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Thread: New to the forum, LC4 640 questions

  1. #1

    Default New to the forum, LC4 640 questions

    Hi, just joined here. Short version of the story: I have ridden street bikes (suzuki bandit then a buell firebolt) for the past 10-15 years. My father in law passed away (on a bike) about 3 years ago. Wife didn't really want me riding at that time, and honestly I was barely riding anymore anyway, so I sold the buell. We had actually just visited them a couple weeks prior and him and I went on a couple day ride, it was a great last memory. I inhereted a few dirt bikes and a 1999 KTM 640 LC4 from him. I rode the KTM once for about an hour prior to all this, it was a fun bike. It had developed a bad knock right before he passed, I remember him telling me about it. When I got it, it would idle but if you gave it gas or tried to let the clutch out in gear it'd die. Drain plug is full of metal shavings of course. It's been sitting about 2 years now. I'd like to get it running again so I can get back to riding some. I'm not very familiar with these bikes, nor any dual purpose or dirt bike. I pulled the side covers off the engine looking for simple things, found no issues with the counter balance shaft or bearing, etc. I would feel ok splitting the engine open and rebuilding it, if I had some good guidelines, but I'm not really there yet.
    I work on cars and trucks all the time and am very capable, but never really dove into motorcycle mechanics. Honestly, due to time and other projects, I'd love to either pay to have the engine rebuild (can't find anyone....) or buy a new engine (probably crazy expensive). So that basically limits me to a used ebay engine, but haven't had much luck finding one that's affordable and worthwhile.

    I did buy a service manual for the bike, hoping to rebuild the engine. It is very overwhelming lol. Any advice is appreciated?

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  3. #2

    Default Re: New to the forum, LC4 640 questions

    I pulled the clutch basket off (first time ever doing that). Wasn't too hard. Every bearing in there seems perfectly fine. There's some in/out thrust on the shaft that the clutch basket goes on, but the bearings seem fine. The oil pump gears have some deflection, but they're plastic so I figure that's normal. I turned the engine over with socket and ratchet using the crank bolt where the timing chaing is and it's making a strange nois sometimes. Kind of sounds like a ratcheting noise, like if you spin a ratchet backwards fast. Maybe normal? Maybe something to do with the tensioner? Sounds like it's coming somehwere from the rear of the cylinder area, maybe the head, maybe nearer to the starter, not sure... Trying to post a video of it...

  4. #3

    Default Re: New to the forum, LC4 640 questions

    Here's a video.....

  5. #4

    Default Re: New to the forum, LC4 640 questions

    Here's another of when I had it idling when I first got it

  6. #5

    Default Re: New to the forum, LC4 640 questions

    Those are bullet proof engines, they can be noisy also. What I heard it that video did not sound unusual to me. How many miles ? Does the noise quite down when you pull in the clutch ?
    Last edited by ejr; 05-23-2020 at 06:29 PM.
    2005 450 exc
    1996 620 rxc
    1986 250 mxc

  7. #6
    KTMTalk Member
    Join Date
    Aug 2002

    Default Re: New to the forum, LC4 640 questions

    The head on that engine has been replaced as evidenced by its color - black instead of gray like the cylinder. LC4 engines are noisy but reliable. What type and quantity of shavings did you find on the drain plug because a small amount is typical? When you changed the oil did you follow the procedure to refill oil in the frame?

    Regarding the bike stalling. Were you able to rev the engine when it was in neutral?

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