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Overrunning Alternator Decoupler (OAD) Pulley Mod

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marsrock7
(@marsrock7)
Reputable Member

This is a simple mod which replaces the stock alternator pulley with a newer overrunning, decoupling type. Nearly all new cars utilize these, so the effects must be worth something. All credit for the research and development of this mod belongs to the user "Bitter" from NewCelica.org. His test vehicle is a GT-S with auto trans.

I also have one of these pulleys installed in my Spyder now. And I'm happy today that the difference is quite appreciable. 

TL;DR at bottom of post.

Data from the original thread below:

[QUOTE=Bitter]Letting the alternator freewheel when it's not driven is very beneficial to belt and tensioner life, it's also a small boost to engine efficiency, and best yet reduces spinning mass on engine deceleration. The alternator rotor and shaft is typically about 90% of the weight of the alternator, so for ours it would be about 8-10 lbs of mass spinning at roughly 3x crank speed due to pulley ratio! That's a lot of energy to slow down each time you want to change gear. I'm a little light on math to figure the moment of inertia and how many lb/ft of stored energy that is,but if you've ever spun an alternator by hand and then stopped it by hand you can feel it's got some serious heft just at 100rpm, now imagine at 20,000 RPM!

I have no idea if it would make any appreciable difference however EVERY new car is using them so there must be some benefit to offset the cost and enough for the bean counters across the industry.[/QUOTE]

[QUOTE=Bitter]RockAuto has a pulley on closeout listed that I'm going to purchase and attempt to install.
DAYCO 892003
It's both over running and decoupling so it'll dampen the alternator from the engine on both acceleration and deceleration which in theory should reduce wear on the belt and reduce the spinning mass of the engine under those conditions. [/QUOTE]

[QUOTE=Bitter]It is a direct swap. That Dayco part number fits perfectly fine and has the same belt dimensions as the original pulley. You'll need a 17mm hex adapter or hex socket and an impact to install it, use loctite on the threads.[/QUOTE]

Bitter's first impressions in April:

[QUOTE=Bitter]It *feels* much smoother when shifting at high RPM, either up or down shift, much less "kick" when up shifting at high RPM. All the time I've had the car when up shifting from 1st to 2nd or 2nd to 3rd at fuel cut there would be a fairly noticeable "kick" from the drive train because the engine is being stuffed back down several thousand RPM by the trans, most of that kick is gone now and honestly I like how that feels because it feels faster because it feels smoother. Whether it actually is any faster who knows, I really doubt it but this was only one drive to run the rust off the brakes with limited high RPM time.

I guess the conclusion is that it works, probably a better effect with a manual trans, and I'll update when/if it breaks or something changes or I have news.[/QUOTE]

My first impressions as of a couple days ago (having not re-read the thread first):

[QUOTE=marsrock7]
Hard off and on throttle is smoother, deceleration out of gear is a bit slower. High RPM shifting is WAY smoother. The best way to describe it is... Smoother. I'm positive this is much more effective for decreasing engine load than a lightweight alternator pulley, or even underdriving. The rotational mass of the alternator itself being decoupled from the pulley system is a respectable gain. There may even be a touch more power, I can't judge that yet... ECU needs to relearn it's fueling still.
My usb charger is also my voltmeter.... So far voltage is consistently 14.2+. No noticable difference in voltage output.

Update: nearly every shift feels perfect. It's very difficult to make a jarring shift now.[/QUOTE]

TL;DR:

Bitter and I have come to the same conclusion on the effects. This pulley reduces drivetrain shock and just makes everything feel so much smoother. The drivetrain feels lighter and more responsive to throttle input. I  love how it feels and don't plan to ever go back to a regular pulley.

This is a direct bolt-on, pulley is same diameter and works with original belt. Both test cars are 2ZZ but if I recall correctly the pulley size on 1ZZ is the same so this mod could also be able to be done on a 1ZZ.

DAYCO 892003 or equivalent pulley

17mm Allen socket 

Impact on, with blue locktite

Enjoy!

5/16/20 Update: this has been working my my Spyder flawlessly.  Also added one to my TSX.

1ZZ pullies are either 52.5mm or 55mm, might be worth checking yours before hunting for the right OAD type pulley. 

Bore diameter for all is 17mm. 

Threads for all are M14x1.5

You will need a 17mm hex head socket and relatively small impact to install. Blue locktite is recommended for the threads. The install can be done with the alternator in the vehicle.

More pulley sizes, part numbers, explanation of how OAD pullies work and more can be found throughout the thread.

 Carpe Viam!

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Topic starter Posted : August 19, 2019 11:07 pm
suoiruc liked
haloruler64
(@haloruler64)
Prominent Member

I kinda don't get how it works exactly and what effect it has on the battery. But I am willing to try it. Bitter is a gem. A sinful, weird gem. 

2000 Toyota MR2 Spyder, 2020 Mazda 3 Hatchback 6MT

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Posted : August 19, 2019 11:22 pm
marsrock7
(@marsrock7)
Reputable Member

Since I'm not seeing any difference in volage output I'd be inclined to think this should have no effect on the battery. The alternator is still spinning even when decoupled from the belt, it's just spinning with it's own inertia rather than being directly driven.

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Topic starter Posted : August 19, 2019 11:29 pm
dev
 dev
(@dev)
Just a member. Moderator

Wow I never thought something like that existed. I like the fact that it is a mass produced item that is proven. 

 Now the question is, is there enough access to remove the pulley or do we need to remove the alternator.

 

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Posted : August 19, 2019 11:50 pm
marsrock7
(@marsrock7)
Reputable Member
Posted by: @dev

Wow I never thought something like that existed. I like the fact that it is a mass produced item that is proven. 

 Now the question is, is there enough access to remove the pulley or do we need to remove the alternator.

Since I removed the old, and installed the new pulley with an impact, this was done with the alternator completely removed. Maybe if someone has a very low profile impact and a very short 17mm Allen socket it could be done in the car... But otherwise it's a job best done with the alternator out of the car.

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Topic starter Posted : August 20, 2019 12:21 am
haloruler64
(@haloruler64)
Prominent Member

$60, not too bad. I talked to Bitter and he says that it only decouples when decelerating sharply, like when you let off the throttle, so there should be 0 battery issues. 

Taking out the alternator SUCKS but it's not the end of the world.

2000 Toyota MR2 Spyder, 2020 Mazda 3 Hatchback 6MT

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Posted : August 20, 2019 12:49 am
marsrock7
(@marsrock7)
Reputable Member

Here is a dayco vid showing the difference between a solid and overrunning pulley. All that chaos on the back side of the belt in the demonstration... Where does it go in our cars? The tensioner, belt slippage, and the other accessories, along with the crankshaft. 

Taking the alternator out isn't too bad, I've done it a few times now (thanks O'Reillys 😡). I have the most trouble getting it back in. The bottom bolt is always a huge PITA for me. Usually takes me 20-30 minutes to hang it. That's a long time to have both arms crammed back there wiggling things around.

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Topic starter Posted : August 20, 2019 1:38 am
marsrock7
(@marsrock7)
Reputable Member

There are slightly cheaper options than the dayco. Heres some options from RockAuto. If you want to look for your own, the subject vehicle is a 2001-2007 Dodge Caravan, 3.3l V6.

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Topic starter Posted : August 20, 2019 2:03 am
haloruler64
(@haloruler64)
Prominent Member

$43 for the Gates, I might give it a shot. Need to order a caliper from Rock Auto anyway, might save on shipping. Anyone got a discount code? 😛

2000 Toyota MR2 Spyder, 2020 Mazda 3 Hatchback 6MT

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Posted : August 20, 2019 4:46 am
suoiruc
(@suoiruc)
Trusted Member

@marsrock7

I like it! That might help with the SMT shifts. How long before my alternator goes bad so i can change it? 

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Posted : August 20, 2019 5:14 am
haloruler64
(@haloruler64)
Prominent Member

Original alternators last a long long time. Might as well do the pulley rather than waiting for it to die. I'm at 149600 and still on the original.

2000 Toyota MR2 Spyder, 2020 Mazda 3 Hatchback 6MT

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Posted : August 20, 2019 5:40 am
Bitter
(@bitter)
Active Member
Posted by: @haloruler64

I kinda don't get how it works exactly and what effect it has on the battery. But I am willing to try it. Bitter is a gem. A sinful, weird gem. 

When a belt tensioner and an alternator love each other very much sometimes they like to team up on your serpentine belt and.....

 

There's a one way clutch that allows the alternator to freewheel on deceleration with some friction and a large thick coiled spring that absorbs shocks in either direction. When you install it with an impact gun you can feel/see the spring working and then also see the one way clutch at work as well. The spring feels weird when the gun hits it, for sure use Loc-tite on the threads to make sure it never comes loose. If it wears out just heat the center with a torch gently to soften the Loc-tite for easier impact removal. These two things combined allows designers to implement a smaller lighter belt or a smaller lighter tensioner, the less tension needed on the belt means a little less drag on the engine and a little more fuel efficiency as well as a longer lasting belt and belt tensioner. But Bitter what if our belt drive system wasn't designed to require that? Well guess what, we can still benefit from all the positive effects of the OAD pulley too. Bonus for anyone spinning their engine up and down a lot is that there's less rotational inertia spinning when you want it to slow down faster, like to grab the next gear. Down side is one more mechanical part to wear out, however they've got a designed life span of about 100,000 miles and I've never seen one failed at the shop with less than that. Often times I see one way and OAD alt pulleys failed with 130-200+ K miles, rarely less than 130,o00 miles. With more vehicles coming with these I'm sure there will only be lower prices and more options in the future. I got this specific Dayco part on closeout for around 1/2 off which was a big deciding factor, the dampening feature was cool but not a primary focus, I just wanted the decoupling part.

This post was modified 2 years ago by Bitter
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Posted : August 20, 2019 6:00 am
neomr2
(@neomr2)
Reputable Member

Interesting concept.  The only issue I see is that special tools are needed for removal and replacement.

Mono Craft GT-300 with a few upgrades...

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Posted : August 20, 2019 6:39 am
NottaMiata
(@nottamiata)
Honorable Member

Dumb question: is an impact absolutely necessary? I have one, but not low-profile. Could a person just use a wrench or ratchet, perhaps with a cheater bar, and a "persuader"?

Loc-tite is not optional, understandably.

🐸, 2003, Electric Green Mica, not enough mods

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Posted : August 20, 2019 12:06 pm
marsrock7
(@marsrock7)
Reputable Member
Posted by: @nottamiata

Dumb question: is an impact absolutely necessary? I have one, but not low-profile. Could a person just use a wrench or ratchet, perhaps with a cheater bar, and a "persuader"?

Loc-tite is not optional, understandably.

The problem with removing and replacing the pulley is that we have no way to stop the alternator internals from rotating. An impact just hits hard and fast enough to get around this problem. If you don't use an impact, you could maybe break the old pulley loose while the belt is still on to keep it from spinning. For installation of the new pulley you would need whatever specialized tool Dodge uses to install and remove these. 

The new pulley doesnt come with a nut, the pulley is threaded and the 17mm hex is machined into it.

s l640
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Topic starter Posted : August 20, 2019 1:51 pm
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