Camshaft flange adjustment range

tom3c75

tom3c75

Hero member
Location
Cape Town South Africa
Can any of the experienced cam (re)timers on the forum tell me what maximum degree of timing adjustment can be achieved by slotting the camshaft flanges on a 180 triple?

Thanks
Tom
 
depends a lot on what cams you are trying to slot and what year they were
the flange profile changed over the years

we need more info

 
It also depends what direction you need to go. On my cams, one of the holes was closer to one edge of the lug than the other. Of course, that was the direction I needed to file the slot so I could only go a few degrees. Fortunately it was enough.

 
Thanks for the info!

The bike is a 3C and the cams are presently A11.    However, I also have a set of 4C's which I may fit as an alternative.   

Current timing is about 6 degrees advanced, based on a rough check, but I'll be measuring more carefully today.  Seems like character building stuff!

Not sure what year of bike the 4C's came from, but I suspect they were from a series 2 Jota.  I bought the 4C's as used items from the local Laverda dealer in approx 1983, as the previous owner had fitted 7C's.  I paid ZAR 100, that's about $10 in today's money.  How things do change.

Tom
 
Hi Tom

The cam sprocket bolt holes are on a radius of 27.5mm, so 1mm of slot gives a 2? change in cam angle, which is 4? when converted back to crank angle. So if you want to move the timing by 6? on your degree wheel, you need to file 1.5mm out of one side of the bolt holes. There should be enough metal in the lugs for that.

I assume you're aware that A11 and 4C cams use different sprockets. The hole positions in relation to the sprocket teeth are quite different.

Cam
 
Hi Tom - Can get more than 6? on 180? cams usually - I often turn wheels round the other way as the offset between the "hills & vallies" of the teeth will often get you nearer to where you want. I like to run my 4/C's with the exhaust advanced and the inlet a tad retarded. - Regards - Phil
 
I have now checked the timing of the A11?s according to Phil?s maximum lift method and get the following:

Inlet:      114 degrees    (should be 108)
Exhaust:  105 degrees    (should be 96)

Am I correct in interpreting the readings as meaning that the inlet is 6 degrees retarded and the exhaust is 9 degrees advanced?      This because of my understanding that max lift for inlet occurs after TDC and the max lift for the exhaust before TDC.

Tom
 
Sounds right to me Tom.

The attached pdf file of timing disks make it clear (the one on the left is for A11).

The pdf file prints the disks out the same size as a CD, so you can print it, cut out the appropriate disk, glue it to a CD and bolt it to the outside of your alternator rotor as a cheapo degree wheel. It's good enough for 1? accuracy. Only slight problem is that you have to bore or file the 14mm hole in the CD out to 22mm diameter to fit over the thread on the end of the crank. Some CDs delaminate when you bore them that far.

One of the advantages of using a CD is that it's light, so you can start the engine to strobe the ignition without it moving out of position. I have a larger diameter metal degree wheel that will often slip out of position on the shaft due to its own inertia when the engine is started.
 

Attachments

Thanks Cam.    Glad I had it right, it certainly took a while to get it sorted in my head!

Those are great diagrams!    A minor observation:  wouldn't the inlet max lift text in blue be better positioned on the right hand side of the wheel?

Cheers
 
Not sure what you're getting at Tom. I'm probably misinterpreting your meaning, but if you put the max lift on the right of the dial it'll be in the wrong place. It'll be some place where the inlet valve shouldn't be open at all!
 
Cam,

Very possible I'm misreading the diagram!
What I meant, is that inlet max lift, which occurs between inlet open and inlet close, is shown on the RHS of the diag, and would be where I would show the max lift figure.  Same applies for the exhaust on the LHS of the diag.

Tom
 
You've still lost me.

All I can say is the degree whee is the conventional way of showing valve durations diagrammatically. Look at any valve duration diagram and it'll be very similar.

Don't forget that the degrees in the diagram refer to crank angle. There are two revolutions of the crank for each revolution of the camshafts, so the valve opening durations overlap on the diagram. The actual valve overlap between inlet open and exhaust close is shown by the overlapping red and blue lines on the top half of the diagram. The overlapping lines on the bottom of the diagram are actually on different phases of the 4-stroke cycle, so there's no real valve overlap there.

If you were to plot the valve opening durations against cam angle, there wouldn't be any overlap on the bottom half. It would look something like the attached pdf
 

Attachments

What side of the engine have you got the disc mounted on Tom, Cams diagrams require the disc to be on the right hand crank end.

    Keith
 
OK, it took a while, but I've got it now!   

When looking at the diagram, for some dumb reason, I rotated the disk anti-clockwise in my mind!
Turn the thing in the right direction & it all makes sense. Thanks Keith!  And, yes, it was on the RHS!

Again:  Great diagram Cam, it puts the whole process together very well in a single view.

Tom
 
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