Re: Internal vs. External Balance

From: Matt Beazer (teseract@moparhowto.com)
Date: Wed Mar 03 2010 - 01:31:08 EST


Perhaps there wasn't enough space in the block for throw on the proper
counterweights on the crank itself due to the longer stroke and larger
main bearings? I thought the block was mostly common between the
318/360 other than certain machining done to the block for said larger
mains, etc.

I just remember the old 2.5L "Commonblock" Mopar 4 cylinders. They had
to notch the bottom of the bores to clear the throw from the longer
stroke, so who knows what they'd have to do with a V8?

On 03/02/2010 11:16 AM, jon@dakota-truck.net wrote:
> "Ray Block"<BPracing@wowway.com> wrote:
>
>>> -----Original Message-----
>>> From: jon@dakota-truck.net
>>>
>>> Assuming that I have understood correctly so far, rather than
>>> imbalance each engine the same, why the heck didn't they just build
>>> the 360 internally balanced in the first place? Seems like this would
>>> save a lot of money since all harmonic balancers, flexplates and
>>> torque converters could them be shared between the 318 and 360 with no
>>> interchange worries or the resulting confusion?
>>>
>
>> I gather it was cheaper to Externally balance the engines. I don't think
>> the factory worried much about interchangeability. Then again, its been my
>> experience that some engineers make changes just to justify their jobs. ;)
>>
>
> Yep, you're probably right about the interchanability, though I
> would have expected the bean counters to be worried about it. So,
> this begs another question - if it was cheaper to externally balance
> the engines, why did they go with internal balance on practically
> everything else?
>
>
>
>>> Were the 360 rods and
>>> pistons simply too heavy to add enough weight to the crankshaft with
>>> the block clearance involved?
>>>
>
>> No. The rods are the same for all small block mopars. The 360 pistons s/b
>> lighter than the 340's since the bore is smaller. They are slightly larger
>> than 318 pistons. The 360, for some reason, has larger mains. Don't know
>> why unless it was perceived durability for the proposed applications and
>> because of the 360's longer stroke. Remember, the original 360 was offered
>> only in two-barrel form in 1971 and became the standard engine instead of
>> big blocks in heavy cars from '71 up. Torque was the apparent goal. They
>> first became available as performance engines in the '74 model year
>> utilizing the 340 cams when the short stroke 340's were
>> discontinued...perhaps due to emissions. I've read that large bores and
>> short strokes are not emissions friendly. ??
>>
>
> Weird. So it sounds like there was no engineering reason (that
> anyone has come up with yet, anyway) to go with external balance on
> the 360 rather than an internal balance. Since the 360 was based off
> the 318 and 340, it would seem to make sense to stay with the same
> balancing system - what the heck caused them to change? Is this just
> one of those "Chrysler" things that makes no sense and yet is? :-)
>
> Possibly it was one of those things where, like you said, an
> external balance was thought to be better for some reason, but wasn't
> actually, however they stayed with that system just because there
> wasn't a good enough reason to switch to internal? Kinda like left
> hand threaded wheel studs on the left side of the car? They
> eventually stopped doing that though. :-)
>
>
>



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