Cilinder angle 3 1/2

[leos]

I remember once reading a topic about the cylinder angle of the morini v-twins not being an exact 72 degrees. Does somebody know if this is true. By heart i remember it being 73° 19' 14". I measured the angle and found it to be about 73,5 degrees so it seems right. Please some information because i will have an ignition being made for me with the angle programmed in it.

[MickeyMoto]

Where (and how) did you measure the angle?

[harrymuffin]

The angle of the cylinders is 72deg but because the centre line of the crank is higher than the centreline of the cylinders measuring the angle across the cylinder base will give a different figure. The firing angles are therefore moved from the "nominal 432deg and 288deg to a longer 433deg 19.4min and 286deg 40.46min" from the Marchesini and Lambertini interview by Vic Willoughby.

[leos]

The measurement was as follows:
I did mount a degree wheel on the crankshaft. With a special plug in the cylinder head of the rear cylinder i did move the crank to both sides until it hits the special plug and did set the degree wheel at the same angle for both sides. One side BTDC and the other ATDC. I am now sure the TDC is at 0 degrees. Moved the plug to the front cylinder and repeated the action on rotating to both sides until it hits the special plug again. Did note the angles at which it hit added them and after dividing them i did have the angle between the cylinders. If someone disagrees this way of measuring i would like to know a better way.

[leos]

Marchesini and Lambertini interview by Vic Willoughby

Is there a link to this interview?

[P&S]

The angle of the cylinders is 72deg but because the centre line of the crank is higher than the centreline of the cylinders measuring the angle across the cylinder base will give a different figure. The firing angles are therefore moved from the "nominal 432deg and 288deg to a longer 433deg 19.4min and 286deg 40.46min" from the Marchesini and Lambertini interview by Vic Willoughby.

Exactly!
But things are even more complicated!
There is another angle on the front cilinder that put's it out of axis and makes the system not symmetric. (Is the reason for different length of pushrods I suppose)
At the end the angle on Lambertini's drawing is 71°50'

[harrymuffin]

Sorry, I only have the photo copy of the original article from I think 'The Motorcycle' . All Vic Willoughby's interviews were collated into book form, including his road tests of most of the classic works grand prix bikes from the early fifties up to when he presumedly retired sometime in the '80s, he was a thinking and erudite motorcycle reporter, unlike the dimple heads who cannot even hold a pencil that proliferate now and are held in reverence. It also shews an exploded view of the Morini engine by Lawry Watts which is a work of art in itself.

[mgelder]

I could be wrong (I usually am) but surely the critical angle is the angle between the crank pins?

This will determine the 'firing' angle.

I think.

[MickeyMoto]

Zero degrees? There is only one, shared, on the crankshaft? The vee will set tdc to be different on both cylinders. To be honest, this is like finding out Santa does not exist. What do I tell people? That I have a 71 degree and 50 minutes vee twin? I think I need to grow a beard and buy some sandals.

BTW, that diagram would be good on a tee shirt, or even printed and laminated. I still miss the exploded engine tee shirt.

[mgelder]

I could be wrong (I usually am) but surely the critical angle is the angle between the crank pins?

You see, i was right. In that I was wrong. Ahem.

Carry on.

[Ming]

I think I need to grow a beard and buy some sandals.
BTW, that diagram would be good on a tee shirt, or even printed and laminated. I still miss the exploded engine tee shirt.

I already have the beard and sandals, and I ride a 72 degree twin. I agree about the tee shirt.

[Steve Brown]

I think I need to grow a beard and buy some sandals.
BTW, that diagram would be good on a tee shirt, or even printed and laminated. I still miss the exploded engine tee shirt.

I already have the beard and sandals, and I ride a 72 degree twin. I agree about the tee shirt.

I think we're all heading in the same direction here...

[P&S]

My God, what have I done.
Really couldn’t immagine to upset you so much!
But this is the hard truth.
Again joking apart, I thought somebody already knew that drawing. I find it on a book, not a factory secret.
I thought it would rather stimulate the topic giving answers and generating new questions.
Please don’t retire in a cloister.
Going back to the matter take a look at Lambertini’s notes on the top of the drawing showing the variation of compression rate at the change of measure ”A” (the distance from the top of piston at TDC and the the head.)
I think is very interesting and helpfull!!

Sorry MickeyMoto, I didn' understand you. forgive my english
"Zero degrees? There is only one, shared, on the crankshaft? The vee will set tdc to be different on both cylinders."
Could you explain it?

[P&S]

Anyway if this only lands to a tee shirt I think I deserve one!
Don't you?

[MickeyMoto]

I could be wrong (I usually am) but surely the critical angle is the angle between the crank pins?

You see, i was right. In that I was wrong. Ahem.

Carry on.

Martin,

Ignore me, my background is telecommunications! That is why I used question marks!