Ok, I've done enough reading to know that the 318/340 Mopar small blocks are internally balanced like most engines. The 360, however, is externally balanced, which requiresthat the flywheel or torque converter provide the balancing act. Here is my question. If you buy a 360 engine, how do you balance a flywheel for it? Do you simply buy one that has been balanced to some spec and bolt it on? (That don't sound right to me.) Or, does someone have to disassemble the engine and balance the whole rotating mass on a balance machine? (That sounds expensive and inconvenient.) That is my question of balance. Thanks for your replies. Rock
You have to get a harmonic balancer for the engine, at the rear the torque converter has the balance weights on it. The flywheel is only a flex plate.
If it is automatic you buy a special flex plate from ATI.If its manual you might be able to still find the flywhheels made for this ap.Good luck!
You need a 360 specific flywheel for the proper balance; although the external balance 340(1972-3) is probably the same. I believe that Mopar Performance or Direct Connection had directions in their tech bulletins on how to modify a standard balance flywheel to use on the 360. I had the PDF saved on the PC that crashed last month. There is hope that I will get that salvaged this month. PM me later this month, to see if I found it. Sorry, but hope this helps a bit.
In the mopar chassis book are the specs for rebalancing a 318 340 neutral balance wheel for 360 use. There is a pattern and drilling specs. Yocan also find it on line. I have done this for folks and it works well. Must follow the instructins to the letter. That is for a manual trans. for an auto use a B&M exernal 360 flex plate . it looks after the flywheel balance and you use a normal un weighted trque converter. Don
I remember learning about this way back when I was an apprentice, I had a Mopar 360 in a Charger. It came with a 904 trans, which didn't enjoy the grief I gave it. I installed a 727 and the converter that came with it. Big mistake. Engine shook like crazy at idle. Local trans. shop guy said peel the weight off of the old torque conv. and mount it on the replacement in the same relative position. I brazed it on and it worked like a charm. So the moral of the story is, try and get an engine WITH the original TQ or manual flywheel.
The easiest way to do this is to just buy/get an external balance flywheel. They're readily available, you can get new ones from all the major parts houses. They're also pretty easy to find (they made a lot of them). Keep in mind you'll also need an external balance harmonic damper as well if there isn't one with the engine already. (here's how to tell the difference in the dampers http://www.moparts.org/Tech/Archive/smallblock/5.html ) If you have an internal (or neutral) balance flywheel, you can also drill it to make it an external balance flywheel, like so... You can do this yourself, but a machinist would probably be a better choice. Its pretty simple, but you need to be precise. You also need to make sure you actually have a neutral balance flywheel to start with. This is a neutral balance, 130 tooth flywheel for a forged crank 318 or 340. All the holes in the outer part of the flywheel go all the way through. Typically (but not always) an external balance flywheel will have a pattern of 3 holes drilled next to each other, partially into the flywheel. But obviously one modified using the template above will only have 1. This is an external balance flywheel (although this is a 143 tooth flywheel, for big blocks (383, 440, etc) or trucks with a granny 4 speed). All of that said, if you're building a new engine you should have the rotating assembly balanced anyway. You're likely using aftermarket pistons, which tend to be lighter, which means the balance of the rotating assembly has changed. If your using aftermarket rods, you're even further into it. If you really want your engine to last and make better power, you should have the parts you're actually using balanced together. This usually costs about $250 to $300, but its well worth it to have all of your parts spinning true. Otherwise you could end up with vibration and premature bearing wear, even if you use all external balance parts.
My 360 specific flywheel came off the shelf at Centerforce in Prescott, AZ. Simple, high quality, and carries SFI spec.
Thanks guys, it sounds like they are balanced to a specification and, as long as you get the correct harmonic blancer, you just bolt it on and go. Live and learn. Thanks for all the detailed suggestions and expanations. Rock
Ok, I have a flywheel from a 3.9 V-6. If I get it drilled as per the drawing above, am I good to go with my 360?
Well, I'm not an expert on 3.9's, but they're basically the exact same engine as the 5.2 (318), just minus 2 cylinders. So my guess would be that its a neutral balance flywheel (88-91 were), and that you could drill it to make it an external balance ***BUT YOU CAN"T USE THE DIAGRAM ABOVE!!!*** The diagram is for a 130 tooth flywheel, you have a 143 tooth flywheel, so your balance holes will need to be somewhere else, the diameter of the flywheel is different. The second picture I posted is actually a 143 tooth external balance flywheel. (I'd sell it to you too, but I traded it for a neutral balance 130 tooth). Somewhere out there should be a diagram for doing this with a 143 tooth flywheel, but I don't have it. My recommendation would be to have the whole rotating assembly balanced anyway. You're mixing and matching a whole bunch of parts, and while that isn't a bad thing, little issues tend to crop up. Even if everything was supposed to be the same balance there's no guarantee it would all be perfectly balanced when you bolt it all up. $200 isn't that much money compared to vibrating your engine to death, or even buying another flywheel. Hopefully you also have the bell housing to go with it, the 143 tooth bell is different from the 130 tooth bell.
You've already cleared up one question. The flywheels are different. I suspected that. The one I have is 13 13/16" diameter with an 11 13/16" clutch disc. The engine is already built and has an external balance harmonic balancer on it. I darn sure don't want to disassemble it to balance it. Now, I need real help. I guess I could buy a 130 t flywheel that is already externally balanced and then I'd need to buy a clutch assembly that will work with that flywheel and input shaft. I'd probably have to change the bell housing, too. Or, I need to figure out how to externally balance this flywheel. I knew this was going to get complicated. Anybody got any ideas or suggestions?
Alright Rock- I think I've got a solution for you. KMJ sells a plate that fits between the crank and the flywheel to provide an external balance, allowing you to use a neutral balance flywheel (which I am now almost completely positive is what you have). The neutral balance fly does nothing for the engine balance, and the plate provides the external balance you need for the 360. http://www.kmjent.com/cart/product.php?productid=2077 Now, that said- I haven't ever used one, or done business with this company before. But for 17.95, I'd say its worth a try. Searching on Moparts is where I came up with this. I also ran into a few folks that claim to have sandwiched a 360 flex plate between the crank and flywheel, which if you could make it fit would also solve your balance issue. The KMJ plate seems like a more elegant solution (definitely smaller). But again, this is all internet research, I'm not going to say that any of it works for sure. Here's the link to the thread on Moparts, just for giggles http://board.moparts.org/ubbthreads...ance++flywheel&topic=&Search=true#Post5950521
My 143t flywheel is supposedly from a 5.2.......and that engine is internally balanced. Correct? There are no large weight removal holes on this flywheel, so I also think it is for an internally balanced engine. Damn, this get's confusing. Thanks for the link on the balance adapter!
Doing this should work. Correct? If so, I think I'll have this done and while they're at it, I'll have about 10 pounds shaved off this heavy sucker.
Yes, the 5.2 (318) is an internal balance. I believe the 3.9 is also, as its just a 318 minus two cylinders. I KNOW the 3.9 is from 88-91, because I've found OE harmonic balancers for it that are internal balance. Now, as for your diagram- there's nothing marked on it, so I have no idea if that's right for a 143 tooth mopar flywheel or not. Where did you get it? I read on Moparts last night that LA 360's require a 120 gram external balance, so that's either what needs to be removed from a neutral balance flywheel by drilling holes, or added to by adding a counterbalance (like the plate I linked to). Now, if you're going to take it to a machinist to have it lightened anyway, they should be able to make it an external balance flywheel for a 360 to begin with! Because, as you said above, an external balance flywheel for a 360 is "set" to a specified, standard (for a mopar 360 anyway) amount. Regardless, if its going to a machinist, they'll be able to spin it up and tell you if its neutrally balanced or not.
Now, as for your diagram- there's nothing marked on it, so I have no idea if that's right for a 143 tooth mopar flywheel or not. Where did you get it? I got it Here. http://www.moparaction.com/tech/quest/internally.html Rick Ehrenberg confirmed that this should work.
As long as the diagram is for a 143 tooth flywheel it should work just fine. Otherwise the diameter of the flywheel will be different, and the holes may need to be on a different radius.
I have a 143t flywheel and clutch. It's an 8 cylinder flywheel because it has 8 notches on the extension on the engine side for the pickup. It does not have the large holes that are the signature of the smaller external balanced flywheel. How would I know if it's been drilled for external balance?
Take it to a machinist and have them spin it up. They'll know right away if its external or neutral balance.
That's what I was gonna do. I just thought that I might be able to i.d. it as "ready", if I knew what to look for. At least everything I have mates up. Now, all I got to do is get to where it spins smoothly together.
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