88 vert guy

I’ve read many of the previous threads and seem to have a handle on all of the Internal vs External balance misunderstandings that are out there. My questions are not about what flywheel to use with what crank….they’re about the flywheel itself and balance of the whole flywheel and pressure plate assembly.

Regarding flywheel:
I have a 1988 305 with lightweight 153-tooth flywheel. I see it has the added weight on the back that used to be on the flange of the 2-pc RMS crank. Is there any way to know how well it’s balanced for my engine? Two of the holes on the perimeter have plugs put in them. In doing some research I see that there was a “pin”, GM #274584 that apparently was used to balance the flywheel (go here: http://www.austinthirdgen.org/parts/html/images/0-72.gif). Anyone know if the flywheel was measured first, pins installed, then metal drilled to balance…or maybe the other way around and used to add weight back when too much was removed? In general, the pins lead me to think that I have a compromised balance situation, but not sure.

The guys at the local machine shop described it as an “externally balanced” flywheel (which if I understand all the threads, is incorrect) and I would have to provide them with an angle rotation and a weight (mass) and the reference point from which to measure, in order to balance it all by itself. Does this sound right?

Regarding Pressure Plate:
I have a brand new NOS pressure plate to mount my flywheel after refinishing. I notice there’s a paint dot on the housing. Is this supposed to line up with a mark on the flywheel? (orientation to flywheel?) If I wanted to eliminate all possible vibration, could I assemble the flywheel and pressure plate with all screws/washers and have those balanced together? Is this process referred to as “zero balancing”, or some other type of balancing?

Pardon my ignorance of this topic….I hope you experts out there can enlighten me J. Just want to get it right and vibration-free before putting her back together.

Thanks

sofakingdom

iTrader: (1)

<Bert&Ernie> One of these things is not like the other, one of these things, doesn't belong.</Bert&Ernie>

I'm thinking it's the "2-pc" part?

Meanwhile:

D00d, I've been assigned to this planet a REAL LONG time; and I can assure you, the ONE THING I've been able to figure out about life here, is the "dominant" species here, is IMPOSSIBLE to figure out "why" they do ANYTHING. These "human" things are COMPLETELY random and unpredictable. Totally irrational and illogical. {Note to self: ask for a transfer to some other planet when the office opens in the morning} You just gotta look at the physical facts and go from there.

88 vert guy

Sofa:

????

Dude, no disrespect intended, did I catch you at a bad time?

sofakingdom

iTrader: (1)

Could be...

Anyway, without actually measuring whatever whoever did to that flywheel, it's pretty much impossible to guess what they did, let alone "why" they did it.

A balance shop will either have the spec for the counterweight, or failing that, can get a new one off the shelf, bolt em up back to back, and adjust the unknown one until it matches the known good one.

cuisinartvette

They usually mark both pieces witha punch or probably some yellow paint

I always take the assy straight to the balance shop and have them triple check it then spin/balance it to perfection. $25 is worth it not to pull the trans again for some annoying vibration issue

88 vert guy

'vette:

I like what you said, but the machine shop I went to (a fairly reputable one in my area) told me I need to know the weight, distance, reference point, blah, blah, blah. Can you provide any details about what your balance shop did? I'd like to pass it on to the shop near me. More details the better You have a 153-tooth flywheel?

sofakingdom

iTrader: (1)

The correct word to use is "stock".

There's a stock spec for all that stuff. If you have a stock motor, then a stock flywheel will balance properly with it.

THINK about a factory for a minute.... the factory doesn't do all that stuff to get their motors right; they make em all the same, and bolt em up, and they work. All you gotta do is duplicate their process, and you'll get the same results.

Don't let the balance shop confuse you into outsmarting yourself. This is really not rocket science here, it's just car parts.

If they don't have the spec, have em bolt up a known vibe-free stock one back-to-back with your new one except 180° rotated, and make the new one exactly counterbalance the other one.

Damon

I agree with Sofa in general. The factory does do things the same over and over. However, they do balance the assy as a whole- from balancer to flywheel. How they get everything right from one motor to another is anybody's guess- drilling holes, installing balance pins- it's all fair game at the factory and every engine is a little different. If you replace one part at a time with "factory spec" replacement pieces it will still be close, but probably not quite as good as the factory did it in most cases.

If you want it dead-nuts perfect you have to give the ENTIRE rotating assy, plus rods, pistons, pins and rings, to the shop. And then let them figure out the best way to zero-balance it. Remember at the end of the day it IS neutral-balanced as a whole, it just depends on whether that balance happens inside the crankcase or outside of it.

Any shop that wants specs on individual parts is nuts and likely to drag you through the gates of insanity with them. You give a qualified shop the whole thing and let them figure out the balance. THat's how the game is played.

88 vert guy

Guys,

Thanks for the feedback. As a piston engineer, I agree with what you’re saying about parts and engine plants… I’m just a little week when it comes to the trans side of things (but now I’m a bit wiser J). During the development phase all those details about mass, balance and dimensions (length, rotation, tolerances) within an engine are all hashed out, put on blueprints and part plants (internal or suppliers) must conform to specs. The individual parts are set up this way because there is no way a mass production process would allow assembling the crank-train parts on a spin rig to balance, then disassemble and follow the engine until place where they’re to be installed. As long as parts are made to print, the engine should come out as intended within an acceptable range.

Now having walked thru this, the machine shop might not be so crazy after all. If I had a blueprint of the flywheel, it would have a datum (reference point), dimensions to the mass, amount of mass…the pin on the crank puts the mass in the right position with respect to rotating parts. Basically, what I think they're saying is if I had access to the blueprint for this flywheel, they could check the part against it and adjust if needed. However, I agree with what you’re saying….if they have a known good flywheel, they can balance mine against that one…..I get it.

Damon, I agree with what you suggested….Unfortunately, not an option for me!

What I’m still a little fuzzy on is the pressure plate. Is there orientation of this assembly to the flywheel (I’m thinking no). And how does a machine shop “spin balance it to perfection” as ‘Vette stated? Same story as the flywheel?…..bolt another known good flywheel + pressure plate assembly to my flywheel + pressure plate assembly? Would appreciate a little bit more feedback from anyone knowledgeable about this.

Thanks.

sofakingdom

iTrader: (1)

The pressure plate is neutral balance (or, supposed to be, anyway).

Same deal as everything else.

As I understand it, the factory doesn't "balance" stuff the way a machine shop does. Instead, they take rods as they fall off the end of the production line, and sort them into an n-dimensional array of bins, to some level of tolerance; the dimensions being things like, length, big end weight, small end weight, and total weight. (they may not use all of those, and/or they may use others, but that's the basic principle) They sort cranks the same way, by "bob weight", which tells what the weights of the other parts needs to be. When a bin gets 8 rods in it, they pull up a crank that needs those weights and whatever else, and build a motor.

As flywheels and balancers are finished, their balance is trimmed to spec; either neutral, or the extra "internal" weight that goes on the flywheel for the 1-pc "internally balanced" motors (305 and 350), or 400 balance (something like 24 oz-in of imbalance, with the "heavy" spot directly opposite the rear throw of the crank), or 454 balance (around 31 oz-in if memory serves). Those are then all exactly equal, again within some tolerance, however tight or sloppy; but certainly, NOT "matched" to some motor.

Clutches and torque converters are all neutral balance.

Then at that point, ALL motors of a given kind are the same balance; ALL dampers are the same; and ALL flywheels are the same. Therefore they can just pull a damper off the shelf, and a flywheel or a flex plate, and just bolt em up. They DO NOT need to balance the motor to some "special" spec, and match a damper and flywheel to it. They DO NOT need the damper and flywheel that will be used with a motor, to balance any of it.

Why some machine shops out here in the outsde world can't seem to figure that out, is beyond me. Some do. Those are the only ones I'll take my stuff to. I NEVER EVER allow my damper of flywheel to even ACCIDENTALLY exist in the machine shop at the same time as the motor, just so there's no temptation to hack the motor to match the flywheel, or to lazy out on the motor and make up the difference in the flywheel. I want my motors to be just like the factory: the motor is ON ITS SPEC, the damper is ON ITS SPEC, and so on, so if I need to replace something, I can just go to the store and get another that's ON ITS SPEC as well, and no "custom" work of any kind is required on any thing at any time. If a shop can't or won't do it that way, I take my business elsewhere.

Damon

What Sofa said (again). The factory does a "tolerance range" with different parts like pistons and rods. Cranks are balanced in an automated fashion as well with a computer controlled spin balancer and robots that drill holes into the counterweights in a matter or seconds to hit a certain spec based on what the spin balancer says needs to be done.

Bears no resemblance to how a local machine shop would do it on an individual engine. And not as accurate as a good machine shop that is going to blueprint the whole rotating assy. The factory can have errors due to the tolerance range of the parts put into that individual engine as well as issues from "tolerance stacking" when everything skews to the + or - end of the tolerance range.

So what is it you are trying to do exactly? I'm having trouble understanding what the issue is. Are you trying to balance and assy. without some critical part so that it will be perfect once you have that part?

brando54009

i agree exactly with sofa. its almost along the same lines and ballancing a wheel, you dont need to send in your axels and all of that just so they can balance a wheel. what your talking about is a bit more critical but along the same lines.

and if your pressure plate is out of balance than you better get your damn money back lol

1gary

I worked at the GM Chevy Tonn.NY engine plant as a engine tester.Every engine at that time was run tested and pin balanced while in the test stand.

88 vert guy

1gary,

Can you explain what you mean by "pin balanced"? Thanks.

gearshifter2

I have an 84 camero I just got but they say it needs a new head gasket on the driver side, many people tell me I should install a new engin should I fix the head gasket or jst put a new motor into it? any feed backs would help. no water in the oil ,,,, so far

88 vert guy

Gearshifter......wrong thread?

Tombowman89

If you give them all your parts and they balance them together then they have performed this process as if it’s a externally balanced engine.
I work in a machine shop and I know how this can be confusing for some new do it yourselfers.
Simplistic way to put it is External balanced SBC engines are balanced with harmonic balancer installed on crankshaft, Bob weights on to crank and drive train parts such as flex plate is installed on crank or flywheel and pressure plate and crankshaft is put onto balancer and run in on machine and drilled or Mallory metal is added to balance the assembly wherever metal is needed or the counter weights can be machined.
Internally is just less parts installed to crank and run parts individually to achieve balance.
Crankshaft gets Bob weights installed on crankshaft and run on balancer to achieve similar balance characteristics as process above.