Yamaha YZ250 & YZ250X Bottom End Rebuild | Part 1: Engine Disassembly

hey this is charles with rocky mountain atvmc today i'm going to show you how to rebuild the bottom end on your yz250 or yz250x now there's a few different reasons you're going to be splitting your cases and getting into the bottom end of your engine you could have transmission or shifting issues or more commonly on these two strokes you're going to have issues with the crankshaft assembly now if the main bearings or connecting rod bearing is going bad you're either going to have bad vibration coming from the engine or you're going to hear a knocking noise coming from that bottom end so if you have either of these these issues we're going to show you how to get them taken care of and this bike right here we actually had a connecting rod bearing that seized up so let's go ahead and jump into this this bike is a 9 2009 yz250 but the procedure is going to be similar from 1999 and newer models for yz250s and yz250xs just be sure to refer to your model specific service manual for more information proper procedures and specs to do this job we're going to need some common hand tools including a torque wrench snap ring pliers and some gasket scrapers you will need a few specialty tools to get this job done so we have our crank case splitter a clutch holding tool this doubles as a flywheel holder we have our flywheel puller feeler gauges digital caliper and then a few tools that will make the job a lot easier you don't necessarily have to have these but a motion pro gear jammer our seal driver seal puller impact driver rags safety glasses and rubber gloves to do this job we have the wiseco bottom end rebuild kit this comes with the crankshaft assembly your two main bearings gaskets and seals that you need to do the job then we also have a lock washer for the clutch hub nut you can get this under the oem parts diagram then we also have some yamabond contact cleaner assembly lube some loctite and some grease to get this bottom end disassembled the first thing you'll need to do is tear down the top end so as you can see we've already done that on ours and if you need help getting to this point check out our video on the top end rebuild for the yz250 so to rebuild this bottom end we need to remove the engine from the bike so what we're going to do is drain our transmission fluid we remove our shift lever remove the stator cover and disconnect the clutch cable and then we can disconnect our stator wires next we need to remove the countershaft sprocket to do that we'll remove the case saver and then we'll straighten the tabs on this locking washer now we'll remove our counter shaft sprocket nut this is a 32 millimeter socket and i'm going to hold the rear brake while i loosen it now we can remove the nut and the lock washer and then we'll remove the counter shaft sprocket if your bike has frame guards like ours does you'll need to remove them to get to the swing arm pivot bolt the next step is on the other side and we're going to remove our radiator hose the kickstarter and our rear brake pedal now we're ready to remove the nuts on these motor mounts and then we also have a nut on the swing arm pivot bolt on the other side we'll remove that and then once the nuts are off we'll remove all three bolts and once those bolts are removed we can remove the engine from the frame now when you remove the swingarm pivot bolts sometimes they can be stuck for ours it was stuck in there pretty good and we had to use some penetrating lube and let it soak in for a little bit before we could remove it so you might have to do that if yours is stuck and that's why it's so important to put grease on these when you go back and reassemble them to prevent these from getting seized in the swing arm it's best if you don't have to hammer this out but since we are we might have to replace this bolt now that we have our engine out of the frame we've gone ahead and moved it to the workbench and mounted it up in our engine stand this one's from motorsport products and what's nice about these engine stands if you've never used one before is they hold everything still and sturdy while you're loosening bolts and removing components and while you're taking everything apart you're going to have some residual oil coming out and it has a drip pan to catch all that and keep from making a mess with that being said the next thing we're going to do is remove the flywheel to remove the flywheel we need to hold this still while we loosen this nut so to hold it still we're using the tusk flywheel holding tool and then we'll use a 17 millimeter socket hold our tool and break this nut loose and just make sure you get the washer behind the nut out next we'll take our flywheel puller this is a reverse thread and we'll screw it into the flywheel and the center bolt will tighten it down and it's going to press against the crankshaft and pop our flywheel off the next step is to clean any dirt from around the stator the next step is to remove the stator now the stator does have adjustable timing so you want to check these timing marks down here and you want to mark where they're actually at i'm going to use the sharpie to do that you could use a scratch all but just make sure you get it back to its original location to remove the stator we'll loosen up these three phillips head bolts with an impact driver the next thing we'll do is remove this right crank case cover and it is not necessary to remove the clutch cover or water pump cover on this yz250 so the bolts that we don't need to remove i just marked with a black sharpie we'll remove everything else and pull all the covers off as one assembly as you loosen the bolts you want to do it in a crisscross pattern also pay attention to where these bolts go because there will be three different sizes of bolts with all of the bolts removed you can rock the cover back and forth to remove it if it doesn't come off just by rocking it by hand you can use a mallet to help break it loose with the cover removed you want to make sure you locate your dowel pins because sometimes they can be left in the cover or the case we're going to remove both of those and set them aside and then the next thing we'll do is remove this governor assembly to do that we're going to pull up on the actuating arm and rock this out of place and on our since we're going to be replacing all the seals we're going to remove the power valve actuating arm to do that we'll remove these two three millimeter head bolts the next thing we need to do is break the bolt loose for our primary drive gear and to help do that we're going to use this motion pro gear jammer motion pro makes a lot of different tools to help make the job easier and this tool is no exception all you do we'll stick it in between the gears and this actually has a magnet to help hold it in place and we'll break the nut loose or the bolt loose and then we'll proceed to the clutch disassembly now before we remove anything from the clutch just keep in mind we're actually laying out clean rags and we're laying everything out in order so it's clean and organized and you just want to stay organized throughout the process to help with reassembly to remove the clutch we'll loosen up these six bolts in a crisscross pattern and then we'll remove the pressure plate okay with the pressure plate off you're going to want to inspect where the friction disc rides on the pressure plate and make sure that it's smooth and there's no grooving and also make sure this surface where our throw out bearing rides is in good condition after that we'll remove the throw out bearing assembly and just make sure that this bearing is in good condition and rotates smoothly after that we'll remove our push rod and now we can remove these friction discs so on these discs what we can do is measure the thickness in several different places and compare them to spec a lot of times if they're bad you can tell that they're burned and glazed as you remove the steel plates you're going to inspect those as well the main thing you're looking for is any blueing or discoloration if they're blue that means these plates are going to be warped and you want to replace the clutch pack i'm going to remove the rest of the stack and we'll inspect it on the bench next we'll inspect the clutch basket and these fingers coming out you want to feel if they have grooves on them if the grooves are deep you want to replace the basket the other check you can do is make sure that the gear on the back side doesn't move separate from the basket itself if that happens you have some bushings in the back that have gone bad and you need to get those replaced other than that on this hub in the center you have these splines and you need to check those for grooving as well and if they're very deep you'll need to replace that next we need to flatten the tab on this locking washer so we can remove the nut on the hub to loosen the hub nut we need to use our tusk clutch holding tool and we're just going to put this in the splines and when you click when you clamp it down you just want to clamp it down loosely you don't want to damage the soft aluminum and then we're actually using a 29 millimeter socket to loosen this up so we'll remove the nut and the locking washer after that we'll remove this hub now behind the hub you have a splined washer and you're going to need to rotate that on the splines to remove it then after that we can actually remove the clutch basket but keep in mind there's going to be a collar a needle bearing and a washer behind here so just be careful you don't want to drop them and make sure you keep track of them with our clutch off we'll remove this primary drive bolt as well as the water pump and primary drive gear behind those we have another spline washer so you'll line that up and remove it next we'll remove this kickstarter assembly and to do that we're going to need to release this spring and we'll just pull the assembly out as one unit keep in mind when you pull it out you're going to have a washer right behind here and you don't want to lose that next we'll remove the snap ring for our kickstart idler gear when you pull it off pay attention to the orientation you've got a round side and a flat side the flat side is going to be facing out then we'll remove the idler gear we've got a washer on the front side of that after that we can remove the shift shaft now keep in mind the side where your shift lever goes on make sure that's clean before you push it through and then right here we have a little collar we're going to want to remove that and set it aside so we don't lose it at this point we can remove our shifting mechanism so we'll just loosen these two bolts and remove it as an assembly now if this assembly does come apart on you don't worry too much we'll show you how to reassemble it when we go back together with the motor looking back a couple steps make sure you get the washer that's on the shift shaft i almost missed it since it's stuck to the case next we need to remove the bolt that goes down into our shift drum we'll remove the shift segment then we'll remove the bolt for the stopper lever arm and you can see that we have a bad stopper arm bearing so we need to make sure we get that replaced on reassembly we also need to remove the bracket that holds on our spring and holds the seal in place back on the other side now that we have the clutch push rod out of the way we're going to remove this clutch actuating arm to do that i'm going to take a four millimeter allen key we'll remove this bolt and then we can just slide this arm all the way out and on this you want to make sure this corner isn't rounded if this thing is rounded off you're going to want to replace it the next thing we'll do on this side is remove this collar for the counter shaft and we're just going to use some channel locks to do that we'll just be gentle with it so this collar is actually seized into place and we're going to have to remove it after we split the cases and push this counter shaft through at this point we're almost ready to start splitting the cases to do that we need to remove all of the bolts that are holding the cases together and we'll remove all of these bolts in a criss-cross pattern again with these bolts pay attention to where they go you're going to have a couple of different sizes at this point we're ready to split these cases and since we're using an engine stand we need to remove anything that's going to prevent these cases from splitting so if you're using a stand like ours we'll just remove this nut and then we can install our crankcase splitter so this point we can use our crankcase splitter and what this does these arms are going to pull up on the crankcase half and the center pin is going to push on the crankshaft separate the two this is going to be the easiest and safest way to split the crankcases to do that we'll center the splitter on the crankshaft and then these arms you want to separate them so they're pretty even all the way around and then we'll install the all thread you want even heights on the nuts that are on the all thread and that way when you're pulling everything apart it pulls up on the case evenly okay once the crankcase splitter is installed we'll use a 17 millimeter socket and we'll start tightening this down and slowly split the cases and if you noticed anywhere binding up you can use the soft base mallet and tap on the crankcase half to help separate it now once everything is freed up we remove our splitter and the right crankcase half and when you pull this off just be aware of any washers or anything that falls down like dowel pins and keep track of them now that we have the right crankcase half off we can remove the transmission and our shift drum as well along with the shift forks now a lot of bikes you can remove these pieces individually but on the yz's you have to remove all these components as an assembly and one tip that the manual gives us is to tap on the counter shaft with a mallet to help drive these out and as you lay these down just keep track of all the parts and lay them out in order all right now we need to get the crankshaft removed from the other case half and to do that we're again going to use the crankcase splitter now as we do this it's going to be the same process as the other side except we're actually pressing the crankshaft out of the case half and the case half is going to stay stationary and as you can see since we had a bad connecting rod bearing we have all kinds of copper pieces down in the crankcase halves now one thing i do want to point out about the crankshaft is you need to keep track of your woodruff key because you will need to reuse that next we'll remove the dowel pins from our crank halves this dowel pin seized in there so i'm using a socket that's about the same size and we are going to have to replace it but the socket will keep this from collapsing and if you do it this way just be really careful that you don't mark up this gasket sealing surface next we'll remove the seals in our case halves and there's one seal for that power valve actuating arm in the right crank case cover and as you go throughout this process just make sure you don't mark up the sealing surface we'll also remove this o-ring and then we'll clean up our crankcase halves and our right crankcase cover and we'll do that with some gasket scrapers some contact cleaner and maybe even a little bit of scotch brite you want to get all of the gasket material gone as well as any searing ceiling material and then make sure you clean up your transmission bearings really well and we'll show you how to inspect those after we're cleaned up and when you're cleaning the surfaces around the bearing it's a good idea to cover the bearings up that way you don't get any debris down in there all right with our crankcase halves cleaned up what we need to do is put a little bit of light oil on these bearings we'll rotate them and make sure they spin freely and we'll also check this inner race make sure there's no play in that if any of these bearings are rough or there's play on that inner race you want to get them replaced now we went through on ours and we're actually replacing all of our transmission bearings and then anytime you're in the crankcase halves you do want to replace these crankshaft bearings so we'll get those replaced as well and the last thing since we did have a connecting rod failure you want to inspect the crankcase make sure there's no damage to either side because sometimes when you have those failures you can have some serious damage all right to get these bearings replaced we're going to use two different methods on the bearings that you can get to the back side of the inner race we're going to use a bearing driver to punch those out and then the bearings that you can't get to the back side we'll use a blind side bearing puller on those the other thing to point out some of these bearings will have retainers and you'll need to remove those retainers so now we're going to go through both cases and remove all of our bearings and to help get these bearings out just a little easier we're going to apply some heat with the heat gun to the case so the blind side bearing puller is this piece we're going to collapse this down into the center race of the bearing and then we'll tighten this piece down it's going to lock these fingers out and then we can use a slide hammer and pull the bearing out again we're going to be driving these bearings you can gain access to the inner race from the back side with the bearing driver but if you don't have that you can use a socket to press these out just be careful not to damage the cases now you can continue this process for the rest of the bearings in both case halves and keep in mind you want to make sure you note the direction of the bearing when it's coming out some of these have one side that has a cover on them so pay attention to that and pay attention to any markings on the bearing all right moving on to the transmission i'm going to remove this o-ring all right so we've already cleaned these gears off with contact cleaner so we can get a better look at them now all of these straight cut gears including the idler gears and other gears on your motorcycle you want to inspect them for any pitting and you want to make sure there's no visible damage or broken teeth and then the other thing about this we have gear dogs down in here and for these gear dogs you want to make sure it has a nice sharp corner if it's rounded off that's where you're going to get the bike jumping out of gear now we didn't have any issues with our transmission when we took this bike apart and if you do we have a more in-depth transmission inspection video but just some of the common things you want to check in here are those two we already mentioned but also make sure that the spline gears slide back and forth easily then you have your free willing gears you want to make sure those rotate freely and then last this gear right here this one is fixed and the inspection on that is the same as any other straight cut tooth gear so as you can see we have a nice square corner right here and you want to make sure this gear that matches with it you want to make sure the edges that it rides against have a nice square edge as well the next thing we'll inspect are the shift forks and on these forks we have pads on them so what we can do is take our digital caliper we'll take a reading on that pad and we'll compare it to the spec in our service manual the other thing about these we have a pin that rides in the shift drum if you have a lot of wear or flat spots on this pin then chances are that your shift drum is going to have some worn out spots on that too so you want to inspect both of those make sure these aren't worn down and then the other inspection you want to make sure is that these shafts aren't bent and how you do that with this style you're going to have to actually install the shaft into the case half and make sure it slides smoothly the next thing we'll inspect is our kickstart idler gear and this right here we're going to inspect this bushing make sure there's no grooving or excessive wear if it looks questionable you can take a measurement and compare that reading to the spec in the service manual now moving on we have our clutch release arm and this is something you want to inspect these bikes a lot of times you'll get a corner rounding off right here and this is going to make it so the bike isn't fully disengaging when you pull the clutch in so if it's rounded off you'll want to replace that and you'll also want to inspect this push rod if the corners of this push rod are damaged you want to replace that as well and that's it for disassembly and inspection for the yz250 bottom end this is part one of a two part series for the bottom end rebuild so if you want to know how to put this thing back together we'll show you how to get that done in part two and if you need any parts for this we have a lot of different options for parts on our website we offer free shipping on orders over 75 dollars and if you need to know how to put your top end back on we also have a video for that so check it out and subscribe to our youtube channel because we have a lot of other helpful videos on there thanks for watching [Music] you

Channel: Rocky Mountain ATV MC

Views: 103,599

Keywords: Rocky Mountain ATV/MC, rmatv, rmatvmc, motocross, rockymountainatv, dirt bike, motorcycle, off road, yamaha yz250, yamaha yz250 bottom end rebuild, yamaha yz250 engine rebuild, yamaha yz250 engine, yz250x, yz250x bottom end rebuild, yz250 bottom end rebuild, yz250 bottom end, how to, 2 stroke engine rebuild bottom end, yamaha yz250x, bottom end rebuild 2 stroke

Id: SFvyYoP3SI0

Length: 27min 38sec (1658 seconds)

Published: Tue Nov 10 2020