Wednesday, February 25, 2009

Post Mortem...

After a complete tear down of the YZ125 engine following the Lake George debacle, a few things have become clear to me. Before I had a chance to split the cases I had speculated that the cause of the engine failure was either 1.) improper jetting (too lean) 2.) old premix that had somehow degraded 3.) a combination of those 2 causes exacerbated by the introduction of ethanol in the fuel that we buy these days.
Now that I have the cases split and the crankshaft in my hand, another kernel of evidence has been discovered. One of the crank seal springs had failed, and had been caught between the crank web and the case. The damage to the case was obvious, but not consequential (I hope). But the seal failure should have been obvious to me much earlier, I just wasn't paying attention to the symptoms.
When a crankshaft seal on a 2 stroke engine fails, the most obvious symptom is a high idle. This is because air is getting past the seal and being consumed as part of the fuel mixture, leaning the mixture because it's downstream from the carb. Add the aforementioned jetting and premix problems with a dash of cold riding conditions, and you have one confused and misguided racer.
I assumed the high idle was a result of having the big bore kit and jetting changes done all at once, so I adjusted it down with the idle air screw. That seemed to work and the bike started and ran fine. Till it blew up.

The crankcase, scored by the spring caught between the case and the crankshaft web.

The remains of the crank seal spring, trying to hide in the web.

As it turns out (no pun intended), it's probably just as well that the engine did what it did when it did. While I was taking the ice wheels off and preparing to put the roller away in the barn I discovered that the 19" front wheel/tire combo had been a tighter fit than I had thought. Tuns out that when the forks were compressed, the screws on the left side of the tire were trying to eat through the left fork. They got as far as the seal and the first layer of ridges on the upper leg. (It's an inverted fork) If I had taken another half dozen laps the fork would have been worn right through. Kinda wish I could have seen the sparks flying though...

Sunday, February 22, 2009

More Ice bikes, not mine though..

Here are some bikes that have been around for awhile. One of the great things about riding on the ice is that some of the older bikes are just as much fun to ride, and aren't as obsolete as they would be on a motocross track or in the woods. Plus they have some character and funk that doesn't really come out on the newer bikes...

This is a late '70s Yamaha YZ460 that was racing at Lake George, the owner was racing in Senior A class. The ice fenders on this bike were very well made.

1982 Honda CR250, liquid cooled, Canadian tires. I get to ride this bike occasionally and it's always a treat, handles great and has surprising power. Lots of fun.

'78 Suzuki RM250, air-cooled, pipey. Also on Canadian tires. A bit more of a challenge to make it go fast because you have to keep it on the pipe, but very satisfying when you get it right.

These two are owned by one of my ice ridin' buddies, pictured here checkin' the tires, Mike, super nice, super fast. We just had a great session, he was riding the CR, I was on the RM and Matt was strafing us on his KTM. Mike and I had some great laps, pushing each other (and the bikes) pretty hard.

Wednesday, February 18, 2009

Cooke Pond

Here's some vid of Seamus and I flogging the XR100 mercilessly on his pond. The amount of time and labor that went into the preparation leading up to this 15 minute session would be hard to believe. Starting with a comic episode involving a canoe and a chainsaw on a cool Autumn afternoon, followed by a couple of plowing/snowblowing sessions punctuated by stepping through the ice, breaking the plow and getting stuck in slush. ( I wish we had some of that on video) Anyway, enough of that.


Me, obviously trying to give a clinic on shorttrack. The rear tire went flat during the filming of this...

The ice was perfect, we were running the XR in 4th gear. Next year (yeah, right!) we'll build a slightly larger track.

Monday, February 16, 2009

The Ice Quiver, part 2

This is my son Scott's bike, a '95 YZ125 that we got as a DTX when he was overdue for a move up from his XR100, way back in '00 I think. This bike has seen quite a bit in the past 8-9 years, it had been lowered and set up as a DTX (dirttrack bike from a stock motocross frame) with 19" front spool wheel. Then we built a pair of 17" supermoto wheels and raced it at Lembo Lake and Cuddebackville. Then we rebuilt the suspension to full moto and ran it in the woods. Did some winter indoor shorttrack at Middletown with the 17"s. Did some ice riding with various wheels and set-ups till I finally thought I had it figured out. Wrong.
So here's the current version, (with more changes in store later).

The only obvious modifications are the additional home-made ice fenders. I made these to comply with AMA rules to cover the wheels above the axles as measured with a string held from the front fender to the rear. Nobody but me has actually held a string up to these to see if they actually comply.

The rear tire is a Chinese knock-off of the Yokohama Super Digger on my KTM. I did my best to copy the screw pattern and angle from that tire. The difference is that for AMA racing you can't shave the tire and you can only use 3/16" screws. The tire works pretty well given those limitations. I built the fenders with scraps of steel I had laying around, I did have to buy a length of 1/8 x 3/4 strap to form the vertical and horizontal hoops.

The front tire is a 19" AMA legal Carlisle that Matt had in his attic. As we have discovered with most of the ice racing stuff in his attic, it works really well! I had tried to build a 21" front, but it wasn't up to the task demanded by the new rear, so on went the 19" tire on the DTX spool wheel that came with the bike. I do plan on building a better 21" wheel that will enable us to have the front brake again, for road course/TT events.

The bike had an inauspicious debut at the Lake George Winter Carnival Ice Races this past weekend. I had just installed a big bore kit (134cc) and I was looking forward to trying my hand at some real sanctioned ice racing. Unfortunately, I overheated the piston during the first practice session, resulting in a seizure as I down-shifted entering T1 at a fairly good clip. After that, the engine lacked compression. I had to load it up and call it a day.

Before I left, I watched this pro heat race, dominated by PJ Jacobsen...

Monday, February 9, 2009

The Ice Quiver... part 1

First the KTM, which is officially for sale so that I can update to a newer one, same model though, I love the 300. This is a '97 300 EXC. Upgrades include; skid plate, factory kickstand, bark busters, FMF Fatty pipe, wider foot pegs and factory rear fender rack. As soon as I got it I had the forks rebuilt and set the sag for my riding weight. The bike has spent some time on the ice and a fair amount of time in the Vermont woods. I registered it to comply with state regulations for riding on the ice.

The front tire/wheel is a Dunlop K491 with a liner mounted on a '99 KTM wheel, single Holiday Canadian spec screws for right and left turns.

The rear tire/wheel is a lined Yokahama Super Digger mounted on an earlier '93 KTM wheel. The tire was built by a Canadian fellow, originally as a left turn only. It is shaved to bias left turns but not radically. I added right side screws to complete the pattern, and it works very well in both directions with a slightly "late transfer" over the top.

This bike absolutely rips on the ice, very stable and confident on ovals or road courses. It has the grunt to loft the front wheel exiting the lower speed turns, or you can feed in the throttle and keep the bike down on the side screws and just rail the turns.

When you put the "summer" tires back on and ride the woods, this thing still shines. Low speed handling and rideability are amazing and if the trail opens up you're back on the main jet without skipping a beat.