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Found 10 results

  1. I have been working on a 1973 Mt250 for a little over a year now trying to rebuild the motor. The parts are impossible to find. I am hoping that someone knows where to locate a complete gasket set for a 73 year model. I have tried gaskets from the 74-76 with no luck. It will be sad to see this bike never be completed because I can't find the right parts! Thanks in advance for any and all help!! Lets get this bike back to its former glory!
  2. Mike Gutierrez

    Shifter Kart

    I'm looking for a local engine builder in Southeastern Wisconsin that has experience rebuilding/tech support for my Honda CR 125 Mod Moto. I'm using this engine for a shifter kart. I went with a builder in Illinois and I'm still having the same issues as before the rebuild and I'm not getting the tech support I need. Please respond with your recommendations. Thanks.
  3. Paul Olesen

    How to Separate Your Crankcases The Right Way

    “Splitting the cases” is often referred to as a daunting or undesirable task, but if you are well prepared and properly equipped then it can be a straightforward job. To alleviate any concerns you may have with the task, I want to discuss best practices and share some tips that you may find useful when dealing with crank bearings that utilize an interference fit with the crankshaft. We’ll get started by discussing preparatory items and work through to completing the job. Preparation I always recommend prepping for crankcase separation by thoroughly reviewing the service manual. This is important in case any special instructions are present, such as guidance on how the crankcases should be positioned. Typically, it is advantageous to lift one half off the other in a certain orientation due to the way the gearbox or other components are installed. Secondly, a review of the manual may highlight any specific hardware that must be removed prior to attempting to split the cases. From a tools standpoint, a crankcase splitter tool is a worthy investment because it will help ensure the job goes smoothly. Case splitters are relatively inexpensive and widely available. Alternatively, for the budget conscious or lesser prepared, a case splitter is something that could be fabricated. Whether buying or making, ensure you pick up a model with a protective end cap for the crankshaft or fabricate one. We’ll discuss the end cap later. The other tools required are all fairly standard and include your typical sockets, wrenches, and soft mallets. Wooden blocks or other soft semi-malleable spacers should be selected which level and raise the crankcases off the tabletop. This allows the cases to be positioned so that the split line between the cases lies horizontally and subsequent splitting can be done vertically. This will help ensure evenness of separation as well as reduce the likelihood of components falling out of the cases unexpectedly. As much as shortcuts are desirable, just about everything external to the cases must be removed in order to successfully split the cases. Clutch, stator, crank gear, etc. must be removed prior to case splitting. Your service manual will provide further clarity as to what needs to come off. Technique & Tips Once you’re ready to separate the cases, the first thing we’ll need to do is remove all the crankcase bolts. The crankcase bolts should be removed via any prescribed patterns outlined in the service manual. Since the crankcase bolts are typically several different lengths, ensuring the location of each bolt is well documented is extremely important. As I discussed in my post on keeping track of bolts, the cardboard gasket method or any other you find suitable should be utilized so that the reassembly process is straightforward later on. After the crankcase bolts have been removed, the crankcases should be inspected one final time to ensure no hardware that should have been removed prior is hitchhiking. Trust me, trying to separate cases only to find there is one last forgotten bolt is quite frustrating! Once you’re confident all the necessary hardware has been removed, position the cases on the blocks with the correct half facing up. Next, install the protective cap over the crankshaft. I advise using the cap whether you own a two or four-stroke simply because in both cases it helps preserve the end of the crankshaft. This is of particular importance on four-stroke engines that utilize an oil feed that passes through the crank. Once the crank end is protected, proceed to install the crankcase splitter. Select threaded holes that are as close to equispaced from one another as possible to promote uniform loading of the case splitter. When threading the case splitter studs into the crankcase, make sure you engage at least 1.5 times the diameter of the stud diameter. For example, if the stud is 6mm in diameter make sure at least 9mm of thread engagement length is achieved. This will help ensure the threads are not stripped when you attempt to separate the crankcases. With the crankcase splitter installed begin tensioning the main bolt against the end of the protective cap. Proceed to tighten the bolt until the crankcases begin to separate about a 1/16” (1.5mm). Once separation has occurred, make sure that separation is even all the way around the cases. Due to the way the case splitter loads the cases, the area near the output sprocket tends to lag. Case separation needs to be even so that the dowel pins used to pair the cases together don’t bind. If the output sprocket end of the cases hasn’t separated, use a soft rubber or plastic mallet to gently tap in that area. Tap carefully and only on case areas that appear sturdy. Once you’ve created an even gap, proceed to tension the splitter bolt, tap when necessary, and fully remove the crankcase. Upon separation, make sure that no gearbox components, such as washers, have stuck to the case. What I’ve described is the ideal sequence of events for a successful case separation, however, occasionally the cases won’t be as cooperative. In the past, I’ve had to deal with crankcases where moisture has found its way into the dowel pin bores and corroded the dowel pins. This effectively seizes the dowel pins in their bores and makes the separation job more challenging. If the crankcases are being resilient to separation, stuck dowel pins may be a potential problem. Most dowel pins are located opposite one another and their exact position can often be referenced in the service manual or in the crankcase section of part microfiches. Once the location of the dowel pins has been confirmed, a torch can be used to lightly heat the dowel pin areas. Heat will expand the metal surrounding the dowel pin and aid in freeing up the stuck pin bore. Usually, a few careful rounds of heat, tension on the splitter, and well-placed tapping is enough to free up the pesky cases and get them separated. Alternatively, if the heat does not help, applying a penetrant to the pin bore areas is another option that may help free things up. If you find yourself dealing with stuck cases, the key is to be patient and think through all your options. In these types of situations, most mistakes are avoidable and are usually the result of rushed decisions. Once the cases have been separated, the remaining tasks of removing the gearbox and pushing the crank out of the remaining case half can commence. I hope you’ve enjoyed this write up on crankcase separation and that it makes you more prepared for the job. If you’ve got additional crankcase separation tips that you want to share, please leave a comment below. For additional engine building information, whether two or four-stroke, check out my engine building handbooks. Each handbook is offered in print or digital form, contains over 250 color pictures, detailed instruction from start to finish on full rebuilds, and contains a wealth of information pertaining to diagnostic testing and precision measuring. Thanks and have a great week! -Paul
  4. GH056

    03 KX100

    Hey everyone just working on my sons 03 kx100. We got it for a song knowing it needed a complete rebuild. What im wondering is if anyone knows about the clutch basket and if theres other years or options for a replacement. We are also going to need a pressure plate as well. Also off the top of my head does anyone know the largest wheel size that we can run for him?
  5. goinon40years

    CR85 rebuild questions

    I have a question, found an 07 CR85b for $750. It needs an engine rebuild and I asked if just the top end or both and he replied top and bottom, but just the crank. My question is, is it worth it to try and rebuild or would I be better off just trying to find one that costs a bit more but is in need of less work? I saw top/bottom complete kits from Vertex for $257, so I would have $1000 in it before factoring in labor, it also needs tires. Any thoughts on should I walk? Thanks.
  6. I own a 2006 YZ250F and currently it has 88 hours on the motor (total), so I`m going to tear it down. About 80% of those hours were logged in the woods. I change the oil and clean the air filter every 6 hours. I typically don`t rev my bike out as I`m only 130 lbs. My question is should I replace the crankshaft? I`m not really sure if it is necessary, but I would like a second (or tenth) opinion. Thanks
  7. ClipClep

    Engine Top End

    Hello everyone! I’m brand new here so i apologize if this is in the wrong place. My top end is shot on my 2007 KX250F. Beyond repair. So, I need a new top end with cams. Now, from my understanding 06-08 models are all basically the same. What are my options? What other years/models fit and where should I go and find something that will work? Thank you!
  8. Paul Olesen

    How The Two-Stroke Exhaust System Works

    In my last post, I shared details about how the two-stroke cylinder works, in today's post I want to provide an overview of how a performance two-stroke engine's exhaust system works. Adding a performance exhaust system can be a great way to increase power and/or alter the power delivery of an engine. I would also argue that optimizing a two-stroke engine’s exhaust system is equally as important as ensuring the cylinder’s ports are correctly designed for the given application. Not all exhaust systems are designed to do the same things, and much like cylinder port design, exhaust designs are intended to alter power in specific ways. Having a basic understanding of how an exhaust system works can go a long way when it comes to selecting the right exhaust pipe for your engine. Two-stroke exhaust design is complicated and there are many different variables that must be considered when designing a pipe. I don’t intend to go into all of them, but I will share a few of the most critical. Each time the exhaust port opens to release spent combustion gases, pressure pulses are created. Modern pipe designs harness this pulse energy and use it to help scavenge and fill the cylinder. The process starts when a positive pressure pulse is created once the exhaust port opens and combustion gases leave the cylinder. The positive pulse travels down the pipe until it reaches the diffuser, at which point part of the pulse is inverted and reflected back towards the cylinder as a negative wave. This negative wave is very beneficial in pulling spent exhaust gases out of the cylinder and fresh mixture up through the transfer ports. The remaining positive pulse continues on its journey towards the end of the pipe where it encounters the reflector. The reflector acts as the name implies and forces the positive pulse back towards the exhaust port. Once reflected back, the pulse remains positive and, if the pipe is designed correctly, will reach the exhaust port just as the piston is about to close off the port on the compression stroke at the desired RPM for maximum power. Any fresh mixture which has escaped out the cylinder will be forced back in by the positive pressure pulse. The tuned length of the pipe is dictated by the exhaust port timing, RPM of max power, and the speed of sound. Pulse length and amplitude are governed by the angles of the diffuser and reflector. Generally, steeper cone angles create pulses with more amplitude but shorter duration. Shallower angles generate pulses with less amplitude but longer duration. Given these variables, it is easy to see how a pipe could be tailored for specific applications. An engine converted for road racing may utilize a pipe designed for peak power which incorporates steep diffuser and reflector cone angles so that pulse amplitude is not sacrificed. This peak power would likely come at the expense of a narrowed range of power. An engine tailored for woods riding may feature a pipe with shallower cone angles, resulting in less pulse amplitude, but a broader spread of power. The last parameter I want to touch on is how the tailpipe, which is sometimes referred to as the stinger, influences the pipe. The tailpipe creates a flow restriction in the pipe which allows the pipe to have a certain amount of back pressure. Enlarge the tailpipe and the back pressure decreases, make it smaller and the back pressure increases. As back pressure increases or decreases, so does temperature and ultimately the speed of sound. As the speed of sound changes, so does the resonance RPM of the pipe. If the tailpipe is sized too small, cylinder scavenging will be inhibited. When this happens, the cylinder, fresh mixture, and piston will all be overheated. While engineers and tuners can estimate starting pipe dimensions and tuned lengths, a great deal of trial and error testing is usually still necessary to fine tune the exhaust pipe and optimize the design. Unless you intend on building your own exhausts, this work will have already been done for you. When selecting an exhaust system, you need to focus on how the exhaust alters the power curve. Exhaust systems are tailored to deliver more bottom end performance, top-end performance, or performance throughout the power curve. Selecting which system is right for you will depend on how you want your engine to perform. If you’ve chosen to modify your cylinder ports, installing an exhaust system that compliments the porting can be very beneficial. You might be wondering about slip-on mufflers. If you’ve followed along with my explanation of how exhaust pipes work, you’ll notice I made no mention of the muffler. While the muffler can have a small effect on performance, it is not the primary factor. Upgrading a muffler is a good way to reduce weight, but there won’t be a slip-on out there which significantly increases power, in the same way, a properly designed expansion chamber can. I hope you enjoyed this write-up on key features affecting the performance of two-stroke cylinders. As for Two Stroke Handbook news, we received our first printed proof of the book this week! Needless to say, we are inching closer and closer to an official release date. To stay updated on The Two Stroke Dirt Bike Engine Building Handbook we created an email sign up for our readers. Click this link to sign up, see the new cover, the Table of Contents, and some sneak peek pages right from the book. Thanks for reading and have a great rest of your week! -Paul
  9. So a couple months back I bought a 02 yz125 too get back into riding again I have the bike for a couple days and one day when I’m riding I pull the clutch in and the bike stalls and when I go to kick it, it’s ceased. I got home took it all apart took the cylinder off and the top end was perfectly fine and the bike was still locked up so I assumed it needed a bottom end rebuild. I ordered a whole entire wrench rabbit rebuild kit and when I started to take the engine apart I started on the clutch side first and as soon as I took the clutch cover off and all the oil drained out and stuff the bike was able to turn over perfectly. I looked it up and assumed it was a temporary ceased bearing but I ignored it and went ahead with the whole rebuild. I rebuilt the whole entire engine with a buddy of mine who is very experienced with mechanics as well as myself and everything was turning over and moving flawlessly I put the whole entire bike together and went to go kick it and it was ceased!!!!! Again!!!!!! Me not even knowing where to start or what happened I decided to just take the clutch cover off, as soon as I took it off the bike turned over flawlessly again. I put it back on and ceased again!!! I was so confused I took the pressure plate off everything looks perfectly fine no cracks or dents or chips anything of that nature took all the plates out everything looks perfectly normal but as soon as I put it back together and throw the clutch cover on ceased!! Also the clutch does engage if I put the bike in gear and pull the clutch in, the bike will roll so I am so lost and I have so much money into it I’d hate to part it out and I haven’t even put 10 hours on this bike!! This bike is becoming a money pit for me with no positive results! Someone please help
  10. I'm looking for someone in the Denver/Springs area to work on my KTM 525 EXC bottom end. Had it shipped to a reputable builder on KTMTalk three separate times and the bike is still dropping in gear when rolling it around in neutral. I've given up, gotten a refund, and looking to go somewhere local. So far I've been recommended Jeff Graves at Apex in Colorado Springs. Anyone else worth looking at? Thinking about TFOG as well. Thanks!
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