Flywheel splitting/big end replacement

[adrie.degraaff]

You can put the second plug in or out for differend balancing or even a heavier plug .

[nevhunter]

A it of a gamble. IF you are serious do it right by doing the balance of each wheel separately. It takes a bit of mind work to see it through. You can do a rough check with both and thin oil on the bigend. on knife edges or even bright shaft bars. Use blue tac and glue washers etc to see how far out it is. Within 2 grammes is close enough. Flywheels that are not aligned well will cause vibration too. You an have a smoother motor for the future if you go to the trouble. Nev

[Paul Gasson]

It would be good to get an idea how (un)balanced the assembly is. I have no machine tools available so is this something I could do at home and can anyone direct me to some sort of instruction regarding how to check balance and adjust?

[Roger Gwynn]

I think the factory used the same stampings for the flywheels and machined them differently, hence the similar drawing numbers.

Some years ago I did some experimenting with balance factors and found that altering it made little difference until it got up to 80%. What did make a difference was less reciprocating weight, heavier flywheels and electronic ignition so that the sparks were exactly 180 degrees apart, yes it was a twin.

I also tried reaming the engine mounting holes, head steadies etc but with little to no effect. Recently I have started using ear plugs, which are worth at least 5 miles and hour as they reduce the sound and give the impression of increased smotheness, most odd.

[Vesa Helske]

Ear plugs are a must for motor bike riding in general
Vesa

[nevhunter]

Heavier flywheels and lighter piston does make a better to ride motor. The VH flywheels are a bit on the light side. Norton singles tend to go a bit heavier Balance factors vary from bike to bike depending on the frame etc natural frequencies. It's usually determined by experimenting Vee twins are dependent on the angle of the V to a great extent. A motorcycle engine installed in a TQ rear engined car will often need a much lower factor..
There's vibrations from the parts that rotate and others from the bit's that go up and down.The FACTOR is the % of the MASS of the bits that go up and down you apply to your balancing of the flywheel asembly on knife edges. Up and down is piston rings gudgeon pin and circlips plus the mass of the small end. To get THAT place the conrod horizontal and weigh the small. end carefully. Do it a few times and average your results. Get the sum of all the bits and factor it by your chosen figure. THEN subtract the actual small end weight because the entire conrod is hanging down and add more weight to achieve the 65% (or your chosen figure Total) Then remove weight equally from each flywheel to get what you want. It's balanced when the flywheels will stop in any position without wanting to move if you nudge them a bit. It's a a lot more complex if you do each wheel by itself. I'm NOT going to deal with it there NOW,but you can kick it around in your mind yourself if you are so inclined. Nev

[Paul Gasson]

Thanks Nev, I understand your explanation but I have nothing to support the assembly rigidly and I wonder how accurately the parts would need to be weighed? I would be really struggling to accurately drill holes in the flywheels if needed, so whilst I appreciate the details, it is probably beyond the capability of me and my tools. It needs an expert or as was mentioned, a good supply of ear plugs!

[Mike Nash]

Paul,
You ask above about checking the balance. See here viewtopic.php?f=4&t=381&p=1404&hilit=ba ... ctor#p1404
It's not difficult if you take care. Regarding measuring the weights, I've found that John Lewis kitchen scales are accurate to the gramme.
MikeN.

[Paul Gasson]

Thanks Mike, it is an interesting series of photos, in particular the one with the flywheel assembly set up with a collection of hex nuts, I presume these add up to the 66% or whatever is required of the piston assembly weight. It’s really good to be able to see how it can be done. I doubt I could drill accurately enough into both flywheels to adjust the weight if needed. There are no holes in the circumference, the existing balancing holes are on the inside faces of each flywheel so where would I drill?

[johnmack]

What is the thread in timing side fly wheel is it a cycle thread?