Takeapart & Putbacktogether CG250

[grumpyunk]

These are pics from splitting the case to find a metal sliver.

Rocker cover removed.
This is not going to be as I planned.
Can't put words by image.
Cylinder head removed, showing piston and pushrod port.

Cylinder removed, showing piston and cam gear
Left side cover removed showing flywheel
Right side cover removed showing clutch plastic pump drive gear spinamathingy centrifugal oil cleaner and balance shaft gear

max 5 pics reached

[grumpyunk]

More as noted...

End view showing piston & cylinder studs
Similar
Flywheel side showing oil seal to cam gear pocket
Clutch side showing oil cleaner removed/clutch bearing removed
Inside of gearbox/sump

Left to right
output shaft
counter shaft
shift drum
crankshaft
balance shaft

[grumpyunk]

And finally
The gears rightside up
balance shaft
crankshaft
shift drum lower
input shaft upper
output(counter) shaft
kick start mechanism

The kick start was the teaser when putting the case halves together.
The lowest part in the picture had rotated. That happened as I split the case, and or course it was not seen. It all fit back together, except something to the 'right'. I rocked the case, trying to figure which part was not fitting. Only one shaft had made a partial appearance besides the crankshaft. Figured out it was the kick. Finally rotated the stamped metal piece a bit CW, and it fit down inside the edge of the case. After that, it just fell in place with little jiggling to make it work.

Left side case.
Holes are:
kick start
upper is output shaft bearing
lower is shift drum
next is input shaft bearing
crankshaft bearing also showing cam pocket & seal
balance shaft bearing
No bearing on shift drum as it moves slowly...

Gears upside down.
A different view of the balance, crank, geartrain, shift and kick
(kick still out of place in this pic. Needs to rotate CW a bit to fall into place)

Flywheel cover showing allen head screws
Spinning oil cleaner showing allen screws

None of the clutch side had to come off to split the case.
The crankshaft would have to be immobilized to remove the flywheel, and I used a 'jam' between gear teeth on the clutch side to do that.
I had to use a three-finger puller to remove the flywheel. The 'gizmo' I bought for the purpose didn't fit. The gizmo with 4 teeth for the cleaner castle nut worked perfectly(24mm I think).
I had to WHANG!!!! on the end of the puller, after tightening more than I thought I would need. Bent the head of the bolt. Then it popped.
I reused some of the gaskets that came off cleanly. New head and base gasket along with the main case and right side case cover.
I took multiple pictures of the wire routing so I could put it back in the same place.
Never did find a torque value for the small sprocket. Blue Loctite did not work for me.
tom

[grumpyunk]

I did not show the cam & gear removal and installation. It is kind of fiddly in that there is a spring washer that fits at the far end of the cam gear shaft. It wants to fall out.
You have to insure it has not fallen out after putting the cam gear in place and inserting the shaft. It can fall out and it is very dark colored. LOOK. Then install the retainer as shown.
I removed the seal to allow cam timing. I could not see the dot/mark to align without doing that. It cam out readily(I was surprised!!) as if it was designed to allow R&R for timing.
The flywheel taper should be clean and dry. There is oil frittering around inside the left side cover, so clean the shaft and the inside of the flywheel before assembly. The taper holds the flywheel in place, NOT the key. The key is for alignment only, not load bearing.
I did take off the spinner, the clutch frictions and steels. I thought the frictions were worn and wanted to inspect them. Measured against new, and they were fine, so PBT. I cleaned the spinner, finding a bit of 'stuff' at the perimeter, around the outer edge. Used a flat blade to scrape it out, and then cleaned the rest with a rag.
I also took off the oil pump, I think to gain access to remove other parts, but who can remember after a month or so. I did NOT remove or fiddle with the balance shaft as I did not know the timing information...
Be careful when removing the clutch basket as there are washers and stuff (tech term) that need to go back in an exact order. Snap ring and Bellville washer, though the Bellville may be on the oil cleaner castle nut.
When doing the clutch springs, start all the bolts and then 'walk' around and back and forth to tighten them all a slight bit at a time until final torque. Things will/may jam if you go to town on one and then another...
I cleaned the case mating surfaces, and then spread a 'wipe' of RTV across the gaskets. I figure it will squeeze into any machined marks on the metal parts. Doing well so far.
Fitting the engine back into place... First tried from the brake pedal side. Not good. In the way. Goes better from the shift lever side. Getting the two 'main' bolts in took slight persuasion(rubber hammer), but they went in OK. Placed all the 'plates' with nuts/bolts loosely. Front lower and upper rear. With the main bolts in, the plates were put back to 'match' the witness marks from original assembly.
I had the down pipe come loose, and lost one of the deep acorn nuts. Working too long and too late, maybe.
Questions?
tom

[grumpyunk]

I replaced the cam followers with roller tipped followers from Aliexpress. Slurped oil all over them to insure they were lubed for startup. They do seem to use less power than sliding followers, so performance is up a bit.
The pivot shaft has to go in one way to insure oil flows properly. The 'fifth' head bolt is external to the rocker cover, and special in that it has a somewhat pointed end. The 'point' is to fit into a recess in the follower shaft, preventing rotation and insuring positioning as designed. The shaft is a 'push in' until the bolt is installed when the head is attached.
I set the rocker arms to .0035" and they have a slight tappy when running, and seemingly a bit more when warmed up. I figure I will check the adjustment a bit more often as I prefer less noise, leading to less wear to the rocker arms where they meet the valve stem.
tom

[grumpyunk]

Was asked about replacing the factory key with a 4 degree key.

The procedure is the same as if you were doing a R&R of the flywheel.

Remove the side cover, immobilize the crankshaft. One method is to remove the spark plug, move the piston down, and feed in some rope. Feed enough and the piston will be blocked when brought to TDC. With the piston jammed, you can loosen the bolt on the end of the crankshaft.
If you have a puller that threads into the center of the flywheel, use that. If not, you can use a pulley puller. Set the legs to fit around the flywheel, and center the bolt into the head of the flywheel bolt. I missed, and bent mine. With the puller feed screw tightened, give the puller a whack with a big hammer. Don't be shy. It may take a good whack. It will pop loose, and move slightly, almost imperceptible, but the puller will get loose.
Remove the puller, and remove the flywheel. The key can be removed with a small screwdriver or a pick. Place the new key into the keyway in the crankshaft such that the 'leading edge' of the key overhangs towards the front of the engine. That will set the flywheel(and ignition pickup) a bit forward, or 'earlier' that the factory key. Install the flywheel, tighten the bolt. I used a new bolt, which I cut to match the original length, and blue Loctite. Install the cover. Yur done.
Remember that the key itself does not keep the flywheel from spinning on the crankshaft. It is the friction of the taper, crank and the center of the flywheel, that keeps it in place. I think torque is about 40-45 ft/lb.
Remove the rope after slacking the piston. You may have to rotate almost 360 the other way when tightening the bolt. Put the plug back in place. Thread all the way down until the plug bottoms against the head, and tighten 1/8 turn more. It is not a contest, just has to be snug and make good contact for heat transfer.
tom

[tknj99]

Was asked about replacing the factory key with a 4 degree key.

The procedure is the same as if you were doing a R&R of the flywheel.

Remove the side cover, immobilize the crankshaft. One method is to remove the spark plug, move the piston down, and feed in some rope. Feed enough and the piston will be blocked when brought to TDC. With the piston jammed, you can loosen the bolt on the end of the crankshaft.
If you have a puller that threads into the center of the flywheel, use that. If not, you can use a pulley puller. Set the legs to fit around the flywheel, and center the bolt into the head of the flywheel bolt. I missed, and bent mine. With the puller feed screw tightened, give the puller a whack with a big hammer. Don't be shy. It may take a good whack. It will pop loose, and move slightly, almost imperceptible, but the puller will get loose.
Remove the puller, and remove the flywheel. The key can be removed with a small screwdriver or a pick. Place the new key into the keyway in the crankshaft such that the 'leading edge' of the key overhangs towards the front of the engine. That will set the flywheel(and ignition pickup) a bit forward, or 'earlier' that the factory key. Install the flywheel, tighten the bolt. I used a new bolt, which I cut to match the original length, and blue Loctite. Install the cover. Yur done.
Remember that the key itself does not keep the flywheel from spinning on the crankshaft. It is the friction of the taper, crank and the center of the flywheel, that keeps it in place. I think torque is about 40-45 ft/lb.
Remove the rope after slacking the piston. You may have to rotate almost 360 the other way when tightening the bolt. Put the plug back in place. Thread all the way down until the plug bottoms against the head, and tighten 1/8 turn more. It is not a contest, just has to be snug and make good contact for heat transfer.
tom

Thank you, great info and much appreciated.. a few questions:
1. the step to immobilize the crankshaft.. does the flywheel puller tool accomplish this step if i buy it or is this completely separate and before i get to the flywheel.
2. If the rope is the only method, i assume it would be a fairly slim diameter rope, would i need to be concerned about rope slivers entering the cylinder and use only a certain type of rope?
3. Also i was informed that an impact wrench may be used in lieu of the flywheel puller tool, can you confirm that?

Thanks, and thanks for bearing with my elementary questions, would always rather be safe than sorry :)

[franque]

You can always jam a penny/nickel/dime between the starter gear and the flywheel. That's what we'd always do in the shop, that and a good impact.

[grumpyunk]

The impact wrench, or jamming using rope/penny/??? are alternatives to remove the bolt that goes down the center of the crankshaft and holds the flywheel tightly in place.
Removing that bolt does not loosen the flywheel from the taper on the crankshaft. You need a puller of some sort to actually pull the two pieces apart. At least in 99.99% of the cases I have encountered with flywheels of any sort.(not auto/truck)
There are pullers that screw into the center of the flywheel, mentioned on other posts on site(from DaRiver for one example) but memory of the post title is non-existent. They screw in, you tighten a bolt screwed into the puller, that pushes on the end of the crankshaft, I think. I do not have one that fits, so eh.
tom