318 flex plate 408 and damper balance help

Bruceynz

Bruceynz

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Hi guys,

Trying to work out what to do for internal balance. Can I knock the weights off the 360 mag flex plate, is a stock mag flexplate strong enough for 408?

Will the older LA style flexplate bolt upto a 360 stroker crank?

Anyone got a 318 mag damper with serpentine pulley?

Crank is mopar performance cast crank 408

Mopar Performance Cast Iron Crankshaft - P5007258

Thanks
Bruce
 
Last edited:
Bruceynz said:
is a stock mag flexplate strong enough for 408?
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The stock Magnum flexplate is strong enough – unless you perform high RPM neutral slams to take off.

Bruceynz said:
Can I knock the weights off the 360 mag flex plate
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A person can take off the weights from a 360 Magnum flexplate – but I wouldn’t waste the time on it. Afterwards, you will need to get the flexplate balanced and make sure it is straight. Slightly bent flexplates causes a lot of hard to find vibrations and other problems.
If you have a way to balance it and can also check it for straightness afterwards – go for it.

You have me wondering now. Why not use the older star (or square) looking flexplate? They are cheaper and harder to harm.

Bruceynz said:
Will the older LA style flexplate bolt upto a 360 stroker crank?
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Yes it will – and might be best option.

Bruceynz said:
Anyone got a 318 mag damper with serpentine pulley
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I don’t have.
A friend of mine just tossed a lot of magnum parts away, including a couple of 318 Magnum balancers, late last year.
BudW
 
Them cranks are made by scat and the scats sell for under $400 on ebay, some decent sellers have balanced kits as low as $1300.

Ditch the mag flex plate use a normal unbalanced La unit and a neutral balanced converter. Im sure you understand there internal balance means all outside fixtures are to be net. balance.

I would just buy a new balancer so to be starting off with good fresh parts that are in good order.
 
Hi

I just bought this in nz for $20usd

Screenshot_20180106-152110.png


Can anyone help me out with a 318 harmonic damper, when I look on ebay they don't have the serpentine pulley

Thanks
Bruce
 
This has both, balancer and pulley. Is that what your looking for?
Dorman Engine Harmonic Balancer
dorman.gif
1010211.jpg
Click to Enlarge

(1 Reviews)
5 Stars
Our List Price: $59.95

Quantity:
(3) In Stock
Part Number: 1969-09035195
ummit ASP-504500 $67.97
A 3.9 or 5.2 from 92-02 will work.
 
That is correct. BUT! BUT! BUT!!!! You want a NEUTRAL BALANCE 3.9, 5.2 harmonic bal, flex plate, Torque Converter for your stroker crank which is Neutral balanced, like the teen.
I screwed that up Bruce, somehow? Swore it had the 3.9 5.2 Bal/pulley above or below the 5.9 in that ad. I think part of the ad was cut off. Glad you caught the error.
 
$40 (US) for a new (OEM) balancer/pulley is a great price!

I have a few different opinions about balancers than what most people have.
The harmonic balancer is a very important part for the longtivity of an engine.
The rubber ring that holds the outer weight (or metal ring) onto the balancer hub wears out in time, which allows the outer ring to slip (and makes setting ignition timing a headache, at times) and in some cases, allows the metal ring to just fall off.

Also (again, my opinion only), heavy balancers are much better than thin or lightweight balancers are. Almost all of all of the broken crankshafts I have seen have all used a tiny (or none) balancer (I’m talking about all manufactures, not just Mopar).

I really like the balancers which the rubber ring is glued to both the hub and metal ring (which keeps timing marks correct and keeps ring from coming off 10 years down the road) – or even better, the balancers which have a metal ring surrounded by a viscous fluid inside of an enclosed metal balancer.

Almost all factory balancers, the hub, rubber ring and metal ring are only held in place by friction (and not glue).
Matter of fact, if you have an engine apart and is looking at a balancer to re-install – look at the rubber ring. If the rubber is cracked – I do not recommend using it (and use it instead as a paper hold-downer).

This link explains more on why a balancer is needed
https://en.wikipedia.org/wiki/Harmonic_damper

This link talks more about the different kinds of balancers.
http://www.dieselarmy.com/engine-tech/engine/how-it-works-viscous-dampers-a-k-a-harmonic-balancers/
BudW
 
WELL, that depends.
If I was racing and was spending a lot of coin on my engine vs. daily driver (where I fit in) vs. occasional driver (less than 50 miles a month – which I suspect you might fall under?).

If you fall under the occasional driver – then I would jump onto that $40 new balancer, quick.

On my engines – I’m going with a fluid dampeners – just because I want to (but might be a bit overkill).
I already have a pair of fluid dampers to use – but (gasp!), they are chrome plated! Blue paint doesn’t want to stick to chrome long term (so I have a small dilemma).

This doesn’t apply to small blocks – but if I could get my hands on thick Hemi (big block) balancers and IF I could get pulleys to fit (Hemi’s didn’t come with A/C for a reason) – then I would jump on that bandwagon (but that is something to talk about in another thread).
BudW
 
Buds right, them fluidampers are one of those you get what you pay for parts that really is overkill for a large majority of engines. The (a) damper is a must, not an option. Its not just balancing, it absorbs vibrations that tare a motor apart. And a heavy one is better than a lighter one for ultimate smoothness and ultra long life engines, like on a diesel. They also add weight to rotating assy slowing acceleration. Personally, I'm happy with oe weight on my street engine build with stock- near stock redline. It should all be balanced together, ultimately, but seldom I done.
I do feel differently than Bud about the oem damper. Maybe Buds being a bit hard on the oe. They are everything Bud said, friction mounted, perishable rubber strip, could slip when neglected and worn out. But, they do and have come new on 100% of every vehicle sold since the beginning of time. On everything. They run 200,000 or more miles, every day for decades and survive fine. Even on medium HP motors. Not that they cant fail, eventually. For $40 + tax and the ride, Id buy that. You will never wear it out. If your concerned it will shift or slide, add a white stripe across both the ring and center like on drag slicks and keep an eye on it.
 
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