Valves and valvetrain

[rolf j]

Going for it...
The valves (mid 44,0/37,1) tangled on the overlap as feared at dummy setup with my Megacycle 620x8 (Norris RR3 copy) cam. Now decided on dropping the intake seat by 2,5mm and the exhaust seat by 3,0mm hoping that the additional distance between the valves of approx. 3+mm (0,120") is sufficient for them to pass eachother. This should also provide the needed addition to the combustion chamber volume to get a comp ratio roughly somewhere between 1:11,0 to 1:11,5. The valves now need to be shortened by approx. 2,0 mm to achieve some sort of tappet geometry not too far off. New stacking of the norris springs will be needed, the titanium discs are sliktly lower than the original alu ones and over 1mm space is available between the rocker arm and the disc with closed valve. Porting will be limited to adaption to the 40mm carb/manifoil and cutting valve seats to old-school hotrod standards and a genaral tidying up around the valves and in the chamber. No chance of any drastic affairs in the intake channel at this stage. The final excitment, that can still push the project back to a milder cam, is the valve-piston distance that is noe possible (for me at least) to work out before the valve/seat job is over. If all this is working out well I believe there is a chance of trying out a 94mmx78mm (1082cc) roundfin V7-Sport in 2011! :woohoo: :angry:

 

[motoguzznix]

Rolf

I would't lower the valve seats by such a big value as seat geometry gets unfavourable. Hard to get it right for good breathing. Apart from the fact that a lot of amterial comes out of the head that contributes for thermal stability. How big is the valve lift on overlap with this cam? The megacycle data sheet contains no information about this.

And how big is cam lift?
The megacycle sheet quotes 0,372 and 0,360 cam lift which is 0,510 and 0,493 valve lift when multiplied by the rocker ratio of 1,37. The quoted Norris figures on the data sheet below show 0,446 and 0,432 valve lift which is a big differenceto the above mentioned figures.

 

[Penis Rotor]

Rolf? Do you want that oil pump and plate? if so you'd better end me an address you numb-nuts!!!!! :mrgreen:

Pete

 

[rolf j]

Rolf? Do you want that oil pump and plate? if so you'd better end me an address you numb-nuts!!!!! :mrgreen:

Pete

drop a line:

roljo3<<funny-a>>online<<dot>>no

 

[rolf j]

Rolf

I would't lower the valve seats by such a big value as seat geometry gets unfavourable. Hard to get it right for good breathing. Apart from the fact that a lot of amterial comes out of the head that contributes for thermal stability. How big is the valve lift on overlap with this cam? The megacycle data sheet contains no information about this.

And how big is cam lift?
The megacycle sheet quotes 0,372 and 0,360 cam lift which is 0,510 and 0,493 valve lift when multiplied by the rocker ratio of 1,37. The quoted Norris figures on the data sheet below show 0,446 and 0,432 valve lift which is a big differenceto the above mentioned figures.

Thanks for the views! I see your points. I only have the max lift figures and my tangling of valves is the first and major problem to solve. I landed on 2,5 / 3,0 mm simply because I've seen heads that seemingly work well with a 2,5mm lowering of the seats. Obviously there has to be some alu going away around the seats in order to bring back the flow to something reasonable. I actually need this opening-up in order to get down from a silly high 13,5 figure which is the current state with the pistons available.

I measured the lobes on the two cams (Norris and Megacycle) and find they are similar, near enough. I believe there could be some discrepancy with figures due to the problem of quoting lift&duration based on a variety of zero-figures as reference. You say tappet arm ration of 1,37, could it be there are several variations here? I don't seem to find anything higher than about 1,25 on mine?

 

[motoguzznix]

Do you still use the V7 heads and Rockers?

I was not aware that these might have a different rocker ratio. When calculating from the megacycle data sheet the ratio would be 1.2. 1.37 was measured and calculated by myself and applies to all newer Guzzis after the V7. Going to the later heads and rockers would be benefical in that case as there is some valve lift to be gained.

Why has it to be that x8 cam?
Apart from the fact you still have it? A cam with shorter duration and less overlap but with good acceleration off the seat shows most better performance on bottom and mid rpm range and rarely losses on top. The X8 seems to be a slightly aged design but I have to admit that I do not have experience with the megacycle cams. When looking at the data sheet the X10 would be my choice.

 

[rolf j]

I use LM1/2 heads and a set of rockers that I do not know the origin of, but the measuremnts to the best of my ability points to 1,25 ratio.

The "choice" of 620x8 is simply what i stumbled across second hand but in great shape, and being more or less a copy of the Norris RR3 it should do the job reasonably well. Judging from the experience of mates that I'm racing with it seems to work ok in many engine configurations and sizes. These are not the latest of cam grinds for sure, and the Guzzi-tuners who are working for a living in Europe use other grinds of their own design. In my case the budget actually controls much of both efforts and progress of the racing project so when there is a reasonable cam at hand, that's what goes in! If I land up with still having problems after the mods of the valve seats, I'll revert to the original V7-Sport cam that actually surprised me with the good performance (especially mid range) in the setup with 88x78mm 949cc mid-valve w/40-PHM that I've used the last three years.

 

[ed]

That's about the right amount to sink for X8 valve to valve clearance.
X8 is the cam you want for racing. X10 is a street grind very close to the P3 street performance cam.

Ed