I’ll get it apart tonight…maybe it’s not actually hitting it just looked suspect when loading up and inspecting last night. could be my eyes playing tricks on me after a long day and again it ran great so maybe optical illusion.
I sent the cylinder / piston / crank to the builder after it broke the piston and he checked crank for runout as part of his analysis and it was fine.
It’s not so much runout on the crank, but play in the bearings (AKA Main Bearings) that the crank passes through. Sometimes the play can be a result of the crank web itself being slightly worn and therefore loose in the bearing itself.
To check you just have to grab the crank and try and pull it up/down. If nothing else, it’s a good check to have in your repertoire.
Great point James…I’ll def check that and thank you!
any play, up or down, in the bearings is bad, real bad!!
When I say any play, I mean, up and down .0005". That’s too much. The only way to check that is with a dial indicator. with a .0001 readout. there’s no way you’re going to feel that by hand. Hopefully you haven’t damaged the crankshaft. the KT1100, when they get loose, will beat the crank (it’s soft) journal out of around.
Well let’s put it this way then… if you can feel it move it’s past that point 
That sounds like a very tight tolerance for a C3 and C4 bearing though.
you may be right. Still, if you can feel it move, it’s way beyond raceable.
It’s a fixed gap, and there is no need to tighten the air gap as you typically don’t even set the advance on KA’s to the legal limit anyway. The stator is a bit finicky as the magnet on the rotor pulls the stator towards the rotor instead of staying flush to the edge of the cage. It would be nice if there was a guide on the inner side of the stator so that it couldn’t be pulled inward. You have to be careful when setting the timing; you have to make sure both sides of the stator are perfectly flush with the cage on the case before you take your reading and tighten it down (it tends to pull on the exhaust side of the stator). If it’s not flush with the guides your timing will be off and the stator pick-up will rub on the rotor. If you stick a light under the rotor and turn the crank, you will be able to see if the stator is rubbing. I’ve seen this on a number of KA’s.
Thanks for the input Christian, that’s basically what happened, thankfully the rubbing was minor very minor, I’ve made certain to set the stator all the way back against the cage and am good to go now, don’t think I did any real damage to either the rotor or the stator thankfully, very faint wear pattern on the rotor is all. put a feeler gauge on it after to confirm and will do so in the future just to be certain…gap was about .015
If it’s not giving away trade secrets, do you mind elaborating on your comment of: “you typically don’t even set the advance on KA’s to the legal limit anyway”. My brother and I both purchased “blueprinted” KA’s second hand, from different builders and both of them came within .001 of legal limit for timing.
First thing we did with them was tear it completely apart to see what really goes into the blueprinting process, after hours and hours of staring at and measuring things the only “interesting” difference was in the carbs.
The KA is still a relatively new package, and the way they are being built is evolving. Initially when I was building them I’d set the timing very close to the limit, but now I’ve played around with and tested some other tolerances and find I can back off the timing a bit to pick up top end. I’ve seen this change on other KA’s I’ve gotten in as well. What did you find “interesting” about the carbs? There have been a lot of rumors going around about carb “shenanigans”, that go well beyond just how the carb is set up (pop-off, fulcrum height, etc.) Not suggesting anything is funky with your stuff.
Has anyone else felt the throttle response in the KA to be a bit laggy? Coming from Yamaha where throttle response was instant it was a surprising difference that the KA seems to take a bit to come alive after opening the throttle.
Is there a tuning method to change that response? Or is it technique like with Rotax where I need to roll into it slower? Or are you guys just getting back to throttle sooner to compensate?
I’ve actually always thought the KA throttle response was really good. Is your carb tuned correctly?
I wonder if the slower response you’re experiencing compared to the Yamaha has more to do with the clutch on KT100s vs the KA which engages at a much lower RPM. Granted, it’s been years since I’ve touched a kart with a Yamaha bolted to it, but I figure that a clutch that can be adjusted to engage at a higher RPM is probably going to feel more responsive on the throttle than an engine that can keeps the clutch engaged well below the powerband. Also maybe your gearing is just too low? What RPMs are you peaking at and bottoming out at?
Carb was set at scribed settings from the builder so hopefully not far off. The kart wasn’t laying down or bogging, but there was a noticeable difference in throttle response for sure between motors having driven them just a week apart on the same track. The Yamaha definitely has a higher slip clutch but in the configuration I was running it would only make a difference (slip) in one corner. Perhaps it’s just the lighter clutch setup of the Yamaha is snappier.
IAME actually make a Stator centering tool ATT-065 which makes installation a breeze.
Cool, thanks Paul. The tool is not imported here, but I will see if the importer can get one for me.
Running Yamaha with pipe last year and running KA this year I get where you are coming from. I think its a combination of things. The KA clutch engages much lower than the typical Yamaha so you’re not getting that rev before engagement. I think the IAME clutch engages at 5k. I’ve found if you have a tighter corner where your rpm is below 7k it will feel a little laggy, but by 8-9K it should be coming on hard. However, if your competitors are pulling on you in the same places you’re noticing a issue, then look to gearing and carb adjustment.
Clutch engagement should be about 3400 RPM if I remember correctly, but yes, if you drop below 8200-ish RPM your motor will bog coming out of the corner until it gets back into the powerband. Generally you should be trying to gear the kart to have the minimum RPM at about 8200 RPM
Aaron, I have struggled with this. I think Christian Fox also list 7500 as a low RPM target on his website. My situation is I have a tight hairpin at the end of the longest straight and even if I gear to hit 16k I have a tough time staying above 7k in the hairpin. So as in many things, it’s a compromise. So I have struggles with balancing the high and low rpm. If I gear to hit 16k I will only see that for about 1-2 seconds at the end, so should I go over 16K to have higher rpms in the hairpin?
Pete Mueller has told us he would regularly see 17,000+ RPM on his KT100 direct drive! I find it hard to believe that the KA100 is any less capable! The KA is superior in every way, shape and parts, it should be more capable than a KT100.
This is racing, not a contest to see who’s motor will last longer.
I understand the constraints that are placed on us by our budget, but deal with it. “Speed costs”, how fast do you want to go?
When I first started driving direct drive I was surprised to find how much sooner I could get on the throttle after breaking into a corner. Work on it!
Honestly this one of those situations where you are close to what the gearing is for your track and you really just need to do as controlled of a test as possible to determine which gear is going to be the quickest. Evaluating power under the curve and min / max RPM for every section of the course will only get you so far. Go have a test day and throw a few combo’s in it and see what’s quickest. Remember to have a control gear and go back to it at the end of the test to prove repeatable results.