screw into
Long Breaker bar, or torque wrench
Brass fitting for
the base of the Optispark. I got mine from the local parts house that
carries various hose/pipe fittings.
3/16″ Drill Bit (slightly bigger
than the hole your drilling out)
Plugs and Plugwires
Converting the new Optispark
your cap from your new Optispark. Nothing like taking apart something
brand new eh?
Remove the rotor from the Optispark. This is a torx T15
Carefully remove the rotor, and the metal disc. Do NOT
remove the slotted one! It’s spot welded on for a reason. Only the disc
directly behind the rotor should be removed.
Remove the middle spacer.
This is the center portion of the Optispark body.
everything, but the back plate. BE careful when handling this. Try not
to get any grease, dirt or anything on the disc.
You will notice 3
holes on the base. Fill the center one, and the one closest to the long
pointed portion of the base in with JB Weld or something similar. I
drilled out the remaining hole. Try not to get the metal shavings in or
on the Optispark. Next I tapped in a brass fitting. Do not use the
center hole for this, as it won’t clear the balancer hub. IF you can
find a brass L fitting, this would be your best bet. I wasn’t able to
find one small enough, so I used a straight brass fitting from a local
Vacuum the metal shavings from the previous step. MAKE
sure it’s clean before you put it back together.
Reassembly is the
same. MAKE SURE you don’t forget to put the metal disc back in place.
If you leave it out, the gap for the rotor and cap will be WAY off. The
rotor and disc are keyed, but still make sure you put them in correctly.
Remove the old RTV Sealant, and put some new RTV on the cap at the
electrical connection. Put it back together with the newer style cap.
Lightly blow into one of the hose connections while closing off the
other. You should hear no hissing.
You aren’t supposed to turn the
shaft on the Optispark (why I don’t know), but I would still recommend
slightly turning it (1/4 turn is enough) to make sure everything spins
The Nitty Gritty
First disconnect your
Drain your coolant. Be sure to open the bleed screws. This
will help it drain much quicker.
Remove the rubber intake bellow.
Remove the upper radiator hoses.
Disconnect the bottom radiator
hose from the water pump.
Remove the coil wire, and the electrical
connections from the Optispark and water pump.
Pull the belt tensioner
out of the way, and loosen the accessory belt.
Remove the water pump.
There are 6 bolts holding it in place. Additional coolant will dump out
when you remove the drivers side lower bolt. Clean the old gasket material
and set the water pump aside for now. You MIGHT need to remove the coil,
but I didn’t need to. Check the weep hole on the water pump to make
sure it’s not damp.
This is the fun part (for me at least). Remove
the 3 bolts from the balancer. The Haynes manual says you can simply pull
it off without a puller. I was not able to. I had to use a 2-clawed
puller. I got mine at Autozone. I believe the one I got was the 6″.
Somebody is borrowing it as we speak for this repair! MAKE SURE you make a
note of the position of the balancer in relation to the hub. Both the hub
and balancer should be marked, but not keyed.
Remove the remaining
plug wires. If they are old, you may want to replace them. Now is the
time to do it!
Remove the 3 bolts that hold the Optispark in place.
Pull it straight out. There is a shaft that connects the Optispark to the
Cam gear. This may or may not come out with the Optispark.
point, you should look at the old Optispark and make a mark of where the
notch (spline) is. This will assist you later.
This would be a good
time to put some gasket sealant on one side of the gaskets, and place them
on the water pump so they can dry. This will make reinstalling the water
pump much easier.
With the old Optispark to compare, rotate the shaft
on the new one until they match up.
I found it easier to insert the
shaft on the cam shaft, and then sliding the Optispark on top of it.
IF there is any gap on any of the 3 mounting screws, you probably
haven’t lined the Optispark up correctly with the spline on the shaft. It
should slide all the way on with no gaps on any of the mounting areas.
Tighten the bolts, but do not over tighten.
Run your vacuum lines.
The clip goes on the alternator bracket. MAKE SURE the hoses are going to
clear the belt.
The hose that has the filter and regulator is the
Poke a hole in the rubber bellow (on the top) and push
the L into it.
Put a T or something similar on the drivers side intake
manifold, and hook the vacuum hose up.
Reconnect the plug wires.
Reinstall the 3 bolts on the balancer. Tighten the bolts to 60
Ft-lbs. Make sure you line it up properly (see step above where you
Put gasket sealant on the remaining gasket material, and
reinstall the water pump. Tighten to 30 Ft-lbs.
Reinstall the belt.
It is much easier to do it now before you do the next step!
all the hoses, the coil wire and the other misc electrical connections
(temp sensor, Optispark connector, etc).
Lightly tighten the bleed
Refill the cooling system until it is full. Place a rag
around the bleed screws, and bleed off the excess air. Don’t let any
coolant get on your new Optispark!
Check and recheck everything.
Fire it up.
If everything looks good, your done!
also pull the hose out of the bellow, and check for vacuum. If it gets
clogged, or a hose gets pinched, it will cause the cap to cave in, and
burn up the rotor.