Complete Rebuild - EC250

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RockefellerGG

New member
I haven't seen a complete rebuild or walk through on the forum. Maybe I didn't search hard enough. Maybe this will be over-simplified, but I thought it might help someone who needed some motivation or confidence booster.

This EC250 belongs to a friend and fellow forum member. He was riding it a few weeks ago when the engine seized up. While washing it down, he noticed that the carb-to-air boot was disconnected. Here it goes:

Tonight, I'll start with the top end:

I started by removing the water pump cover:
open


The water pump impeller was seized to the bolt:


Gently pried out the shaft seal:


Remove the clutch cover:


Remove the right side power valve cover:


Removed the kick start lever:


Removed the shifter:


Remove the 6 bolts that hold the right side cover on. Gently pull that cover off:


Removed the lower nut that retains the power valve lever arm:


Removed the upper nut that retains the power valve lever arm:
 
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Gently slide the lever arm off the posts and down through the hole:


Remove the two bolts for the thermostat cover and the 6 cylinder head bolts:


A view of the head underside. Notice the gouge marks:


A view down the cylinder. Notice the damage to the top of the piston:


Remove the left side exhaust valve cover:


There are 4 nuts that connect the cylinder. 2 are located under the side covers:


A gentle tap with a deadblow hammer helped pop the cylinder off the engine. If you're not doing the bottom end, be sure to stuff a rag under the piston to avoid dropping anything into the bottom end.

Remove the circlip from one side of the piston and gently press the pin out from the opposite side:


The piston walls look pretty good. No real signs of blow-by or low compression.


This piston top took a beating:


 
Notice the big piece of brass that was sitting under the piston:




A couple good gouges in the cylinder wall, right above the power valve:
 
So... what's the verdict here? Foreign matter in the combustion chamber... who knows what's in the crankcase. I hope you document everything if you decide to do the bottom end - love these kind of threads.
 
Looks like foreign matter in the combustion chamber based on the gouges in the head and piston. I assume it locked up the piston and destroyed the connecting rod bearing. I don't know what the brass/copper piece is, but I'm sure I'll find out. Lots of slop in the connecting rod:

Not sure if photobucket videos work here, but here it goes:


With the amount of debris down in the bottom, I'll be splitting cases and documenting. Just not tonight. ;)
 
Upon closer inspection, you can see a brass or copper spacer on the left side of the connecting rod. I assume there was one on the right side as well. This is the big piece of debris.

Not sure if a piece worked it's way up into the combustion chamber or if it started from the top down.

Chicken or egg?
 
RockefellerGG said:
Looks like foreign matter in the combustion chamber based on the gouges in the head and piston. I assume it locked up the piston and destroyed the connecting rod bearing. I don't know what the brass/copper piece is, but I'm sure I'll find out. Lots of slop in the connecting rod:

With the amount of debris down in the bottom, I'll be splitting cases and documenting. Just not tonight. ;)
Click to expand...

It looks like one of the thrust washers off the bottom end of the rod.

and from reading further I can see you've found that too :D
 
My guess is the crank bearing / thrust washer let go.....chicken.....

please keep this thread going!!!
 
Here we go! Time to split the cases:


Clutch Disassembly

Start by removing the clutch spring bolts, the springs and spacer:


Slide out the clutch press plate, the friction discs and steels:


Drive down the safety washer using a hammer and screwdriver or punch:


Remove the clutch hub nut. This is pretty easy with an impact wrench, but you'll need to hold the clutch hub. It can be done with a standard ratchet set, but will take some patience.


Remove the clutch hub. The washer may stick to the back. Keep an eye out for it:


Lift off the clutch housing:


Remove the clutch bearings:


Remove the bushing:


And Washer:
 
Remove the two bolts holding on the shaft block and remove the assembly:




Lift out the centrifugal mechanism:


Lift the kick start return spring out of the hole and release the tension:


Remove the starter pinion circlip:


Lift out the inner starter pinion and spacer washer:


Lift out the Starter pinion assembly:


Remove the gear selector spring:


Lift the gear selector unit straight out of the case. Mine didn't come out too easily. It got tighter the further out i pulled it. There is a small white plastic bushing under it. Don't forget to grab it.


Remove the spring from the hole and remove the bolt that holds in the gear lock:
 
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Time to remove the crankshaft flywheel nut. This is opposite thread. YOU NEED TO TURN THIS CLOCKWISE TO REMOVE IT.


Lift of the washer, crankshaft gear, and flywheel:


Don't forget the drive pin:


Remove the reed block:


Remove the ignition cover:




Remove the ignition flywheel nut:


Remove the flywheel using a flywheel puller:


 
I marked the timing position to help reassembly:


Remove the ignition: It looks like there should have been three bolts holding it on, but this one only used two:


Remove the c-clip and front sprocket:


Fragments are everywhere!


Remove all the cap head bolts from this side. Notice that there are three lengths of bolts. Keep track of what goes where:


I used my Tusk case splitter. I know this can be done with other techniques, but using the right tool for the job makes this a snap. It came right apart with no drama. It happened so easily, that I forgot to snap a pic of it all mounted up.





All the sub assemblies are removed and put into labeled bags:
 
Awesome post! Thank you for taking the time and effort to document the tear down. I appreciate the detailed informative pictures.
 
Glad you guys like it. More to come soon. Sending parts out and I hope to document the case mating and cylinder stacking in a couple weeks.

For now, I leave you with the removal of the inner bearing ring from the crank:

Installed the bearing splitter and tightened the base under the ring:


Tighten down and the magic just happens:
 
Removing the power valve internals from the cylinder

Ok, to send off the cylinder for repair, I needed to remove the power valve and bearings from the cylinder:

On the left-side, start by removing the bolt and washer that retain the two bearings:


The bearings were frozen in there pretty good. I used a small torch to heat up the aluminum around the bearing and using a small L-shaped pick, they popped right out:


There should also be a small washer behind the two bearings, but it might be adhered to the exhaust valve.

I pulled the pin and the exhaust valve came with it. Notice on this one, the washer is basically baked up against the little valve. They all separated with very little force.


I slid my long 4mm allen wrench through the hole of the shaft that was just removed and lined it up with the hole on the right side. With a little pressure, the right side valve assembly came right out:


I inserted the 4mm wrench again into the small hole and drove out the other pin that acts as a hinge pin for the power valve. Push the pin out the right side and fish the power valve flap out of the cylinder:
 
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