In block balancing?

[dbv8]

Im rebuilding my 450 engine with forged pistons and a fairly wild cam and will be adding a fair amount of nitrous into the mix.

I want to get the engine balanced and found these guys on 't net.
http://www.amb-engineering.com/

For £300+vat they balance the whole assembly, ie crank, rods, pistons, fly, clutch and front pully etc in the block.
Looks good to me.
What do you reckon?

[rev-erend]

No oil there .. can't see how they won't shag your block.

But I guess it depends how fast it turns.

[Boosted LS1]

It would be better to hand balance the individual parts and then do a dynamic balance of the crankshaft IMO. I don't like the lack of oiling either. No oil on the piston pins, shells, rings etc.

[TVR_owner]

Dynamic engine balancing is nothing new. Been having my Essex engines done that way for years.

[spend]

Different ways of balancing, that way is a false economy IMHO. If you have it apart get everything balanced separately and keep notes, that way you can easily add/replace components when necessary.

Will that company still do that work?, IIRC they couldn't even balance a front pulley for me a while ago..

In an article Carley said:

..the centripetal force created by a crankshaft imbalance will depend upon the amount of imbalance and distance from the axis of rotation (which is expressed in units of grams, ounces or ounce-inches). In fact, the magnitude of the force increases exponentially with speed. Double the speed and you quadruple the force.A crankshaft with only two ounce-inches of imbalance at 2,000 rpm will be subjected to a force of 14.2 lbs. At 4,000 rpm, the force grows to 56.8 lbs.! Double the speed again to 8,000 rpm and the force becomes 227.2 lbs.

Don't take balancing too lightly if you want to push the limits

[TVR_owner]

spend said:

Different ways of balancing, that way is a false economy IMHO.

Its not the cheapest way to balance and good engine builders will already have statically balanced before dynamic so individual component weights will be a best fit. Dont see how you can say its any kind of economy in this manner.

[rev-erend]

I think my balancing cost me about £300 - with £80 being Malloy metal.. it's expensive stuff as we keep fighting wars (Iraq, Afganistan..)

[JR]

These people have been highly recommended: http://www.vibrationfree.co.uk/

[Boosted LS1]

TVR_owner said:

spend said:

Different ways of balancing, that way is a false economy IMHO.

Its not the cheapest way to balance and good engine builders will already have statically balanced before dynamic so individual component weights will be a best fit. Dont see how you can say its any kind of economy in this manner.

Because the OP says:

"For £300+vat they balance the whole assembly, ie crank, rods, pistons, fly, clutch and front pully etc in the block."

There's no mention of all or any of the individual parts having been balanced first. They're not doing very much at all imo.

This is basically external balancing as opposed to internal balancing. Internal balancing is the preferred route imo and then it can be finely adjusted with external balancing with the pulley and flywheel assembly installed. You also external balance when there isn't enough mass in the counterweights but this is a rover

[BlueOval57]

AMB have now balanced over half a dozen engines for me and the results are outstanding. I am a professional mechanic and engine builder and I have found the quality and ACCURACY of their balancing unequaled. When I have purchased rotating assemblies that has been pre-balanced on Hines type equipment I always have them re-balanced by AMB, to a greater degree of accuracy. A few points for those uneducated in this process,
1. Each component is individually weight matched, con rods especially are balanced at each end not just weight matched.
2. Most companies quote a weight discrepancy of +/- 2 grams for pistons and rods, all of my spec. sheets show a less than 1/2 gram discrepancy.
3. The piston rings are substituted during balancing, no bore wear or scuffing occurs. The bearings also are pre lubed and because there is no load on the assembly I have never had any markings on these items. The whole assembly is spun at very low speeds so there is no worry of any wear on any component.
4. All my engines are balanced internally where piston weight and crank configuration allow and because each components weight is documented, replacement if ever needed would be simple.
5. Because the assembly is finally balanced in the environment that it is going to live in (the block) there is no room for human error.
I hope this has thrown a little light on this type of preparation and dispelled a few myths.

[WokingWedger]

Balancing a final assembly should provide a better final result as it takes into account tolerances and fit of components. We do this at work, we have motor rotors balanced, then the impellers balanced, but then the assembly is balanced, as we can not otherwise acheive the specified levels due to motor shaft/impeller bore tolerances.

[350Matt]

I'm with Blue Oval

Although I haven't used the AMB guys I've know of several people (Ilmor) who've used this method to very good effect with these guys:

http://www.vibrationfree.co.uk/

[heightswitch]

350Matt said:

I'm with Blue Oval

Although I haven't used the AMB guys I've know of several people (Ilmor) who've used this method to very good effect with these guys:

http://www.vibrationfree.co.uk/

Don't know what you are all arguing about.

any engine build requires a static balance of componants during build then a dynamic balance as a rotating assembly.

you are arguing about doing one or t'other when in fact you always do both.

N.

[350Matt]

I think you're missing the point here, the entire bottom end is built up, piston, rods , crank etc and then spun up on the crank so normal dynamic balancing doesn't include the pistons and rods and only adds a dummy weight on the b'end pin .

This 'in block' method is superior to the normal method because of this.

Check out the website

[Boosted LS1]

^
Why is it? Whether you have pre-weighed lead shot in cans attached to the crank pins or rods and pistons makes no difference as far as I can tell. All the crank needs to feel is the weight of the componants.

What's different is whether mass is added/removed to/from the crank internally or externally or a bit of both once the flywheel and damper have been fitted.

[350Matt]

Its superior because the mass of the rod moving through its ellipse creates a couple about the big-end pin, conventional dynamic balancing with a dummy mass on the big-end pin does not re-create this couple.

Careful positioning of where the balance weight is can minimise the effect of this couple and reduce vibration at the crank, this is done at the design stage by calculating the position of each web and considering it as a single item and getting the moment of inertia to coincide with the crank centre.

However as soon as you fit a different piston / rod etc the position of the balance mass has to change and while you can get away with grinding away the existing balance web, this shifts the position of the balance point.

its a fine difference and one you're probably not going to notice on a 6KRpm engine but as the rev's increase then you'll notice it.

[Boosted LS1]

350Matt said:

Its superior because the mass of the rod moving through its ellipse creates a couple about the big-end pin, conventional dynamic balancing with a dummy mass on the big-end pin does not re-create this couple.

That's interesting but would you think we're talking less then a gram here, it can't be significant enough to be unbalanced if you get what I mean? IIrc Rover cranks used to be balanced away from the engine and so are a lot of other cranks. Then, after final assembly they'd spin the engine up and add/remove weight to the pully just to fine tune it a bit. This seems to work well enough. They do this to current vettes but not the camaro whiched revved 500 rpm's less.

[350Matt]

Agreed
it will work well enough to keep vibration to acceptable levels, especially on a 6Krpm engine however there's something to be had from the method and its not that much more expensive than conventional balancing.
Plus if you're building a revver (9K+) then its well worth doing