Well, that's weird
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From: Krusty on 30 Jul 2010 07:29 Mark Olson wrote: > Krusty 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]. > > Surely there's 0 degrees between the big ends, because they're on > the same journal? It would seem so from you've posted. I don't know Guzzi engines though so didn't know that. > > So saying "the flywheel marks are about 155deg apart. It's a 90deg > > Vee twin engine." doesn't really mean much to anyone who doesn't > > know Guzzi engines as the two don't have to be related. If that > > translates to "the flywheel marks are about 155deg apart. The big > > end journals are 90deg apart." then yes, something sounds a bit > > 'wrong'. Probably a drunken Italian going mad with the stamp on a > > Friday afternoon... > > 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. -- Krusty Raptor 1000 MV 750 Senna Tiger 955i Tiger 885 Fantic Hiro 250
From: Eiron on 30 Jul 2010 08:10 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. -- Eiron.
From: Krusty on 30 Jul 2010 08:29 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. -- Krusty Raptor 1000 MV 750 Senna Tiger 955i Tiger 885 Fantic Hiro 250
From: Mark Olson on 30 Jul 2010 08:46 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
From: Eiron on 30 Jul 2010 09:03
On 30/07/2010 13:46, 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 You can do that in 5 minutes on a Ducati with wasted spark ignition. Just turn one camshaft 180 degrees and refit the cambelt. Although the standard firing interval on a slow-revving V-twin gives the tyre enough time to regain traction and make a cup uf tea. -- Eiron. |