It's May!Only 29 days until the 100th running of the Greatest Spectacle in Racing.
And that means it's kart season. WooHoo!!
Most of my time lately has been spent working on graphic design and letterpress projects. ( Selfish plug: tagdesignstudios.com )
Christmas was a "KARTFEST!" I received many kart related gifts including a new starter ( more of a Pam gift to herself since she will be using it), a GoPro camera, a new smoked helmet shield, two new chains, two new chain breakers, and several new sprockets. All suggestions from my list.
Compared to last year I am way ahead as we approach Mid-Ohio in June. Last year I did a full engine and brake rebuild, along with new axle bearings and adding the Digitron. Not this year. I will be testing for air leaks, pop-off, and check on timing. Hopefully, that will be all before heading out.
I know it's silly... but one fun thing I put together over the winter was a new push stick. The one I created a couple years ago was steel tubing and bolted together... loosely. And with the tach/temp Digitron onto steering wheel now, the design was wrong and did not work as needed. I found aluminum tubing at Home Depot then took it to a local tool/welding shop - Jerrett Welding - near Pam's workplace. The design came from the pushsticks engineered by the guys from Boston.
|My new push stick|
|The Boston guys' design|
One of the problems I had last year was with the left brake. It was always engaged and would not retract. And brakes were spongy with only one caliper working effectively. Over the winter I took an Airheart brake caliper off the Hartman kart and got to know the mechanism much better. Doing research on http://vintagekarts.com forums I found out even more from the kart veterans. I also tracked down a vintage kart magazine article about the magic of Airheart brakes and the legendary "drag ring," which looks like a warped washer. Instead it is a highly engineered and machined means to keep the puck exactly the right clearance as it wears.
|The Airheart retaining ring|
Another important factor is not to "snag" or "catch" the piston stem as it is pushed through the drag ring. Many vintage guys suggested using a hydraulic press to install the piston (NEVER USE A HAMMER--woops! another rookie mistake), but after investigating and looking at videos on youtube.com I thought that was overkill. So I started thinking about how to make a small one. Then BINGO! While at an antique store in northern Virginia I saw it... an antique bottle capper!
It delivers nice, even pressure I can control and also feel if there is any "catching" in the process. I purchased it for $12. The I made a tool from a PVC pipe fitting which gives a surface to press against during the "press out" process, flip it over, and use it for the "press in" process. It works great. I am right proud of it!
Last week I took the offending caliper off the cart and worked through a couple things. I replaced the bolts attaching the caliper to the frame from grade 5 to grade 8. That's when I noticed washers between the two pieces of the caliper... which should not be there.
|Where the extra washers were...|
I took the caliper to the workbench and I pressed out the piston (the press worked great!), changed the o-ring seals, checked the retaining ring, and pressed it all back together in about 10 minutes. This time the piston pressed all the way in by hand. No need for extra washers.
|Looking into the caliper at the drag ring with retaining ring removed|
|Looking into the caliper at the retaining ring, drag ring, and o-ring seal.|
|Piston and piston stem. Note the silver scratches on the stem made by the drag ring.|
Since I have two master cylinders, I use an adjustable linkage between the two. Originally, it was designed to bias the front or rear brakes when this kart had four-wheel brakes. I am working on getting the two master cylinders to work exactly together.
I have been dreaming of getting an automatic kart stand so I can work alone. Then during a conversation with Rick he asked if I had a push stick. I said that I did but was dreaming of a kart lift. He has one and offered it to me for a great price.
It has a boat wench action so it will still be some work, but much better than lifting... and looking for help. :-)
One of the problems last year at Mid-Ohio was the chain. I dropped out of two races with a broken chain then a chain off the sprocket that clanged around and damaged the clutch sprocket. It actually cracked or broke off the tips of the hardened steel teeth on the clutch.
I asked Rick about it and he suggested I not use it. Fortunately, I have a second one from Dad's stash, but it did not have the bearing. I identified it, looked all over for it, then Rick sent me three... for free. I found out how to press-in the bearing with a bolt and nut on youtube.
Due to the sprocket alignment problem last year, Rick suggested giving up on the Lemelo aluminum oiler sprocket. It is a pain to align due to how it grips the axle. Dad's stash had another light sprocket but it also had a tricky system. I started looking for what Rich suggested - a sprocket with one sprocket head bolt for easy alignment. While looking for something else in the vintage stash bin, I saw something...
A never-opened GEM sprocket! That's real NOS...NEW-OLD-STOCK! Exactly what I needed.
Even before I got the kart running I had heard of setting-up the carb properly so it four-cycles at the end of the straight. At Mid-Ohio it does fine on the main straight but only lasts about 1/2 of the backstretch. So I sent a GoPro video of me at Mid-Ohio to Steve O'Hara, karting demigod, to ask for help. He was gracious and made two big suggestions:
- Since the engine was topping out at under 10,000 RPM, I should move up to a 64 tooth sprocket with the 14 tooth drive gear. This should allow higher revs.
- The clutch was not engaging coming out of corners, so add weight to the clutch arms to get it to grab earlier.
To help with adjusting the carb, I have looked into using a remote carb adjuster. I bought one over a year ago but had let it sit. Recently, a vintage forum post asked about them and I joined in. SteveO posted some pictures of a set-up he used with great success using gears from remote control cars:
I have finally found similar gears and am now in the middle making a bracket from aluminum. The larger gear ratio will allow me to get more torque to the High Speed needle for easy and precise adjustment. We'll see how it goes.
|future bracket being cut|
|19 tooth, 48 pitch, 5mm shaft R/C gear|
|57/36 tooth, 48 pitch, 5mm shaft R/C gear|