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Found 17 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. 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
  3. Hey everyone, Just bought a seconded hand 2009 CRF 250 R it has nearly 120 hrs on the clock. It runs well, starts well, pulls well, sounds good doesn’t smoke and I’ve done the valves (one intake was out by .001”) but has a compression of 40 psi (the service spec is 52 psi). I’ve never owned a proper race bike only ever owned old XRs just wondering if I should bite the bullet and do a rebuild on it straight away or if I can get away with taking for a few rides and watching the valves closely, changing oils etc...? I’ll only be trail riding with it, doesn’t need to be perfect just don’t want to risk dropping a valve or munching a bearing and cost myself heaps more to get it back going again Thanks for for any insight you fellas can give!
  4. 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.
  5. 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
  6. 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!
  7. 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
  8. 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!
  9. 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?
  10. I have purchased a DRZ400e electric start engine (less the cams and stator cover). I have a stroker crank and big bore kit coming (happy birthday to me). Given that we are going into winter this side of the world I though it might make a good project over the winter. This engine build thing is all new to me so I will have plenty of questions in the coming months I'm sure (I also have beers with a couple of old-timer engine builders of a Friday evening and have been receiving a fair amount of encouragement from both of them) . The first few questions that you, @Erik Marquez or @Noble might know the answers to: What sort of cams does a 462cc DRZ run? @ohiodrz400sm you use WEB 539's? for what characteristics? This is a road bike, not a race bike. Next question valves, standard size, Ferrea, Ferrea spring kit as well? to suite the performance/lift/duration of the cams?. I guess I need to find a reputable head shop here to fit the valves to the head. Going through the bottom of the engine is a must as well. Do I replace all bearings / seals as a matter of course, this motor is unknown to me so a replacement water pump and oil pump (at least have the oil pump apart to check for service specifications), replace plastic oil pump gears anything else I anyone can suggest? I am considering an ACT wide ratio gearset at the same time. I understand that RS Yoshi exhaust may be impeding the performance at the top end but I see the 38mm throttle body to be the bottle neck at the moment (as well as only 398cc). I have a RMZ450 throttle body to fit. It's 43.8mm including the butterfly - so probably about the same at an FCR 41 in total flow volume. I have just started to machine up an adaptor to fit the airboot on my current setup I'll fit this shortly to my current setup and see how it affects breathing. I'll probably go the velocity intake route on the big build as well. Clutch - standard with new components - fibers / springs? I consider the motor in the bike have too low km's to mess with. In the meantime I can still ride on what I have.
  11. Ok so I have a 2000 ktm 125 sx and need to rebuild the lower, I can only find rebuild kits for 2001 engines will they work?
  12. Hey, Im rebuilding a really neglected old 72 TS250 engine and have it completely apart. I have all new bearings to install except the gear shift select drum bearing which is a 12x18x15 needle bearing I dont have. The old one is completely rusted out. I do have a tin-bronze sintered bushing that is the correct size. Would this work in place of the needle bearing that the shift drum rides in? I doubt it would wear being a hard bronze bushing submerged in oil, no? Ignore the dirty engine internals in the pic - All has been disassembled and cleaned now, and any rusted parts are being replaced if they are unusable.
  13. Super low hour head gasket failure, brought to you by an aftermarket company - in this case, cheap parts that work sometimes. My standard advice is to use OEM parts in critical locations of the engine because they have a track record of being thoroughly tested and the quality controls on the manufacturing end are more stringent than the aftermarket, however, I decided on this build to see if the aftermarket could deliver since it's more cost-effective and convenient to buy seals, gaskets, etc. as a package. I get asked often which companies/parts to use and from time to time like to independently test components I wouldn't normally run. I built this engine using new parts from the bottom up and the engine has less than 10 hours on it. Specifically, a new OEM cylinder was used and the OEM cylinder head was skimmed .003" at the time the valve seats were recut so the components comprising the joint were 👌. Tightening torques and procedures were, of course, used and referenced from the Honda service manual. What Does a Head Gasket Failure Look Like? The failure occurred opposite the cam chain side of the cylinder. For those of you new to diagnosing problems you have to look for gas tracking across the gasket. This failure perpetuated slowly and eventually enough coolant pooled in the cylinder while the engine was shut down that at startup it became obvious. A plume of white smoke leaving your tailpipe is a dead giveaway that you're burning coolant. Prior to that, I was seeing a small amount of coolant blow out of the radiator overflow - another sign of a potential head gasket leak. Hot starting was also harder than normal. What are the differences between a Honda OEM head gasket and a cheap aftermarket head gasket? In this case, the manufacturer of the cheap gasket chose to remove the orifices used to control coolant flow from the cylinder into the head. These are the four small holes on the Honda gasket that are much larger on the cheapo. Honda spent energy on strategically applying their coating while cheapo did not. Lastly, there could be differences in materials and formation of the protruding beads that help seal everything up, however, I can't say for sure. Do any of those differences matter? That's up to you to decide. For me, I'll need to be compensated before I run this brand of aftermarket head gasket again. The risk/reward doesn't seem to be worth the minor savings the aftermarket gasket provides. Are you implying all aftermarket parts are bad? No, to make a sweeping statement like that wouldn't be fair to the companies out there working hard to bring consumers good quality products. Just like most other industries there are differing levels of quality present in the market place. What do you check if your head gasket fails? The flatness of the cylinder and cylinder head mating surfaces. Often times gaskets fail because these components overheat and become warped. The ideal way to check flatness is with a surface plate and feeler gauges, however, when the engine is in the frame parallels or anything with a straightedge will do the job. To get even more gritty your OEM service manual will prescribe how to check and what amount of warpage is acceptable. When I checked after this failure the parts were still perfectly flat. Other tips and pointers? Clean the engine and surrounding area as best as you can before you open the engine up while it’s in the frame. Dirt contamination in your engine will lead to premature wear. While you have access to your cylinder take a look at the cylinder walls for abnormal wear. Deep striations or scratches are a no-no and cause for concern. Check the top of the piston for signs of detonation. Remove any carbon buildup that easily comes off with a paper towel, however, refrain from breaking large deposits free. Carbon deposits are extremely hard and if they get stuck in your ring lands or between the rings and cylinder will cause scratching. When installing the new gasket be extremely conscious of the possibility of dirt getting on the gasket mating surfaces. Dirt stuck between the cylinder, gasket, and cylinder head will impeded sealing. Need help rebuilding your engine? Check out my books - The Two and Four Stroke Dirt Bike Engine Building Handbooks. Each book will walk you through diagnosing engine issues and teach you the right way to rebuild your engine. The books feature stunning, high-quality color pics that make text explanations come to life. Available at: DIYMotoFix.com Amazon Anybody else get burned and should've known better? - Paul
  14. hi all. my drz blew its top end last year and im in the process of doing a full rebuild on the engine.(i want to do it myself for the learning experience... and bragging rights of course) ive stripped it down and have bought a rebuild kit from wrench rabbit, im now at the stage where i can start putting the bottom end back together and ive suddenly got the fear. im worried that i might do something wrong in the rebuild prossess, i am wondering if anyone has any tips or knows of anything i should be aware of before starting reassembly. for example i learned when installing a new cylinder it needs to piston, i thought the rings would account for this. any tips are apreciated however small they may seem. thanks
  15. 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.
  16. “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
  17. Hey forum! Picked up a free RM85 with what I believe to be a bad crankshaft bearing, and broken piston skirt. I believe the bearing is gone by the vertical play that I can feel when I grab the connecting rod and move it up and down, is this a good assumption? The cylinder walls have no gouges either, so I am thinking that I could just buy and replace the crankshaft bearing, and piston? Should I just go ahead and replace the connecting rod as well? Is there any chance with the use of a press that ill be able to remove the connecting rod off the crankshaft? So that I dont have to buy a whole new crankshaft, in returning saving money. I'm removing the flywheel at the moment so a ways to go still. Thanks,
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