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From: Krusty on 30 Jul 2010 09:05 Mark Olson wrote: > Krusty wrote: > > Eiron wrote: > > > > > On 30/07/2010 12:29, Krusty wrote: > > > > > > > > You appear to be talking about Vee engines that have > > > > > split/offset crankpins similar to what Honda does with their > > > > > narrow angle twins in order to give them 90 degree firing > > > > > intervals. > > > > Harley flat-trackers used to have something similar too. > > > You got any references for that? It seems like a pointless > > > exercise. > > > > No references to hand, it's just something filed in my brain from > > somewhere. The point is to make the cylinders fire more closely > > together so there's more time for the tyre to regain traction. Same > > as the GP big bang engines. > > I'd be quite surprised if any of their flat-trackers deviated from > the knife-and-fork conrod design but I'm not au fait with all things > Harley by any means. I think firing the cylinders one right after > the other 0/45/720/765 etc rather than 0/405/720/1125 would give the > desired big-bang effect. > > In fact that appears to be exactly what was done with the XR750, no > offset crankpins employed, just changing the cam & ignition timing > so both cylinders fire 45 degrees apart instead of 405 degrees > apart. > > http://en.wikipedia.org/wiki/Big-bang_firing_order#V_twins Ah, that's probably what my feeble memory was on about. The name 'twingle' certainly rings a bell. -- Krusty Raptor 1000 MV 750 Senna Tiger 955i Tiger 885 Fantic Hiro 250
From: Mark Olson on 30 Jul 2010 09:19 Krusty wrote: > Mark Olson wrote: >> http://en.wikipedia.org/wiki/Big-bang_firing_order#V_twins > > Ah, that's probably what my feeble memory was on about. The name > 'twingle' certainly rings a bell. Pah, the twingles they are talking about are just conventional 360 degree twins that fire both cylinders at the same time. This is the _real_ twingle: http://home.sprynet.com/~inniss/sears.htm OIC, the Wikipedia page does has a link to the Puch smoker twingle as well. http://en.wikipedia.org/wiki/Split-single
From: Pip Luscher on 30 Jul 2010 13:33 On Fri, 30 Jul 2010 09:14:44 +0000 (UTC), "Krusty" <dontwantany(a)nowhere.invalid> wrote: >Pip Luscher wrote: > >> On Thu, 29 Jul 2010 08:07:53 +0000 (UTC), "Krusty" >> <dontwantany(a)nowhere.invalid> wrote: >> >> > The fact that it's a 90deg >> > V-twin has no bearing on the angle between the timing marks, so I'm >> > not sure why you mention that. >> >> I'll explain: on older engines with points, the left & right cylinder >> timing can be checked individually and the engines thus have >> individual timing marks for each cylinder. These marks must be at >> 90deg to each other otherwise one cylinder would have different >> ignition timing to the other. > >Sure, if the crank turns 90 or 270 deg between firing. The point I was >(badly) trying to make is that just because there's 90deg between the >pots doesn't necessarily mean there's 90deg between the big end >journals (& therefore the timing marks)[1]. Well, as Mark has pointed out, the overwhelming majority of V-twins (including the TL motor in you Raptor) have a single-throw crank with a double-width crank journal. Also, as has been implied above, conventional 90deg Vees are inherently balanced (more-or-less) against vibration from both linear piston movement and angular acceleration due to piston acceleration, though if you ride a Guzzi V11 you might not believe this. -- -Pip
From: Pip Luscher on 30 Jul 2010 13:39 On Fri, 30 Jul 2010 07:46:40 -0500, Mark Olson <olsonm(a)tiny.invalid> wrote: >I'd be quite surprised if any of their flat-trackers deviated from >the knife-and-fork conrod design but I'm not au fait with all things >Harley by any means. I think firing the cylinders one right after >the other 0/45/720/765 etc rather than 0/405/720/1125 would give the >desired big-bang effect. That was what I thought. >In fact that appears to be exactly what was done with the XR750, no >offset crankpins employed, just changing the cam & ignition timing >so both cylinders fire 45 degrees apart instead of 405 degrees >apart. > >http://en.wikipedia.org/wiki/Big-bang_firing_order#V_twins According to my 'buying Harleys book'[1], they also had to reduce the standard motor stroke to conform to the 750cc limit and fitted ballraces instead of rollers, which apparently reduces friction, something else I didn't know. [1] No, this isn't a 'coming out' post. My dad bought me this: he guessed that they weren't my sort of bike but thought I might be interested anyway. I think it was a bargain purchase. -- -Pip
From: Pip Luscher on 30 Jul 2010 13:40
On Fri, 30 Jul 2010 14:03:15 +0100, Eiron <E1ron(a)hotmail.com> wrote: >On 30/07/2010 13:46, Mark Olson wrote: >> I'd be quite surprised if any of their flat-trackers deviated from >> the knife-and-fork conrod design but I'm not au fait with all things >> Harley by any means. I think firing the cylinders one right after >> the other 0/45/720/765 etc rather than 0/405/720/1125 would give the >> desired big-bang effect. >> >> In fact that appears to be exactly what was done with the XR750, no >> offset crankpins employed, just changing the cam & ignition timing >> so both cylinders fire 45 degrees apart instead of 405 degrees >> apart. >> >> http://en.wikipedia.org/wiki/Big-bang_firing_order#V_twins > >You can do that in 5 minutes on a Ducati with wasted spark ignition. >Just turn one camshaft 180 degrees and refit the cambelt. Wouldn't that put the sprocket on the wrong side of the engine? <fx: D,R&H> -- -Pip |