Strange timing observation

[memper]

I am under the impression that when at TDC the view in the window has the pointer, the hash mark, and one of the dots all in a line and the center belt pulley's dot is lined up with the hash mark on the engine case.

When I use the dot on the center pulley as my starting point and line it up, the markers in the window are not in line. The pointer and the one dot are in line but the hash mark is a bit to one side of the pointer. To the left maybe 1/4" if I recall correctly.

Has the PO advanced or retarded the timing?
I checked this a couple of times to be sure.

[brad black]

there should be a dot on the flywheel (well, 3, full adv, idle adv, tdc), but the marks on the alt rotor are irrelevant.  also, lining up the dot on the timing shaft at the pullies will not have you accurately located in the lh window.

[memper]

So then what's the point of having the dot on the timing shaft at the pulley? From what I have read there are many folks who do not look in the lh window and just use the dot/markings on the pulleys. Seems misleading.

So in other words, what you are saying is find TDC to the timing marks in the window (as illustrated on Ducati Suite) and physical indication (ie. a dowel touching the cylinder) as my markers of true TDC and don't worry so much about the center pulley?

[Speeddog]

Depends what you're doing.

If you're installing cam belts, the markers on the pulleys are the way to go.

If you're checking ignition timing, the dots and pointer in the window are your only data.

If you're timing the cams, then you've got a degree wheel on the end of the crank, indexed to physical TDC of a piston.

[memper]

I just assumed the dots on the pulleys were there to give the right side of the bike some sort of TDC indication when doing a belt change.

[brad black]

I just assumed the dots on the pulleys were there to give the right side of the bike some sort of TDC indication when doing a belt change.

that's correct, and within the accuracy of one tooth (40 degrees crank rotation) it's obvious.

what are you trying to do?

[memper]

Just simply understand an observation. Thats all. I just noticed that the window TDC was not matching the pulley TDC. But it seems that the pulley being "off" a tooth is normal.

[brad black]

if you look at the flywheel, you have a small dot on the flywheel and a pointer on the alt cover in the sight glass.  the flywheel is around 150mm diameter and it's quite easy to be accurate.

if you look at the pulley you have a dot and a line cast into the primary drive cover and the pulley is around 50mm diameter, so you have a 1/3 less accuracy on less accurate marks.

but it shouldn't be a tooth off.  make sure you have the right marks in the flywheel window.

i have a 98 or 99 m750 on the bench, i'll try to remember to look later when i do belts on it.

[memper]

if you look at the pulley you have a dot and a line cast into the primary drive cover and the pulley is around 50mm diameter, so you have a 1/3 less accuracy on less accurate marks.

This is probably the case and likely due to the nut that sits between the bars and the taillight.

[ducpainter]

This is probably the case and likely due to the nut that sits between the bars and the taillight.

Loose nut behind the wheel is often the issue...