Good Vibrations..

[BluzPlayer]

Well I was listening to some tunes and must have been driven subliminally toward this posting.
A topic I have been considering for some time.
The vibration encountered on these machines borders on legendary. There have been numerous posting in this regard about the various countermeasures that members have utilized in an effort to reduce the effects and severity of said vibrations. I am not looking to rehash those solutions, nor am I looking for yet another evaluation of their effectiveness.
These solutions would include and are not limited to...:
Rubber isolators on the handlebar risers
Stuffing the handlebars with various materials.
Rephasing
I would like the direction and focus of this thread to center around isolating the source of the vibration (the motor).
Isolating motor mounts have been the standard for vibration reduction forever within the automotive industry. They are also commonly utilized in industrial applications with drive motors in some applications.
There are some examples within the motorcycle industry as well. The xs650 was designed with solid mounts which transfer close to 100% of the vibration to the frame and thus the rider.
It appears from a cursory look at the motor mounts that they could be modified from either of the attachments points (motor or frame side).
The rubber isolater that would be sandwiched between the frame and the mount appear to be commonly available and faily cheap.
I am curious whether anyone has any experience attempting what seems like a potentially simple solution to this issue. It is my thinking that solutions are generally more effective when they can be applied directly to the problems causation. I haven't seen this discussed with any specificity. I am interested in other members viewpoints, opinions, experiences, or thoughts in general. I know that I will be making an attempt at some point to implement this idea.

 

[gggGary]

@Jim??? ;^)

 

[Jim]

@Jim??? ;^)

Conversation starts here.

 

[BluzPlayer]

Wow...
I usually scour about everything @Jim writes.
Obviously missed this one.
Very nice concept with that front mount.
Different approach as to what I have been considering, which is basically spacing the mount solid at the frame and the same space with rubber, or perhaps a poly at the motor. I don't think that the poly would dampen as well but could be longer lasting. I am thinking that I can apply that to the front, top, and rear mounts. The lower mount is another animal, but it is lower and I believe it would transfer the least vibration of the 4 mounts. There may be a workable solution for the lower bolt but if not I believe that a significant amount of vibration can be reduced by modifying the other three.
The article provided by @Skull in that thread is quite interesting and informative as well.
The mounting brackets may need to be modified or made to create the mounting I've been envisioning.
Then again Jim has opened my thoughts up with his approach.
After reading that as well as the article provided by skull I am confident that such a mod is feasible. Thanks for the link.
Exactly the kind of information I was hoping for.

 

[gggGary]

imho you can have (only one) bolted mount, my suggestion would be the lower rear. (furthest from the up and down piston shaking plane. That mount would act as a pivot for all the other mount's flexing.
A rephase is easier........... ;^)

 

[BluzPlayer]

Thanks Gary..
Yes I can follow that...
The distance from that plane.
I'm hopeful to be a point to test a few possibilities. The bike will be rephased.
The runout and balancing of the crank will be critical aspects as well obviously.
I will use other known countermeasures as well.

 

[grizld1]

Sure, you can move the vibes around with a rephase, but they'll still be there. If you want to do something affordable to actually reduce vibration, beam balance the rods and piston assemblies, assemble with <.016" big end side clearance, work the runout out of crank until you can't read any at the end journals, and tack weld the pins. The motor I did years ago with a local shop was very smooth. The crank I paid to have done at Crank Works is only better that average. If you don't have your own hands on the job you'll get whatever the shop's standard is, and that will conform to Mama Yama's book spec, which allows for up to .002" of runout. That's a whole lot of jumpin' around, and most factory cranks I've examined were wide of that mark.

I hope I'm wrong, but it looks to me that rubber mounting the engine is going to take a whole lot of frame redesign to get something both rigid enough and light enough for a satisfying ride.

 

[Jim]

imho you can have (only one) bolted mount, my suggestion would be the lower rear. (furthest from the up and down piston shaking plane. That mount would act as a pivot for all the other mount's flexing.
A rephase is easier........... ;^)

Don't think so. If you could, the Norton engineers and Tony Hall would have had a much easier lift of it. For starters, a single solid mount is gonna set up a fore and aft, and vertical rocking that can't be damped out without hydraulics (think shocks, forks etc...) because rubber is basically a spring. You could get into a pretty nasty elliptical coupling.... one that could turn out to be worse than the vibe we're trying to get rid of.

 

[Jim]

looks to me that rubber mounting the engine is going to take a whole lot of frame redesign to get something both rigid enough and light enough for a satisfying ride.

Yup. A highly modified XS frame can get you there. The unknown is how much of a porker will she be after all the mods.

 

[gggGary]

Norton swing arm rigidly bolts to engine cradle...............
shrug.

 

[Jim]

Norton swing arm rigidly bolts to engine cradle...............

.... and make up a complete assembly that's rubber isolated from the frame at all points.

There's a reason Norton (and Halco) made the swingarm rigid to the engine and not the frame.....
Consider a rigid swingarm pivot and a rubber mounted engine.... every time you twist the throttle, the rubber shifts... compresses one way and stretches the other. Think what that does to sprocket alignment. Their choice was to call out a 500 mile sprocket/chain replacement interval.... or figure out a way to keep the tranny and rear sprockets in alignment. Hard mounting the swingarm and engine together as a unit fixed that.... had nothing to do with vibration isolation.

 

[BluzPlayer]

Thanks for the input guys.
You are expanding my thoughts on this idea.
I appreciate the input Griz.
Yes indeed a rephase is only a piece of the equation. Although I am truly doing the rephase more for the sound and whatever vibration reduction will be a bonus. I do realize the importance of the balance within the rotating assy as well as the runout on the crank as being ultra critical aspects. I will be twisting the crank and doing the static balancing. I am in no rush and will work it until it is correct. It will be tigged.
But to the issue with the motor mounts...

It seems that the front mount can be attached solidly to the frame giving the added structural support required for the two down tubes, yet by moving each of the "triangles?" outward would create space between the motor side of the mount and the engine itself. That space would be filled with whatever dampening material (most likely rubber that is bushed) is decided on. It would isolate the engine at that point.

The rear mount could be modified similarly and perhaps more easily as it would merely need to be offset solidly against the frame and space created between the mount and motor filled with the dampening material...

The top mount would be done similarly as well although some modifications may need to be done.
Indeed all the mounts may need to be modified. I think that is possible without modifications to the frame.
This is simply an idea and thoughts I have on the subject and I most certainly have no definitive answers. If someone has thoughts or knowledge as to why this approach would not be effective I am hoping they will speak up.No intention here to be argumentative.
Simply trying to utilize the community's vast knowledge to find a path forward...

 

[gggGary]

"

.... and make up a complete assembly that's rubber isolated from the frame at all points.

There's a reason Norton (and Halco) made the swingarm rigid to the engine and not the frame.....
Consider a rigid swingarm pivot and a rubber mounted engine.... every time you twist the throttle, the rubber shifts... compresses one way and stretches the other. Think what that does to sprocket alignment. Their choice was to call out a 500 mile sprocket/chain replacement interval.... or figure out a way to keep the tranny and rear sprockets in alignment. Hard mounting the swingarm and engine together as a unit fixed that.... had nothing to do with vibration isolation.

Well then going with that you got a pretty complicated mount system to figger out.
Why I was suggesting a single rear pivot point (that just happens to line up with the swing arm pivot)......... as a reasonable compromise. But I'm not an engineer.

If the pivot point is far enough from the vibration source mainly pistons up and down it allows an effective up and down motion. Is the rear mount far enough to cover a lot of the up and down motion? Don't know.
A blow up of the rear mount from the yam-brit frame.
Kinda looks like the motor/swing arm support a short pair of "pivot arms", the frame hangs on those?
Seems like that would introduce it's own set of problems under braking acceleration forces.

Norton ran into cost constraints and didn't use an isolastic mount at the head frame junction, it affects the handling. There are now isolastic retrofits for that joint.
A major part of the (redesigned in 73 for easier adjustment) isolastic mounts was a way to keep side to side tolerance very tight to avoid a side to side wobble. First done with shims, later a vernier setting ring.
Too tight and vibration doesn't stop transferring until high RPM too lose and the handling suffers.
Harley did a rubber mount without the tight side tolerance, it was a disaster, one quietly swept under the rug.
lots to consider.
The rephase changes the orientation of the vibration from more or less straight up and down, to more of a side to side wobble.
Somewhere there's a nice animated vector diagram pic of the differences.
There's a reason many current vertical twins have gone to a 270 crank.............
And it's not just hugh... LOL

 

[BluzPlayer]

I agree gggGary.
Not going to be simple.
Although I will attempt to simplify it.
I will be able to return to the stock solid mounts should I meet with complete failure.
I will without question test the setup with different configurations. The rear solid makes some sense to me and will be in one of those configurations. I will be measuring the vibration as well as opposed to simply a seat of the pants testing. Obvious inspections on the mounts after each ride once I get there.
Jim's approach to problem with his front mount is an interesting idea as well particularly if combined with the the other mounts as I have described. It may well quell a different set of vibration dynamics.

 

[toglhot]

The long bolt at the bottom mount would be a sticking point without modification to the frame and that would be a fairly big job. These engines must be really badly balanced from the factory, mine shakes like crazy, much worse than I remember my BSA and Triumph 650s. I never found vibration on the Brit twins that uncomfortable, although one of my Triumphs did lose a cross brace from across the seat hoop. The bike was an OIF Triumph, as in gary's picture. The same bike had the crank electronically balanced back in the mid 70s, when I did finally get it on the road around 76/77, it ran very smoothly. I later had a 750 Triumph twin which also ran quite smoothly, despite the increase in capacity. One of the Brit twin designers actually considered 650cc as the max size for a 360 degree twin. Mind you, the early twins were balanced on knife edge straights, whilst the later models were electronically balanced. The Brit twins also had a fairly heavy flywheel in the middle of the crank, which helped, somewhat, to even out the vibrations. Unfortunately, balancing 360 degree twins is usually aimed at a specific RPM range, so while the engine may seem reasonably smooth at say 3k, elsewhere it will shake your marbles loose. I personally think a good balance job on the crank would at least make the XS sort of comfortable.

 

[fred nurk]

The long bolt at the bottom mount would be a sticking point without modification to the frame and that would be a fairly big job. These engines must be really badly balanced from the factory, mine shakes like crazy, much worse than I remember my BSA and Triumph 650s. I never found vibration on the Brit twins that uncomfortable, although one of my Triumphs did lose a cross brace from across the seat hoop. The bike was an OIF Triumph, as in gary's picture. The same bike had the crank electronically balanced back in the mid 70s, when I did finally get it on the road around 76/77, it ran very smoothly. I later had a 750 Triumph twin which also ran quite smoothly, despite the increase in capacity. One of the Brit twin designers actually considered 650cc as the max size for a 360 degree twin. Mind you, the early twins were balanced on knife edge straights, whilst the later models were electronically balanced. The Brit twins also had a fairly heavy flywheel in the middle of the crank, which helped, somewhat, to even out the vibrations. Unfortunately, balancing 360 degree twins is usually aimed at a specific RPM range, so while the engine may seem reasonably smooth at say 3k, elsewhere it will shake your marbles loose. I personally think a good balance job on the crank would at least make the XS sort of comfortable.

what happend to the set of carbys you were going to sell to me.

 

[Raymond]

It's an interesting engineering problem which many people have tried to solve in different ways. The problem Norton ran into with the Commando was it didn't handle as well as the earlier Featherbed bikes, hence expensive solutions like the Vernier adjustment. The story there runs out, like a stream into desert sand - the company went bust and the alleged problems have been blamed on owners not knowing how to set up the adjustable isolastic mounts. (Yes, Norton Commandos are being built now but they are different beasts which I know SFA about.)

Eric Buell had a go at the problem with a rubber mounted Sportster engine. I've owned & ridden three Buell X1s, at which point I always say some people never learn. He succeeded in making the Sportster engine go like stink and the handling was superb but the plot vibrated like . . . I don't think we're supposed to say that these days. But let's say after a medium to long run your vision was blurred and your gentleman parts were numb. Rest assured, sensation returns in time.

Good luck with your venture, BluzPlayer!

 

[gggGary]

A comparison of vibration vectors 360 - 270 in the vertical plane can be found here;
http://old.xs650.org.au/Technical Info/rephase angle.htm
more reading on crank configurations and balance. http://old.xs650.org.au/Technical Info/vtwin.html
Jim I'll visit the point again. Having one engine mount at the rear act as a pivot creating an arm with roughly a foot of length from the piston centerline how much vertical movement of the motor mass are we talking about? the curve of an arc at the end of a 1 foot arm with a 1/4" oscillation would be what? a couple thousandths? @TwoManyXS1Bs math skills needed here..........
riffing from whole cloth; a desmodromic front mount that requires the motor to move up and down in relation to the frame at crankshaft speed?

 

[takehikes]

If you know anything about motorcycles then you know old vertical twins shake. Big whoop. It’s solid and decently reliable.
I’ll take it over shake and fail too in an old bike (I’m looking at you HD).

 

[Jim]

Only way to know for sure Gary is to try it. Not having any historical examples of a configuration like that seems pretty telling to me though.
I can't imagine Norton came lightly to the decision of cradling the swingarm pivot in rubber and then having to work backwards through the R&D of a rear end that moved around like a noodle..... when all they had to do in the first place was hard mount the rear of the engine.