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420A Heres the how and why of Under Drive crank pulley install for the 420A N/T

Warning, this is a long write up. I’ve intended to be as detailed as possible since I understand how vague some of the available information is.

Ok, im going to attempt to walk you through a Under Drive crank pulley install for the 420A N/T motor. This is also written for the Manual Transmission. Im sure some are wondering as to why. Well, after finishing my install myself I noticed that there was a rather large gap in available information for our motor when it comes to the pulley install. There were several tools I had to buy just for this job for instance. And both the manual and the pulley instructions were rather vague on what needed to be done. This is my attempt to put all the information in one location.

First off….tools.

You’ll need all the usual tools such as sockets, ratchets and wrenches. To be more specific…..17mm/19mm/14mm sockets……and size 15 and 14 wrenches. A nice big torque wrench is also a must. Now depending on the pulley you install there may be more of less. Ill warn you ahead of time that the Unorthodox is a two piece assembly. The center steel hub fits inside the outer aluminum pulley itself. It’s held in by some damn unusual Allen wrench bolts. And no, you can’t use an Allen wrench on em. You’ll need the proper ratchet attachment that AutoZone doesn’t seem to sell in my state….in fact it took me a day to find one. So be prepared for this one. Also don’t forget the jacks and jack stands please.

One unusual tool that was very helpful was a blowtorch. Nothing fancy just a torch or even an oven. You’ll find out why later on….

You WILL need new belts for this job since you’re putting on a smaller pulley. Unorthodox recommends Gates brand belts. They can be had at any auto parts store.

The most important tool for this one is also a pulley puller. Now, you can rent these pretty cheap (I got mine for $20). Be warned however that the clerks don’t know what there talking about usually. There may be several pullers at your local store. You’ll need one that has a rather long center shaft. This shaft MUST travel all the way down the crank hole when you remove the bolt! Be warned that about ½ the pullers for sale WILL NOT be long enough!

Now to start…..loosen the passenger side tire, go ahead and jack the passenger side of the eclipse up as normal, making sure to replace the jacks with real jack stands…please be safe as we’ll be spending time under the motor also. Pop the tire off. The first thing you’ll see in here is a plastic mud guard. Remove this. It’s held on by 3 small bolts and 2 plastic screws.

By now you can see the pulley you’ll be tackling. Now for the oh so fun part. Belt removal. (this is intended for people that don’t know already…im sure a lot of people can skip this part.) Stand in front of the engine bay and look down on the left hand side. You’ll see the belt curve around down there. There’s a smooth pulley it touches. That’s the tensioner. It has 2 bolts, one to loosen and another that holds the tensioner on itself. Loosen the bolt holding it on first, the inner one. Then crank the other bolt over to the left..again…and again. Its going to take awhile Just keep it coming until you can get the belt off.

Now the fun one….I hope you jacked the car WAY up. Crawl under….way under to the alternator. It’s going to be way up there. We need to go under here for the purpose of loosting one bolt. When you look up under the alternator you’ll see it. Crank it loose but don’t remove it.

Crawl out and go to the top of the alternator. There’s another retaining bolt that needs to be loosened, but not removed. Then another one of those annoying tensioner bolts is on the alternator, on the backside by the firewall. Reach way down there and crank that sucker a few million times until the alternator bolt can be pulled off also.

Shew, now onto the fun part! You’ll need to get the bolt off the pulley itself now. This is where having a friend helps A LOT. Get a friend (or brick, or dog) to stand on the brake pedal. Get under the car again and yank the HELL out of that pulley bolt. It’s on there tight as all hell, so be prepared for a bit of a fight. It will come though…..

Now, something that Unorthodox and my Haynes manual COMPLETELY forgot to mention was the fact that in order to get the pulley off I had to drop the damn motor. This isn’t to hard though. Just get a jack and a block o wood (or I used my damn Haynes manual instead by this time…) and place it under the oil pan and jack it up just a tad…on the passenger side inside the engine bay you’ll see the motor mount. Just remove the group of 3 bolts (yea there awesomely tight as well) nearest the motor then let the jack down SLOWLY. The motor will then sink down and you’ll notice the pulley will have fallen just enough for easy removal…..which of course it wont be.

Now grab your 3-jawed pulley removal that im sure you remembered if you’ve made it this far into my lecture. Put the center piece all the way down into the crank bolt hole. Remember, it needs to go ALL the way down. Attach the 3 hooks and start cranking like there’s no tomorrow. This also can take some time but trust me it will come out. Pop! Set to old one off to the side when you’re finished.

Now some more fun stuff. Remember that center steel ring? Ok remove the bolts from it and crank up your handy blow torch and let it have it all over the ring. Lacking a torch you can use an oven at 500 degrees for 45 minutes, but a torch is both cheap and faster. This is being done to expand the ring so we can easily get it on the crank snout. Believe it or not this step will make you’re life easier in the long run, and ensure it’s seated properly.

Now that’s its all hot, use gloves or a towel and slip the steel center onto the crank snout. When it stops going on grab a hammer and a block of wood and give it several good hits. It’s probably going to slip on even more. This is good, because if you don’t get this on correctly you’ll throw your belts and have to just do this all over again….so get it right the first time man.

Once on, and while it’s still hot re-bolt it in using the same bolt you just removed from the old pulley. Torque for this is 30 ft/lbs. Don’t be shy you want this on good and snug. Then place the outer pulley part onto the center hub, and line up the holes. Its going to be tight so don’t forget to use your ole block o’ wood and hammer to get it on nice and tight. Attach it using the supplied bolts. These 3 need to get torqued at 19 ft/lbs. Again this is important…so do it right.

Viola! Looks shinny eh? OK raise the motor back up first and re-bolt it in….then do everything in reverse. Attach your new belts, tighten up the alternator bolts in reverse order, and tension everything just right. Lookie there! You’ve done it! And im sure you can get your car off jacks without my help so I won’t even go into that………….

Ok according to Unorthodox it may take up to 5-7 days before a noticeable difference is felt from the new pulley. Apparently the ECU may need time to adjust for the lighter rotational mass….however I noticed a huge difference on my first test drive. The car just generally rev’s a lot faster. It’s not really more power, but its ensuring you get to your peak power faster. This install is not overly difficuly, just take your time and be safe. In the end im sure youll be vary happy with the results. I know i am!

Questions? Comments? Need pictures? Ill do my best to help anybody out!

EDIT: the new beltsizes you will need are.....

Alternator Belt: Gates K040320 (32.75 inches or 830MM)
Power Stearing/AC belt: Gates K050490 (49.5 inches or 1255MM)


N/T DSM Wiseman
DSM Wiseman
Dec 17, 2004
East Hampton, Connecticut
ShadoWulf, appreciate the write. You seem to have covered a lot of the bases for those who use the unorthodox. Just a couple of points of interest. If you get the AF/X from Howell it comes with the belts :thumb: . One thing about heat is it can warp out metal. You just want to be aware of this so you don't take out your acetylene torch and roast up your pulley :p . I pulled my UDP on by using an inch longer crank bolt. I started out straight, I pulled it right on. I just put my AF/X on and used GSGoinFast info as a reference. I was happy with the info but I can see that you put a little more specifics into your install.Thanks
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