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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.....

    https://youtu.be/ky9eLb__vvU

  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
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    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?

  8. #7

    Default Re: New to the forum, LC4 640 questions

    I honestly can't remember if the engine would rev, it's been 2 years since that video I think. I know I tried to ride it once and remember it stalling, I think as I gave it gas and let out the clutch. Don't recall if it stalled while revving alone. The metal shavings were significant. The cylinder screen filter was also packed with shavings. I didn't pull the other filters. I have a picture I'll upload in a bit. I didn't change the oil I just drained it, I know there is a weird procedure I'll have to follow when putting it back together, but for now I was just investigating the cause of the noise and issue. I understand some engines can be noisy, but I am knowledgable mecahnically, work on cars all the time, and this is definitely not a normal noise. The video doesn't do it justice, it's probably 5x louder in person. Additionally, my father in law told me right before he passed that it had a knock and he had to address it. I recall him saying he thought it was the balance shaft. I looked at that and it's bearings and no issues there. I have also ridden the bike once prior about a year before he passed and it didn't make noise like this. I'll have to look but I think the bike has like 10 or 15k miles on it. There was another previous owner (a friend of my father in laws), so I don't really know the history of the bike.

    At this point, I nearly have the engine removed from the frame. I just have to disconnect the chain and the engine mount points. How heavy is this engine? Can I simply lift it out?

    Thanks for the help.
    Attached Thumbnails Attached Thumbnails 20191207_114759.jpg  
    Last edited by snrusnak; 05-28-2020 at 06:01 PM.

  9. #8
    KTMTalk Member
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    Default Re: New to the forum, LC4 640 questions

    I found an old post on google that stated 88.4 lbs for an engine. Two historical problems to check on those engines were wear on the cam shaft and transmission main shaft bearing behind the clutch. On the cam the lobes will show uneven wear. The service manual should show how to pull the engine out of the frame.
    Last edited by beech; 05-28-2020 at 07:44 PM.

  10. #9

    Default Re: New to the forum, LC4 640 questions

    The 620 engine wasn't that heavy to pull out, I did it by hand. The 640 should be similar.
    It's not bad to tear into after. If you just drained the oil and refilled it might be low, it depends whether or not you have an oil filter at the bottom of that tube.
    2005 450 exc
    1996 620 rxc
    1986 250 mxc

  11. #10

    Default Re: New to the forum, LC4 640 questions

    Thanks. I can manhandle <100 lbs. I'm gonna try to finish getting it out of the bike tomorrow. I already pulled the clutch basket and that bearing appears fine. I am pretty sure I'll find a bad rod bearing. I'm very mechanical, but motorcycles are a bit different than cars so this is a slow process for me...

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