Hello all, I have a 64 W100 with the /6 and an NP435 (6.5 1st gear).
I have removed the original /6 and an trying to replace it with a newer /6 (unsure of exact year, but appears to be a mid- late 70's engine).

The newer /6 CS does not match up to the earlier flywheel (144 tooth). The center hole AND bolt pattern are different. There is also the issue of internal vs external balancing I believe.

How can I get this to work? The mechanic is saying swap crankshafts, but isn't there an easier way?

Wouldn't a later model flywheel and balancer mounted on the newer motors crankshaft work? Is the flywheel something a parts house might have vs trying to locate a used one?

Thanks.....from Baytown, TX

They made the crank register bigger in '68.

You need a flywheel with the proper bolt pattern and register size.

Balancing is the same.

_________________
Official Cookie and Mater Tormentor.

All slants were neutral balanced unlike the V-8's where it depends on the year and type...
Like 'zilla said they changed the crank register in 1968, so you get a number of options, pick one that fits your budget:

1) if the slant is a 1976-1987 cast crank engine the 1960's forged crank won't fit (bearing widths changed and a few other items that won't work as a direct 'drop in', that limits you to your early 60's block and a 1968-1976 forged crank.
2) less work can be had getting a similar flywheel from a 1968-very early 70's truck with a slant and NP435 (11" clutch)...the late 70's NP-435 equipped slants have a different bellhousing and flywheel tooth count to use the more common starters with the 10 tooth gear...the early ones like your uses the old direct drive starter with the 9 tooth gear (typical 3 bolts holding it to the bell)...most of the later trucks came with the A-833OD and the smaller flywheel (9.25-10" clutch disk) which won't work with your setup.
3) Take your current flywheel to a known good machinist and have him hone the center out to properly fit the newer crank (this is the easiest, quickest and least expensive option for you).
Balancer is irrelevent at this time as the slant is neutral balanced so you can use the one on the engine (and it's matching timing tab), or swap your old on one (and timing cover).

If you go that route instead of #3 above, you will be going through junkyards for this item and they will not know if they have the correct tooth count to match your flywheel (i.e. pre-72-ish vs. the late 70's version).

I am hoping your mechanic took the time to rotate the flywheel to compare bolt patterns as it only clocks in one position on the cranksahft, if put on a number of holes will be off at first glance...all cranks should have 6 bolt holes (if you get a small block V-8 flywheel one hole will be way off and need to be drilled and welded to correct).

-D.Idiot

Parts house sends me a flywheel that has the CS holes in a pattern not even close. One hole is way off. My CS has the bolt holes evenly spaced.

I am just about done with this truck. 1964 W100 parts truck for sale. Ashamed that all because of a flywheel the truck will be parted out.

The parts house sent you a small block flywheel, that's why one hole is off...so if you are going to use it you will have to egg that hole out to bolt it up...that being said...the flywheel may not be correct for your application as mopar changed the flywheel in the mid-70's applications so they could use the traditional starter instead of the one application only direct drive starter common for your generation truck...so you get a couple choices:

1) Egg out the hole and install the flywheel...and get a standard starter and a bellhousing for a 1975-1987 truck (and adapt your hydraulic clutch to it, or change to the late truck mechanical linkage).

or:

2) just take your old flywheel to the machinist and have him hone the center hole to the outside dimension on the new crankshaft and put it all back together (this is like a $30-50 job for the machinist...tops)

You give up too easily...go with #2 and git 'R done...

Last resort option #3 is a junkyard search for a 1968-1972 dodge truck 225 slant six and 11" clutch...that will have your flywheel that just bolts right in...

-D.Idiot

I really don't give up easy, but I am just totally frustrated with this.

2) just take your old flywheel to the machinist and have him hone the center hole to the outside dimension on the new crankshaft and put it all back together (this is like a $30-50 job for the machinist...tops)

Mechanic keeps telling me this will not work because of the way the engine is balanced. I researched this and from what I can find that this engine (1979) is neutrally balanced (whatever that means). He claims the 64 engine was internally balanced and the 79 is externally balanced. Or vice versa, I am totally confused about the whole swap.
I guess the old flywheel has the same CS bolt pattern as the 79 engine, just the CS center register hole is too small?

Walk away from that mechanic.(he's on Crack!)

Find a good machine shop, have it bored to the correct size. Mount it and go on.

_________________
1964 Dart GT

Hard to walk away with my truck and engine strewn all over the shop . You just cant teach an old dog new tricks I guess. I think I have a line on the correct flywheel now.

Tell your mechanic I'm running a forged crank flywheel (1974) on a 1979 engine(cast crank) and I have yet to have it fly apart even with a 6000 rpm clutch dump...all slant sixes are internally balanced (aka neutral balanced or "0" balance) regardless of the crankshaft type or the year made...the only classic mopar engines that are "externally balanced" are the cast crank 340 (1973 only), the 70's cast crank 400's, the 440 six pak, and various years (mostly 70's) of the 440, (and the 5.9L magnum if we go up the food chain a bit)...you can even swap the balancers between them (6 spoke cast crank vs. the 3 spoke forged crank).



I hate to say it, he's going to cost you more than he's worth. Get your flywheel bored out to the late CS size and have him plug and play it and be done with it. Too bad you weren't looking during the summer, the flywheel you need is in my drag car pending the final starter conversion so I can try the 11" clutch in a car (and have a ministarter that will work in your truck...)

-D.Idiot

Too bad you're not in Oregon, he wouldn't be the first mechanic I've had to 'straighten out' concerning our engines and why we do the things we do...some move right along, others just don't believe and lose business soon afterwards.