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Thread: CR125 problem solved!

  1. #1
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    28th May 2009 - 20:00
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    CR125 problem solved!

    For a while now - i.e. since i bought the bike - i've been wondering why it had had no bottom end. I've been told 125 2T's have no bottom end etc., but it wasnt until i rode a mates KX125 that i realised my CR125 had something seriously wrong. After returning the bike to stock jetting, checking float height and needle condition, rebuilding the gearbox etc I have just pulled the head off and apart. The pistion and cylinder look in great condition (except for the carbon on he piston cause it is running crap. So looking at the powervalve is about the only thing i can think of. What I found odd looking up from the exhaust port was that I could see above the powervalve when it was in the static position (i.e. closed). As it turns out I cant actually see a way to adjust the CR125's powervalve, so it seemed particuarlly odd to have such a gap above the powervalve (as this would let the petrol air explosiion decompress too early off idle.

    So after much head scratching I pulled out the box that contains the 'spare' engine that I got with the bike - which was the one that had a big end bearing blown. I started looking at the head, and noticed that the edges of the exhaust port looked much sharper, and almost a different shape. I sat it next to the head that i have just pulled off the bike and it looks like whoever "rebuilt" the engine has taken a dremel or the likes to the exhaust port, and bored it out so the powervalve does not actually fit any more (hence the gap above it). Furthermore, i notived that the powervalve flaps in the current head also have holes drilled in them (bout 1mm dia. in each flap) for god knows what reason. I dont think this is a standard feature!

    So quite interesting really, whoever 'rebuilt' that engine is a bloody butcher, and the guy i bought it off trademe obviously either did it himself or figured that out and offloaded it!

    So my question is therefore who reconditions motorcycle heads in the manawatu region, and what does that cost? the old head that i was comparing the current one to looks ok, except it seems to have a few vertical marks (not scratches though) in it, and a couple of patches where it has some build-up on the surface. everything else looks great though, so im hoping i can get that one reconditioned (properly) and then the bike should be a great runner!

    Im acutally quite happy i figured out what was wrong as its the first bike i';ve really pulled to bits and only paying 2k for it, i dont want to be paying a shop to fix the thing cause its so easy. and it will be good when its running properly too as the rest of the bike is in mint condition!

  2. #2
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    so looking at both cylinders again this morning, the piston obviously fits in the cylinder i just took off the bike, but it is too big for the old cylinder. i presume therefore that the current cylinder has been bored and a bigger piston bought - and i presume that i will have to have this done when i get the other cylinder reconditioned. any ideas how i would specify size for the rebore/piston?

  3. #3
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    2nd August 2006 - 22:17
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    it sounds like the second barrel has had a sleeve fitted to it as the 01 has a nikasil bore standard if the piston is still in the second motor it will have a number or letter stamped on the top of it which will tell you what over size it is
    [SIGPIC][/SIG

  4. #4
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    Quote Originally Posted by barty5 View Post
    it sounds like the second barrel has had a sleeve fitted to it as the 01 has a nikasil bore standard if the piston is still in the second motor it will have a number or letter stamped on the top of it which will tell you what over size it is
    na no piston with second motor unfortunately

  5. #5
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    Quote Originally Posted by morg_nz View Post
    na no piston with second motor unfortunately
    you will need to get someone to measure it unless you have a Vernier to do it you should be able to tell from the bottom if it has been sleeved easy to work out what size piston is needed once measured
    [SIGPIC][/SIG

  6. #6
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    Quote Originally Posted by barty5 View Post
    you will need to get someone to measure it unless you have a Vernier to do it you should be able to tell from the bottom if it has been sleeved easy to work out what size piston is needed once measured
    interestingly enough, the current cylinder has had a sleeve fitted, and the second one does not look like it has had anything done to it (that i can see anyway)

  7. #7
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    post up a pic of what you think is wrong with it, ill compare it to my 02 in bits atm... pretty sure they are the same

  8. #8
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    Quote Originally Posted by honda_power View Post
    post up a pic of what you think is wrong with it, ill compare it to my 02 in bits atm... pretty sure they are the same
    good idea our 01 has the top end off at the mo as well
    [SIGPIC][/SIG

  9. #9
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    took the cylinders to honda yesterday to get a price for a resleeve - they rang back saying that they could get a brand new cylinder from honda nz for $369 as they are having a bit of a sale on their older parts (it was going to cost aobut $450 for the resleeve) so i should have a brand new cylinder arriving today, should be excellend :-)

  10. #10
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    Quote Originally Posted by morg_nz View Post
    took the cylinders to honda yesterday to get a price for a resleeve - they rang back saying that they could get a brand new cylinder from honda nz for $369 as they are having a bit of a sale on their older parts (it was going to cost aobut $450 for the resleeve) so i should have a brand new cylinder arriving today, should be excellend :-)
    You will need a new piston to match the cylinder as well!

  11. #11
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    Quote Originally Posted by D dub View Post
    You will need a new piston to match the cylinder as well!
    yep, ordered one of those too! although the bloody cylinder arrived today, but not the piston! grrr, was hoping to rebuild tonight so i can ride at the weekend, but now i'll be out of town till then!

  12. #12
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    25th April 2009 - 17:38
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    sounds like a pretty good deal! you got new powervalves for it too? or try with the old ones
    "A shark on whiskey is mighty risky, but a shark on beer is a beer engineer" - Tad Ghostal

  13. #13
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    Quote Originally Posted by bogan View Post
    sounds like a pretty good deal! you got new powervalves for it too? or try with the old ones
    na, i'll tidy up the old powervalves from the second cylinder (which look pretty good) - the powervalves that came out of the cylinder i was using had holes drilled in them!

    really looking forward to riding the bike like it was meant to!

    haha i was just about to order some v-force 3 reeds as well, but the bloody engine check light came on in our murano and it wants $1k worth of catalytic convertor so guess further performance upgrades for the bike are on hold for a while (note to anyone reading this - nissans are very reliable, but bloody expensive to fix!)

  14. #14
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    Quote Originally Posted by morg_nz View Post
    na, i'll tidy up the old powervalves from the second cylinder (which look pretty good) - the powervalves that came out of the cylinder i was using had holes drilled in them!

    really looking forward to riding the bike like it was meant to!

    haha i was just about to order some v-force 3 reeds as well, but the bloody engine check light came on in our murano and it wants $1k worth of catalytic convertor so guess further performance upgrades for the bike are on hold for a while (note to anyone reading this - nissans are very reliable, but bloody expensive to fix!)
    yeh, she'll be a completely different animal ofter those upgrades I reckon. Personally i see no reason to mod any furthur, the bike certainly isn't the one inhibiting my lap times, and it's a bucketload of fun with the power its got now!

    You ride trail or tracks?
    "A shark on whiskey is mighty risky, but a shark on beer is a beer engineer" - Tad Ghostal

  15. #15
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    Quote Originally Posted by bogan View Post
    yeh, she'll be a completely different animal ofter those upgrades I reckon. Personally i see no reason to mod any furthur, the bike certainly isn't the one inhibiting my lap times, and it's a bucketload of fun with the power its got now!

    You ride trail or tracks?
    trail mostly, but joined the club earlier in the year - really enjoyed riding the tracks but the bike couldnt get out of its way in a corner. once fixed thought i think i'll get back into it cause its a great way to build skills i reckon. im more interested in riding enduro long term but need to work on riding skills/physical fitness first!

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