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Thread: Yamaha NXC125 20,000km

  1. #106
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    12th February 2004 - 10:29
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    Couple more photos. the crank and head are SD branded and the piston is FJN. Everything seems pretty good quality and nicely finished apart from the previously mentioned porting and piston surface.
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  2. #107
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    12th February 2004 - 10:29
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    Quote Originally Posted by husaberg View Post
    Is there only two squish areas rather than 4 on that piston head combo?
    More or less. There is just a small perimeter each side with matching flat surfaces. With larger valve sizes for the given bore having a squish area between exhaust and intake each side would mask the valves I would think. The only time it wouldn't be masking the valves is if the valves were at a very shallow angle and the valve seats were more or less in line with the flat plane of the head. Then as soon as the valves lifted they would be in free space with no combustion chamber surface close to their perimeter. This sort of thing: https://www.psychobike.com/forums/10...n-chamber.html.

    The downside might be a lack of swirl in the chamber which back in the old days was a big deal. I'm thinking of Suzuki's TSCC system. I think in that case that the majority of flow was from one side of the valves which probably happens in any case with port directions and valve masking though good port design should reduce it a lot.

  3. #108
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    20th January 2010 - 14:41
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    Quote Originally Posted by speedpro View Post
    More or less. There is just a small perimeter each side with matching flat surfaces. With larger valve sizes for the given bore having a squish area between exhaust and intake each side would mask the valves I would think
    I was just basing it on say a CRF150R
    which would be similar bore.
    22.5 and 26mm valves
    I think even the old VT250 were similar to the CRF150R



    What size is the pin on the piston 15mm or 16mm
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  4. #109
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    12th February 2004 - 10:29
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    Those valve seats are a lot further out and closer to the plane of the head gasket surface compared to the scooter head, by the looks. I would think it would flow better but would need to see it on the cylinder to see if the side of the bore would have an effect. Flow bench wouldn't lie of course. Being a very flat valve angle would also effect the piston dome profile and as you say the CRF has the flats between the exhaust and inlet valves and there's a bit matching it on the head. The scooter head is probably a bit older style.

  5. #110
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    12th February 2004 - 10:29
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    Some real nerve wracking grinding this weekend. I had to grind down real close to the valve seats without touching where the valves seal. It wasn't too bad cleaning out the ports and I only had to take out a small amount to clean up where the valve seats and the actual port meet. Comparing it to the old Taida head I actually think the Taida head has slightly a better intake port. The exhaust port is about the same. I've got it sitting on the vice at the moment with the combustion chamber full of WD40. There may be just a very small amount got through on both sides but it may also be oil from fitting the valves in the head. I'll know tomorrow morning. The final photo looks a lot worse than it really is but I would still prefer it to be better.
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  6. #111
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    12th February 2004 - 10:29
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    Coming along. Getting the roller rockers in were a mission as usual. It's a tight fit inside the head and the rockers have to be slipped in more or less to where they go and then pushed up out of the way to fit the cam. Once the cam is in the rockers can be slid down to where they go and the pivot pins put in. Everything else just bolted together like normal with the spacer plate and extra gaskets.
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  7. #112
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    12th February 2004 - 10:29
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    As usual when an aircooled bike is converted to watercooled it turns into a mission. Just finding a radiator that was probably an acceptable size and had hoses in more or less a useable position and angle was a problem. In the end I went with a FZR250 radiator I had lying around. It's hopefully too big but the way I've mounted it makes it easy to downsize. Any pretense of being just another scooter is now gone. A smaller radiator may be able to be tucked out of the way but this one only had one place to go and that was out front.
    There are 2 studs that the front fairing mounts on. I made extensions to screw on and to which the bracket for the radiator then mounted to. The radiator mounted to the bracket using the standard radiator mounting points. Hoses are run down inside the front fairing on both sides.
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  8. #113
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    The watercooled cylinder came with 90deg fittings. In the end, in conjunction with a collection of odd bits of hose, it seems like the hoses on inlet and outlet both connect OK and allow for motor movement without causing a problem. I only have the one temperature sensor at the moment which I've used to connect 2 bits of the engine inlet hose. Until I get the other sensor sorted the fan is going to be run from a switch. I have a fan controller which checks both oil and water temp. The oil cooler is going to be put back exactly where it was originally which isn't ideal.
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  9. #114
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    12th February 2004 - 10:29
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    I wanted the water pump low down in the cooling system. The pumps aren't self-priming. I've ended up jamming it inside the front lower left corner of the bodywork. Cool water from the radiator drops into the pump and is pumped back to the motor inlet. It's far from ideal as the cool water is taken from the top of the cross-flow radiator which isn't too much of a problem from a cooling perspective. The issue is if the water level drops for some reason the first thing that will happen is the pump will suck air from the top of the radiator. The temp sensor location won't help alert you to a problem as it is on the inlet side between pump and motor and without water circulating will probably indicate a low temp. If i stick with this radiator the hoses will definitely be swapped over somehow.
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  10. #115
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    20th January 2010 - 14:41
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    I am pretty sure i have a Cr80 one kicking about,the smallest square one i have ever seen is what the KTM50's run. 2001-2009

    that pic is about life size.
    the 2009 ones on run these


    I can measure both if you want Mike.
    I would have thought for a 4t cylinder only it doesn't need to be to big?
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  11. #116
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    12th February 2004 - 10:29
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    I'm hoping the radiator is oversize and will allow a smaller one to be fitted. Supposedly this combination of watercooled cylinder and aircooled head does not need any forced air to the head from the fan. I'm going to keep the fan and direct the air to the head to assist with cooling antway. Dimensions of those radiators might be useful. I have an RG50 radiator which would fit nicely and has the radiator cap on top. It just looks too small and probably is. Given the engine is probably making more power than a CBR150 I'm thinking it needs at least that size radiator and the FZR250 radiator seemed like a good starting point.

  12. #117
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    20th January 2010 - 14:41
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    KTM50sx 2001-2008
    Radiator approx 200mmx115mmx30mm 690,000mm3

    Honda CR80 olderstyle 310mmx100mmx30mm 930,000mm3

    all sizes approx core not including neck..
    i would suggest that the CR80 one would be good for mid 20 at least HP. when covered with mud operating at low speeds sustained loads.No fans
    I think the KTM50 were arround 12hp they all ran hot but ran tiny amounts of oil with slipper clutches at low speed covered with mud and no fans
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  13. #118
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    12th February 2004 - 10:29
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    I've been working on it for most of a week and finally it's alive. Still more to do but the motor runs and sounds as mean as before. The water circulates and when it gets to the temp set on the fan controller the fan is turned on and immediately starts dropping the temp. I'll take a few photos tomorrow after it's sorted properly.

  14. #119
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    12th February 2004 - 10:29
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    All together and taken on increasingly longer rides around the area. I taped off more and more of the radiator and currently only have a section 90mm wide by 160mm high uncovered and it still runs way cold. There is a tiny oil leak which may be coming from under one head stud. I did have a problem riding along Christian Road. It started running quite rough and eventually stopped. It felt like fuel and refused to even kick when pressing the starter button. Turned out the air filter had fallen off and disappeared. This wouldn't have been a problem except that the carb had come off as well. So it was a fuel problem. Gary came and rescued me with a few tools and I was back riding in a short time.

    It runs great, pretty much like before. If anything it may even be a little better. It popped an unexpected wheelie down the drive and even at minimal throttle is doing 80Kmh pretty quick. The engine is tight and requires running in so that is as far as I went.

  15. #120
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    20th January 2010 - 14:41
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    Quote Originally Posted by speedpro View Post
    All together and taken on increasingly longer rides around the area. I taped off more and more of the radiator and currently only have a section 90mm wide by 160mm high uncovered and it still runs way cold. There is a tiny oil leak which may be coming from under one head stud. I did have a problem riding along Christian Road. It started running quite rough and eventually stopped. It felt like fuel and refused to even kick when pressing the starter button. Turned out the air filter had fallen off and disappeared. This wouldn't have been a problem except that the carb had come off as well. So it was a fuel problem. Gary came and rescued me with a few tools and I was back riding in a short time.

    It runs great, pretty much like before. If anything it may even be a little better. It popped an unexpected wheelie down the drive and even at minimal throttle is doing 80Kmh pretty quick. The engine is tight and requires running in so that is as far as I went.
    Gizza yell if you want the CR80 one Mike i can through in a FZR250 rocker cover that for the stuff you got of Greg as well.

    Honda CR80 olderstyle 310mmx100mmx30mm 9
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

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