'00 M750 Motor Making Most Unpleasant Noises

[Raziel]

Line up the layshaft mark on the case and see if the cam pulleys line up with their respective marks. Crank position is automagically in the right place. It is designed that way.

They did line up, which you can extrapolate from the pics above, and apparently they can be returned to that position without fear of being off by one rotation on any of the three pulleys. Gotcha.

Which can only mean that one full revolution of the layshaft/pulley equals four strokes/one full cycle for both cylinders. EDIT: The following is flat-out wrong, for anyone playing the home version. Since the layshaft tick mark indicates true TDC for one of the two cylinders (likely the rear vertical) then only two positions of the layshaft/crank should allow unrestricted movement of the valves by turning their respective cam pulleys -- those being 90 and 270 degrees. At zero and 180 degrees, both cylinders are at TDC: one compressing, one exhausting, and either or both will limit valve and thereby cam pulley travel.

Think I got it, but someone please correct me if I don't. Tomorrow I will align the ticks again and fire her up after confirming free pulley travel at those positions. But not until I've looked into this...

as far as a quick thing you could check to see if the flywheel nut is loose, don't ask me why, but the clutch pushrod is usually broken, sheared in one spot into two pieces.  Something to do with increased vibrations or some other magic thing, but it's a good sign that's super easy to check without having to tear open the side casecover...

That's a brilliant tip, I will have a look! Thanks.

[ducpainter]

The two cylinders are not at tdc at the same time.

If the marks line up forget about that being the problem.

Look elsewhere.

[Raziel]

Please illustrate. A simple explanation of what transpires during a full revolution of the layshaft would suffice.

[ducpainter]

Please illustrate. A simple explanation of what transpires during a full revolution of the layshaft would suffice.

One revolution of the layshaft is two crank revolutions. A 4 cycle/stroke engine requires 2 revolutions of the crank for a combustion cycle. The layshaft spins at half crank speed so it's mark will always line up at tdc of the compression stroke for the horizontal cylinder.

The two cylinders are not at tdc together. Otherwise you wouldn't have to overcome the assist spring on the vertical cylinder to install the belt.

I don't know how many degrees of rotation apart the 2 cylinders are. Someone here does.

You can verify what I say by lining up the mark on the layshaft and sticking a screwdriver in the plug holes. The horizontal will be at tdc and the vertical won't.

[mitt]

I don't know how many degrees of rotation apart the 2 cylinders are. Someone here does.

The pistons share the same crank pin



And, the cylinders are 90 degrees apart



So, if one cylinder is at TDC, the other is 90 away from TDC. If on cylinder is a bottom center, then the other is 90 deg from that, etc etc.


mitt

[ducpainter]

The pistons share the same crank pin



And, the cylinders are 90 degrees apart



So, if one cylinder is at TDC, the other is 90 away from TDC. If on cylinder is a bottom center, then the other is 90 deg from that, etc etc.


mitt

that makes waaaaay too much sense.

[OT_Ducati]

check the flywheel nut