Complete Rebuild - EC250

[RockefellerGG]

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:


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:

[RockefellerGG]

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:

[RockefellerGG]

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:

[GGRider01]

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.

[RockefellerGG]

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.

[RockefellerGG]

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?

[Jakobi]

Originally Posted by RockefellerGG

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.

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

[barossi73]

Id say both the chicken and egg are overcooked m8!

[Rick]

My guess is the crank bearing / thrust washer let go.....chicken.....

please keep this thread going!!!

[RockefellerGG]

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: