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Motorcycle Top End Rebuild on Yamaha Four Stroke (Part 2 of 2)

Motorcycle Top End Rebuild on Yamaha Four Stroke (Part 2 of 2)


This is Part 2 to our four stroke piston and ring
replacement on our WR 250F. Please refer to Part 1 for disassembly
instructions and for valve replacement and valve shimming, you can check out our valve videos. First things first – we’re gonna need top
end gasket kit, and Rocky Mountain’s got you covered. We carry a wide variety of top end gasket kits for you to choose from. It’s gonna come with everything you need to rebuild your top end. At this point we’ve already got the rings installed on to our piston. We’ve also got all of our sealing surfaces
clean and ready for assembly. So we’re ready to start putting it all together. For the first thing we’re going to do is oil everything up so it goes together
smoothly. We’re gonna oil the connecting rod and the piston – so where the wristpin slides through. Then we’re also going to oil the wristpin. Now we’re ready to install the piston. There’ll be a little arrow or marking on
top your piston which usually always points to the exhaust
side of the motor, but always refer to your service manual for proper piston installation. So we’re gonna slide the wristpin
through the connecting rod and remember we’ve already installed one
of the circlips on the other side, so we just need to install the one. You want to rotate the circlip up into place. You don’t want to bend it at
all. So now we are just going to make sure that its seated in its groove. Once we’ve got that installed we can
remove that rag. We want to make sure there’s nothing sitting on the sealing surface and then we can just set our base gasket into place. After that’s in place we’re going to put our centering dow pins into their holes. There’s two of them and
once those are both installed we’re going to put a little oil on the
piston and rings to help them slide into the cylinder easier. We’re also going to throw a little oil up into the cylinder and then we can
work on installing the cylinder. This can be kind of tricky because you
have to compress the rings as you are sliding them into the cylinder. Take your time with
this step. You’re going to want to watch the rings and make sure they’re staying in their
groove not getting hung up on anything. When you get the cylinder to slide down
onto the piston, you’re going to want to double check your work, turn the motor over couple times, making
sure the piston and rings run up and down smoothly in the cylinder. Now we can just put our
other centering dow pins into place. We’ve just got two of those which sit on top of the cylinder lined up with the cylinder head and they were going to sit our front cam
chain guide down into place. Remember we’ve already cleaned all of our
sealing surfaces so we can just sit that head gasket
down into place. Go ahead and install the cylinder head. Be sure that everything goes on smooth
and everything is sitting flat. With the head in place we’re gonna put a
little anti-seize on each of our cylinder head bolts and drop those into place. Make sure that each one has a crush washer going on with it. And then we’re going to tighten the head bolts down. First get them tight with a regular
socket. It’s critical that these are tightened down and torqued in a criss-cross pattern. this will
prevent any damage or warping that may occur. So now we’re
using our torque wrench. Start on one side and then move to the
bolt diagonal and continue this pattern until you get all four bolts torqued to the proper setting as listed in your service manual. And then I like to double check each
bolt. So go over it once more and make sure all of them are torqued evenly. The next part of this rebuild is
we need to time the motor. The first step in timing is getting the
piston to TDC – or top dead center. So we need to remove
the engine plugs from the left crankcase cover. The bottom plug is so you can get a socket in there and turn the motor over if needed. The top plug has the aligning mark and shows the mark in the flywheel and as you can see, both marks are lined up, telling us the piston is at top dead center. If you don’t see the mark on the
flywheel, you need to turn the motor over until both marks line up. Now we’re ready to install the camshafts, so we’re going to wipe some assembly lube on the lobes and journals of each cam
and then go ahead and install those. We need to refer to our service manual
for proper timing instructions. As you can see, each cam sprocket has
timing marks on it. Mark C and D need to sit level with each other, and also with the top of the cylinder head.
It’s important to start with the exhaust cam and pull the cam chain tight up off the
crankshaft so there isn’t any slack. Align the timing mark where it needs to
be and then run the cam chain over the intake cam and align those marks
accordingly. It’s basically starting at the front of
the motor and then working your way back. The slack in the cam chain will be taken
up by the tensioner. So we’ve got our camshafts installed and
timed using the mark on the flywheel and the marks on the camshaft sprockets.
Go ahead and double check your work according to the service manual. Make
sure everything is how it should be. Remember the cam chain tensioner will
not be installed until a little later. So now we’re going install our camshaft caps. First we set the locating clip down onto the bearing. Be careful not to drop it and then make
sure we’ve got our two dowel pins still in the cap and set that down on to the camshaft. It should just pop into place and then
we’re going to do the same thing for the exhaust side. Sit that locating clip down into the
groove on the bearing and then sit the camshaft cap down into
place. Then we can put the camshaft cap bolts
into place and begin tightening those down. Again we need to tighten these and
torque these bolts in a criss-cross pattern to avoid causing any damage. Refer to your service manual for proper
torque specs. So after those have been properly torqued
we can go ahead and put those two engine plugs back into place and tighten those down. After that we need to install and
tighten the small bolt on the left side of the cylinder down, and also the two nuts holding the cylinder to the head. Now that those are tight we can install the
cam chain tensioner. So to reinstall this tensioner, we need to remove the bolt from the end and using a small flat blade screwdriver, suck the tensioner back into the housing
by turning the screw driver clockwise. You need to hold the screwdriver keeping the tensioner arm sucked up while you install the tensioner into the cylinder. Make sure you’ve got your new gasket on there and then we’re going to thread both bolts
into the cylinder and tighten those down. Once you’ve got the bolts tightened down,
simply pull the screw driver out and the tensioner will automatically extend,
applying pressure to the chain. You can check your work by inserting a
screw driver and rotating it and then letting go. You should feel the
tensioner spring back out. If it’s been installed correctly, we can
install that end bolt and tighten that down. Make sure the crush washer goes on with the bolt. The next thing we’re going to do is apply a light coat of silicone to the cylinder head surface. That’s going to help the valve cover
seal a little better. Then we can just set that valve cover up into place. You’ll notice we’ve already got the gasket on the top part of it. Then we can reinstall the two bolts on top
and tighten those down. And once we’ve got those both tight, we can just reinstall that top radiator hose down on to the spout coming out of the cylinder head, and then just tighten that hose clamp
down. After that we’re going to reattach the
ground wire running to the cylinder head and reinstall the spark plug cap. Now we can work on reattaching the oil
supply lines. We’re going to sit a crush washer on both the bottom holes and then sit
the lines on there and thread both bottom bolts into their holes. Make sure there’s a crush washer going
on with the bolt so it seals the line fitting on both sides.
Now we can install the top bolt placing the crush washer on the backside and then threading the bolt with the crush
washer into the cylinder head. Once that’s in place we’re just going to tighten all three of those bolts down. And now it’s time to reinstall the carburetor. So fit that up into place. We’ll slide it up into that front carb joint and
then were going to reattach the TPS sensor, hot start cable and both throttle cables.
After that we can swing the subframe back up sliding the air boot onto the back of the carb and reinstall that top bolt. We’re going to tighten that top bolt down, and then snug both bottom bolts up as well. With the carb in place, we can tighten the rear carb clamp and then tighten the front carb clamp as well. Now we’re going to slide that cylinder head
breather hose down into place and route that accordingly. After that we
can reinstall both sides of the top motor mount and tighten those five bolts down. We need to refill the cooling system
with coolant and we figured we do this before putting the tank back on to make it a little easier. Once we get that full we’re just gonna
put tank back on, tighten those bolts down. Then we’re going to reinstall the
header put the two nuts on front and tighten those both down and then reinstall the
muffler. After the muffler’s tightened down we can
reinstall that side panel. And once the seat’s installed, we’re
done with the rebuild. Double check your work and make sure you got everything together correctly, and refer to your service manual for proper
braking instructions. This concludes our two-part top end
rebuild on the WR 250 F. If you have any questions, call in or visit our website. Rocky Mountain ATV/MC is the leader for
parts, accessories and apparel for your UTV, ATV and motorcycle. Thanks for watching!

100 comments on “Motorcycle Top End Rebuild on Yamaha Four Stroke (Part 2 of 2)

  1. I know they are very similar but Yamaha has made a few changes over the years here and there… If rebuilding your 2004 you could surely follow along with this video and be just fine… Just refer to your service manual for tolerances and specifications

  2. i have put my bike back together after reshimming each valve and now my bike has little to no compression and will not start but will occasionally backfire? what have i forgot or what do i need to do? thanks. please help

  3. Hi i recently changed the water pump seal and head gaskets on my yamaha 426yz since the oil and coolant was mixing. Everything was fine until the next day of riding, the radiator over flow kept spitting back out coolant constantly when riding and now the compression is low once more and the oil stick looks abit milky again. What could be the problem there?

  4. I recently changed the timing chain and tensioner on my 08 yzf250 because the tensioner was defective. The timing was way off and the inside of the muffler was soaked in fuel and smoking just a little, but enough to cause concern. After I got everything reinstalled, cams to tdc and put everything back together, the engine now puffs white smoke. The smoke is pure white, doesn't smell sweet like coolant and it isn't damp. It smells like exhaust and nothing else. 

    Would being off by one tooth on either cam cause this? Or do you think it may be a ring or head gasket? 
    I've ordered new rings and gaskets for it regardless because I was planning a rebuild this winter. 

    The bike will idle without a problem which it wasn't doing before the changes, throttles up without issues either. It is just puffing smoke. I did let the bike idle for about 20 mins to see if it was condensation. The higher the rpms the more smoke would appear. 

    Any suggestions? 

    Great video, thank you for posting that

  5. @christian johnson You'll have to tear back into the engine to figure out what is causing the kick-starter to bind up. I wouldn't try to kick it anymore or force it to move because you could end up breaking something especially if the timing is off. It could be that a valve is hitting the piston or it could be something jamming up a gear inside. It's hard to say without more information.

  6. You forgot to mention the surclip openings on the piston should be at 6 o clock or centrifugal force can pop them out into your cylinder.

  7. Your surclips looked like they were at 3 o clock which could compress under force  out when running. byebye cylinder.

  8. Hey Guys, Great video … im thinking about a high comp piston (13.5:1) or big bore kit for my 2007 WR450f, I just wanted to know will I still be able to e-start my bike with either of these mods???… Thanks in advance.

  9. I think this show was alsom now i can do my top end and bottem doing this will save me $500.00 thank u rocky mountain u r bad peace from hawaii.

  10. Your guys videos are awesome!!!!!! I just put my yfz back together and got it running. Omg. I followed the video step by step. I had it disassembled for about a year. As I've had no extra money to take it to the shop. I just have to fine tune the clutch and carb now and I'm hitting the trails next weekend. Thanks for taking the time to make these videos. Thumbs up!

  11. P.S the shop was charging me $325 to do exactly what part 2 of 2 shows I payed $600 for bottom end work and it was ready to just be put together. Watching another YouTube video I learned how to replace valves and valve springs with household tools. And with this video saved myself $325 in about 2.5 hrs. Thanks.

  12. i have an 07 yamaha yz450f and for the timing i have 3 lines side by side on the flywheel which one of those should line up with the mark on the case to indicate that the bike is in top dead center?
    -jon

  13. hi mate my cousin just bourt a 2002 yzf 426 theres water getiing into the oil and theres water getting ontop of the piston and into the exhaust…any sugestionss?hes changet the top head gasket and the water pump seal

  14. my valves on the inside are coated in a black char, just like the piston. can I clean that with varsal or something? what does that tell me about the engine?

  15. hey sir does it matter to TDC before disassebling? and how do I knew its not Dow Dead Center before disassembling? coz i want to make marks before disassebling, I want to rebuild my engine it same version as yours

  16. Well directed informational video, for the instructions were to the point and explained so that even guys like me who never worked on a YZ250F could manage this choir of timing the cam to the crank. Thank you for the information.

  17. Some of the instructions were not needed for this motor is going on a mini sprint car. That is all good for I would rather have extra information then not enough. I hope my nephew wins his race.

  18. You didn't show unhooking the cam chain every time you have to thread it through the head/cylinder/gaskets. Must be a pain in the ass. What happens if you drop it?

  19. very helpful vid thanks for sharing ur knowledge, can u make a vid how to increase hp??? will be awesome hope to see it soon

  20. Thanks for these videos, they're very well done and uber helpful to someone learning the ropes like me. I'm curious why you didn't include a new cam chain in this process. Seems most articles I read say they are prone to break and do a lot of damage, and since they're so cheap to buy it's a wise thing to do. Or are they not considered part of a top end? Thanks.

  21. I know it's an older video but never rebuilt a dirt bike so was looking into it to rebuild my 04 yz250f. I've rebuilt a few car engines of mine (dsms) and the only thing I noticed bad about your video is using anti seize on the head bolts. antisieze reduces torque which results in lower clamping force of those bolts. this has been test proven many times. to achieve best clamping force from a bolt you use a new bolt with oil, it will be greatly decreased with an old bolt and antisieze. just thought I'd throw this out there whether you use the info or not. I am a mechanic and not trying to be a key board know it all.

  22. Hi , I have one very important question , What kind of motor oil to use after the renovation ? such as commands manufacturer or some special? because it is a new piston and rings, Does it matter?

  23. I was thinking of doing the cylinder works 270 big bore kit on my WR. I was wondering if you had to rejet your carb after the big bore install?

  24. can you use gaskets again if bike hasn't been started?payed 100£ and had transmition issues and had to strip

  25. Question…i put my cams back on my head without puting the head on the bike to clean the sealing surface by the valves so that the buckets would not fall out. The cams were tight and would bearly move. I only just snuged the cams caps…? The cams worked fine before i took them off the bike.

  26. What would happen if your oil expander ring were to over lap? I had the hardest time putting the cylinder over the piston and rings. I finally got it on and it goes up and down smooth, but i was having issuses with the oil expander overlapping not sure if it did or not.

  27. Great video. For me 2:05 was the biggest pain in the ass on the whole job, using a new jug and piston. Getting the rings to compress evenly did not want to happen and it took a long time. It's together now and I'm wondering if I tweaked one of the oil control rings on the bottom slightly because the last OC ring did not slide in smoothly and the bottom of the jug pressed against it, so I am debating whether or not to take the jug back off and put another new set of rings in it to be safe.

    I am not sure if any ring compressor tool would work with this or not.

  28. Hi, great vid. I’ve a wr450f to do the same too, apart from torque settings , piston sizes etc… would it be basically the same layout to do ? Cheers

  29. My camshaft dots do not line up no matter what I do the left cam (exhaust side) aligns perfect. On the right cam (intake side) the dot either sits above or below the surface of the head. If It will not align straight. Should I go slightly above or slightly below the head surface?

  30. With upgrading the piston/cylinder with a big bore wouldn't you want to upgrade crank and bearings as well. I put an oem piston/rod in my crf250r and it ended up destroying my crank and bearings. Had to replace everything at that point.

  31. Are those after market gaskets reliable? I've rebuild my xt600 with an gasket kit and ALL the gaskets where leaking. The only genuine gasket I had purchased was the cylinder head ones.

  32. I have a Yz400f that I replaced all of the gaskets on and timed right during installation . Now, these old bikes have compression levers on them. I went to start and now there is no compression in the motor and my kick moves without holding the lever down. Would you guys have any idea what that may be?

  33. Great video. Good detail and clear logical explanation of what you're doing. I've never done thus before, but I think I can now. Thanks a lot.

  34. Hey I just got a 2003 wr450f but I am having an issue. Every once in a while something causes bike to seize? Basically Kickstarter won’t kick anymore. But if I rotate motor through peephole its spins freely. I tore apart the clutch assembly to see all the gears, they all look fine. Everything that I’ve seen so far is good and functioning. Any ideas for the random lockup. Btw it literally happens randomly you can kick it forever and have nothing happen or you can kick it once and it happens. Also when it runs the motor sounds and feels tight (if that makes sense). Please help have no more ideas other than tearing down motor.

  35. I brain farted… on final assembly I used assembly lube rather than motor oil as the lubricant on the piston/rings and the inside of the cylinder. I am still in process… should I disable and clean it all out is the lube innocuous? Thanks a ton for all the help!

  36. Corrected bad info – My 2007 WR450 has three marks about 5mm to 6mm apart…. i have no idea which mark to use. I assume the middle one?

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