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So with no history Nickj decided that the little CRF two Fiddy should get an overhaul so he has a platform to maintain his bike from. Read carefully when I say overhaul I mean maintenance as in a piston and a set of Kibble White valves. He has decided to throw a cam at it as well.
So I bought the bike back from Wauchope the first steps are to remove the seat and tank, so you can get at the valve cover. This is easy with T-handles and sockets and once removed gave it a good and proper pre tear down wash
The valve cover removes easily up through the top of the frame. It has a rubber gasket that is reusable if you don’t damage it. Take care popping loose the cover, and you should have no problem. There is a passage cast into the cam cover and the cylinder head for the spark plug to go through. The passage is sealed with a reusable rubber seal between the head and cam cover. Take off that seal as soon as the cover comes off, so it isn’t misplaced or, worse, knocked into the engine. Also, remove the spark plug at this time.
I set the engine up on TDC there are inspection covers on both sides of the engine at roughly crankshaft level. I removed the right-hand side and rotated the crankshaft (easier because the spark plug is out remember)
Once the covers are removed, turn the engine over slowly with the kick start lever. It should turn over easily with the spark plug out. With the timing mark in the case aligned (on the crank gear and the notch in the plug thread) the timing lines on each side of the cam sprocket should be lined up parallel with the gasket surface. The lobes on the cam should be facing to the rear of the engine. If they are not, you need to rotate the engine one more turn and realign the timing marks. The crank turns over twice for every time the cam turns once, so the additional turn should line everything up
I checked the valve clearances at this time. Both inlets had clearance as did the exhaust
Left inlet in spec
Right Inlet out of spec, but still had some clearance
Exhaust in spec
The cam chain tensioner is removed to release the tension on the chain, remove the bolt from the back of the cam-chain tensioner. The Honda shop has a tool you can use I didn’t have it. You can leave the tensioner locked and in place if you are just doing a piston and rings replacement. You can use a small, flat-bladed screwdriver to wind the tensioner back, but you will have no way to lock it there. I found it easier to remove the tensioner from the cylinder. You are trying to create all the slack you can in the cam chain and the automatic tensioner will keep trying to take up that slack.
The cam chain tensioner
Loosen the bolts that secure the cam-bearing caps.
Hold each cap down low at the base and rock back and forth carefully to work it off the locating dowels. There is a cam-bearing locating clip in the cap, and it can come loose and fall into the engine.
Watch for it as the cap lifts, and make sure it doesn’t drop out. Remove the clip and put it with the bearing caps I put them in reseal able sandwich bags to make sure it doesn’t get lost. You need to make the cam-bearing caps go back in the correct position, they are marked on top left and right side to make it easier. Just be aware that they must go back on the same side, and facing the same direction that they faced when they came off.
Most dirt bikes have removable cam sprockets, but the CRF250’s do not. The only way to get enough slack in the chain to remove the cam is to slide the drive-side cam bearing toward the cam sprocket. The clip in the cam-bearing cap locks the bearing in place when the caps are on, but with them removed, the bearing should slide easily to the side. That will allow the cam to drop down and give enough play in the chain to remove it from the cam sprocket, and for the cam to come out of the engine.See the bearing on the left in place, the groove in the bearing is where the clip for the cap locks it in place.
Now you can see how I have slide the bearing on the left to the left allowing the left side of the cam to drop and the chain can be removed.
Tilt the cam (throttle-side up, clutch-side low), and remove the chain with one finger. Let the cam chain drop into the head. It can’t really go anywhere, but it is a good idea to refrain from moving the kick start. I held it up with an ocky strap
I am putting the same picture in again so you can see the exhaust rocker is still in place, the axel it pivots on needs to be removed
The exhaust rocker axel is removed through the side of the cylinder head as seen below
I removed the exhaust header
Drained the coolant
Top engine mount was then removed
Removed the two small head bolts on the left hand side
I had to loosen the sub frame to allow the carby and boot to be pulled back enough to get the head off. It wasn’t much just a little as seen in the photo
And remove the cylinder head. If the gasket seal is stuck tight, check to make sure you have all the fasteners removed, then tap both sides of the head casting lightly with a rubber mallet
You’ll need to remove the head gasket, then the white or neutral-colored cam-chain guide. The white cam-chain guide has a notch in the top surface of the cylinder for two nubs to ride in and a notch down in the cases for the bottom point to sit in, so check out how it looks and feels before you pull it out.
Note the two locating dowels in the top of the cylinder. Make sure you keep track of them, and don’t let them get damaged. The dowels are on the water-pump side of the engine.
If you have any brake clean or the likes, add a couple of teaspoonfuls of solvent into the port on one side of the head. With the port up, so you don’t dump the solvent, hold the head up to a good light and see if the valves remain fluid-tight. If the valves are not fluid-tight, the head needs a valve job. The darkened carbon around the valves tells me that the valves need replacing. Tip the solvent out, turn the head over and repeat the test for the other two valves.
Next the barrel was removed and inspected note great cross hatch basically no wear
Checked the piston out
Crankcase was packed with rags so the if the piston pin clip dropped in didn’t end up in the engine
Piston out
More as the head gets done and I rebuilt it
Bloody hell an I glad I didn’t attempt that
Awesome job mate , great write up too
Looks like I’ll be building your deck and new roof as a barter off pretty soon hey !!!
Can’t wait to see the next stage
Nick
Yeah I couldnt do the deck work on my own mate, well I could but it would be shit :laugh: Got to love the barter system
TB
So I picked the head up from Teknik’s, Nick fitted a Kibble White intake valve kit. The kit includes valve springs to suit the new valves, seals etc. While it was there Nick fitted a cam he and Nickj had decided on and set the valve clearances for me to save me having to set them up. That is a better idea has he has all the shims etc there. I tucked around to Sutto’s picked up the Pro-x piston kit and gasket set. Included was a new rear tyre and grips to fit.
I have a video here showing how the auto decompression works, I should have included in the video that at the slower cranking speed the cam doesn’t spin fast enough to throw the arm out so the decompression works, when it starts it then as the video show throws out and the exhaust valves operate as normal
http://www.youtube.com/watch?v=GfAg2w4dXjQ
I cleaned up all the parts and got everything ready for assembly.
I inspected the barrel again, it is in excellent condition, plenty of visible cross hatch.
A little carbon was cleaned from the top of the cylinder using a scotch brite pad.
Ring end cap was checked
Rings were installed on the piston, remember care needs to be taken and the rings need to be staged on the piston correctly. The manual specifies a direction of installation for each ring to stagger the ring ends. Put the rings on with the marks stamped into their ends facing up. The oil “ring” consists of two side rails and a wavy spacer. The ends of the spacer butt up against each other. They shouldn’t overlap or interlock. I then fitted one piston circlip, I have always struggled with this style of clips so I went to youtube looking for a tip, and here is a red hot tip that works great
http://www.youtube.com/watch?v=bh3Kwn9tFvc
I then installed the piston, slide in the pin until it seats on the side that has the clip installed and insert the final clip. Keep the crankcase packed with rags in case you drop the circlip, remember other is installed on the bench
All in happy days
Removed the towels, and then installed the base gasket. Make sure the locating dowels are still in the correct locations and are installed properly.
Clean the cylinder with contact cleaner on a paper towel, and follow all the directions in the service manual regarding measuring the cylinder bore and cleaning the oil passages and gasket surfaces. After the cylinder is clean, apply oil to it, the piston and the rings before assembly check the rings are staggered correctly again. You should be able to lower the cylinder with one hand while compressing the rings with the other. As the rings slide into the cutouts on the side of the cylinder, make sure they don’t hang up on the edges. Do not force the cylinder or twist it while working the rings into the bore.
Carefully
Home
Slide the white cam-chain guide down into the cylinder. There is a notch in the case and cutouts in the top of the cylinder for the little locating nubs on the sides of the guide, and they both have to be engaged. Rock the guide back and forth to make sure it is seated correctly
Install a new head gasket, and make sure the locating dowels are in place. The cutouts in the head gasket will not match the openings in the water jacket. Don’t be tempted to change the size or location of the coolant holes in the gasket. Slide the head on, while pulling the cam chain up and out of the way with the zip-tie. Install the washer and nuts that hold down the head, then torque all the head bolts to the correct specifications29 foot-pounds for the four large nuts and 7 foot-pounds for the two smaller external bolts. The washers are shaped, so the narrow side faces the aluminum of the head. You should be able to tell which side has had a nut spinning against the surface. Don’t forget to put a drop of oil on the threads and the bolt head contact areas
The small bolts that go to 7 foot pound
I had all the shims and buckets installed left the rocker arm in place. Make sure the timing marks on the crank are still aligned, then start to install the cam chain on the cam sprocket. Slide the cam in with the lobes facing rearward. Once the cam is in, don’t worry if the cam chain is off a bit. With the play in the chain from the bearing being slid to one side, it is easy to “wrinkle” the cam chain to move it one tooth at a time. Move the chain tooth by tooth until you line up all the marks. Check your work twice here; a mistake can allow the valves to hit the piston. After all the marks are lined up, slide over the cam-chain-side bearing. Align the retainer clip cut in the bearing with the bearing-cap bolt hole.
From there the exhaust, the carby, coolant hoses, sight plugs, valve cover, spark plug, top engine mount, fuel tank, fuel line etc were installed. Lefty called over we chewed the fat, had a beer discussed today’s events.
I packed up, washed the air cleaner and set it to dry. I was going in to watch the footy and have a rum when I thought I wonder will it start
http://www.youtube.com/watch?v=O4WFjywrQS4
Tomorrow I will oil and fit the air filter, the new tyre, the new grips and take it for a ride and run the new piston in. More later
Trailboss wrote:
Excellent work on the deck building TB. Was looking at the above photo and was thinking the cam looked awful like someone went to it with a chisel. Then watched the video and realised it was lumps of grease.
Looks like you’ve done a great job mate
, thanks again for fitting the job in and having it ready for Bulls ride next week :woohoo:The explanation you gave was better than any manual and I’ll maybe attempt the next piston change myself
Nick
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