Twin Valve Timing
- Thread starter youngjohn
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re the 105 question- it appears to mean different thing to different people. Terry Prince told me that all of his cams are 105s. In this case the 105 degrees is centre line measurement between lobe centres, giving 210 degrees peak to peak exhaust to inlet spacing ( cam turns half speed to engine) In his autobiography, PEI discussed development of the MK2 cams stating that he altered exhaust closing and inlet opening angles from the MK1s to give "105 degrees of overlap" So these are two totally different 105 degree measurement, almost opposite in fact since if no other changes are made to the profile then widening the centre line measurement, say from 100 degrees to 105 degrees decreases overlap, whereas increasing the overlap from 100 degrees to 105 without changing profile, can only be accomplished by reducing the centre line measurement.
A Vincent owner on the Norton site mentioned that he had Godet install 105 cams in his Bespoke Egli, wit the inference that the 105s were a much hotter than stock cam. First off , you would have to know what the 105 refers to. If it refers to centre line , then that measurement on it,s own indicates aa milder cam that stock MK 2
A Vincent owner on the Norton site mentioned that he had Godet install 105 cams in his Bespoke Egli, wit the inference that the 105s were a much hotter than stock cam. First off , you would have to know what the 105 refers to. If it refers to centre line , then that measurement on it,s own indicates aa milder cam that stock MK 2
which from my reading has a centre line measurement of 97 degrees. 97 degrees being tighter than 105 means a wider overlaps than with the 105, same profile. In car and truck engines, hot car cams are down around 100 to 105 degree lobe separation truck and RV low end torque cams are around 120 lobe separation.
It all gets rather confusing, especially when all of the profile variations are added in. For example, while Terry has used a wider lobe separation ( 105) than Irvings 97 degree Lightning cams, Terry's MK 5 profiles are very tall and wide giving about 170 degrees of overlap, so a much "hotter" cam than the mk 2.
A friend asked Mr. Robinson what the 105 of his 105 cams referred to and the answer coming back was " I think it is the difference between the opening of this and th closing of that"
It all gets rather confusing, especially when all of the profile variations are added in. For example, while Terry has used a wider lobe separation ( 105) than Irvings 97 degree Lightning cams, Terry's MK 5 profiles are very tall and wide giving about 170 degrees of overlap, so a much "hotter" cam than the mk 2.
A friend asked Mr. Robinson what the 105 of his 105 cams referred to and the answer coming back was " I think it is the difference between the opening of this and th closing of that"
So even he was unsure. This may be because he makes every effort to copy known good cam designs rather than reinvent the wheel.
Terry on the other hand, is one for experimentation, hence we are up to MK5 with many un-named grinds in between the Mks.
Terry on the other hand, is one for experimentation, hence we are up to MK5 with many un-named grinds in between the Mks.
The main problem is in dealing with a lever type of cam follower, and not a straight solid type. This just adds to the confusion.....The MK 5'S I put in the racer have 0.400 lift at the inlets...not quite the high lift I thought it might have.....although the duration is good....perhaps the lower lift may save some ware on the parts. I pulled the cams out the other day, and all looks well....although this is with about 2 hours total run time, and I am using castor oil, which seems to be doing a great job. The engine is by far the most powerful Vincent engine I have built, and with the bikes weight at around 160 Kg's (350 lb's) it certainly gets moving. Cheers..........Greg.
FWIW -
My alleged Mk 1's have a cam overlap of 100 degrees of crank rotation (50 degrees of cam rotation) and a lobe separation (peak to peak) of 190 degrees crankshaft which equates to 95 degrees of cam rotation. Peak lift is 0.321" for the inlet and 0.327" for the exhaust. Both hold their peak lift for 10 degrees of crank rotation
That seems low Greg. The chart Terry provided shows .440 lift at the inlet valve for the Mk5s. I did check mine against that and recall that it was very close.
Mk4 s are a little higher lift again, but they are an earlier design done by Terry.
The Mercedes Formula One Cam Development program which Fritz Egli Jr. used to design the Mk5 s determined that there was no advantage in lifting the large Vincent intake valve beyond .440 for any RPM up to 6,500, that is where the .440" number came from.
Mk4 s are a little higher lift again, but they are an earlier design done by Terry.
The Mercedes Formula One Cam Development program which Fritz Egli Jr. used to design the Mk5 s determined that there was no advantage in lifting the large Vincent intake valve beyond .440 for any RPM up to 6,500, that is where the .440" number came from.
Martyn, I used the term lobe centrelineto discuss lobe separation, but your term peak to peak is better. This is because the while lobe centreline is a common North American term, it refers to symmetrical cams, where the lobe centreline runs thru the peak. Symmetrical/cam profiles seem to be most common in the auto industry.
With the asymmetrical Irving designed Vincent cams, the lobe centreline does not run exactly thru the peak, so I think peak to peak simplifies the discussion.
It is also interesting to me that while Irving no doubt had good reason to make his cams asymetrical, the Prince cams are symetrical.
Glen
With the asymmetrical Irving designed Vincent cams, the lobe centreline does not run exactly thru the peak, so I think peak to peak simplifies the discussion.
It is also interesting to me that while Irving no doubt had good reason to make his cams asymetrical, the Prince cams are symetrical.
Glen
Hi there Glen, I also checked mine with a DTI on each inlet valve stem, and both cylinders read almost exactly 400 lift at the valve. The cams now seem to have quietning ramps on the opening and closing sides of the lobes, whereas I think the original cams had no ramps at all, except the original MK 3 which did have ramps but only on one side of each lobe. The newer cams definitely make the engines a lot more quiet, especially if the locking rocker feed bolts are used as well.....provided other items aren't flogged out, as is so often the case..........Greg.
With our lever followers, I would think that for symmetrical action at the rocker tip or valve stem that the cam would have to be asymmetrical. There are surely CAD programs that could generate a cam profile now, but PEI probably used a graphical approach to it. Maybe the ideal opening and closing profiles are not identical for Vincent max rpms?