Before Attempting to install an Underdrive Pulley (420A)

[Mikelb]

Wow, no one ever really did a write up (to my knowledge) on how to replace the harmonic balancer on the 420a, or how to swap it with an underdrive pulley...

I have had problems here lately with my harmonic balancer tearing through belts (like 3 in a month)... I looked at it closely, and found the grooves to be worn and the outer rings (to hold belts in place) cracked and missing in places.

So, I went on e-bay, and bought a BOMZ underdrive pulley (~$30)...
I didn't expect this to be such a rough job...

Ok, the pulley came in with instructions... I run down to my local Advance Auto parts and grab a harmonic balancer puller kit (the deluxe version ~$80, get the loaner, you'll get your money back). I get back to the house. All is good.

To start with, jack the car's right side up, enough for the wheel to come off of the ground. I suggest removing the wheel (not a must, but it gves you more work room, I just turned my wheel all the way to the right). Now that the car is jacked up, remove the plastic shroud surrounding the pulley. You should be able to see the pulley now.

Now, I used a hydraulic jack (didn't have a cherry picker)... place the jack under the oil pan (use a block of wood to keep the jack from denting the oil pan). Raise the jack to just barely brace the bottom of the oil pan.

Looking into the engine compartment, there should be an engine mount right above where the belts sit. There will be a radiator reservoir here, remove that. Remove the bracket that held the reservoir in place. Now you can access the bolt through the motor mount. Take out that bolt. Also remove the three bolts holding the motor mount to the engine (I suggest a breaker bar, a socket wrench just wouldn't cut it for me). Remove the bracket.

Now, the engine will be free of that motor mount, this is where the jack comes in handy. Slowly allow the jack to descend, keeping an eye on the harmonic balancer. You will want to lower the engine on this side enough for the balancer to clear the front clip. Once it has been lowered enough, secure the jack.

Now, use the harmonic balancer to remove the pulley (I used the long pushrod, not sure if the short one is long enough). Once the puller has pushed itself completely in, you are most likely going to have to pry a little. The pulley will be free from the heavy torque, but I found mine to still have about 1/4" to go.

Once the pulley has broken free, the rest is a piece of cake. Simply attach the underdrive pulley. Use the installer and bolts to torque it back into place. Then retorque the bolt through the center. Jack the motor back into place (CAREFULLY!!! make sure to line up the motor mount and brackets, makes reinstallation much easier).

Once you have torqued everything back, drop the jack from underneath the motor. Make sure everything is sitting right, install your new belts (be sure to let them seat [mfr suggests 5 mins of letting the car run]). I would suggest re-torquing all of the bolts the next day and again in another two days, to make sure everything is fitting right after expansion and contraction.

[gthompson97]

Nice write-up. The job is much, much easier if you take off the wheel though.

[Mikelb]

Thanks,

The wheel wasn't the problem... My problem was, I had the pulley almost off, then I realize it wasn't coming anymore. That's when I realized I had to take off that motor mount... at first I just removed the center bolt, but the motor didn't drop down quite enough to clear the pulley... I was doing this in my back yard, and it was dark... so I had to replace the mount (I didn't want the jack to sink into ground and possibly damage the engine or mounts)... and start all over the next day...
it took three days, because I first bought the cheap harmonic balancer puller, and realized it was meant for balancers that had threaded holes (for the puller to screw into)... and the 420a doesn't have them. So I took the kit back, and borrowed the deluxe version, and it was closing time. When I got back to the house, I realized the thread on the puller was messed up and wouldn't allow the bolt on the puller to turn.
So the next day I got the right kit and all, had the thing damn near done, and realized I'd have to drop the motor...

[gthompson97]

Yeah, you basically have to pull that pulley if you're going to take out the motor and I've done that numerous times so I've had lots of experience with that part of the motor. But taking the wheel and splash guard off gives you much, much more room to work.

[l_eclipse_l]

I always wondered how much work this job actually was, since these things are so damn cheap. Nice write up man. Notice any difference at all?

[Mikelb]

Thanks, Yeah... I've noticed a bit of difference... It's not much of a gain, but it allows you to get to the higher RPMs and the hp levels faster...

Sorta like a lightweight flywheel, but the gains aren't as much... it seems to have gained more torque than horsepower, but it revs up nicer...
I think it's just nice to have it back after 3 days... lol...

I'd say for the gain, the $$$ and time was worth it... I don't think I would have taken it to a shop to do though...
Like I said, I did this in my backyard(not even a slab of concrete, it was in the grass) with the car's jack( to lift the passenger tire) and a hydraulic jack (to raise/lower engine)... It was more time consuming than anything...
after that little project, I feel more confident with this motor... as I knew very little a/b it before...