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,
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