Flywheel modification

[alexanderfoti]

I have spoken to a company who does flywheel balancing locally and they told me the same thing, if the weight is remove concentrically then there is no need to balance it when redline is 3600 rpm. My thoughts are that it does still need to be balanced, its finding somebody to do it!

[Rhynri]

If 3600 rpm doesn't make a difference, by balance a tyre with a tiny little weight when it's only turning 1500rpm~ at 80mph? I mean, when they cast your flywheel, of course they did so homogeneously, perfectly uniform density, etc. That's why you never see flywheels with factory balancing bores...

It's a shame they don't want your money. I always thought it was hard to run a business if you refuse to take people's money in return for a service or item.

[tappy]

I think an issue we might face here is knowing what's "acceptable".
For a typical flywheel on one of these diesel engines, does anyone know how much Out Of Balance mass is acceptable? Does anyone know what limits they're balanced to at the factory?
Essentially, a shop that specialises in balancing petrol flywheels will already know how accurately a flywheel has to be balanced for typical car engine speeds.
When they're faced with your diesel flywheel and say "it's not worth it" what they possibly mean is:

"We'd do an 8000rpm fly-wheel to "x" gramme-millimetres. A fly-wheel spinning at 3000rpm doesn't need balancing to better than "y" gramme-millimetres, and we've never had a customer come in with a flywheel that out of balance"
If we walked in with a diesel flywheel and said "I need it balancing to "z" g-mm, and by the way, I've cut 2lb off it with an angle grinder" then they might understand it a bit better.

So - does anyone know what's "acceptable" for these flywheels?

We do (did?) have some balancing rigs at work where we assembly gas turbine rotors so it *might* be possible for me to get mine measured before I hack it about. It would be very useful to get more than one "standard" flywheel measured tho...

[XLerate]

Seems you might be overthinking this. First, yes there are factory engines with factory balance bore on flywheel on production line. All Mopar smallblocks of either 318 or 360 CID, can't remember which one of the two, run a factory bored flywheel. I believe 413's did too.

But the thing is, factory engines may have a balanced flywheel all right, but that's about it. The rest of the engine is a pile of parts grabbed off the shelves with different weights in each piston, connecting rod, crankshaft, lifter, pushrod etc. The flywheel is the one part along with clutch & pressure plate that can be uniformly balanced to a certain extent, so they do. The rest of it is unbalanced, sometimes a little, sometimes a lot, depends on what they grabbed off the assembly line to stick inside? Not at all unusal to measure those differences in ounces, not grams, and there's 28 grams to an ounce!

[tappy]

Yeah, well that's why I was kinda wondering what the safe limits are - a crank & con-rod assembly is unbalanced by its very nature so even if the piston combines with it to create primary balance, there's still going to be secondary, and I'd expect that to out-weigh the flywheel OOB somewhat!
BUT, car engines etc DO have balanced flywheels, and they have the same crank arrangement, so there must be SOME reason why factories do it. If it didn't provide some value they just wouldn't bother.
Could it have more to do with flywheel OOB introducing loads / problems into things driven off the flywheel? Clutch assemblies, generators etc etc?

[XLerate]

I think the flywheels are balanced to prevent the cranks snapping like a pretzel from harmonics, same reason vibration dampers are used.

[mark_in_manchester]

Is it possible that flywheel imbalance might be bad news for main bearing life?

Most bikes and cars incorporate some kind of 'shock absorber' which is often in the form of radial springs in the clutch plate, which soak up pulsations in the power delivery...and perhaps spare the gearbox and drive train bearings a little. Though on my Urals the shock absorber is the rubber couple just after the gearbox (and on my MZ it's the cush drive in the QD rear hub), so any imbalance plus the power pulses (such as they are ) end up banging away at the mains and all the gearbox bearings.

Having once worked for a company balancing big fans and generator sets, I feel I should know rather more about this than I do!

About all I can remember is one needs a tacho pulse (one per rev) as a phase reference, and some form of accelerometer, to balance something. A colleague once reported resourceful engineers in India using record player pickups as accelerometers, and a tacho pulse could be derived from an optical cell and some tipex on the flywheel. It would be fun to try - dual-beam oscilloscopes are free these days, if one has a stereo soundcard and some freeware.

[tappy]

Ah, that makes a fair bit of sense.
The con-rod assemblies and crank weights are *relatively* light and close to the crank so the resonant frequency of those assemblies is high.
The flywheel has a large inertia, and is all the way at the end of the crank - the length causes it to act like a long tortional spring - so this can create a low frequency resonance. So maybe balancing the flywheel is just to try and stop creating large forcing functions causing resonance in that low frequency region?

[alexanderfoti]

Just a quick update, I have not been able to find a replacement flywheel cheaply so haven't done the mod yet

[XLerate]

This reply seemed off topic because I forgot to give a quote of exactly what I was replying to, sorry for any confusion! I was answering this question:

"As I have 2 tanks, I was thinking of running a copper pipe from the Veg fuel tank, down the past the left hand side of the oil cooler/cylinder block, and either wraping the copper through the fins, or just along side it, then feeding the end into the fuel filter, this should definitely help things when switching to WVO, and would mean I dont need to waste money and electricity on heated filter setups. Thoughts?"

So my reply to that question was:

I planned to use some veg fuels in my Cummins 4BTA rig at one time. One might heat the fuel using a little sheet metal 'oven' formed over an exhaust section with copper fuel tube running inside. Fuel line exiting oven insulated to retain heat. Oven placement along exhaust pipe has a large effect on actual temperature, closer = hotter of course.

Oven interior temperature is easily adjustable with one or more cable controlled flapper doors on oven to admit outside temp air. A Pyrometer efectively gauges what temps you're dealing with, though a remote sensing thermometer might be used also, can't think of the proper name. Just the oven and copper fuel line is cheap, quick and easy to set up.

Another alternative is to run the copper fuel line in a coil around exhaust but there's not as much adjustment available, only the static distance surface to surface.

.

[alexanderfoti]

Thanks for tha Xlerate, that bike is no longer in one piece. I did have success with running a veg oil /petrol mix. about 95% veg and 5% petrol.

On another note, I have started the flywheel modification, and I have found somebody who will balance it after I do some of the work.

Here is the start of it:



Im going to keep about 5-10mm of the vanes, as my tach sensor uses them for the rpm gauge,. I am going to grind down the additional longer vanes flush and then once all that is done, it will go down to dynamic balancing in bristol. (I am waiting for them to get back to me on pricing).

I have a spare flywheel now, so if this goes tits up, its not the end of the world.

[alexanderfoti]

I have decided to keep most of the mass. My engine wont really idle below 1000rpm, and I dont want to make that higher with a lighter flywheel.

[alexanderfoti]

Did a bit more work on it:

[coachgeo]

Did you weigh before you started? Would be interesting to know how much weight you just shaved off.

[alexanderfoti]

I didn't but I kept all the bits I week give them a weigh

[coachgeo]

here is another thread you should review on this topic

viewtopic.php?f=30&t=1250

[alexanderfoti]

Lots of interesting talk on that thread. The 2 planes of though appear to be, keep it heavy as the engine needs it, or lighten it as its over weight for our applications (motorbike not generator).

I am of the thought that it should be lightened as well, for our applications also.

Its a shame that the balancing place etc is so far from me. I have 2 flywheels, so I could always experiment quite easily. Shame engineering time isnt cheap either

I have read on line of methods of static balancing a flywheel using a bar and some very low friction bearings. Any thoughts on that?

[gearhead1951]

The only advantage to dynamic over static is if there is a chance of there being a "rocking couple" , no such condition is possible with a single disc flywheel !

[alexanderfoti]

In which case I might get the stuff needed to do that. That way I can play about with 2 flywheel s without having to send them off

[pietenpol2002]

It will be interesting to see whether the mass removed impacts your idle. I do believe the 1.5 lbs. removed is more than compensated for by the additional mass of the flywheel, sprocket and chain. Others have suggested that poor idle may be as much about the quality of the pump. If idle is unaffected after the shave, it could suggest the pump.

[alexanderfoti]

Agreed, I have heard that the pump quality also affects the idle.

However I think the injection timing also affects the idle, and while mine knocks very hard at low rpm, its quiet at high rpm (which is the way it should be I think).

I think changing the timing would change the idle characteristics as well. I wouldnt mind having a low(er) idle, as 1000 rpm is quite high of an idle speed!

[alexanderfoti]

Right, I have bought the bits to statically balance, after reading up on it.

Static balancing only balances one axis (the one that goes through the middle of the flywheel), whereas dymaic balancing will do the whole thing (and will illustrate off center imbalance).

Im pretty sure that static balancing will be fine, so im going down that route

[gilburton]

I don't think just removing the fins will make much difference to weight or balance however it may cause a reduction on drag? effectively giving a small return in power?

[alexanderfoti]

Thats why I have removed them!

Best to be safe and to balance it just in case though. It is spinning in between my legs after all (and I dont want the big end bearings to get shot either)

[Nanko]

Why not using the flywheel without finns before having it balanced ?
It probably will vibrate more than nessecary , but it would be good to know if the engine does not overheat , and I am quite sure that will happen....
It might save you some bucks

[alexanderfoti]

I have a cooling fan from another motorbike and a thermostat with a temp sensor that I will install at the back of the cylinder where the cooling it's worst. It will be okay

I will see how got it gets

[HondaJohn]

Also remember that the flywheel fins are forcing cool air through passages in the cylinder head. None of the head's cooling fins are external, they are all cast inside those passages, so they won't benefit from being mounted to a moving bike in cooler air as much as the cylinder fins would be. You might risk burning a valve or seizing the valve stem, since the top end is just poor splash lubrication anyway.

[alexanderfoti]

Can you elaborate a bit, im finding that hard to get my head around

[HondaJohn]

There are two passages that are fed by the bolted-on plate that I removed. The plate tucks under the flywheel housing, and air is blown up to and through the head. You can see the internal fins in the pics I posted. None of them are external or can be reached by ambient air, although you might be able to cut off the cover at the front of the head, since it doesn't look structural.

[alexanderfoti]

Ah right, that makes it easier to visualise.

Is that the air intake in the middle? I have 60mm ball bearing fans that are very high CFM, I could run them at 20/40% power constantly, it would still be less taxing than the flywheel spokes.

I will have a look on my engine to see where the air flow is and if its the same on my engine.