Vibs from Gen?

[iamdouglas1]

So, I'm sitting here starring at my '69 'CH engine and pondering upon a ponderable point.

My observation is (sit tight now, this may strain a brain the generator is what... 12 or 15 pounds? And it sits on a moment arm of about 4 inches off the mounting flange of the cases. Can that unsupported weight add harmonic resonances to the engine/frame? I've never heard of cases cracking around the generator mounting area of the engine cases but that doesn't say that harmonics are not being fed into the motorcycle.

I'm thinking that if there was a way of adding weight strategically then the generator itself could be tuned to cancel engine vibration.

What do you think Sirs? 

[garyajaz]

an ironhead vibrating?
surely you jest sir.

[Ohio HD]

an ironhead vibrating?
surely you jest sir.

         

[iamdouglas1]

Hey Gary,

I remember in some early H-D sales brochure the wordsmith worded in as positive terms as possible, the v-twin naturally feeds the engine vibration into the road due to the flywheels rotating the same direction as the wheels. a stretch huh?

[rigidthumper]

In order to counterbalance engine vibrations, the RPM of the generator with heavy offset weights would have to match the crankshaft RPM- not sure how effective the generator would be as a charging unit at that point- and the offset weights would crack the current mounting points pretty quickly.

[iamdouglas1]

Hey there rigid,
I'm not sure what you say is the whole picture. I think it's the resonant frequency of the gen vibs and that would be independant of engine vibs. Like rotating counter balancers on some engines. They're "tuned" to vibrate in happy relationship to the engine imbalance.

not sure though. I've been wrong before

[garyajaz]

ask any of my ex'es
they all loved the vibration.
got a shovel and it was so smooth they did not get pre wet.

really though, if vibration is a problem just stroke it.
the cranks, rods pistons and stuff are balanced.
my 80 incher is smoother than it was stock.

[rigidthumper]

" They're "tuned" to vibrate in happy relationship to the engine imbalance."
Yes, and they are also timed to the crankshaft, so when the crank is heavy in one direction, the counter balancer is heavy in a different direction, to offset/quell  the vibes. Counter balancers are also very heavy, and supported on both ends by big bearings.  Like 3-4 pounds each.  Generators are fairly well balanced internally, so they don't break mounts- imagine adding 3-4 offset pounds to the end of the shaft, then rotating it at a thousand RPM?

[iamdouglas1]

I think I know what you mean about your ex'es Gary. . . when I told my wife this idea of a 4 inch moment arm being large enough to do the "work". She laughed. She says for years I've been trying to convince her that 4 inches is more than enough.   

[iamdouglas1]

Rigid, what I'm suggesting is the gen will respond to the flywheel's imbalance by resonating and like you said relates to the engines vibs. that resonance is what I'm talking about tuning by finding the weight which will counter the engines vibs when mounted to the end of the generator.

I'm talking theoretical not knowing numbers. I'm just looking at the idea. I'm thinking in theory that it should work to some degree?

[iamdouglas1]

. . . and Rigid. . .
I started thinking about this as wondering if the gen might resonate or buzz feeding vibs into the bike.
I was kind of playing by suggesting it could actually smooth the engine vibs.

I was just wondering if the gen buzzes and how to quell that.

[JW113]

Convert it to an alternator, and save 10 pounds or more.

-JW

[iamdouglas1]

Hello again JW,
I've thought about an alternator. I'd have to rig a small battery to excite the field coils of the alt. but it is an option. An alternator might fix the dimming headlight issue at idle for the XLCH.

I wonder what the smallest battery I can use to excite that alternator. hmmm?

[JW113]

If you have pile of money laying around, check out those lithium ion motorcycle batteries. They don't come any smaller and lighter than that I think.

I have an alternator conversion on my chopper. Works very well, have to say. As the whole body of it sits there and spins, give the motor kind of a farm implement quality. I had put a yin-yang sticker on the end of it, looked cool but eventually fell off.

-JW

[farmall]

Some permanent magnet modified Kubota alternator conversions exist which have the aforementioned "spinning body".  I found one at the swap meet but have not run it yet. Nice short little unit.

Here's a pic of what they look like.  http://xlforum.net/vbportal/forums/showthread.php?t=599461

Later alternator Ironheads vibrate too. I'd forget the generator as an important vibe source.

If you want modern smoothness, get a different motorcycle or do some epic chopperdom and rubber mount the engine in a custom frame. Not all rubber mount conversions have to be 100-percent "rubber".  I emailed this gent about his big twin engine conversion and he uses a bronze-bushed rear pivot (which could be fabbed to bolt to a stock Ironhead rear mount) and controls the other mount points in the usual manner with rubber mounts and Heim jointed rod ends. "Isolastic" mounting worked for Norton and later for Harley on big twins (they shared some design personnel like John Favill) so it's thoroughly proven.

https://www.youtube.com/watch?v=rag_xU9FCg4

I don't see it as being worth the hassle vs trying to isolate the rider from vibes, but I don't bother with that much either. It's an Ironhead. They vibrate. Trying to make them not vibe without a mounting change is what the Brits refer to as a snipe hunt.

I have an old wishbone swingarm Berdoo Choppers frame (or at least that's who it came from when I ordered it in the 1980s) that has ample room for a front and rubber mount conversion if you modded the rear mount.  Front frame mount (wandered off somewhere) is a horizontal plate welded to two vertical mount plates. I'm going to use it again but you can still order wishbone style Ironhead frames IIRC.