Which Flywheel for a 401

[MMinMN]

Hello IFSJA Forums

Need a little guidance here.

I recently picked up a 401(automatic), that I need to convert to a manual.
Having a little trouble ID'ing the proper flywheel.

I've heard that the flywheels differ for each of the V8's because they are balanced specifically for that motor.

JEGS has this one 555-601450

http://www.jegs.com/webapp/wcs/stores/servlet/KeywordSearchCmd?storeId=10001&catalogId=10002&langId=-1&Ntk=all&Jnar=0&Ne=1%2B2%2B3%2B13%2B1147708&searchTerm=601450

but it lists the 360 as an application as well

Any thoughts or recommendations on sourcing?

Thanks all

[MMinMN]

BJ's too

They also list both motors in their offering

http://www.bjsoffroad.com/prod-556.htm

[Carnuck]

Hold up! Which crank flange do you have? (one has a centering ring and one doesn't)

[MMinMN]

How do I tell the diff? Is it year based? If so, this supposed to be a 77

Guess I can take pic.

[SC/397]

The 401 counter balance lug is about 1 1/4" wide and goes nearly flush to the outside of the flywheel.

The lug on a 360 flywheel is below flush by about 3/8". I have no clue what the aftermarket is selling. I asked for photos of the lug and they can't seem to supply it..

Here is the difference in crank flanges. '67 through '71 are flat like the 343. The 1972 and latter all have the flange like the 360 in the picture. The flange is based on year.

[MMinMN]

360/401 Flywheels

The 401 counter balance lug is about 1 1/4" wide and goes nearly flush to the outside of the flywheel.

The lug on a 360 flywheel is below flush by about 3/8". I have no clue what the aftermarket is selling. I asked for photos of the lug and they can't seem to supply it..

Do you know what years the 360 and 401 are respectively in these photos?

I will go snap a pic of my flange, to at least answer the year question

[MMinMN]

Casting Numbers

Any chance you have the casting/part numbers from each?

[MMinMN]

My 401 Crankshaft Flange

[SC/397]

ALL cranks are flat from 1967 through 1971.
ALL cranks have the boss from 1972 until the bitter end.
If you have a 1977 then, the crank will have a boss on it.

Regardless, each engine WAS balanced individually. So if you swapping from a flex plate to a flywheel, you should have the engine balanced. The same can be said for vibration dampers. Most of the time, you can get away with swapping flywheels from engine to engine of the same displacement and it MIGHT be close enough. Not always.

The part number for the '72 and latter Flywheel is 321-2655

[Carnuck]

That flexplate on the 401 looks like it's for a 360 unless there is an extra weight on it? Maybe someone did the 360 crank in a 401 block?

[SC/397]

You can't tell if the flex plate is a 360 or 401 with out seeing the weight that is welded on it. Bur you are right, I don't see a weight in his picture above.

[MMinMN]

Is that info year dependant?

I'm being told by JEGS, that after 72 the flywheel/flexplates were externally balanced(meaning not included in engine rotating mass balance process).

So are either of those flexplates pre 72?

[MMinMN]

That flexplate on the 401 looks like it's for a 360 unless there is an extra weight on it? Maybe someone did the 360 crank in a 401 block?

Can I verify crank without dis-assembly?

[SC/397]

NEVER ask Jegs or Summit for advise. You can look something up in a catalog as well as they can.

From the SAE report on the initial release of the American Motors Typhoon V-8 Engines: " Final balancing is accomplished on an engine assembly containing all rotating and reciprocating weights. This is accomplished on automated equipment, and final total engine unbalance is maintained at less than .5 oz,-in front and rear"

They did this by drilling to take weight out in both the flyhweel/flex plate and vibration damper as a rotating assembly. Granted, swapping common engine size flywheels and dampers will be close. However, most of the time is it is not close enough and the engine will vibrate.

[MMinMN]

NEVER ask Jegs or Summit for advise. You can look something up in a catalog as well as they can.

From the SAE report on the initial release of the American Motors Typhoon V-8 Engines: " Final balancing is accomplished on an engine assembly containing all rotating and reciprocating weights. This is accomplished on automated equipment, and final total engine unbalance is maintained at less than .5 oz,-in front and rear"

They did this by drilling to take weight out in both the flyhweel/flex plate and vibration damper as a rotating assembly. Granted, swapping common engine size flywheels and dampers will be close. However, most of the time is it is not close enough and the engine will vibrate.

And that was maintained throughout AMC V8 360/401 production?

I agree about the mass parts guys, hence the questions. My level of trust isn't that hi

Thanks for all the assistance and education.

Even though this motor has supposedly had a rebuild(20K) I think we will tear it appart to see what we have, crankshaft, rods, pistons, etc..
So adding the balancing isn't really a matter of time just more dinero

M