Stanton

I'm going to cut an old case, leave the bearings and see if the piston and rod balance with the couterweight. Is it that simple?

DANE_TRAIN

iTrader: (20)

Haha, I'll answer that.

It's a trick question, because a "top fuel" engine does not run on Methanol or Gasoline. Not to mention, I have never herd of anyone having to re-balance an engine due to changing fuel.

Should we begin a new thread in the "chit chat" section so we can further debate 1:1 engines....?lol

one8updragracer

iTrader: (5)

Actually the balancing process is the same. What fuel you run doens't have an effect on the balance of a crankshaft and its rociprocating assembly.

I have balanced all of the above.

but balancing and porting these little engines are two different topics. I'm sure when these engines are designed they take a lot of care making sure the crank and rods are balanced because at more than 30k they will shake the heck outta themselves if outta balance and bearings wouldn't last long.

pdmustgt

I'm guessing we don't need them counter weights on the crank (key word counterweight) just cut them off ...Yes these are very simple engines just some are over thinking them.




Answer the 1st question they do a over balance for very high rpm engines. But not every builder agrees with this because cause imbalance at certain rpm ranges

Cadimman

iTrader: (41)

Balance is balance. How can it be balanced at 30,000 RPM, but not at 18,000?

Roelof

Resonance.... depending the weight you will get a resonance at a certain rpm, you want that in a range the engine does not stay much time on that rpm. In resonance you could damage the whole engine.

Drilling holes is simple and cheaper but it will enlargen the crankcase volume and that will loose performance. From IDM (made by Novarossi) I have seen full round shaped crankshafts. A low crankcase volume will give more pressure to pump up the mixture faster to the combustion chamber what will give more bottom power.

maxflo777

Since its a single cylinder, and you cannot balance it to the fullest, what you want is to get the resonance at least out of the operating range, and definitely out of the natural frequency of the engine - which shouldn't be a problem considering that we do not see many engines exploding to pieces.

But that does not mean that there are "many balancing points" there's only one, for all rpm ranges, its just that it gets more and more critical the wider or higher the rpm range is, since basically all engines will be at idle at a certain time.

That's the reason you see it more in on-road engines that operate from idle to 40-45k and not in off-road ones that mostly do idle to 30k-35k. It's less critical for the smaller ranges.

x

Maximo

iTrader: (11)

even changing fuel % and tune will alter the resonance...so even if you have the engine dialed in perfectly ( using a vibrex type machine ) the parameters will change as soon as you start altering the explosion on top of the piston....EB Mods is the only modder I know who owns the proper equipment for balancing these engines.....

Racecrafter

iTrader: (25)

So you don't compensate your counter weights for nitro?

Up to 40% I can see. Something like an exhibition car. But for TF or anything upward of 80%+?

You have to compensate for the twist or you'll eat the mains out of the block.

one8updragracer

iTrader: (5)

Way off subject but on BIG power like TF, those engines only need to last 5 seconds at WOT. With that ammount of power on all the working parts a little twist is inevitable. By the time the crankshaft in and engine twists enough to throw the balance off...its already too late, and something bad already happened.

houston

iTrader: (96)

you boys are just getting silly now

these are not top fuel drag race engines

if we are talking about 1/8th nitro off road .21 or .28 engines then lets do so

there is a vast wealth of knowledge out there to be had simply by using your favorite search engine on your pc or mobile device or however you choose to do it .

as far as crankshaft "balancing" goes, its pretty broad as far as the generalization of "balancing" goes , if you actually want to understand the mechanics of why it needs to be balanced ( or imbalanced ) then it takes a little greater deal of knowledge retention and being able to understand the physics of it all . why a crank has a "counterweight" and what it does to effect the firing program of the combustion chamber and all kinds of BS that most people dont even need to know


my 2 cents

M.Gustafson

iTrader: (3)

http://www.modelenginenews.org/etw/etw_bal/p2.html

Good info.

houston

iTrader: (96)

principles are correct but it doesnt take into account the force from the firing of the cylinder nor the amount of force (inertia) it takes to get the piston/rod assembly back into the firing chamber.

overall a most excellent understanding of crank balncing is to be had out of that article , especially for being published in 1951 holy smokes !!

great find!!!

M.Gustafson

iTrader: (3)

Very true on the firing. Unless the throttle is set to a constant RPM there is no TRUE balance in a single cylinder engine. The force you mention is changing with every change in RPM. Different Force = no TRUE balance.

Thanks by the way. Been around these engines and this conversation for way too many years. And NO not since 51.. lmao

Roelof

At the end you want a lower weight for all internals, the lower the weight the less you have to balance.