360 balance question

-
R

R3dplanet

Well-Known Member
Joined
Apr 18, 2008
Messages
283
Reaction score
50
I'm confused. Deeply so.

I'm in the process of building up a 360 (numbers reveal it dates from '71-'74) from the block up. Aside from the block and heads, everything will be new. The crank is in, the cam is in, the pistons are in, and the heads are being worked on by the shop right now.

What I'm not sure of is the balancing act. I've read a lot of pages on how V8 engines are balanced in general, and I understand that more or less. I also found that the 360 is an externally balanced engine. But I'm not sure how to do that. I do not yet have a harmonic balancer, but I do have a steel flywheel I just bought from 440source.com, which you can check out here:

http://440source.com/flywheels.htm

But as I've peeped around the forums I see many members drilling three large holes in the flywheel to remove 19.75 ounces of weight in the correct places. I've taken note and copied the diagram for this. The question is, do I need to do this? My machinist looked at me funny when I asked him about it. Worse, I've been told by some that the only thing necessary to balance the engine is the balancer and a whole, unmodified flywheel.

I'm not at all sure what gives here.

I can tell you that I'm going to mate it to my A-833 manual gearbox and I have a centerforce clutch sitting in the box if that makes any difference.

Huh?
 
I just had my 340 motor balanced at the machine shop. i supplied the pistons,rods, crank, dampner, clutch. the machine shop will balance the rotating assembly of your motor. Just for Warranty assurance ask them to assemble the short block it will only cost about 300 bucks extra but its worth it in case anything goes wrong.
 
Stock cast crank with normal early 360 range bobweights?

It should require a weighted flywheel/flexplate and balancer to balance.

Otherwise, you'll have to load the crank up with mallory to get it balanced.

Find a different shop or if they are chevy guys, ask how an early 454 was balanced! Same concept as a 360.

I'm sure the "minister of misinformation" will be in to fill you in on the wrong way to do it soon!
 
If the link you provided is for the flywheel you bought it will NOT bolt up to your 360 crankshaft.

The 360 has an odd spaced bolt pattern so the flywheel is timed to the crankshaft.

By the way if you resurface to much off the flywheel when replacing the clutch it will be out of balance and you'll have to replace it.

I just love externally balanced engines ... NOT !
 
GGs66GT said:
If the link you provided is for the flywheel you bought it will NOT bolt up to your 360 crankshaft.

The 360 has an odd spaced bolt pattern so the flywheel is timed to the crankshaft.
Click to expand...

If it's a 6 bolt mopar flywheel, it will bolt up no problem to a 360. I use 318/340/440 flywheels and balance them to 360 stds all the time. Isn't any difference in the flanges on 6 bolt mopars.
 
It will fit just fine. The bolt pattern is irregular on the actual flywheel and it matches the crank perfectly.
 
you will need a 360-specific harmonic balancer and either a 360-specific flywheel or a properly weighted torque converter. if you get the unbalanced flywheel, it opens up converter selection quite a bit. if you get the neutral balance flywheel you will have to have a converter custom made. either way you still need the proper harmonic balancer.
-Tim
 
Since you are going with a manual transmission ignore all the comments about weighted torque converters and flex plates.

You will need a pre-magnum specific 360 harmonic balancer for the front of the engine and you will need to have the flywheel you have the link to machined with the three holes you mentioned.

I would check around and see what the cost is to have that flywheel modified verse purchasing a 360 flywheel. As I recall I paid about $150 for a 360 flywheel from the local dealer.

Also, don't worry about refacing, that only applies if using a used flywheel and you would have to remove enough material to break into the drilled holes for it to disrupt the balance.

BTW, if you have used anything but stock replacement parts in the bottom end you really need to have the entire rotating assembly balanced. When I built my 360 I used KB pistons and Eagle rods, these parts are significantly lighter than stock. The balancing removed about 200 grams from each end of the crank, that is almost a lb. Can't imagine how that bad boy would have shaken if I had not balanced it.
 
dgc333 -

Thank you very much for the straight answer. I'm on a quest right now to find exactly the right balancer. I already purchased the flywheel, and I'm on excellent terms with my machinist friend so the cost will be minimal to have it modified. Thanks for setting my mind at ease.

btw - the bottom end of the engine was rebuilt with all stock parts, so I think this should be a bolt-up affair.

-m.
 
360 can be neutral balanced fairly easy. You only need to supply the machine shop with 1 piston/pin/rod/bearing (assuming all of these assy. are within a gram of each other, fairly easy to do if the pistons are good and the rods were reconditioned as a set from a competent machine shop) He sets up a bobweight to this weight (and may add oil weight.. yeah, it gets that close) Now you can buy a neutral damper and neutral flywheel/convertor. It was cheaper and easier to do a "Detroit" balance on these assemblies once they were thrown together with parts (this was Chrysler back in the day) than to spec out weights for each part prior to assembly like a neutral balanced 318/340.
 
But the mallory metal that needs to be added to the crank is quite expensive plus the side drilling of the crank to install it adds more cost. You take a balance job that would normally cost $200 and turn it into a $500 job for absolutely no benefit if you aren't turning in excess of 6000 rpm on a regular basis.

The reason the 360 (and cast crank 340's) are externally balanced is because the cast iron in a cast crank is not as dense so the rotating assembly can't be balanced with in the size constraints without adding extra metal. For a street going motor it only made sense to go external balance verse the cost of adding mallory metal to the crank.
 
You must log in or register to reply here.
-

Back
Top