Quote:
Originally Posted by Trackrash
A couple of things come to mind here. How accurately can one really determine the lobe center? Are we to assume the lobe center is at the highest point of lift? What about an asymmetrical lobe design, does that matter?
Also the alignment pin used to time the cam may only get you close to your desired exact degree location, from my limited experience.
Neil, thanks for your expert experience here, and I am just thinking out loud.
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Lobe center will be full cam lift/valve lift.
As for accuracy, that will depend upon your equipment and how clever you are at measuring true TDC and max lift.
A or symmetrical cams will both have the max lift at the designed lobe center. Cams with lobes that are more rounded, will appear to have a moving lobe center, but this is where you need to take two readings before and after full lift and average them out.
Alignment pins etc, will always have some slack in them. This is why it is important to always turn the engine in its normal rotation when taking measurements, so all parts are on their loaded side. Often the play in the alignment pins is enough to find the desired lobe center number. I cannot remember, but you could see 1° crank in the slop. I may be wrong here on the amount, but I do know its quite common to get the desired number just by taking the slop out of the pins.
How accurate do you need to be? We try to obtain a max of 0.25° ether side of the desired number. A lot comes down to the accuracy of the degree wheel too. Most of the mass produced wheels are Ok, but the larger diameter and the more expensive wheels are more accurate.
Many will think its not necessary to go to this extent. "The engine runs just fine". If that floats your boat, then that's Ok by me. We all have to choose our own level of expertise.