I bought these Instruction sheets from the club in November 1998. Revised edition dated August 1998, edited and revised by Frank Griffin.Published by VOC publishing. Page 80 includes the info for the Mk3 cams giving 0.100", inlet at BDC.. These are from the originals by Paul Richardson, dated 1949. Surely they're right ? which makes the red book etc at 0.190" wrong ? I did contact two of the main names at the club a couple of years ago but no response, there must be someone who knows ?
ET: Engine (Twin) Mk3 cams - timing figures
- Thread starter fogrider
- Start date
I timed mine in a similar way to Robert but without the heads on. I made some stubby push rods and put the dial indicators on there. I only had two dial indicators so I did the cams one at a time.
I doubt the weight of the camwheels makes any difference to the valve action. The holes do look good though. Narrowing the wheels might reduce drag a bit.
I doubt the weight of the camwheels makes any difference to the valve action. The holes do look good though. Narrowing the wheels might reduce drag a bit.
If you care to read off the values on this graph then you should get what you want. These were newly manufactured cams from the IOW lent to me by Colin Jenner.
TDC is at 360 degrees along the horizontal axis and therefore BDC is at 180 degrees after that, i.e.540 degrees. On these cams the lift at BDC is 0.205" Centre of the overlap is at about 4 degrees BTDC.
TDC is at 360 degrees along the horizontal axis and therefore BDC is at 180 degrees after that, i.e.540 degrees. On these cams the lift at BDC is 0.205" Centre of the overlap is at about 4 degrees BTDC.
I just cannot see why one wants to mess around with odd numbers from old handbooks when all you need is to set cams for equal lift at exactly TDC - or max. 5 degrees before or even 5 degrees after TDC. Equal lift at TDC is the best compromise, 5 degrees before gives a bit more torque, 5 degrees past TDC a bit more top hp, less torque - or so I was told from someone who does a lot of SR 500 tuning.
My guess is, funny handbook numbers stem from measuring a completed engine once it could be tested in the factory and that is how it was produced in big numbers, not necessarily how it was planned from the design board. Real life can be quite a bit different to what a customer would think. When you compare old records of Lightnings shipped to customers you will see a big variation of these timing numbers for individual bikes - from the same factory , supposedly with the same type of cam.
Vic
My guess is, funny handbook numbers stem from measuring a completed engine once it could be tested in the factory and that is how it was produced in big numbers, not necessarily how it was planned from the design board. Real life can be quite a bit different to what a customer would think. When you compare old records of Lightnings shipped to customers you will see a big variation of these timing numbers for individual bikes - from the same factory , supposedly with the same type of cam.
Vic
Just had a longer look at that graph, it's obvious that the 0.100" quoted in my factory instruction sheets is the wrong figure, some 20 deg out. Obviously an un-corrected type error from 0.190. I read the graph as 0.200 at BDC which is as good as 0.190, just a few degrees in it, manufacturing differences would cover that.
Result.
Result.
There is a person who is mandated to tell you He is called the technical officer inside page MPH
Terry,
I was not trying to be obtuse, I was curious about the question and I don't really understand the procedure's merits, but it is plainly working well for you and I would not argue with success.
Of course, looking at Norman's graph I don't understand why some cams have a taller lift for the exhaust than the intake. The air struggles to get into the combustion chamber and could use all the lift it gets. The charge is compressed and explodes out of the exhaust leading me to believe the high lift exhaust is not a great benefit.
Jack,
That is a great story. I would have been interested to know that. There was a discussion about fly wheel weight on the forum earlier and I mentioned that heavier flywheels produced higher top end speeds. I stopped using lightened gears in the racers about a decade ago when I realize they could be considered part of the flywheel as they were so attached. It seemed easier to lighten the fly wheel than all those gears if that is what you desired.
Phil's comment was proved to be true with the spintron work of top motorcycle drag racers. The fly wheel and gears that were lightened caused visible valve bounce.
I think the Vincents have always been quite good about valve bounce.
Regardless, that is a fine looking motor by Robert!
David
Just so you know, those gears (as shown) are all the current offering from Maughns.....