Home Forums 2-Cycle Racing KT100 SA Blueprint

This topic contains 12 replies, has 5 voices, and was last updated by  Walt Gifford 11 months ago.

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  • #16750

    Walt Gifford
    Participant

    Ok, After a few health problems, continuing the SA build. Here’s the link to part one. http://eknclassic.com/viewtopic.php?t=122536&postdays=0&postorder=asc&start=0

    Now, the piston is 17.5g heavier than stock and I’m adding 31g of lead to the crank pin for extra mass so, I have to add some little tungsten counter weights. Weights are 14g each and spaced 1/4″ outside the stroke circle. Weights are from the pinewood derby world and are a nice press fit with a “T” drill. After pressing I peened the holes in 3 places.

    Here’s the pressing operation. That’s my home made crank alignment fixture.

    And the finished product.

    More to come.
    Gif

    #17170

    Jim Silverheels
    Participant

    Giff, ever do a before and after dyno test on a yammy for can or pipe please? results? thanks

    #17171

    Jim Silverheels
    Participant

    After the BP of course.

    #17186

    brian downing
    Participant

    Nice job!

    It would be nice to see full size pics.

    Clicking  on those photobucket links just brings same pic.

    Please upload larger images for more detail

    #17618

    Walt Gifford
    Participant

    Got the crank and bottom end together. Pretty standard stuff really. One mod I do on all my engines is to cut the shoulder on the pto back .050″ to give room for the chain on a 10th 219 gear and also allows a nice thick spacer. From shoulder to end of pto is 2-1/8″ now.

    LOL, look at that big ‘ol piston.

    I left a little more end play on the rod and crank this time. .032 on the rod and .014″ on the crank.
    The main bearing pockets weren’t that deep on this one so, I had to use a few split line gaskets to get those numbers. If not the rod side play would be too tight to oil the big end. In fact, looking at the rod, I think that’s why this engine blew up.

    Checking the timing with a .010″ gasket the exhaust opens .035″ too late so I’ve got some head scratching to do but will probably just use 4 aluminum shims. Dang, this engine needs allot of gaskets.

    Gif

    #17845

    Walt Gifford
    Participant

    Got enough gaskets to set the exhaust timing at 1.155″ with the WKA tool then checked the intake timing. Had to cut .065″ off the skirt to get .775″, again using the WKA tech tool. Here I’m cutting a .030″ chamfer at 45 degrees on the skirt with brass shims on the jaws to keep from scratching the piston.

    Putting the wrist pin clips in with my (Snap On) duck bill pliers. Here’s the grip you want so the clip doesn’t fold back. the open end goes at 12 O’clock.

    On the first clip don’t let the open end of the clip go past the groove when you first push it in. Hold the wrist pin in place from the other side.

    Next push the clip in the hole at a steep angle. Once it’s in bring the nose of the pliers as close to the piston as possible. Then put your left thumb nail hard on the clip as you release the pliers (not in pics, had to hold the camera).

    Before your thumbnail gives out push the bottom of the clip into the hole with the nose of the pliers. Then push the clip the rest of the way into the groove.

    I inspect it with a strong light and 5x jewelers loupe.

    I usually use IAME clips because, they are slightly thicker than oem Yamaha. On this piston they wouldn’t fit because, the wrist pin was chamfered on the ends and fit so perfectly to the clips it came with there was no side to side movement after both clips were installed. Nice attention to detail from Burris.

    Gif

    #18103

    CLIFF BRYANT
    Participant

    I like your poor-mans crank jig… Keep posting.

    #18928

    Walt Gifford
    Participant

    Got the cylinder on and the reeds move freely and seal quite well.

    Time to get a head in life. Keeping with junk parts theme of this build I have gathered several heads over the years from various places.

    Top left is a rare find, an old 9CC head with no yamaha lettering and uncut the plug depth is .580″. Top right is the 11CC new style die cast head that came on the engine plug depth .550″. Bottom left is an old black fin head (SKS) Heli coiled with a very round and smooth combustion chamber about 11CC maybe made for enduro racing on gas with a pipe, plug depth .650″. Bottom right is an old style 11CC red fin head (Emmick) plug depth .540″.

    The heat and pressure under the head nuts make the aluminum squeeze into the hole so, I like to spot face the top. First I drill with 11/32″ then I use a counter bore with a special pilot I made that’s .333″ diameter. The plug boss is cleaned with scotchbrite and not cut.

    Next I mounted each head on my home made billet mandrel and found the bottom two in the pic above to be off square and off center so much I can’t re-cut them using this method. I think some one re-cut these using a crooked spark plug for a mandrel. Note to self: don’t but heads on eBay lol.

    I’m saving the uncut head for an alky motor and the new style head was only out .005″ so, it seems to be the best candidate even though I wanted to use one of the denser castings.

    I want to run this engine on high test pump gas and possibly use a full wave pipe. Here I’m cutting the squish band to 17 degrees. I inked the gasket area so I can make a good measurement after each cut. More later.

    Gif

    #19056

    Walt Gifford
    Participant

    Here’s the finished head shape polished with 1/16th radius and gasket area lapped on a surface plate.

    Checking the deck clearance I can use a .005″ head gasket which is my thickness of choice. I made this tool that lets me bore out the ID for the bigger piston size. Basically you center the gasket then clamp a plate over it and bore it out. If someone makes head gaskets for these bigger pistons please let me know.

    Checking the head space to find I’ve got 10.5CC, should be trouble free for any kind of fuel or exhaust system I want to use.

    Gif

    #19062

    Glenn L Riggs
    Participant

    Hi Gif I read your  posts regulary and was wondering if you found any performance differences in the location of the plug  if cutting the top of the head to lower plug into compression area. Yes it will lower compression but was wondering on effects of the burn in the cylinder. Just thinking out loud as there is a bad storm here and nothing to do. By the way I like your press made one close to it but have 5 spots for contact leaving one stud out for rod location. Thanks Glenn

    #19166

    Walt Gifford
    Participant

    any performance differences in the location of the plug when cutting the top of the head to lower plug into compression area.

    If there was an advantage there would probably be a new rule against it. I guess some guys are doing this to cheat the 11CC rule, impetuous.

    I have no hard data but I do know you need a big increase in compression before you feel it in the seat of your pants coming off a turn.

    You only get to extend the plug about an 1/8″ before you’re trapping air with the tech tool. If you use an extended tip plug it’s dang close to the piston. It’s easier to strip the head at the track.

    I go for a clean bee hive combustion chamber centered on the bore for maximum fuel burn because, I know that works.

    Gif

    #19314

    Walt Gifford
    Participant

    Here’s a tool I use to spot face electrical connections. It’s a wire brush with a pilot. Great for getting corrosion off the aluminum coil mount.

    Ok Here for all time is how you set up a KT100 ignition. First put the flywheel on with the factory key installed. (Note the spot faced bolt holes.)

    Now here’s the trick. Get the bonded paper cover off a Pitt catalog and cut two strips. The two together should measure .021″.

    Put the two strips around the flywheel. Push the coil in tight and tighten the bolts, top one first. That’s it, done.

    I put some heat shrink and spiral wrap on the plug wire where it touches things and wrap the TCI wire with electrical tape where it goes through the clip.

    I’m working on a TCI mount for the back of my seat but I need to get some good ground wire. Never had a problem mounting it on the engine though.

    I’ll set the engine aside for now while I work on the stock appearing carb.

    Gif

    #19823

    Walt Gifford
    Participant

    Here we go, my favorite thing in the world, a box of junk parts.

    Someone tried to bore this out for WKA and went too far at .960″ perfect for me though. I ground out the choke stop and lettering on the venturi then smoothed it out by hand with sandpaper and polished it with a scotchbrite muff spinning in the drill press.

    I lapped the front, back and pumper surface with 600 grit and on the metering side I use a flat file and work around the nubs to take down any high spots. I also drilled the transition jet with a #55 drill to increase the fuel signal to the low needle.

    Here’s something I always wanted to try. I opened up the pumper area on the crankcase side to the edge of the gasket seem. Maybe it will give the pump more effective area.

    Now I mount the carby euro style and you have to do a couple of things for this. You have to drill new holes in the carb plate and you have to grind the cable arm to fit around the metering plate screw.

    You also need to cut back some cooling fins on the cylinder to clear the throttle arm and you need a longer pulse tube. This allows me to comfortably reach the needles while driving. It also makes it easy to clean the screen or change pumpers at the track.

    That’s it for now because it’s still freezing outside but I’ll get this thing on the no load dyno when the weather breaks. Hopefully the ground hog won’t see his shadow this year.

    Gif

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