Subject: Re: points/timing
Author: Bill Cohoon
Date: May 8, 2003, 9:22 AM
Post ID: 1712915077
Well I'm certainly sold Patrick.. but it sounds like they were
suggesting that splitting the difference (if there was some kind of
minor irregularity in the lobes) was better than having the left perfect
and the right off by 2 for example?. I dunno.. I know I'll never care..
I couldn't deal with hopping back and forth between 1 and 2 attempting
the 'compromise'...
Patrick Hayes wrote:
Sorry, don't buy it. And, BTW, Frank Wedge was once known to put police handlebars and a double bucket touring seat on his LeMans 1! (Don't worry, he's a longtime friend.) Here's the problem. I dislike use of the term "second cylinder" for semantic reasons. The loopframe Guzzi is timed by the left side cylinder. (by convention, left and right, sinistro and destro, are always referenced to the rider astride the bike) Since both connecting rods attach to the same crank journal, side-by-side, one has to be centered more forward than the other. Oddly, the left side cylinder is further back on the crank and could confusingly be called cylinder #2. Hence my concern about "second cylinder" usage. Now as to timing. Let us imagine you have absolutely, perfectly set the point gap and the ignition timing for the left hand cylinder. If you thereafter do ANYTHING to alter the rotational position of the distributor or the clamp screw of the points, you will destroy the precision of your timing effort for that left cylinder. So, if you now rotate the engine to bring the right side cylinder into spark position and if you find it is not sparking at the precise correct point, what are you going to do? If you change the gap to alter the timing on the right side, you have just screwed up the left side timing. If you turn the distributor to alter the right side timing you have just screwed up the left side timing. The ONLY thing you could do to alter the timing of the right side without effecting the timing of the left side would be to recreate the distributor drive shaft with one of its cam lobes in a slightly varied rotational position or lift altitude. (Don't try this at home, kids.) So, what do you do if you inspect and find that the timing of the right cylinder is not precise after you have timed the left cylinder? You have two options. "A", you can realize that this is a very low stress motor and that the fuel you are using today is not the same as the fuel the engineer designed to in the 60's and its not really going to make a whole lot of difference and just ignore it and go ride and ..... or "B" let us suppose after your left side perfection work that you now find the right side to be two degrees too retarded. (there is a two degree error separation between the two sparks) You can now go back to the left side to re-time and split the difference. Set the left side one degree too advanced and now the right side will be only one degree too retarded. A good compromise. See? You CANNOT alter the two degree error in the relationship between the two cylinders other than by distributor shaft alteration. Not by turning the distributor, not by moving the points. Although the parts are in rotational operation, it is all just straight linear math. You CANNOT alter the relationship between the two sparks. After you set the left side perfectly, they are either both perfect or you have a slightly erroneous distributor cam and can only split the error to correct............... |