640 625 lc4 KTM seized, suspected cooling problem

Discussion in 'Australia' started by unclemitty, Aug 16, 2018.

  1. unclemitty

    unclemitty uncalamity superhero

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    Here is a better picture of the piston. It’s hard to say if there is a “clean spot” on the piston. The carbon buildup is on the intake side and it’s cleaner on the exhaust side. It’s possible that I’ve external of the engine.
    [​IMG]


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  2. unclemitty

    unclemitty uncalamity superhero

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    No, there’s no reservoir on this model.


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  3. unclemitty

    unclemitty uncalamity superhero

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    +1 on the piston carbon build up, I don’t think water has been going into the chamber

    On the other hand, the oil is black as the ace of spades - no milky discolouration from coolant. Furthermore the bottom end has never experienced this common LC4 issue.


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  4. unclemitty

    unclemitty uncalamity superhero

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    Additionally, it seemed to crank and occasionally start after the incident. I think the sprag clutch is ok.


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  5. troy safari carpente

    troy safari carpente #501 Team f5oolery

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    Lots of guesses (a lot of the good ones) on the evidence and testimony provided...

    there's still only the one solution (for all of them collectively)...

    That is to pull 'er apart down to the cases, and rebuild it meticulously by the book... then all of the "possibilities" will be eradicated.
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  6. enookway

    enookway Are we having fun yet?

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    Agreed. If you did the spring recently then it rules that out. If it was original then it would be suspect around 30,000k as you know.
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  7. unclemitty

    unclemitty uncalamity superhero

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    Good point re pressurising the cooling system to try an identify a weak point (ie radiator cap). I remember reading Meat Popsicle’s old post about the same concerns regarding the cap. The fact of the matter is that the water has gone somewhere and if the cap isn’t always getting a good seal then I’d be wise not to keep using it once the bike is back together.


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  8. unclemitty

    unclemitty uncalamity superhero

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    This is true, Troy. However given my current lack of a workshop and the (very) basic information I have regarding the bottom end, I’m likely to try get away with rebuilding from the cases up only. One thing I haven’t done is drain the oil. If it’s full of brass or has significant metal deposits then I’ll consider splitting the cases or even chasing a second motor.


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  9. unclemitty

    unclemitty uncalamity superhero

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    Here are some more pictures of the cylinder and piston. Although the marks are tiny, it still shows evidence of the seizure. I have to say that it was the smallest every seize I have experienced and it freed up straight away. Nevertheless it has damaged the bore.

    I also took several measurements with the bore gauge and it is round. 101.00mm in several locations at the top and bottom of the cylinder. Note: the exhaust side of the piston can be seen in the image showing the split in the oil and compression rings. [​IMG] [​IMG][​IMG][​IMG]


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  10. unclemitty

    unclemitty uncalamity superhero

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    Richo, I’ve just had another tinker with my crank, turning it through several cycles whilst holding the cam chain. It is silky smooth. Again, I haven’t drained the oil (it’s jet black and 1700km old so only 1/3 of the way through its service life) yet but I am confident with the bottom end at this stage.


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  11. richo360

    richo360 Long timer

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    If that’s a seizure, it’s the nicest one I’ve ever seen.....
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  12. Gunerdo

    Gunerdo fromwanerbe

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    Have to agree, looks more like dirt, after a second look. As in air filter not doing its job.

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  13. OldDog

    OldDog non impediti ratione cogitationis

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    Yeah that doesnt look bad. Glad the bottom end is good that was my greatest concern. If you can grab that barrel and piston for a decent price then grab it!! And fit that but don't think what you have there is scrap. Keep em as spares. I see you were using tap water but has it been losing water when you had coolant cos that shit leaves stains. Pressure test after assembly and run your overflow hose into a small tank to act as a catch can. Does that bike have a temp guage?
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  14. unclemitty

    unclemitty uncalamity superhero

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    So I literally put 250ml of green ethylene glycol in the morning the bike seized. I was riding it for just 15km. It didn’t appear to have “used” or burnt off any coolant so unfortunately I can’t say if it was staining, etc. had I run it for a couple of hundred km prior to the seizure then I might have had a better idea. It’s annoying to not be able to come to a conclusion on whether the cap was leaking or elsewhere in the system a leak had occurred. Retrospectively I should have performed that test before tearing the bike down. Hindsight is always 20/20.

    Whilst there is no water temp gauge on my bike I do have a thermostat controlled fan installed. I bought a lower temp thermostat than the stock KTM part for the 640. Mine will turn the fan on at 95 deg C and turn off at 90 as opposed to the 98/93? degrees KTM part (or thereabouts). Hence the fan comes on regularly and will also cool enough to turn off. I guess it had been working somewhat thus fluid was circulating through the engine but how well the cooling system was working, I can’t say. An important note is that the thermo fan is on the left radiator whereas the temperature control plug is plumbed into the right radiator. Therefore there had to have been some circulation effect for the fan to be coming on and off during the last couple of months.


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  15. OldDog

    OldDog non impediti ratione cogitationis

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    At the risk of starting the usual commentary. What oil are you running? What condition is it in?
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  16. unclemitty

    unclemitty uncalamity superhero

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    I’ve been running Penrite full synthetic 15w 50 motorbike specific oil (clutch friendly engine oil without the friction modifiers). I’ve previously only ever run full synth Shell (optimax?) or Motorex 4T. They all meet the specifications as designated in the manual ranging between 10w40 and 15w50.

    To me, the oil looks the same as any other brand of that quality in the LC4; it turns black in the first 1000km then stays roughly the same viscosity to the naked eye. As for what is scientifically happening, I don’t know. I have never had a lab test my oils ever so I can’t even give you a real baseline or answer. In short and without flogging a dead horse, the oil seems fine to me.


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  17. Aussie Steve

    Aussie Steve Long timer

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    Not much info to go off but when the betting poll goes up my 2c is on cracked head in the exhaust ports.
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  18. unclemitty

    unclemitty uncalamity superhero

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    I’ll take the $0.02 and DM you my bank details

    In all honesty though, the head does look good. That’s not to say that there isn’t a crack in it but I just haven’t had any of the symptoms of a cracked head:
    - the piston doesn’t have any washed carbon effect of a wet cylinder
    - compression was good until it wasn’t...
    - the head gasket was uncompromised

    I’ll try get some photos up soon of the head. I haven’t cleaned it yet or check if it’s true but it didn’t seem visibly warped. Perhaps you’ll get $0.02 from me yet Steve..


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  19. GodSilla

    GodSilla I did that.

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    "compression was good until it wasn't"

    Did it also lose compression?
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  20. unclemitty

    unclemitty uncalamity superhero

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    Yes, it lost enough compression to struggle starting and running yet with coaxing, the motor would start occasionally on the e-start. When I would try kick start the motor, it felt low on compression and only had some compression when at TDC. Again, Unfortunately I don’t have a number for the compression after the seizure.


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