To Balance or Not to Balance

[kingmick]

Yes but Jeffro, is involed more with circuit boat engines that are very similar to a sportsedan V8, just bigger,blown and run meth.
Drag engines are a diffrent beast depending if the person has the money to do an engine thats rebuilt every run or rebuilt every couple of years.

[GasedT18]

Back to topic,

Marc - Keeping in mind before the car was stripped down the motor was running fine and the only change has been the addition of the forged pistons (which I have weighed and are all matched in weight to within .002 of a gram..)

For that money I kind of see it as a pointless (could be very wrong) exercise as the motors come balance from the factory..

Yes but .1 gm would be sufficient. Match up new pistons - pins etc - factory spec or twice as good.

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

Yes you've got to be on the lookout. If and when I needed it I'd be finding a place that had a wiz bang machine - drill & fill in place - computer etc - I'd want to see it. But to break down a factory bottom end when the engine was running smooth would be nuts and you could end up worse off - not only in the hip pocket.

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

You might not be able to 'fix' it but some compensation can be made with balance shafts (remember were not talking inline sixes) at the extra cost of weight and parts etc I remember all the whoo ha about the Astron (2.6 - ?) when it first came out and it was a smooth engine for a 4.

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.

Given the mass and size/diameter of the flywheel and clutch assembly - and as these components are routinely pulled - there is good reason to pay attention to balance and fit and spend money there. There's also your feet to consider - a flywheel shattering at 8k rpm can make a bit of a mess of things, and why scatter shields are used. Precision doweling (on configs that don't have precision location) on flywheels makes sense to me.

My 3T vibrated noticeably more after a stock cheep clutch housing upgrade independent of a flywheel resurfacing - it should have been done all together at the same shop, and even though it is a daily drive there was a lost opportunity and lost $$$'s

[YelloRolla]

Given the mass and size/diameter of the flywheel and clutch assembly - and as these components are routinely pulled - there is good reason to pay attention to balance and fit and spend money there. There's also your feet to consider - a flywheel shattering at 8k rpm can make a bit of a mess of things, and why scatter shields are used. Precision doweling (on configs that don't have precision location) on flywheels makes sense to me.

You are quite correct that the further from the centre an imbalance is, the greater its loading (radius of gyration goes up to the square of rpm).

My flywheel and clutch are about as safe as they come (cro moly flywheel with ring gear machined into it - not pressed on - this is just part of why they cost $2500) and IS balanced. Consider how a twin plate works and the clearances required in order for the secondary plate to operate, without binding, through a wide variety of operating temps and you will understand what I am trying to say (which was an aside to the tolerance stack-up point). Furthermore, NONE of the balancers that I have used EVER balanced the clutch plate itself - only the pressure plate and flywheel are balanced.

I am sure that there are other racing clutches, with smaller diameters and better configurations that are ultimately less likely to cause an imbalance, but I am sure that they will be priced accordingly.

[kingmick]

My opinion is to balance it!
new slugs, new clutch and a rebuild i wouldnt even think of not balancing it, unless your like to putt around at 2500rpm, but i guess you wouldnt put forgies in if thats what you wanted

[TheDarkRaver]

WOW dont check the post's for a day and this thread got HUGE!!

Thanks everyone for the reply's but you have all left me more confused then when I started..... Some say do it others say that its not worth it... I am leaning more towards getting the balance done as the car has also been converted from auto to manual (so new flywheel installed) as far as the rest of the setup goes everything was indexed so will be going back to its original location. And I have a set of scales accurate down to .01g (1mg) so will be weighing rods, pistons and bolts to make sure they all match.

So if the flywheel is balanced from factory should installing that without a balance cause a problem, as from what I understand the crank is balanced on its own from the factory..

I also checked out the balancing machine at the shop (H.B Sales in Newcastle) the other day and its an older looking machine with a few digital led readouts (no computer setup) I was told that most balancing machine's only have one point were the crank sits (bolted in one end with the motor drive and then the other end of the crank sits on a set of rollers and the readouts come from the drive and the roller) this machine has two points for the crank to sit on plus the motor drive at the end which also messured vibrations..... I also phoned a couple of other machine shops, and the ppl working on the desk could not really give me any info on there machine and were ment to get back to me after talking to the guys in the shop but never did Tho one shop said they used a repco machine but thats all the info he could give me..

Marc,