engine balance and lightening

[dasicvtec]

Hi

Just wondering if anyone knows of any workshops which specialise in engine balancing and also lightening of internal engine components. Also, if anyone has had any experience doing this to their own motor.

For people that might not understand what this involves the simpliest way i can put it is applying the same theory to an Lighter Under Drive pulley (less mass to accelerate/decelerate) but to internal engine components such as Conrod's, pistons and so on.

thanks

[Slaz]

You wouldnt really bother lightening standard internal's for the cost involved and what your left with afterwards strength wise due the materials used on standard components.

Aftermarket lightweight cranks, rods, pistons, flywheels, pulleys are readily available though.

What engine and what application, or you were just wanting to lighten things up when considering a rebuild?

[dasicvtec]

Going to undertake a rebuild in the near future and wanted to know if there was any options for improving general rev happiness of the motor. The application would be for Circuit racing. thanks for the reply

[Slaz]

Like i was saying, the money spent doing the work to standard components isnt really worth it and you'd be better off buying lightweight new parts for the build, especially if you intend on using it as a curcuit motor, they see sustained rev's for longer periods of time and have to work hard compared to street/drag applications.

[JohnL]

Going to undertake a rebuild in the near future and wanted to know if there was any options for improving general rev happiness of the motor. The application would be for Circuit racing. thanks for the reply

If you want a very 'zingy' engine, by far the best bet is to fit a very light flywheel. It's a lot of work to lighten the stock parts (crank, rods...), and you won't make nearly as big a difference as with a lightweight flywheel.

You also risk weakening the components, not so much because you've removed metal, but because you'll break through the 'forging skin' on the surface (similar skins exist on cast components too). The surface is hard from the forging process, and this tough skin is resistant to the initiation of cracks. Remove the skin and the new softer surface is more prone to developing cracks. You can treat the new surface to reharden it (e.g. polishing, then Nitriding, shot peening etc...), but the result may(?) not be as good as the original surface hardness (and the costs build up and up).

the simpliest way i can put it is applying the same theory to an Lighter Under Drive pulley (less mass to accelerate/decelerate)

It's a very bad idea to use a lightweight front pulley because a pulley with inadequate mass (and incorrect design, which means more than just being able to run the various belts) will not act as an efficient harmonic vibration damper. The mass of the harmonic damper should not only be at least X, but should also be mounted to the crank by means of a rubber insert that allows a significant degree of damper motion independant of the crank.

The stock 'pulleys' are not only pulleys but are also very carefully and well designed harmonic dampers that are designed to dampen out excessive crankshaft oscillations that can cause crankshaft failure, particularly with engines that often see higher rpm. The pulley is made from two metal parts bonded together with a vulcanised rubber insert between them. You can see the rubber insert if you look (as a 'ring' on the face of the pulley), and while it may seem like an almost rigid connection between the two metal parts, in use the rubber insert is subject to enough force at high enough frequency to cause the rubber to flex and heat up substantially (this heat coming from oscillatory deformation of the rubber itself, not heat soak from the engine nor ambient engine bay temp), and over time can result in failure of the rubber insert.

This is not likely to be an issue for road engines (not much time at high rpm), but high revving race engines place a lot more stress on the harmonic damper (i.e. heat cycling the rubber insert, eventually degrading the rubber). With this in mind, if you are building a high revving race engine it would be a good idea to use a new harmonic damper (or at least newish, or failing that at least one that's been carefully inspected on an ongoing basis). And no, it's a very bad idea to not use a damper at all...

[Chr1s]

What forging skin? A forged item has a uniform grain structure unlike a cast item. It will not matter if its forged to re-shape. You can buy forged blocks of metal and machine them to the desired shape, when re-working forged items or any item of that matter, if it's for circuit use, it would be questionable to ask why the item was not heat treated/case hardened after re-working.

If you take some time to look at the relationship of a flywheel and weight, on a flywheel that is 5" in diameter, removing 1kg from the outside (near the ring gear) will correspond to a similiar reaction of removing 40kg from the car.

Just because aftermarket items are bought this does not mean they are in perfect condition, we do not live in a perfect world. You're entering the blueprinting process here - weighing the rods, weighing the pins, pistons, etc etc. Deburring any odd marks, removing material from the underside of pistons, knive-edging crank - I question this method as I have not yet seen a direct result of a gain, running smaller bearings to reduce frictional losses, linishing the crank purposely to reduce the diameter of the journal (minimise frictional losses, increase heat, etc etc)

All of the above is pushing the motor to the limit, some people go that far the engine lasts that one race, which for some teams is what they want. You CAN rework some aftermarket items for street use as we said above, nothing is ever perfect but we have the ability to bring it closer to our desired need.

I love these topics.

edit: I didn't really talk about balancing here, balancing is the last thing that is done after the whole assembly has been inspected individually.

Don't fall for the lightweight trap, there is otherways to get reliablity and reach the same "responsiveness". Longer rods and higher piston pin comes to mind .

[tinkerbell]

Aftermarket lightweight cranks, rods, pistons, flywheels, pulleys are readily available though.

aren't many aftermarket forged internals similar (or heavier) in weight compared to the OEM Honda parts?

for example, B20B: 500g rods and 300g pistons...

i.e. the purpose of changing rods and pistons is not to save weight, but to improve reliability...

[JohnL]

What forging skin?

A really quick search finds this reference (note the last sentence):

“Two thirds of our production volume is comprised of the 3.0 TDI engine. The crankshafts for this engine are made of 42Cr- MoS4, and rough machining of these products represents a difficult task, as it consists of a hightensile material at the limit of soft machining. The hard forging skin virtually ‘eats away’ the tool.”

From this page: http://www.forgingmagazine.com/featu...ed_crankshafts

Note that this is in reference to crankshafts, but the hard forging skin is more important for rods than for cranks because the weakest sections of cranks are typically located at the corner radius of the journal / web which is machined in any case (though modern cranks are surface hardened in the corner radii by various means). Rods need the hard forging skin on the flanks of the 'I' beam and cap etc to minimise the possibility of crack propogation.

A forged item has a uniform grain structure unlike a cast item.

A forged item has a compressed grain structure that follows the shape into which the component has been forged. The metal has a uniform grain structure prior to forging, but not after. This is actually one of the reasons why forgings are quite tough compared to castings, and even to components machined from billet.

Cast components will be much more uniform in metallurgic structure than forgings, but the metal grains will typically be larger (coarser) and 'non-directional' causing the casting to have a somewhat lower tensile and shear strength, a lower elastic limit etc than an equivalent forged component...

It will not matter if its forged to re-shape.

Who's talking about re-forging any components? The issue issue is loss of the forging skin when a component is substantially lightened (or in any way modified) by removal of metal. When components are matched for mass and adjusted for rotational balance some metal must typically be removed, but an experienced technician should be very careful about exactly where any metal is taken from.

If you take some time to look at the relationship of a flywheel and weight, on a flywheel that is 5" in diameter, removing 1kg from the outside (near the ring gear) will correspond to a similiar reaction of removing 40kg from the car.

In principle I agree with this (not sure about the numbers, I won't dispute them). I've found the greatest benefit of lowering rotational inertia is to do with the speed with gears can be changed etc.

Just because aftermarket items are bought this does not mean they are in perfect condition, we do not live in a perfect world. You're entering the blueprinting process here - weighing the rods, weighing the pins, pistons, etc etc. Deburring any odd marks, removing material from the underside of pistons, knive-edging crank - I question this method as I have not yet seen a direct result of a gain, running smaller bearings to reduce frictional losses, linishing the crank purposely to reduce the diameter of the journal (minimise frictional losses, increase heat, etc etc)

This sort of work doesn't usually result in any sort of significant "gain" if we are defining gain as an increase in power (or effective power increase). Such work is more associated with enhancing engine reliability...

All of the above is pushing the motor to the limit, some people go that far the engine lasts that one race, which for some teams is what they want.

Blueprinting does nothing to "push the motor to it's limit". It's purpose is to increase the chances of the engine surviving when it is pushed to the limit...

edit: I didn't really talk about balancing here,

Yes you did:
"weighing the rods, weighing the pins, pistons, etc etc." then, "knive-edging crank" are only to do with balancing the engine.

[Chr1s]

A really quick search finds this reference (note the last sentence):
http://www.forgingmagazine.com/featu...ed_crankshafts

Good article. However, to me, this is negligible as I've seen reworked "forged items" plenty of times.

Who's talking about re-forging any components? The issue issue is loss of the forging skin when a component is substantially lightened (or in any way modified) by removal of metal. When components are matched for mass and adjusted for rotational balance some metal must typically be removed, but an experienced technician should be very careful about exactly where any metal is taken from.

Thats right, in the blueprinting process, it's not uncommon to rework rods and pistons. Even cranks for that matter which are forged. As I've said earlier though, removal of this "skin" hasn't been an issue as you also said earlier, shot-peening, polishing, etc is done!

This sort of work doesn't usually result in any sort of significant "gain" if we are defining gain as an increase in power (or effective power increase). Such work is more associated with enhancing engine reliability...Blueprinting does nothing to "push the motor to it's limit". It's purpose is to increase the chances of the engine surviving when it is pushed to the limit...

Hmm, gotta disagree there, blueprinting is a abused term as we know. It is used to ensure a powerplant lasts for the desired application however there is many gains to be had in a blueprinted motor. A motor straight from the wrecking yard won't be as fast down the straight as a blueprinted one.

Yes you did:
"weighing the rods, weighing the pins, pistons, etc etc." then, "knive-edging crank" are only to do with balancing the engine.

Ok, I must of missed that one, it's quite challenging typing up a reply while doing your "work duties" in the background and keeping a constant track of whats been said.

You sound like you've played before? Whats your background?

[Slaz]

aren't many aftermarket forged internals similar (or heavier) in weight compared to the OEM Honda parts?

for example, B20B: 500g rods and 300g pistons...

i.e. the purpose of changing rods and pistons is not to save weight, but to improve reliability...

Either or Tink, forged components are used to improve reliability due to their strength properties due to the material used, design and process used once formed such as peening, hardening ect, but depending on the application the weight of the components is up to the builder/owner, most of the heavier items that are forged are used for turbo applications or those not to worried about the compete rotating assy weight, normally with lightweight parts being used in N/A or low boost appliactions, but off shelf forged pistons and rods can be had under those stock rod, piston weights, aftermarket B series cranks can be had as low as 12kg and we havnt even started talking about exotic materials yet like carbon fibre, aluminium rods, skirt design on pistons, friction properties of FRM liners, amount of rings used, bearing surfaces ect.

My point and as mentioned by others, is spending that amount of time and money on stock items to lighten and balance them when you would be left with a part that would owe you as much as new forged items, which in this example would i believe be a better option for his build.

Some classes of racing are imposed by say using certain OEM components within the engine, then i would consider modifing OEM parts, otherwise, bang for buck and added insurance especially in a stressed motor, i would just buy new items, even if it was slightly dearer.

[dasicvtec]

Thanks for the replies guys, alot of good info. I wasn't too specific in describing if i would be using after market parts or not so fair enough that you guys thought i would be using the OEM parts. The replies were still good either way.

Basically, the motor that i will be using will be used for super sprint's/Time attack. The target power is 120kw at the wheels but reliability is sort after as well. Im thinking it would be better to purchase an aftermarket forged item's, getting the motor blueprinted/balanced/lightened. Once that process is finished, use methods to regain some strength in the forged item how it came from the shop.

What i mean is if a particular con rod has a rated figure of 200kw, i remove materials from these parts, balance and so on. Now the strength capacity of the part is say 180kw, but i use a process such as cryogenics (deep freeze) to bump the strength back up but now the rod is lighter but still strong enough for my application.

Does this work in the real world ?

Thanks

[Slaz]

It would but once again your probably putting in too much effort and expense for what you want to achieve and that extra money would be better spent elsewhere.

If your only looking to produce 120KW then any of the lightweight forged rods such as Crower maxi-lights, Carillo A-Rods, or standard Manley/Eagle style rods would be a good choice with the Crowers & Carillo's being double the price of the Manley/Eagle rods but they are lighter, i would be buying any of these and just checking they are weighted properly as per their spec sheet, not trying to remove anything and having them post treated.