Stock appearing kt100

Audi, sorry, but that was years before I started using a digital camera, or started saving images.
If I have any, they were taken with a 35mm, and packed away somewhere in a large box.
The final version before we got away from KTs, was pretty close to the JLO head above, and we did it without welding anything (which I think would have been illegal for a stock class).

But you can get a better understanding of off-set combustion chambers in Gordon Jennings book.
Here is one on-line: https://vintagesleds.com/library/manuals/misc/Two-stroke%20Tuner's%20Handbook.pdf
 
What type of exhaust system were you running and what head pipe length were you running from the piston face to the start of the front cone? The damage you see on the piston can be caused by the pipe setup being too short or by using a pipe with too little volume. Your piston shows that the damage occurred and then it looks like you richened the mixture and began covering the damage with carbon deposits. It goes without saying... but I will say it anyway... that whenever you boost the compression in an engine it will become more sensitive to the air/fuel mixture and setup flaws that would otherwise be masked by low compression will be exposed. At 11cc to the top of the spark plug hole the KT100 engine is a very low compression engine and that spec was an artificial limit imposed by the rule makers for IKF and WKA way back in the late 70s. It has nothing to do with the best performance or the limits the engine can handle. I run the KT100s with a stock head that has the entire step machined off which drops the squish clearance down to around .025". I do not touch the original factory shaped dome so the result is around 9 to 9.2cc to the top of the spark plug. With the stock ignition setup the engines run best on pump gas with castor at a 16/1 mix ratio. The engines run around 375 to 400 CHT and in the mid 1,100s on EGT using the same plug you ran. They are very easy to tune and the change in compression from an 11 cc head is typically worth around 1 second per lap on a 50 second track. The difference is most noticeable at the bottom of the power band and to maximize the benefits the clutch should be set up to stall about 1,000 rpm lower than you would use with 11cc. I run my L&T or DXL clutches set up to hook up around 9,200 rpm when running a good RLV or Pitts blimp type pipe.
What skirt clearance does your engine have? When you boost the compression the engine will naturally generate more heat on the crown of the piston so that must be taken into consideration when determining the correct skirt to cylinder wall clearance. I set them up at .004" or .1mm. Any less when using a slipper clutch is asking for trouble. If you run direct drive or a low stall clutch you can reduce the clearance down to .0025" and be safe.
Steve O'Hara
 
Steve O'Hara said:
If you run direct drive or a low stall clutch you can reduce the clearance down to .0025" and be safe.
Steve O'Hara
Click to expand...
I think Pete Muller might have some thoughts on that! I've heard he sets up his direct drive KT's with only .001" piston clearance.
You might also point out that you're talking about premium pump gas, not regular. Using regular, unleaded, at Sears Point (infinity Raceway), Sprint sit up, while leading the class, we only saw 1050° on the EGT. On my dyno, using race gas, I normally saw about 1150° EGT on the KT. On one particular KT, one that was often the fastest at the track, I even saw 1200° EGT.
 
I always set mine up with .0015" clearance, the way Yamaha did on their air cooled road race bikes.
Broke them in by spinning them with an electric motor for an hour with fuel going through, then with the plug in, ignition on, on the chassis, spinning the axle, at about a 5k rpm 'idle'.

Never worried about them after that, hit the track running hard, no additional break-in.
 
GoFast said:
I always set mine up with .0015" clearance, the way Yamaha did on their air cooled road race bikes.
Broke them in by spinning them with an electric motor for an hour with fuel going through, then with the plug in, ignition on, on the chassis, spinning the axle, at about a 5k rpm 'idle'.

Never worried about them after that, hit the track running hard, no additional break-in.
Click to expand...
Not saying that there's anything wrong with your method, but you might try this. I would let the engine run, on the kart, at an idol, with the carburetor just a little rich. I found that, at some point, the engine would suddenly pick up a lot of RPM. I attributed that, rpm increase, to the rings seating. One practice session, at a moderate load, and the engine was broke-in. Never had any problem with that method.
After this break-in procedure, I would always check the compression pressure using my Snap-On gauge. 160 PSI was the goal. That's with an IKF, to the spec, KT.
 
Hi Al, yes I am familair with time area the 80 degrees refers to the piston port for intake timing only, remember this is for a stock appearing kt100 not a all out open hence exhaust ports are somewhat mild, about the clutch I see a lot of disc type clutches set to correct engagement rpm but linger at this rpm level creating tons of heat, poor kart acceleration and eventual clutch/en gine failure. I am not telling you this is the only way but it sure does work and ALL who I have done this for are "Happy Campers".
Mike Berg
 
Horstman made 'Z' weights for the DXL when run on a Mac, that would lock up quicker, with the same initial engagement rpm.
 
Steve O'Hara said:
What type of exhaust system were you running and what head pipe length were you running from the piston face to the start of the front cone? The damage you see on the piston can be caused by the pipe setup being too short or by using a pipe with too little volume. Your piston shows that the damage occurred and then it looks like you richened the mixture and began covering the damage with carbon deposits. It goes without saying... but I will say it anyway... that whenever you boost the compression in an engine it will become more sensitive to the air/fuel mixture and setup flaws that would otherwise be masked by low compression will be exposed. At 11cc to the top of the spark plug hole the KT100 engine is a very low compression engine and that spec was an artificial limit imposed by the rule makers for IKF and WKA way back in the late 70s. It has nothing to do with the best performance or the limits the engine can handle. I run the KT100s with a stock head that has the entire step machined off which drops the squish clearance down to around .025". I do not touch the original factory shaped dome so the result is around 9 to 9.2cc to the top of the spark plug. With the stock ignition setup the engines run best on pump gas with castor at a 16/1 mix ratio. The engines run around 375 to 400 CHT and in the mid 1,100s on EGT using the same plug you ran. They are very easy to tune and the change in compression from an 11 cc head is typically worth around 1 second per lap on a 50 second track. The difference is most noticeable at the bottom of the power band and to maximize the benefits the clutch should be set up to stall about 1,000 rpm lower than you would use with 11cc. I run my L&T or DXL clutches set up to hook up around 9,200 rpm when running a good RLV or Pitts blimp type pipe.
What skirt clearance does your engine have? When you boost the compression the engine will naturally generate more heat on the crown of the piston so that must be taken into consideration when determining the correct skirt to cylinder wall clearance. I set them up at .004" or .1mm. Any less when using a slipper clutch is asking for trouble. If you run direct drive or a low stall clutch you can reduce the clearance down to .0025" and be safe.
Steve O'Hara
Click to expand...

Steve. Sorry I missed this I put the head on the shelf and had put this topic out of my mind for awhile.

Pipe is the SR-Y pipe that WKA converted to for a couple of years, running 9.75" flex length (face of piston to end of flex). Min WKA flex for this pipe was 9.5 when run in competition. Fuel setting on the carb was 2.5 turns on the low and 1/4 turn on the high.

Head was cut as you describe, machined down to .27 squish value, slight angle cut on the squish band and no work done to the bowl of the head.

stock ignition setup with the coil as far away as possible from the rotor (not slotted or modified).

Caster and synthetic oil mix at 8oz per gallon with 110 race fuel.

L&T clutch set to 8800rpm

piston clearance is .0035 I believe, I'd have to double check

as I said earlier, I don't own a burette to double check the work, the compression numbers seemed abnormally high compared to what most here thought that they should be (240-245psi). Maybe the bowl should have been opened up some when I had it machined? Everything else lines up which is what's left me scratching my head.
 
The squish band should be at a 17 degree angle with a 1/16" radius where the squish band meets the combustion chamber and head clearance should be .028" IF the head is perfectly centered (check 4 places). These are minimum numbers that can be increased for more streetability and it's best to work with the old style head as it dissipates heat better.

You should use a retracted tip or at least a regular tip spark plug. Stay away from the extended tip AR51 for this set up. You don't want flame propagation to start on the piston you want it to start burning from the top down like God intended.

You need to run VP C12, Sunoco Purple or something like that, high test pump gas ain't gonna' cut the mustard when you get the carb tweaked down. Your oil should be 8 ounces of Blenzal Green Label to carry away heat not the thinned out castor they run in Rotax ect. to keep the exhaust port clean.

These things get to be more trouble and more money for less and less speed gain so at some point you have to ask if we're still having fun with a 9cc head. Answer "Yes we are" but, if you're 35 Lbs over you might have some physics you can't fix by tweaking out the motor to the Nth degree.

Sundog
 
Thanks I need to fully read and understand it all first .
First question was adding exhaust ports .
VS Opening the port up ?
 
flattop1 said:
Thanks I need to fully read and understand it all first .
First question was adding exhaust ports .
VS Opening the port up ?
Click to expand...
If my understanding of Area/Time is correct, from Gordon Jennings Two-Stroke Tuners Hand Book, adding port area, (widening the ports) or raising the ports, (adding port area) does the same thing. More peak power, at a
higher RPM. Adding exhaust ports, just simply adds more area. Adding more area, widening the ports, or raising the ports, more area, should be the same.
I have a copy of that book, in almost pristine condition.
 
sundog said:
I don't know how you would add exhaust ports on a KT100, most just eyebrow the top.
Click to expand...
1590935678285.png

I have seen at least 2 done this way.

Brian #89
 
That's pretty cool and looks like a tremendous amount of work but I don't know if you'll get a significant amount of flow through those narrow channels. Would like to see some dyno charts comparing that to eyebrow ports which are very easy to cut. That metal has got to be thin right there. I wonder how many cylinders they did where they broke through to the outside before they got it right.

Sundog
 
I know what you mean. Better know exactly where to drill & cut. I choose eyebrow. Just easier to do. Not sure how much advantage but must have been some. That cylinder is a Buller that just recently sold for a pretty penny.

Brian #89
 
Here is the other KT with 4 port exhaust. It was by Cook Racing.

1590950584573.png


Sean Cook stated this modification is based off the Parilla TT-36 & Komet K-30.

Brian #89
 
You must log in or register to reply here.
Back
Top