FXR balance shaft

[Henk]

Has anyone tried leaving it out and if so what was the result?

[sidwyz]

I believe Gavin V did, I think you will find a lot of vibration

[Henk]

Enough vibration that he put it back in?
Tempted to leave it out and see what happens in any case. If it's unrideable I can always tear the engine to bits again.

[Kickaha]

There's one or two down here minus the balance shaft, the vibration isn't that bad that anyone put it back in, personally if I was taking it out I would balance the crank

[Henk]

Thanks for that. I'll leave the balance shaft on the bench then. At worst I can use the bike to make milkshakes for my lunch.

[koba]

Na, It can be worse than milkshakes.
It probably won't matter so much on a bike as small as an FXR but if it has been on a severe diet it may mean things have to be made thicker (heavier) to stop them fatiguing, thus negating any gains.
Also it could have an effect on mainbearing life and the like.

[Henk]

Well the cases are together with the balancer left on the bench for now. If it's too bad I'll pull it back down and stick it back in.
I'll let you know how it went after the next Mt Welly meet, before then if I start it up post assembly and the bike tries to walk out the door by itself.

[Henk]

Ok so that didn't work. Runs OK revs happily to the limiter BUT so vibey through the bars that you can kiss goodbye to anything over about 10grand on the tacho.
Engine will be coming to bits again next week so it can go back in.

[Kickaha]

Ok so that didn't work. Runs OK revs happily to the limiter BUT so vibey through the bars that you can kiss goodbye to anything over about 10grand on the tacho.
Engine will be coming to bits again next week so it can go back in.

Why not just rebalance the crank?

[Henk]

Why not just rebalance the crank?

No time or budget right now. Probably would have been the thing to do.

[TZ350]

No time or budget right now. Probably would have been the thing to do.

Its real easy to balance the crank your self. There is a whole lot on the Team ESE thread about balancing single cylinder cranks, with, why and what to do, trawl through the pictures to find the posts. The balance factor is probably 50% now, and the balance shaft makes up the other 50.

Me, I like balance shafts. But if you want to run without one, you could try a 60% crank balance factor for starters and move on up 62-65-68 etc until the vibration is acceptable.

I have read in the advertising blurb that the latest 4-Stroke Kawasaki MXr's are 62%, and that they were 60% in 08. Another short cut to a good starting point would be to measure the balance factor of any of the Honda singles CB,SL,XR 100,125,175 etc.

I have also heard of bolting washers onto the flywheel untill the vibration is acceptable, as a way to find the balance factor needed.

[Henk]

I'll just put it back in for now.
Heard about a number of people who have tried and failed with the same mod today, wish I'd been told a month ago, never mind you live and learn.

[Bren_chch]

i've taken a few out, never put them back in, all engines and cranks quite different though. run softer grips lol

[Henk]

I don't think softer grips would do the trick. Could only ride it by running a gear higher and forgetting anything over about 10 grand. Be in the garage over the next week or so putting it back in.

[Bren_chch]

wow, must be very very bad!!! :( try balancing it. not to hard.

[Kickaha]

I rode one of Brens, it was ok right up to the point we fixed the engine mount and made it stiffer then it vibrated like a bastard, although the big end did shit itself a meting later so it may have already been on the way out

[Bren_chch]

soft the lot of ya, i rode it in the BOB and it was sweet as! I wonder if its because the aluminium frame i run with soaks up more vibration then the hard steel frame?

[Kickaha]

soft the lot of ya, i rode it in the BOB and it was sweet as! I wonder if its because the aluminium frame i run with soaks up more vibration then the hard steel frame?

Piss off, it had a different motor in it then, it vibrated enough to make my hands go numb at Raupuna

Did the first motor I used at Levels have a balance shaft in it?

[Bren_chch]

It was the same motor u inbred goat. after u fucked it i stuck another rod kit in it.

[DEATH_INC.]

Can't be that bad is it? We did this to my brothers XT250 years ago and he rode that all over the country....though it did make ya feet go to sleep after a while.....

[Kickaha]

It was the same motor u inbred goat. after u fucked it i stuck another rod kit in it.

Maybe you put this one together properly then? :finger:

[jasonu]

http://www.oldskoolperformance.com/

Cool pix especially the H2 pro street

[Henk]

Can't be that bad is it? We did this to my brothers XT250 years ago and he rode that all over the country....though it did make ya feet go to sleep after a while.....

20 lap race at Mt Welly this afternoon and at the end my hands were buzzing. And that was without revving it as hard as I usually do.

[Buckets4Me]

20 lap race at Mt Welly this afternoon and at the end my hands were buzzing. And that was without revving it as hard as I usually do.

10 laps into it I felt like that all over

[Henk]

:dodge::dodge::dodge:
10 laps into it I felt like that all over

Get a diesel then, much better :dodge:

[Buckets4Me]

:dodge::dodge::dodge:

Get a diesel then, much better :dodge:

no way is it as much fun thow :)

[Henk]

To be honest I think it probably is. Don't get me wrong I love two strokes but at the end of the day it's all about going out and riding around in circles and coming off the track with a huge smile on your face. I don't think it really matters what you ride as long as that's the end result, and if that isn't the case you should probably go and find another hobby.

[marsheng]

Why not just rebalance the crank?

The crank is already balanced in a FXR. The vibration is from out of phase motion, hence the balance shaft is set out of phase with the crank and soaks up the motion.

That is why V twins are smooth. The 90 degrees between cylinders does the same thing as a balance shaft. (PS a Harley at 45 degrees does not work hence they vibrate your fillings out)

The vibration is caused when the piston slows down at the bottom or top of the stoke from its maximum speed 1/2 way down the bore. If you have a V twin, when one is at the bottom or top of the stoke the other is at maximum speed 1/2 way down the bore.

Th only -ve thing the balance shaft really does is add to rotational inerta which means is picks up revs a bit slower.

[speedpro]

I love the interweb.

There is of course that little problem with a single where the crankshaft is creating a force whose direction changes as the crank rotates. It's all good at "ONE" rpm when the force is equal and opposite to the force generated by the piston but even then only in line with the bore. At no time is there ever any force perpindicular to the bore that needs counteracting. The problem is that without something to counteract that force generated by the crank perpindicular to the bore, say by a second cylinder or a balance shaft, the vibration will only get worse as the revs rise. Because the forces are generated by a rotating mass it is a square law that determines the forces - double the revs=four times the force. It's complicated and simple at the same time. A single tries to counteract a reciprocating force with a rotating force. One force increases linearly and the other increases exponentially(?). Other factors affect "feel" as well. Different chassis construction, engine layout and other things. I could go on, and often do.

[koba]

I love the interweb.

There is of course that little problem with a single where the crankshaft is creating a force whose direction changes as the crank rotates. It's all good at "ONE" rpm when the force is equal and opposite to the force generated by the piston but even then only in line with the bore. At no time is there ever any force perpindicular to the bore that needs counteracting. The problem is that without something to counteract that force generated by the crank perpindicular to the bore, say by a second cylinder or a balance shaft, the vibration will only get worse as the revs rise. Because the forces are generated by a rotating mass it is a square law that determines the forces - double the revs=four times the force. It's complicated and simple at the same time. A single tries to counteract a reciprocating force with a rotating force. One force increases linearly and the other increases exponentially(?). Other factors affect "feel" as well. Different chassis construction, engine layout and other things. I could go on, and often do.

So, Supermono = good?

[F5 Dave]

It was the same motor u inbred goat. after u fucked it i stuck another rod kit in it.
Now there's some quality ragging!;)



So, Supermono = good?
No, because Ducati = Italian = bad

also its a 4 stroke. What am I doing here again?:crazy:

[Buddha#81]

What am I doing here again?:crazy:

You know why!!!!!! Join the dark side master Dave, its your destiny!

[F5 Dave]

As we talk I'm daydreaming about converting the Van to the enlightened path.


Wonder where I'd fit the spannies?

[Henk]

As we talk I'm daydreaming about converting the Van to the enlightened path.


Wonder where I'd fit the spannies?


In the back for the run to the tip?

[koba]

As we talk I'm daydreaming about converting the Van to the enlightened path.


Wonder where I'd fit the spannies?

Under the floor! You don't need all that ground clearance!

I often daydream of building a 1000cc 2 stroke V8 for my fibregalss beach buggy.
It would be quite expensive to get someone to make the crank and cases...
As a rally/hillclimb/gravel sprint car it would be class B, so in with 1600s and 1800s mostly but the power to weight ratio would be WAAAY better.
It would need lots of other handling stuff.




Lotto.

[Kickaha]

The crank is already balanced in a FXR. The vibration is from out of phase motion, hence the balance shaft is set out of phase with the crank and soaks up the motion.



So that would be the same for all singles then?

Because the mighty GN with the rebalanced crank after it was lightened (on the rare occasion when it was going) was a damn sight smoother than a FXR sans balance shaft

[marsheng]

So that would be the same for all singles then?

Because the mighty GN with the rebalanced crank after it was lightened (on the rare occasion when it was going) was a damn sight smoother than a FXR sans balance shaft

Balancing is a black art. The piston trings and gudgeon pin are weighed and a % of this is taken for balancing the crank, anywhere between 50 and 70%. A single will always vibrate, the question is when you take the whole weight and springiness of frame and motor etc, can you get get the balance factor at a point that gives minimum vibration at the riding speed.

Twins are just as bad. Think of old Nortons. It was found that if you took a Norton and set one crank at 76 deg to the other, the vibrations were drastically reduced.

To get a single 'balanced', what has been done in the past is a few tapped holes are drilled in the crank and then various different weight materials are screwed in and run and then tested for vibration.

I was thinking that a plug hole in the crank case could facilitate this.

My hand gets numb on my Honda CB150 after 4-6 laps.

Cheers Wallace

[F5 Dave]

Under the floor! You don't need all that ground clearance!

I often daydream of building a 1000cc 2 stroke V8 for my fibregalss beach buggy.
It would be quite expensive to get someone to make the crank and cases...
As a rally/hillclimb/gravel sprint car it would be class B, so in with 1600s and 1800s mostly but the power to weight ratio would be WAAAY better.
It would need lots of other handling stuff.




Lotto.
Well in the absence of that one of Jimmys V6 750s should suffice, Find that 50k & you're away



. . . Think of old Nortons. . .

I'd prefer not to.

being 360 twins they were like two singles anyway.

Not sure I like the idea of screwing things into a crank while still in the cases & hoping it stays put at 12,000rpm.

You could try a flywheel weight with offset, while it would create a rocking couple would give you an order of magnitude test. Seen it done before

[Kickaha]

To get a single 'balanced', what has been done in the past is a few tapped holes are drilled in the crank and then various different weight materials are screwed in and run and then tested for vibration.

My hand gets numb on my Honda CB150 after 4-6 laps.
Cheers Wallace

My GN got a few extra bits of metal welded to the crank, even in a 1 hour race there is no numbing of the hands
It was done by HPE when they lightened it

[SS90]

As we talk I'm daydreaming about converting the Van to the enlightened path.


Wonder where I'd fit the spannies?

Fpppt.....

Mine IS a two stroke, 600cc air cooled 4 speed, and, if you lay the rear seat down, you can actually fit a vespa in the back...... I drove it from Imola to Münich with a vespa in the back last year...... I wonder if it could haul a bucket round NZ?

My younger brother came to visit a few months back and was embarassed to be in the passenger seat, and just about cried when I had to mix the oil in the fuel!

[jasonu]

So, Supermono = good?
The Supermono had a 2nd rod that connected to a weight to imitate a 2nd cylinder at 90 deg.
As for the FXR vib issues with the balance shaft removed, I have a sure fire cure. LEAVE THE SODDING BALANCE SHAFT IN. That will work every time.