KT100 problems

Bill Faulk · Posted: Tue Aug 28, 2012 4:43 pm Post subject: KT100 problems

Going down the back straight @ at 14k rpm then lost all power. I did not notice any noise or warning signs. I dont know what happened however the engine will not start.

running 110 at 9oz/gal castor927
engine has (to my best knowledge) .6 hrs on it.
Driver(me) is very new to karting
Compression test dry 70 wet 75 (Normal is around 160 i have read)

So i started to trouble shoot.

Spark plug:

Took the head off.

I noticed there is like a half moon where there is no carbon build up is that normal?

I cleaned off the top with a shop rag.

Inside

The rod moved side to side. I don't think it is supposed to?

After i took everything apart i noticed this hanging down from the motor. I dont know what exactly it is or its function.

Does anyone see anything that jumps out at them?
I have Several more photos available and i have time.
At the moment i don't have money to take it to a shop. I can afford parts.
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-Bill

Ron Gordon · Joined: 27 Dec 2009 Posts: 150

JT Miles · Posted: Tue Aug 28, 2012 5:22 pm Post subject:

Thats the TCI unit...needs to be ground to engine some how...looks like the tabs to hold it on the chain guard/stator cover have broke off..thats why you have no spark...
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Miles Racing
2nd Place 2012 Kid Kart Nationals
Energy Kid Kart/ CKS C51
Birel Kid Kart/ LAD C51 #7C
Intrepid/MY09 Comet Leopard #722
Emmick/K78 and TT25

Walt Gifford · Posted: Tue Aug 28, 2012 5:22 pm Post subject:

You lost spark. Too bad you took the motor apart, all you had to do was reconnect the TCI box to ground. They make a special holder for those after the tabs break off like yours did.

Gif Cool

_________________
FAA certified jet engine and aircraft technician
Nicholson Speedway class champion 2001
Yamaha KT100 Service Center
40 years karting experience

JT Miles · Posted: Tue Aug 28, 2012 5:26 pm Post subject:

Beat me to it..haha
_________________
Miles Racing
2nd Place 2012 Kid Kart Nationals
Energy Kid Kart/ CKS C51
Birel Kid Kart/ LAD C51 #7C
Intrepid/MY09 Comet Leopard #722
Emmick/K78 and TT25

Dan Rudd · Joined: 15 Oct 2009 Posts: 198

I agree with the TCI diagnosis but if your compression is 70-75 you have some issues there as well. As long as it's torn down, sounds like time for a hone and piston at the very least.

Dan

Jim White · Joined: 21 Jul 2001 Posts: 994

I'd put it back together and get the TCI properly grounded and see how it runs. Looking at the pics it's not stuck.
To check compression you need to ground the sparkplug while cranking the motor with the throttle wide open. You will get low readings with the throttle closed.

Sean Kisselbach · Joined: 04 Feb 2012 Posts: 18

I dont know about a new piston but i would hone it and get a gold ring.

Bill Faulk · Posted: Tue Aug 28, 2012 9:31 pm Post subject:

Thank you for the quick diagnosis i will re attach the TCI in the next few days.

Sean Kisselbach · Joined: 04 Feb 2012 Posts: 18

Its a type of ring.

http://www.cometkartsales.com/store/p&p/yamahaoh.htm

Walt Gifford · Posted: Wed Aug 29, 2012 9:33 am Post subject:

I was going to mention that bore looks kind'a bad. Also, I hope that's camera distortion in the pic of your big end bearing because it looks like the cage broke and the pins are off square. Even so those pins look frosted.

That's allot of carbon build up for an engine with .6 hrs on it unless you're running 30w motor oil.

Since you're new to karting I'll tell you there are builders out there that will scuff the bore with a crap hone, put in a new ring on the old piston, carb kit and spark plug and call it a total overhaul without even scraping the carbon off the piston/head. They stay in business because allot of people are in and out of the Yamaha class so fast they don't notice.

You need to find a real engine builder if you are serious about staying in that class.

Gif Cool

_________________
FAA certified jet engine and aircraft technician
Nicholson Speedway class champion 2001
Yamaha KT100 Service Center
40 years karting experience

charles hunter · Posted: Wed Aug 29, 2012 1:44 pm Post subject:

I'ts a good thing you took it apart cause now you know what things look like and wear like in relationship to how the motor is running and you are now SMARTER!!! Just trust the force and hone the cylinder, measure the bore, order a new piston and ring and kick back knowing you'all are now a mechanix. Listen, none of this is hard whatsoever but you do need some tools BUT they don't have to be expensive and if your going to be a karter you need to do this stuff yourself (unless you are a "professional") and you should be friends with someone who has the tools and loves racing enough to help the newer guy so the sport will grow. Besides you start askin questions on this site and I guarantee you will get answers, alot of answers, I mean a really lot of answers. Some wont even be relative to your question, but that's a good thing. Don't quit!!
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Sam Zavaglia · Posted: Thu Sep 06, 2012 10:21 pm Post subject:

Those TCI tabs always snap from vibration.
Get a TCI holder like this and it will fit "snug as a bug" and mount your current broken TCI to the engine mount. Simply mounting this will ground out the TCI to the engine without having to use any ground/earth wires.
You will never have this problem again. By far the best way to ground the TCI to the engine and now only way since the tabs are broken.
http://www.andrewsmachineservice.com/Products/TCIMounts.html
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www.samzavaglia.com

Patrick Hubbell · Posted: Wed Sep 26, 2012 9:58 am Post subject:

That engine looks like it has more than .6 hours on it. I would not mount the TCI to the engine. I would attach a wire to the tci then attach the other end to the engine, this will ground the tci to the engine. Mount the tci to the pulse line or fuel line. Electronics don't like heat and vibration.

Have you checked the piston to cylinder clearence or the end gap of the piston ring?
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Patrick Hubbell