Well, that's weird

Guzzis.

As I've been assembling the V11 engine I have had to make sure that
the flywheel was properly aligned on the crank so that the timing
marks are positioned correctly.

Now, both my Guzzi flywheels have three timing marks: an arrow; an 'S'
and a 'D'. I always thought these were: full ignition advance on one
cylinder; left TDC and right TDC respectively. The Guzzi manuals don't
actually call these marks TDC marks, however, the Moto Guzzi Twins
Restoration book does. Diagrams for the older Guzzis show S & D strobe
marks for various amounts of ignition advance, so I guess they must be
90deg apart for the two cylinders.

Except...

As a final sanity check, I turned the assembled crank so that the S &
D marks aligned approximately against where the reference mark would
be if the gearbox were fitted. For each mark, I looked down the
cylinder bores to check the position of the big end journal. Upon
checking the LH cylinder mark I thought "Huh?" and double-checked the
marks. And a third time.

I've found that the 'S' & 'D' marks o the V11 flywheel are about (at a
guess) 155deg apart. It's a 90deg Vee twin engine. Only one mark
matched a TDC, and that's the 'D' mark.

As all the marks are on the same bit of metal - the flywheel itself -
and I took care to put paint blobs on the crank & flywheel before I
dismantled them to ensure I assembled them correctly, I'm sore
confused. This doesn't actually affect engine operation; there are no
sensors that trigger off the flywheel, unlike a Quota's engine, but it
is a mystery as to what the marks actually mean.

 

Are you sure you're not getting confused between the angle of the
cylinders & the angle between the rods? 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.

'D' (dextrous) should indeed be TDC for the right cylinder, & 'S'
(sinister) TDC for the left. If they don't match the TDCs according to
the journals, I'd suggest you need to check again with a clear head.

 

I've got a nold T3 HBoL to hand, and it describes the timing marks on
the flywheel as S for the LH cylinder and D for the RH cylinder -
which makes me think they mean "sinistra" and "destra". Maybe your
flywheel is twisted...

 

Quite sure. As I said in my OP, I was looking at the big end journals,
not the rods. In fact, the rods weren't even fitted when I first
checked. Also, if I mark the ring gear by the S mark and again by the
D mark and look at the flywheel from the end, they are clearly not
90deg apart. As a further check, there are eight evenly-spaced bolts
that hold the flywheel assembly together, so 45 degrees between bolts.
One mark is close to a bolt, the other is midway between two.

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.

I did also consider that there might be some illusion caused by a
desaxe offset, but again, if both cylinders are to have the same
timing, the timing marks on the flywheel would be the same.

 

Heh. Or maybe one of the timing marks was mis-stamped, or maybe they
aren't both used as TDC marks on the FI motors. This is a possibility
because they only have the one common timing system.

For the purposes of doing valve clearances, I've painted an extra mark
on the flywheel.

I also can check against the Quota when I find a tuit. All I need to
do is remove the alternator cover and turn the engine by spanner to
check the marks on that - it should be pretty obvious.

 

<Nods>

I did that on my Guzzis, back in the day.

 

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].

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 don't actually know what a V-twin is, do you?

 

<points at sig>

 

It would seem so from you've posted. I don't know Guzzi engines though
so didn't know that.

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.

 

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.

 

Ah, that's probably what my feeble memory was on about. The name
'twingle' certainly rings a bell.

 

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.

 

That was what I thought.

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.

 

Wouldn't that put the sprocket on the wrong side of the engine?

<fx: D,R&H>