Sunday, December 30, 2012

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.



Anonymous said...

I have absolutely no business commenting; I am, however, a fool who's learning lags his experience enough to turn the joy of discovery into the agony of regret at every turn of the wrench.

If the wasted spark is to be the culprit (or the accomplice to the culprit) then it must be due to it's starting a fire where one is not desired. Since the front cylinder is generally thought of as number one my way of thinking and explaining may be reversed but the rear cylinder is 45 degrees advanced from the front cylinder(in rotation). If your advance is about 25 degrees a wasted spark is occurring at about 20 degrees after TDC on the rear cylinder while it is on intake. At this point in rotation the piston is retreating down the cylinder about as fast as it's going to go so an ignited fuel charge may not be noticed, especially as the furiously incoming, but uncompressed, air/fuel may put the fire out for a bit. If so, this would heat up the cylinder prior to compression (which heats up the cylinder even more) and then a lean main burn when the spark isn't supposed to be wasted.

But I am totally guessing.

My Ironhead will sometimes backfire through the carb. Usually on a hot day in busy traffic. Since it's the kick variety, it means pushing her over to the curb for some Ironhead callisthenics. When I told my (rather knowledgeable) parts guy that I had taken off the airbox support because it was ugly, I thought he was going to reach over and hit me. He said he could pretty much guarantee backfires due to the carb jumping around, unsupported as it is.

My point, wrongly based perhaps, is that most of the time in most circumstances, dual fire ignition works pretty well. If it doesn't it's usually the result of a further problem. In my case, over lean mixture or raw gas from my accel pump hitting the plug.

I found a website that suggests that dual fire ignition may not work so well for hot cammed engines:

Brad Ervin

PS My post is not to be taken as arrogance but more in the vein of sitting in class and waving my hand to test my knowledge against the superior knowledge of the class and the teacher.

Anonymous said...

Holy cow! 42 degrees. I should learn how to read. The rear cylinder was almost at TDC when the wasted spark went off. Both the valves were probably open and the initial rush of fuel charge must have just been pulled in by the exhaust inertia. The spark may have ignited the escaping exhaust gasses.

I love mysteries.

Brad Ervin

St. Lee said...

Brad, all I will say for now is that if you were the student with raised hand, you would be at the top of the class.

Anonymous said...

Happy New Year to you and yours. May your new year be full of victories of the most important kind, all your uphills be downwind, all your cloudy days be full of rays of happiness and your eyes behold nothing but the goodness of the Lord.

You are too kind. Actually, I can only apply what I've learned on your blog.

Let us know what your opinions are of the piston coatings you tried. I'm wondering if it's worth it to send out the pistons for my 91XL. Also, where to send them (if you've an opinion on that).

Thanks Again
Brad Ervin

St. Lee said...

I am a fan of coatings. Your 91 XL may have a skirt coating from the factory (don't recall just when they started), but if not and you already have it apart, I would suggest it. The ceramic dome coatings, on the other hand, I think are more application specific. With an all aluminum motor and no known heating issues, I would probably not recommend it for your engine, unless maybe you live where the usual temps are significantly hotter than normal. If you had an Iron Head XL, on the other hand, I would say by all means do ceramic on the piston domes and combustion chambers of the heads.

There is likely someone in your local area that can apply coatings for you. Maybe check with your local speed shop or performance engine builder.

Knucklenutz said...

Hi Lee,
Patiently awaiting the rest of the story.
Respectfully John

St. Lee said...

Yeah... soon I hope ...never enough hours in the day.

Anonymous said...

Maybe this will make you laugh. We can never laugh enough; and it's okay to laugh at me.

I've noticed that when I go around a corner in the car, I can feel the air currents shift in response. This isn't just due to the change in direction, turning in a circle puts you in an acceleration field.

I don't know the particulars of your bike or the conditions of a race at Bonneville but assuming drag strip performance you may go from "0" to, say, "100" in maybe 10 seconds. Your average acceleration would be about 15 feet per sec/per sec. Since gravity is about 32 feet per sec/per sec this is about 1/2 G. Since the intake for your front cylinder is in the rear and the intake for the rear cylinder is in the front, the front cylinder would be drawing it's fuel/air charge uphill and the rear cylinder would be getting it's charge downhill. This would be as if the bike were going up a hill with gravity pulling down and acceleration pushing back.

Since it looks like you have two carbs at least the acceleration can't work against equal air/fuel mix as it might in a single carb situation. Or, maybe the acceleration is irrelevant in the situation.

Brad Ervin

St. Lee said...

Well Brad, your comment couldn't help but remind me of what the guy who ported the heads for what would be my first experience with drag racing told me. He said that he had ported the Shovelheads with slightly better flow on the front head to compensate for the acceleration of the bike. It sounded reasonable at the time. It was years later when I started to port heads myself that I realized that a front Shovel head ALWAYS flows more than the rear due to the difference in the ports (until you take specific actions to correct the rear port). Never did find out whether he believed that bit, or if it was just an excuse for leaving the ports mismatched.

In practice though, if you consider that the mixture velocity in the port reaches over 250 feet per second, the effect of the acceleration of the vehicle is probably negligible.