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KJ790 last won the day on July 8 2011

KJ790 had the most liked content!

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About KJ790

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  • Location
    New York
  • Interests
    women and bikes...enough said

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  1. Hi everyone, I just moved from Syracuse, NY to Winchester, VA this week. I have been spoiled in NY for years with 10 tracks within 1-1/2 hour drive. I haven't been able to find much down here so far. I know that there is Tomahawk near here, but I haven't found too many other tracks and I don't know anybody to ride with in this area. Anyone else from around here that rides tracks? I see a ton of trail riding, but that has never really been my thing. If anyone knows of any tracks, or wants to meet up at Tomahawk, hit me up.
  2. KJ790

    2016 YZ250F crankshaft failure

    Got it all back together and running today. I am hoping that the Carrillo rod makes it stay together this time.
  3. KJ790

    2016 YZ250F crankshaft failure

    I got my crank back from Crank Works. I will say they did a heck of a job, it looks brand new! They sent back the old parts so that I could see them. All of the rollers were still between the rod and the crank pin, but only one little piece of bearing cage was left. The rest of the bearing cage was in tiny pieces at the bottom of my engine, along with the thrust washers.
  4. KJ790

    2016 YZ250F crankshaft failure

    I don't have any pictures, though there isn't much to see until the crank comes apart. Crank Works rebuilt the crank yesterday and it is on its way back to me so I will be able to see the old parts. I talked to the guy from Crank Works for quite a while yesterday. They build the cranks for the Star Racing Yamaha team, so he has seen quite a few of these cranks. He said that the failures are not oil related or bearing related, as the OEM bearing is a high quality bearing. He told me that the Star Racing Yamaha team has been running the OEM lower rod bearings with CWI connecting rods in their bikes for a few years, and this setup has worked out well in their practice bikes (which see more hours than their race bikes). He says that the failures are related to the design of the rod itself. The '14s and '15s were snapping the rod in the center, so Yamaha beefed up the rod in that area for '16. The '16 rod is too thin in the lower bearing area and flexes at high RPM's. This little bit of flex around the bearing at high RPM's causes the bearing skid and the cage to fail. He said that Yamaha made the lower portion of the rods thicker for '17 and '18 and they are not seeing as many failures so far. He also said that the Carrillo rods and the CWI rods are thicker in the lower portion to prevent this issue. I have no clue if this is correct or not, but they have a lot more experience in this area than I do. I guess time will tell.
  5. KJ790

    2016 YZ250F crankshaft failure

    This failure did not give me any warning. I had ridden it about 45 minutes since the previous oil change and there was no metal in the oil or oil filter at that point. There had never been a knock or strange noise to give any warning. I was accelerating out of a corner and it suddenly felt like it was losing power, bogged down, and died.
  6. KJ790

    2016 YZ250F crankshaft failure

    Hi William, thanks for the welcome. I am not sure what failed first, the cage is completely missing. I am not sure if a roller failed and then took out the cage of if the cage itself failed first. This was a completely stock motor. I am not sure who is making the bearing for Yamaha. My gut feeling is that this is not necessarily an issue with the bearing itself, but rather the design of the crank or engine. Perhaps there is an issue with oil getting to the bearing, or the bearing is seeing excessive loads at high RPMs? I called Crank Works yesterday and will be sending my crank to them today to have it rebuilt with their pin and bearing and a Carrillo rod.
  7. KJ790

    2016 YZ250F crankshaft failure

    I just talked to the father of one of the local pro's who races Yamaha's. He said that they had 3 lower rod bearings come apart with less than 30 hours on them on their current YZ250F's. The first two were OEM cranks, the third was with a Carrillo rod and Crank Works bearing and pin. He said that he had Crank Works build them a couple cranks with their pro series rod, pin, and bearing with the pin welded to the webs and they currently have 75 hours on one of them so far. I may try that option.
  8. KJ790

    2016 YZ250F crankshaft failure

    I planned on rebuilding the crank with a Carrillo rod kit. I was told that the kit would come with the rod, pin, and lower rod bearing. I just received it and it did not come with the bearing or the pin. I am fine with ordering an OEM pin, but does anyone sell a lower rod bearing that is better than OEM?
  9. It has been a long time since I have been on here. Wednesday night my 2016 YZ250F lost power and locked up the motor. I split the cases this weekend to find that the big end bearing on the crank had disintegrated and locked the rod to the crank. The bike is completely stock with 44.3 hours on it. The oil was changed every 3 hours or less. I knew that the '14 and '15 YZ250F's had crank issues, but I thought that they were fixed for 2016. My friend's 2017 had the crank come apart last week with less than 30 hours on it. Talking with a few local mechanics they tell me that the issues were never really fixed and that I was lucky to get as many hours out of the crank as I did. I am rebuilding it with a Carrillo rod kit in hopes that the bottom end will stay together longer this time. I have to say, I am pretty disappointed with this type of failure. I have had 16 Yamaha's since 2001, 6 of which were previous generation YZ250F's and this is my first bottom end failure. Is this really that common of an issue on the 4-valve YZ250F engines? Is there a way to make this bike last?
  10. KJ790

    YZ125 coolant leak

    Only if the problem is with the o-rings themselves. I have seen a few people, Eric Gorr bine one, that claim the head stay causes too much flex on the head when ridden hard, which allows coolant through. Not sure if it is true, but it seems like there could be something to it.
  11. KJ790

    YZ125 coolant leak

    I'm not convinced it is detonation though, with rich jetting, 100 octane, and retarded timing I don't see how it could be. The way that the cylinder is eroded behind the plating makes me go along Eric Gorr's thoughts of coolant leak issues on these bikes.
  12. KJ790

    YZ125 coolant leak

    Yes, I'm sure I retarded it.
  13. KJ790

    YZ125 coolant leak

    I run Yamalube 2R mixed 24:1. I have been using Yamalube 2R for the last 17 years in all of my two strokes, never had a problem like this. I have had 9 YZ two strokes over the years, 3 of which were YZ125's, never seen this before. I haven't measured squish on it, but both heads were unmodified OEM heads. I can't imagine I could have gotten 2 randomly bad heads from Yamaha.
  14. KJ790

    YZ125 coolant leak

    I do not have the stock pipe for it. All of the engine parts have been OEM. I actually retarded the timing a couple degrees from the stock mark after the last failure because I was worried that the stock mark on the case was incorrect. All that seemed to do was decrease the top end power, nothing more.
  15. KJ790

    YZ125 coolant leak

    I am running an FMF fatty with an FMF shorty silencer. The bike has a Boyesen rad valve, but is completely stock otherwise. Here are some pictures, this cylinder and head have 8.3 hours on them by the hour meter. The last cylinder and head looked the same when I replaced them. I am running 100 octane Sunoco race fuel, I would think that would be enough octane.