EL Bonnie Wrap Up 2012

Here we are at the very end on 2012, and I have still not finished writing about EL Bonnie (recently re-named The Grey Goose).  Since I was not there, perhaps the best way to sum up the actual Salt Flats portion of the effort is to borrow from the writings of team member John Endrizzi as follows:

"We spent Sat and much of Sunday preparing The Goose for tech. After passing tech Sunday afternoon we had a freak thunderstorm, which left 2 inches of standing water on the Salt. Racing resumed Tuesday morning! We made our first pass that day after waiting in the starting queue for over 4 hours. By the time Terry set off from the starting line a very brisk crosswind had come up. He found the bike being blown from one side of the course almost hitting a marker flag on the opposite side. This was in the measured mile. He backed off the throttle. Later, he said that he was at 1/2 throttle and accelerating when the gust of wind hit him. The result was 115.929 mph. This was enough to break the Sid Biberman Vincent’s standing record of 109.079. By the time that we got the bike back to the pit, the wind speed had not died at all. It was decided not to make the return pass, which would be needed to post a new record. The next morning it was another long wait for our turn to run. Terry got off the line in good fashion and the bike sounded good thru 1-3rd gears. At the top of third, a little change in the motors rhythm was heard. While on the way down the return road, we heard the announcer say that our bike had run 59 MPH! Once back at the pit we found the rear cylinder had a holed piston. That was end of racing for The Goose!"

And, indeed that was the end of racing for the Grey Goose ...for 2012.  The motor is back in my shop, apart and waiting for new pistons.  If you read the previous posts on this engine build, then right about now you are no doubt saying to yourself, "So, welding the pistons turned out to be a bad idea after all!"  Or maybe even, "What kind of moron would weld on pistons anyway?"

I must admit, those were my first two reactions also.  After discussions with various sources ranging from fuel manufacturers to legendary engine builders,  it seems not to be so cut and dried.  (And a big thank you to John for taking the initiative to seek out those conversations!). 

First off, a few clues.  The front piston survived its excursion to the Salt Flats with absolutely no sign of any problem.  The team had not yet even started to lean out the jetting from its Minnesota baseline.  That in itself makes the possibility of a lean condition being the culprit very improbable.  The rear piston not only had a hole through the flat of the intake valve relief, it had also started to "sag" on the flat of the exhaust valve relief.  Drilling a small hole through the center of the "sag" allowed me to get an accurate measurement of the thickness at that point.  It was approximately .200" thick, which was just about the figure I was shooting for when I modified them.  The "sag" along with the appearance of the hole itself lead me to think that it was a heat problem rather than a detonation problem.

But all of that really left me none the wiser as to what had actually gone wrong.  Obviously new pistons that would not require the drastic modifications I performed on the last set were in order.  And I may have left it there, trusting that the hole in the piston was due to my overzealous welding in pursuit of compression, but for one dissenting opinion. One of the experts who John contacted in search of answers was Minnesota's own Mike Roland.  Mike did not think that the welding was to blame.  In fact, were it not for the fact that I personally believe that Mike is one of the brightest people to ever get involved in the Harley performance arena, I would have dismissed his idea without giving it any thought.  But when Mike speaks, I tend to listen; and closely at that!

When John contacted Mike for his thoughts, he immediately asked if it was the rear piston, and if it was a dual fire ignition.  Yes, and yes.  Well, it seems that at Bonneville, it is very common for Harley's to hole (using "hole" as a verb) the rear piston when using a stock style dual fire ignition.  I did not know that.  The team members for the Grey Goose did not know that.  Judging from other Bonneville stories I have since heard which feature "holed pistons", many others did not know that.

John's conversation with Mike Roland suggested a cure for the holed piston phenomenon (single fire), and even a reason for it (dual fire), but not an explanation.  That is not to say Mike did not have an explanation ready; just that John did not ask for one.  This left me with several options.  I could dismiss the dual fire scenario as the cause of the hole in the piston ...but I have too much respect for Mike's reasoning skills to make that mistake.  I could just go with Mike's advice and tell the team they need to switch ignitions. That would be the simplest solution, but hardly gratifying intellectually.  I could give Mike a call and ask for his explanation.  That would certainly be the quickest, but where is the satisfaction in that?  Sort of like turning the page over to get the answers to a crossword puzzle rather than fully exercising you brain to get them.  That bring us to the last option, and the one I ultimately went with: I could sit down and spend the time to figure out why a dual fire ignition could cause the problem.

My conclusions will be the subject of another post in the very near future, Lord willing.  In the mean time, readers are encouraged to submit their ideas in the comments section.  I already have my own explanation worked out and I promise not to borrow from anyone else without giving proper credit.