To Balance or Not to Balance

[kingmick]

Yes ive seen it on 4ag cranks from time to time but i have a feeling its more to show they have done something!

[GasedT18]

1jzracing,

that's my thought too. Inline 6 is a primary balanced configuration. If the crank was factory balanced with harmonic balancer and flywheel in place and indexed pulling it apart may result in a worse outcome if the indexing was 'overlooked'.

I'd still like to know what the difference in weights are between the original and replacement pistons though and how the originals weighed up down to the 2 mg level?

D

[oldcorollas]

Tosco manual states 2grams maximum difference for rods and/or pistons.

one of the end caps in a 4K was 7grams out compared to the others (not so good), but everything else was already to within 1-1.5grams.
i balanced down to about 0.1-0.2 (or was it 0.01-0.02??) grams for rods total and end to end, and piston weight, and pin weight...

there was a noticable difference (mostly due to that 7g off endcap )

2 grams out of 200 is 1%. 2 micrograms is 0.001%... somewhere bwteeen the two might be good

Jeffro, what do you balance the boat motors to (piston and rods.. before dynamic.)

Mick, are you sure all those pretty holes are done for show?
considering the cranks have excellent balance from factory, you don't think the holes have anything to do with it?

edit: i have toyota GZE pistons here, but the only scale that takes more than 220grams is only 0.01gram accuracy.
if they were under 220grams, i could do them to 0.0001 or 0.00001 grams

[kingmick]

Ones from the machinist, sunshine,.Im sure you have had many crank done!hehehehe
Same as touches on Rod's that would be lucky to be .00000000005 of a gram, to say they have done it and justify the money you spend getting it balanced.

[oldcorollas]

Same as touches on Rod's that would be lucky to be .00000000005 of a gram, to say they have done it and justify the money you spend getting it balanced.

you know how much metal that is sunshine
10x10x5microns...

i'm talking about the sometimes significant drilling that occurs ont he cranks from factory

ps, i've only had a few done, but then again.. i don't count ones i have seen in the workshop as my own

[jeffro ra28]

Stu, CNC machined rods comes as close as you'd want them anyway!
But yeah we do a few cast rods and we get them to within half a gram.

[oldcorollas]

Stu, CNC machined rods comes as close as you'd want them anyway!
But yeah we do a few cast rods and we get them to within half a gram.

cheers for that info
half a gram would be around.. 0.5% for them then... seems like a reasonable target, any less may be overshadowed by the flung oil anyway... but closer is always better

Mick, what do you personally balance your rods and pistons to? or what does your balancing shop do them to? or is it secret?

[kingmick]

Exact for everything,to the accuracy of the scales.
When you blend pistons you can take very small amounts off and get them perfect, the diffrence is the scales you use!

[SillyCarS]

i really wouldn't bother with it mate, think about what happens in any engine when compression or spark drops out in a cylinder. The inertia of the fly wheel is a major contributor and design factor in balancing an engine, there really wont be much difference when your talking about that kind of mass gained, sure its doing x 1000 rpm but so is the 5kg+ plus flywheel. A race car team would consider it insurance, but with so much to go wrong with a street car; you could spend the money else where, like on a better bov or wastegate which i would consider far more important.

just my opinion, if you really want the peace of mind i'll photo copy some notes for you about dynamics and control, or you could just pay $270

craig

[jeffro ra28]

Half a gram basically is the standard. Like mick has said. Unless you go flog off a set of scales that are worth around $2000 you wont be able to get much better then half a gram.

Like sillycars has said anyway, their are way to many un even variables that would confuse the situation.

Did you know that top fuel run different rod lengths and compresion ratio's through out the engine? Besides the fact they use 65 degress ignition timing.

Every engine is unique and despite what the performance bible says, every engine reacts differently to any changes.

[GasedT18]

Marc, I think the consensus is don't fiddle with your bottom
end. You don't need to spend money and time getting it balanced.

There's heaps of stuff online about balancing - this link is a basic intro and overview and shows why more effort is made and needed to balance 4 and 8 cylinder engines.

http://www.autozine.org/technical_sc...ne/smooth1.htm

Cheers

David

btw
1kg = 1000gm
1g = 1000mg
.001g = 1mg < Laboratory Scales
1mg = 1000 micrograms µg

[SillyCarS]

even further to the point (now that we're getting down to detail) if you have four or less inline inline cylinders there are going to be secondary vibrations that cant be cancelled, no matter what. any amount of enginering thus far wont fix it. all we do is smooth out the primary cylinder fires as much as we can and balance the pistons, rods, crank, etc for linear vibrations and then whack a big flywheel on the end of it. 6 cylinders or more means an overlap in the firing cycle of 1 rpm which cancels secondary vibrations

[YelloRolla]

Plenty of engine shops would grind and drill to say that they've balanced the job - an undeniable fact is that people oare often looking to get free $$$.

If I suspected that MY engine machinist would tickle the crank for the $$$ - then I would get another machinist.

So - for the sakes of the topic. How much is an acceptable amount for an engine to be out? kingmick says that serious engines are balanced as close as the scales will allow. Fair to say that "how good the balance is depends on the situation".

Now tell me, how close is the engine in question? Nobody knows! So nobody knows what the value of a balance is in this situation.

My 3T has seen the rev limit on a number of occasions (8500rpm). I had it balanced, which is prolly not worth a shit now that I put a twin plate on it - as I cannot see the intermediate plate being able to be balanced (as it can move and unlikely gets clamped at the same point each time). The thing is - if the crank and rods were out and the flywheel is out and the intermediate clutch plate are out - then the whole shooting match could be very out of balance (if all of the weight is lined up). If it is balanced, then the available tolerance is reduced.

[oldcorollas]

balancing, like (supposedly) blown headgaskets, are easy $$

so a good start is just to get it weighed? see if the moving bits are out, then maybe get the dynamic balance checked to be sure nothing is too bad...
if i was in Aus, i would offer to do static weighing for the fun of it

as for acceptable.. the old toyota racing manuals say 2grams static and 2 grams dynamic... Jeffro says 0.5grams.. Mick says whatever the scales allow (most of the scales i use are 0.01 or 0.001gram accurate, and that is probably a bit over the top)

if a scale had 0.1gram graduations, i would not be trusting it to 0.1grams, or for repeatability either.. which is somewhat more important that the actual weight itself...

as for the bits out of balance, it depends on how fast and how much acceleration they go thru as to how much difference it makes....
if you have buddies at uni or in a lab.. ask them to check the total weights of pistons, pins and rods as a free start

All this speculation about engines past and how good Toyota does them etc tells you nothing about your engine.

If it is a serious engine build (that is if you are serious about it) then get it done, without question.

[1jzracing]

Did you know that top fuel run different rod lengths and compresion ratio's through out the engine? Besides the fact they use 65 degress ignition timing.

Every engine is unique and despite what the performance bible says, every engine reacts differently to any changes.

haha.... getting a bit sidetracked .... i read a top fueler 's engine only does about 3000 revolutions and thats IT..... TOTAL!!! then its rebuild

.... thats from first start up, idles for a few seconds at 1500 rpm, 5sec burnout at 5000 rpm, few more seconds ideling and staging then a 5 second pass at 7500rpm total run time about 1 minute

our engines do more than that before we even reverse out the drive