I've mentioned this in a couple of other posts, but it prompted little discussion. Either I'm the only one who's interested or it deserves its own thread.
Check out this post from the board archives...
http://ridersofvision.net/rovforum/index.php?topic=7779.msg71403#msg71403 (http://ridersofvision.net/rovforum/index.php?topic=7779.msg71403#msg71403)
I was going to do this later but since I was doing the shims anyway and had messed up my cam timing no time like the present so I've done the small amount of work required but have some wiring to do yet before I can fire it up.
Apparently it's a common mod for hill climbers and flat tracers as it improved torque immensely, though at some expense to the top end where I never go anyway
People do side by sides as well. They also make side by sides fire 90 degrees out to give it a V twin sound and power delivery but that means messing with the crank and custom cams.
I've seen nothing negative from people who have actually done it. A few armchair wankers saying it will do in your big ends, clutch, rip tyres apart, cause teenage pregnancies etc. (Actually that last one might be true :-) )
All I've done is invert the cam so the front and rear fire in the same crankshaft rotation rather than opposite ones so firing will be 70 / 650 degrees rather than 290 / 430. The bike is wasted spark with sensors for each cylinders and individual carburetors already so all that can remain without change.
As far as I can see it creates NO balance issues as balancing is typically only for the reciprocating mass of the piston, and this does not change. It must be this way on the XZ because cog on the crank and the bancer both have 45 teeth - the balancer goes round with the crank, not with the cams. So yes vibrations (from explosions) will double, but they will be half as often, so the Root Mean Squared (RMS) vibration should be identical.
You can see from the picture the sound would be quite different. At 1200 idle it should sound almost like it's doing 600RPM (10Hz) - That's the frequency they use to give you the shits in horror films. :-) apparently long term exposure to 18hz can cause hallucinations so I'd best be careful At open road speeds it should be quite relaxing.
It's only a few hours to undo it, so assuming it hasn't done in the big end, no harm in trying.
The nice thing is that RMS power should be the same, though delivered differently so it has a different effect on road holding – more controlled rear wheel breakaway apparently - not that I care much about this as I'm not usually riding anywhere near the limits, but interesting that no-one I found says it makes things worse. After a couple of incidents I tend to over compensate but if this gives advance warning of breakaway it might change my riding habits a bit :-).
Adhesion is not really the primary reason for doing it. I'm much more interested in the torque change – it should feel gruntier, and the sound change - it should sound gruntier, and the mod factor – I like having mods just for the sake of them. Of all the possible benefits, only that last one is guaranteed till I've actually got the machine going again.
Any thoughts on this?
I've talked with POD about some of this so I'll keep this (relatively!) short. ;) Actually, the 2007 forum discussion I was unaware of until just now. Thanks for the link, I'm definitely going back to study that more... :)
I like how (relatively) easily achievable and reversible this seems to be. I'm glad POD has the time and inclination to investigate as I'm really anxious to hear a report. I'm particularly interested in torque delivery differences but hadn't considered engine note much. But since you mentioned that I'm curious to know how that's changed too.
Any thoughts re: less/more strain on the starter motor and clutch? Is the close interval firing purportedly detrimental to rod journal bearings?
So how far off is the maiden voyage?
So reading the '07 post it seems treedragon rode one and thought it a torque monster. He also claimed it felt stronger up top although some have theorized lower top end performance. This was all seat of the pants dyno so that could be a thing.... :)
Superfly claims to have altered his but then went back to stock. Treedragon expressed a desire to alter his but I'm guessing ended up not? Any further info on why to either?
This is fascinating stuff. I haven't got my head around the theory and what has actually got to happen to make the mods but would love to see the documentation and results. Should it just be a matter of rotating the cam sprocket so that both cylinders are on an intake cycle at the same time?
I used to ride a Panther 600 sloper single back in the UK. The prospect of a twumper from a v twin really fires up my imagination.
Quote from: pinholenz on January 06, 2014, 05:25:22 AM
I used to ride a Panther 600 sloper single back in the UK. The prospect of a twumper from a v twin really fires up my imagination.
Mmmmm, you wish you still had that I bet. I just found a 1926 Matchless engine I want to build bike around (after the Vision is finished)
I don't know why Superfly went back to stock. Unfortunately he's long gone from the forums.
Good thinking about the starter and clutch...
Both power strokes are overlapping so would expect some extra stresses there. If it slips, then perhaps some heavy duty springs and new plates would be advisable.
As for starter, the compression strokes will be overlapping also. Not much to be done about that except perhaps a freshly rebuilt starter, high CCA battery and good cabling. All of which I've done already
I'm still a fair way off running, but I'm all over excited about this and tempted to crack the 400 open and twingle it as well except at the moment I can't get the stupid thing going.
@ pinhole
Careful study of the picture in my earlier post should help visualise it. The pic is split into two sections, what happens to each cylinder now, and what happens when twingled.
In stock form, our bikes fire one cylinder per crank rotation, but 70 degrees apart. so while one is on a power stroke, the other is on an intake stroke. This leads to a slightly lopsided but largely even bang (290) bang (430) bang (290) bang (430)
The crank makes the piston go up and down, but on the vision the ONLY thing that determines if a piston going Upwards is on a compression or exhaust stroke or a piston going downwards is on a intake or power stroke is the orientation of the cams. Fuel delivery and spark happen the same either way. It's just that the (wasted) spark has no effect on a cylinder not primed with fuel.
By re-orienting the cams on one cylinder, you can make what was the intake stroke the power stroke, what was the exhaust stroke the compression stroke etc.
We do this by popping one of the cylinder valve adjustment cover off, releasing the cam tensioner, and re-positioning the cams so they are where they would normally be exactly one crank rotation later. That's all there is to it. It takes less time than doing shims - mostly the process of juggling with radiator, removing valve cover etc is identical. Realigning the cams against the marks can be a little tricky but fuzzlewump wrote a great tutorial a week or so in the "Shimming Woes" thread about cam alignment.
By firing very close together, the sound will be quite different as the crank will rotate 650 degrees after the rear fires before the front fires again.
Bang(70)Bang(650) Bang(70)Bang (650)
The effect of this is that the bangs will be (almost) twice as loud, (almost) twice as powerful, but (almost) half as often. It should sound a bit like an old slow single, yet still maintain most or all of the power as that is largely a function of the size of the explosions rather than when they happen.
I must be missing something.... As I look at the schematic, it would appear either front or rear could be altered to achieve the pulses 70 apart followed by the long 650 degree pause. I'm going back to the diagram for more investigation.... :)
Quote from: ProphetOfDoom on January 06, 2014, 06:10:29 AM
Good thinking about the starter and clutch...
Both power strokes are overlapping so would expect some extra stresses there. If it slips, then perhaps some heavy duty springs and new plates would be advisable.
As for starter, the compression strokes will be overlapping also. Not much to be done about that except perhaps a freshly rebuilt starter, high CCA battery and good cabling. All of which I've done already
Actually I was referring to the starter and
it's clutch, not the drive clutch so good point about the HD springs and plates if needed. :) Maybe heavier springs in the sprag if need be?
If I remember correctly, the close firing order was done to improve traction by spreading the power pulses at the expense of maximum power. I suspect that on the Vision it will make a different exhaust tone and increase vibration. The balancer is set up for the standard timing.
@ Rikugun
Yes you are right of course. Either way would have the same effect. I'll edit my last post.
Unlike the drive clutch, I don't think the starter clutch uses spring force to enhance grip, so much as to position the rollers so they wedge into place. They are pathetic little springs. Perhaps roughing up the surfaces for additional metal on metal grip ????
@Walt
The balancer on the Vision as far as I can tell rotates once for each crank rotation (both gears have 45 teeth). It can't be set up differently for power and intake strokes.
Could stronger sprag clutch springs enhance starter clutch grip? Mine sometimes slips a little when cranking.
Corrections - I misidentified the starter clutch as a "sprag" when it is actually a trapped roller type. I also overemphasized the importance of the springs.
If the springs aren't use shortened or bent they apparently are deemed serviceable. If the rollers aren't being kept in contact with the hub and ramps it may not be the springs fault. Gouging of the flywheel or sheet metal cover may impede roller movement. While a stiffer spring may help compensate for the added resistance, the spring wasn't the culprit. Galling on the rollers and hub surface also may contribute to the clutch not holding under load. Start attempts with a less than fully charged battery may also cause a weak clutch to slip. A load beyond the design parameters may also. This last one may apply with the close firing cam timing.
Apparently the 2007 referenced bikes started OK. No mention was made of any problems anyway.... I guess I was just wondering aloud if both cylinders' compression strokes now overlapping to some degree would cause a weak starter clutch to fail or shorten the life of an otherwise healthy clutch.
I think there will be more strain on the electric starter and battery rather than the starter clutch. But, maybe we will see, is anyone gets their XZ sorted for long bang. Remember that the same starter clutch is fitted to the V-Max and other rather large Yamahas.
Quote from: fret nut on January 08, 2014, 01:02:08 AM
Remember that the same starter clutch is fitted to the V-Max and other rather large Yamahas.
I do remember that but am unsure if they suffer the same failure rate on those other models?
Here is an excerpt from "Motorcycle Tuning - Four Stroke" by John Robinson.
"...the V motors, especially those with two crankshafts, make it easy to get pretty well any firing interval at all, and when the intervals were made unequal - one short, one long, the so-called big bang engines- the riders found they got better, more controllable drive out of corners. The penalty was more severe loading in the driveline, with gear and primary drive failure becoming more common."
Don't think the "drive out of corners" concerns us as he was referring to 500cc GP and flat track bikes, but the "more severe loading.....and failure" might be a worry for longevity of bike.
First time I read this book most didn't sink in, but the more I read on forums, the more points I pick out of books that have relevance. All helps my lazy beer swilled brain to learn. ???
Failure of gears and drive lines would be expected to be more common in racing machines due to the extreme sort of function they are subjected to. Can you imagine the loading of the surfaces during high RPM racing conditions? Usually our street machines don't get treatment that harsh, not on purpose anyway, so, I don't think that is a major concern for street bikes.
The modified XZ referenced in the 2007 thread linked earlier had purportedly been in the modified state for as long as a decade or more at the time the post was made. If this is true, it speaks to longevity for that particular example.
Moto GP prepped bikes would have far greater stressed engine and driveline components. I can certainly expect there would be failures of any new configuration going through development. Were there V configured twin crank 4 stroke GP bikes or is the author referring to two strokes?
Yes the author was referring to two strokes in that case I think. Thanks guys for your replies, that makes sense to me.
Quote from: Rikugun on January 08, 2014, 11:14:55 AM
Quote from: fret nut on January 08, 2014, 01:02:08 AM
Remember that the same starter clutch is fitted to the V-Max and other rather large Yamahas.
I do remember that but am unsure if they suffer the same failure rate on those other models?
starter clutch...on the venture and vmax is the same in the early 80's. But the v-4 engine fires more often...thus the clutch actual receives less ABUSE. simply a v-4 starts easier than a v-2
So I've got my twingled engine running...
Certainly it didn't seem particularly harder to start, and it idles pretty much the same.
I was expecting it to sound a whole lot slower - but it doesn't so much. It does have a bit more of a bark and I think with a more open pipe like my predators it would sound better still. I have to remind myself this is the 400 which is a fair bit quieter than the 550
Road test coming soon. I need to synced and set the mixtures but I don't think the setting is that far off.
I know you'll be wanting pictures so here is...
http://youtu.be/sVCuii3Vti0 (http://youtu.be/sVCuii3Vti0)
We'll be waiting to hear if there is a benefit to the change in firing. You might have to go power sliding in the dirt to find out.
hmm, I think I expected it to sound different. Or more different than it does? Is the "Starting the XZ400" clip in the stock firing configuration? They are idling at different speeds in the two clips which doesn't help the comparison but I'll listen a few more times. Did changing firing pulses change idle sync?
How did you resolve the weak spark gremlin? Is this the same TCI as in the December '13 clip?
Never mid, just read the CHECKLIST post... So new question then - does this mean the other TCI's you tried may be good after all?
Yes, that first clip was stock cam timing. In my head it was going to sound like an SR500. It doesn't.
I was having starting & overflow issues so the carbs were stripped (again) between times and the floats reset. It's impossible to say what effect twingling has on sync and mixtures. The twingled video is with mixtures at 3.0/3.0 turns and sync set by eye. I'll shoot another shortly once I get it adjusted
Good thought on the TCI - I've fished it out of the waste bin
Wahoo, that's brilliant! When you get a moment can you write the mod. up in idiot proof language so that others can have a go?
Good to hear the 400 is running. Does that mean you have to give the flying Citroen back? Or maybe trade it in for this crazy car built by another Kiwi that I discovered while listening to your Youtube clip. Slightly OT, but his next project isn't
http://www.youtube.com/watch?v=UexiOL8I_3Y
Not so brilliant, today it won't start. However it's dipping below 10V on cranking so I've got the battery charging overnight. I can't say I'm sold on this new Motobatt - It holds a charge well, and keeps cranking longer, but at a reduced voltage unless fairly freshly charged.
@ pinhole All you are doing is holding both cams on 1 cylinder still while you rotate the crank 360 degrees (one full turn). That's it.
Have another read of post #5 on this thread. Ask any Questions and I'll try and answer
I'm not giving the flying Citroen back, but I'll flog the 400 off on Trademe as soon as I can get it to start and go down the hill and back up a few days in a row. That hotrod guy sounds like Sam Hunt
Quote from: ProphetOfDoom on February 07, 2014, 03:03:26 PM
@ pinhole All you are doing is holding both cams on 1 cylinder still while you rotate the crank 360 degrees (one full turn). That's it.
Have another read of post #5 on this thread. Ask any Questions and I'll try and answer
I realize this is a simplistic description to get the point across but... Make sure where you are holding the cams, the valves aren't open as there may be piston interference as you turn the engine over 1 revolution. Starting the process at TDC compression for the cylinder being altered might be a good idea.
If you don't want to jiggle the chain around the sprockets as you slowly advance the crank a revolution, start with either cylinder at TDC
EXHAUST stroke. Loosen cam chain tension a bit on that cylinder and carefully remove the cams. There will be a bit of pressure on the valve springs so loosen the cam cap bolts incrementally. If you had thought to measure valve lash prior, now would be a good time to exchange shims. ;)
Leave the crank where it is and reinstall the cams except now oriented for
COMPRESSION stroke per the manual instructions, cam and sprocket reference marks etc. The cams will install easier as all the valves are closed at TDC compression so there is no spring pressure to deal with.
QuoteThat hotrod guy sounds like Sam Hunt
That show has some interesting episodes. Anyone into Pro Touring cars may enjoy this episode filmed in my home town.
http://www.youtube.com/watch?v=0Gaewg3RepU (http://www.youtube.com/watch?v=0Gaewg3RepU)
I have to say, the sound change is really noticeable now that I've dropped the engine down to 1000 RPM.
Road test soon
PoD......when you did this twingle thing, did you also turn around the sprockets on the ends of the camshafts?
For example (assuming you did it on the front cylinder) in stead of the front cyl sprockets having an 'F' facing outwards, did you end up with the 'R' facing outwards?