David,
from the cam plots, would you expect a SIGNIFICANT improvement from the megacycle cam over the standard Mk1?? Megacycle appears to provide more lift and greater lobe separation.
Comet Inspection/Repair after 10,000miles
- Thread starter craig
- Start date
from the cam plots, would you expect a SIGNIFICANT improvement from the megacycle cam over the standard Mk1?? Megacycle appears to provide more lift and greater lobe separation.
I think you may be correct. I was surprised that this cam was so different from the spec. I have Megacycle do quite a few cams and they are quite good at hitting the spec. The quality is high. I remember doing this cam a few times thinking it must be me. So, we have to take your advice that they are all different. I think the slightly higher lift and the overlap would help quite a bit even thought the intake duration is a little shorter. I tried to talk the owner into keeping the cam in the engine, but he wanted a MK2.
David
Thanks David, Martyn and all you wonderful Vincent owners who take the time to particapte at this forum.
here are my current timing settings that were in question. I only have exhaust dial indicator
Ex open at 44 BBC at 0.055" lift and rising
Ex open at 77 ABC at 0.330" max
Ex open at 5 BTC at 0.145" and closing
Ex open at 30 ATC at 0.035" and closing
Everytime i rotate the crank back and forth thru ex open and close and back again to repeat things vary plus or minus 2-3 thou.
So it was the .145 at crossover equal lift that was my problem comparing to my graph of a couple years ago showing .169
Cheers
Craig
here are my current timing settings that were in question. I only have exhaust dial indicator
Ex open at 44 BBC at 0.055" lift and rising
Ex open at 77 ABC at 0.330" max
Ex open at 5 BTC at 0.145" and closing
Ex open at 30 ATC at 0.035" and closing
Everytime i rotate the crank back and forth thru ex open and close and back again to repeat things vary plus or minus 2-3 thou.
So it was the .145 at crossover equal lift that was my problem comparing to my graph of a couple years ago showing .169
Cheers
Craig
I've never used the equal lift technique (mainly because I didn't know about it the last time I set the valve timing) but I'll shortly be checking my Comet, and this seems to be the quickest method. It occurs to me, if I set the tappets equal and turn the camshaft to roughly equal lift, then remove the large idler, the valve springs would naturally turn the cams to equal lift ??? Does this work, or am I trying to be lazy?
H
H
Here is Megacycle data from their catalog. And this just confirms David's advice. I am using a 554-x1.
I have ridden 10,000 miles on this cam and been perfectly happy, not a race bike, easy start, good touring.
I would not be unhappy trying out other cams, but you must be careful about lift and having enough clearance to avoid pushing a valve stem collar ET35 into the valve guide.
So with my current today setting of 55 thou at 44deg BBC , I am a little early, but seems reasonable. all else considered
I have ridden 10,000 miles on this cam and been perfectly happy, not a race bike, easy start, good touring.
I would not be unhappy trying out other cams, but you must be careful about lift and having enough clearance to avoid pushing a valve stem collar ET35 into the valve guide.
So with my current today setting of 55 thou at 44deg BBC , I am a little early, but seems reasonable. all else considered
Howard,
I don't think that will work. I mentioned that I have a bench engine. It is mismatched Comet cases with half a flywheel and main shaft so I can degree cams. I have very weak springs in the valves so it does not want to move much, but I think the stock intake spring will want to close and the exhaust spring will want to close also by resisting the cam ramp and it will want to reverse.
David
Hi David,
I haven't really thought it through, I was just having a spell at work that didn't actually require my brain to do much. Surely all things being equal, if the two valves are open the same amount, the springs will be exerting the same force on the pushrods, one pushes exhaust cam back and the other pushes inlet cam forwards. The only problem I can see at this point in my thought train, is that the cam ramps will/may be different creating different turning moments.
Howard
I haven't really thought it through, I was just having a spell at work that didn't actually require my brain to do much. Surely all things being equal, if the two valves are open the same amount, the springs will be exerting the same force on the pushrods, one pushes exhaust cam back and the other pushes inlet cam forwards. The only problem I can see at this point in my thought train, is that the cam ramps will/may be different creating different turning moments.
Howard
Might be a good way to chop off the end of your finger, Cheers Bill.
Well, buttoned the Comet up with new large steel idler, retimed cams and Magneto.
My final exhaust cam check showed -
Ex open at 44 BBC at 0.050" lift and rising
Ex open at 77 ABC at 0.330" max
Ex open at 5 BTC at 0.148" and closing
Ex open at 30 ATC at 0.040" and closing
Supposed to be 12°F tomorrow with snow. Not sure I can test ride Comet at that temp.
I will have to cut an exhaust hole in the door, and run inside.
Cheers
Craig
My final exhaust cam check showed -
Ex open at 44 BBC at 0.050" lift and rising
Ex open at 77 ABC at 0.330" max
Ex open at 5 BTC at 0.148" and closing
Ex open at 30 ATC at 0.040" and closing
Supposed to be 12°F tomorrow with snow. Not sure I can test ride Comet at that temp.
I will have to cut an exhaust hole in the door, and run inside.
Cheers
Craig