Engine Balancing Basics - Need help
 

Harmonic balancers come in different sizes. Can somebody explain why? If the crank, rods, and pistons are balanced do I need a zero balance harmonic balancer? What about the flywheel? Do I just take the parts to the machine shop and let them figure it out?

As you can tell I am pretty confused on this subject so please fill me in if you know more than me :D

Thanks

i believe on a motor that is internally balanced you need a 0 balance balancer, or if you have a removable weight on yours (like i do mine) you have to take off the weight

They come in 0, 23, and 50 oz. You bring your damper, and flywheel with the rotating assembly to the machine shop and they ballence it all together. One thing that I don't understand though is than my machine shop said I shouldn't use my stock damper:confused: So i just got a summit one that you can adjust the weight, and put it where you want.

The HO 302's came with a 50oz imballence, and i think that 23oz is what they use for the 351's. You can get yours ballenced to 0oz but would cost a couple hundred more because of the extra slugs that they add to your crank. I would do it though.

I wish more then ever that I had mine to 0oz. That is one thing I did not research when I did my motor and now regret it:( I don't know the exact number or how to figure it out but look at it this way. 50oz hanging about 6" off your crank and spining it to 6500rpm. That adds up to like 200lbs and puting a huge amount of stress on the mains.

28oz not 23oz

What is the direct advantage to a 0oz, in comparison to some disadvantages of 28oz and 50oz?

Caymon

my bad:o

Internal balancing is always a better route. The factory longer stroke motors used external balance since there was less room for the counterweights inside the engine. The heavy Mallory metal used to create a 0 balance motor is wayyy too expensive for any production motor. That said, a properly balanced external balance motor will work just fine (buliding an external balance 454)

In the case of the 302 50 oz balance, Ford wanted to reduce the static mass of the crank, this probably saved a few bucks, and some total vehicle weight. The 50 oz of weight makes 200# of force, but this is not mass, so the motor burns less gas etc....

As for why the shop did not want a stock balancer. The stock counterweights are probably prone to inaccurate weight or location, plus they are not as durable as a good aftermarket one.

You should always have the flywheel and balancer you plan to use when the motor is balanced to make sure everything is smooth. The shop will check the flywheel and balancer to make sure they have the correct counterweights, sometimes they will balance the motor with your balancer and flywheel as well.

I'm not going to state anything that hasn't already been stated, just going to back-up everything the guys mentioned.

Zero balance is the way to go if you want to pay the extra dough. 28oz imbalance is the next best setup... just be sure to specify what imbalance you're going to use when you order a flywheel and balancer, as the best way to balance a rotating assembly is with these components bolted up to the crank.

I also made the mistake of not doing any research on this topic, and went with a 50oz. imbalance on the last combo I ran, and, because of current financial situation, I will be doing the same with the R-block combo in the works. I will be reusing my flywheel and damper, so I don't have much of a choice.

I will say that, even though I split my block, the rod and main bearings still looked good enough to reuse. I was spinning my combo to 7000rpms on a gear change and crossing the 1320' at 7200rpms spraying 200hp worth of nitrous. I didn't encounter any serious issues (other than pushing the limits of the stock block) with a 50oz imbalance, but could've picked up a few HP going with a 28oz. setup.

The combo I'm planning for after next year will be a serious setup... with a zero balance rotating assembly. ;) I will be in search of an 8 sec. timeslip at that point :D

Depending on how serious your getting with the new combo, you may just want to go with the 28oz. setup... ultimately it's up to you, of course.

-Ryan

Lots of questions...
 

Please keep checking this post because I will probably think of more questions as this thread gets responses.

This may seem to wander off topic a bit, but bear with me...
I will be doing one or the other options below.
OPTION #1:
Go all forged internals and stroke the engine to 393 cubes with a main support, windage tray, etc. In other words Satan himself under a hood.

OPTION #2:
Freshen up the stock 5.8L, add a main support, and drive it until I can afford option #1.

I don't plan to race the car other than an occaisional trip to the drag strip, but I do want it to be streetable and more importantly - dependable. I'm guessing I will be able to pull somewhere in the vacinity of 12lbs of boost from the T3 turbos I have and I have been told I should see max boost by 2500 RPM. I could not even venture a guess at how many RPM the engine will be turning at max HP, but I'd like to keep it under 6500 RPM.

With that said I won't be altering balance if I use a stock bottom end, but what do you think I should do if I do go with the 393 kit? Should I go zero balance or will 28 do? Any idea what the price difference would be for a 28oz balance and zero balance? Also if I decide to go zero balance, or actually if I can afford to, does it require a special crank? Or will any forged stroker crank do?

Thanks for the info and advice.

IMO, where the weight is placed is not as important as the overall weight. I want my rotating assembly as light as possible. If you were to take for instance, a 1 pound weight off of your flywheel that is approximately 5 inches from the crankshaft centerline, it might take a 2 or 3 pound piece of mallory to make up the difference in the counterweight of the crank, which is only 2 inches from the centerline.

If I was building a 10,000 rpm motor I would opt for internal balancing. The bearings in a motor of this type wouldnt have much of a life expectancy if it were externally balanced. The machine shop that I deal with tells me that internal balancing 'is a little easier on parts', thats all.

Andy

Just cruisin through the post,

I dont like windage trays for the simple fact you can burn up a camshaft using one. The oil splashing down onto it also cools it.

Pre 1980 302 & 351 had the 28.2 oz imbalance.

Hyper pistons are the way to go. I also like plasma molly rings best. Stock rods work fine unless your going to twist it up pretty high.

my .02$

I've never heard of that happening from using a windage tray. :confused: How could a windage tray, that's mounted to the mains and located in the oil pan, "burn up a camshaft" when the cam gets oiled thru the holes in the cam journals?


...not if you're using big doses of nitrous or cramming a ton of boost in the cylinders. ;) Hypereutectic pistons work fine for stock type replacement pistons in the daily commuter. For any serious effort a quality forged piston is the only way to go.

-Ryan

I went with internal balance on my street car. I only run a crank hub, and I was not as knowledgabe about this as much as I would have liked to be. After a year of drag racing (driving to the track) and cruising, I have to say that there is no other way to go if you have the money. The berings still look great, and I have had zero problems with the motor even after abuse with nitrous and boost. Nothing but smiles here! Now if I can only stop shattering my stock axles...

Smiff

This is something that has troubled me for a long time and i've never heard it explained to my satisfaction .... the cylinder walls and to some extent the cam lobes (not journals) get lubed by oil splashed up from the crank counterweights. So when you put a deep sump pan (lower oil level) or a windage tray in you lose that splashing oil. So now how do the lower cylinder walls and cam lobes get lubed ???
As to the Hypereutectic piston thing ... i don't think you guys are giving nearly enough credit to the new technology in Hyper pistons. They have vastly improved ... true, if you're gonna build a monster 8,000 RPM motor or one thats gonna get a huge dose of nitrous or ton of boost, the forged pistons give you a lot bigger safety margin (will tolerate detonation longer before meltdown)... but the newer high performance Hypereutectic pistons will hold up to all but the most punishing of motors, and they are quite a bit more streetable (you can run them much tighter because they don't expand when heated nearly as much)... so they don't slap when they're cold.

I should have stated lobes, sorry for the general statement. Any oil that gets onto the cam is good for it. I also spend alot of time making sure a cam/lifters are broke in properly. Alot of people over look this when firing up a new motor.

I only run main girdles. I use custom pans/baffles to keep the oil where it belongs.

I don't run nitros so hypers have always worked fine for me. I ran forged a few times but I dont like them on the street.

you aight dogg :cool:

Breakin isn't much of an issue if you're running a hydraulic roller cam. Do you have any pics of your custom oil pans with the baffles inside? I'm thinking about doing the same on my new engine.

As for the balancing issue, you'll probably find that 28 oz.-in. imbalance will be the closest to most crank/rod/piston combo's. Exceptions may be in situations where you have a really light piston/rod combination, combined with a heavy (forged) crank. Neutral balance will cost a fair bit more, as mallory slugs are pretty darn expensive. Yes, the flywheel and balancer both have to have the same imbalance. I do agree a lot with Andy669's post...where the weight is matters a lot, so neutral balance would be the best if you can afford it. Having the weight closer to the center of gravity will make it easier to spin.

Cam lobes and to an extent, piston skirts (I've seen rods that pump oil through them to the underside of the piston) rely on oil splash for lubrication. The oil that enters the rod bearing surfaces comes from the main journal oil holes. The oil is pumped through the gap between the rod and the crank and out the sides of the big end rod bearings. This oil route is ALWAYS flowing no matter where the crank is on it's rotational tour. It is this oil that splashes up on the inside of the engine. It does not rely on dragging it up out of the pan so that should make little difference where the oil level is. to a point! Too high a level can cause all sorts of maladies. The crank does drag a little up with it but it can survive without this. Windage trays help to reduce the drag caused by oil clinging to the crank by "scraping" it off as it spins past the tray.
Another note, make sure that the machine shop keeps records on what they did to your rotating assembly, especially the balancer so when it takes a s*** you can reproduce the results on a new balancer. This is what I'm having to do now. Luckily, (for me) my machinist keeps such records.