Thumper Club Forum
Technical => Bike Problems/Questions => Topic started by: SHimmer45 on April 08, 2015, 12:59:03 PM
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Just got my XL500 engined 250RS on the road and its rather vibey any one had experiencing bar end weights to tune out vibration?
or any suggestions or experience of other things like "bar snake"
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First thing to do is make sure your balance weights are timed correctly, then if you haven't already, fabricate a top engine mount, finally get some of those foam handlebar grips. The RS is a small framed bike and not designed for a thumping great 500 engine so it doesn't have the mass to absorb the sort of vibrations the 500 produces, oh a heavy duty chain helps and make sure your cush drive rubbers are in good condition as well.
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the engine has had the balance shaft removed, however it "only" produced a 20% balance apparently.
have fitted a 35/36 tooth sprocket to the rear which has sorted the cruising revs nicely.
fitted a couple of small bar ends but i think they need a little more mass.
i havent heard of people making a top mount for the engine.
its still early in its "development" but usable enough for me to trundle about on it.
taking inspiration from
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I'm in love! Aren't specials just fabulous, there's something about making a unique bike that really appeals to me. Well done and keep up the good work.
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that's a really clean xl ,rs you have shimmer45 grate job if the bike is very vibey it could be down to removing the balance shaft removed , tommy
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Love it!Bet it wheelies like no tomorrow!Hope you can sort out the vibes.......
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Removing the balance shaft will make it vibe, it may also cause the frame to crack. One of the selling features for the RS was that the balance shafts allowed them to use a lighter frame. You should fit a top mount.
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Aye shimmer,
Further encouragement to be had from this video, nice bike and smooth riding! ;D
XL500_quick! (https://youtu.be/s-3w5SaNw6Q)
My regards, Bill
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the posted bike isnt mine im afraid.
will be looking at a top mount over the winter then
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An xbr without the balancer? I'm glad I don't have any fillings to rattle loose.
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An xbr without the balancer? I'm glad I don't have any fillings to rattle loose.
Its been done, on a race engine it can, apparently, give a 2bhp power increase but it wasn't something that I was inclined to try.
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If the balance shafts run at crank speed I wonder why the issue wasn't dealt with in the crank?
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If the balance shafts run at crank speed I wonder why the issue wasn't dealt with in the crank?
There is only one balancer on the XBR engine so it works like a 180 degree parallel twin, the dual balancer shafts on the earlier models are supposed to be better, I forget why, something to do with harmonics.
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If the balance shafts run at crank speed I wonder why the issue wasn't dealt with in the crank?
There is only one balancer on the XBR engine so it works like a 90 degree V-twin, the dual balancer shafts on the earlier models are supposed to be better, I forget why, something to do with harmonics.
Thanks rhinoman.
I read all this stuff back in the seventies, but I'd forgotten it all!
Here's an easy to read little article I picked up on google. It shows the basic principle involving the two balancer set up. I think secondary forces act at twice engine speed. Maybe this is the harmonic "thing" you were thinking of?
http://www.jampot.com/TechTips%5CGeneral/QuestionsBalance.pdf
Edit: this Looks better. Not read it as I'm off to work now. But the diagrams on page 10 pretty much explain the difference between the one and two balance shaft arrangement.
http://www.tonyfoale.com/Articles/EngineBalance/EngineBalance.pdf
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I just corrected that, I should have put 180-degree parallel twin, it was the Ducati Supermono that was balanced as a 90-degree V-twin. Twice engine speed is the second harmonic as described in the second article linked.
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the engine has had the balance shaft removed, however it "only" produced a 20% balance apparently.
have fitted a 35/36 tooth sprocket to the rear which has sorted the cruising revs nicely.
fitted a couple of small bar ends but i think they need a little more mass.
i havent heard of people making a top mount for the engine.
its still early in its "development" but usable enough for me to trundle about on it.
taking inspiration from
I might be getting confused here, apologies if so. But aren't there two balance shafts in the xl500? Like the 250RS? If so, do you mean the front one? Which is a "shaft". Whereas the rear one is on a bearing sat on the gearbox shaft, if my memory serves? But then that raises a question. If the front shaft is gone, then I assume the chain must be missing too? If that is the case, then the rear counter weight won't be driven either. It might even be removed? If any of that is right, then you might be 50% down, but at least you won't have a rocking couple! ;D
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If the balance shafts run at crank speed I wonder why the issue wasn't dealt with in the crank?
There is only one balancer on the XBR engine so it works like a 180 degree parallel twin........
I can see what you mean, but, assuming I've understood it correctly, there are lots of differences too?
The single cyl/single balance shaft setup creates a couple, as does the 180 deg twin, but the couple acts in a different plane and is a lot weaker since it is acting at only 50% mass? On the xbr the centre distance looks quite small, as you'd expect, so this will reduce the effect as much as possible?
The single balance shaft won't create any "extra" secondary vibration, like the alternately opposing crank assembly on a 180 deg twin would.
I'm wondering why Honda went away from a theoretically superior idea, in the form of twin balance "shafts", onto just one? Different frame design?
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The single balancer is simpler, cheaper and easier to package, though the first versions were unreliable on a race engine until they changed the dampers on the backlash gear from two rubbers and two springs to four rubbers.