I just rebuilt a Jawa 225 (which is basically a kickstart 210 with a CDI) and took some pictures along the way mimicking the Rebuild a Puch E50 Engine tutorial which I used frequently when first rebuilding moped motors. [note: some of the photos are from that topic and aren't my own] The one-speed 207 motor will be very similar minus the few extra parts that make up the transmission. Most everything follows the same procedure no matter what motor you're rebuilding, but I hope this might help those few out there with Jawas. Please feel free to edit if you have any improvements to make.
For additional info, check out the Jawa 210 workshop manual. Have fun, and have patience. Don't smash, pry or put excessive force on anything.
You will need:
- New Crank Bearings - 2 ea. 6203/C3 bearings (same as Puch)
- New gaskets - available on eBay or cut your own
- New Seals - 17x28x7 and 22x32x7
- Impact screw gun
- JAWA crank and flywheel puller tool ( 22mm x 1.5 pitch) or alternately a universal 3 Jaw puller
- Rubber mallet (don't use a metal hammer or you WILL damage things)
- Strap wrench, or alternatively an Air Ratchet
For starters drain the motor while on the bike, there's a small screw in the center of the bottom of the motor. Next take off the side covers, the carburetor, exhaust and chain (by removing the masterlink), and unplug the wires from the engine and spark plug. You should now be able to take the 3 engine mount bolts out and remove the engine from the frame.
Clean it while it's together so you don't get dirt in there. WD-40 does a great job of loosening up oily gunk.
Before you take the cylinder and head off, you should loosen the nuts on the crank holding on the rotor and clutch. This allows you to use a piston stop to keep the crank from rotating. You can remove those nuts after the cylinder is off, but it's easier using a piston stop. With the piston stop in, screw out the nuts holding on the clutch and magneto. If you've already pulled the cylinder, you can also use a driver through the crank, use a strap wrench around the clutch or magneto, or even shove a screw driver through the magneto and brace it against the case inside (if possible) in order to hold the crank from turning as you remove the nuts on the clutch and rotor.
- An air tool makes this job incredibly easy and you do not need to use a piston stop, strap wrench or brace anything with a screwdriver
Once you have those loose you can go ahead and remove the cylinder and piston.
Removing cylinder head, cylinder and piston
Remove the spark plug and insert something into the hole and rotate the flywheel to make sure the piston is at its lowest point. Remove the four M6 nuts holding on the cylinder head with a 10mm socket. The whole stud may come out, which is fine. You can then pull the head off, followed by the cylinder. The cylinder may be slightly stuck due to compression of the base gasket, but should be fairly easily knocked loose using a rubber mallet. It might take just a little wiggling but as long as it's not seized, it should slide right off. Before you take it fully off place a clean towel or rag inside the case so when the piston falls out of the cylinder it doesn't hit metal. Keep all the hardware together in a cup or box so you don't loose it.
Now you can remove the piston. There are circlips on either side of the wrist pin (the pin that the piston pivots on) which must be removed first using needle nose pliers. You can then push the pin through carefully using a drift tool if you have one, or using an appropriate sized socket that fits in the wrist pin hole to push the piston pin out from one side or tap it out with a rubber mallet. Take it easy, you don't want to be stressing the crankshaft by knocking it side to side. You can then remove the piston. There should also be a set of 25 2x8 needle bearings around the pin between it and the small end of the crank. Yikes.
Removing the stator
My motor had a stator with external flywheel magneto and a CDI, yours is likely the typical Jawa internal rotor with thyristor.
First remove the cover and spring. Take note of the position or make a mark on the case and the stator to set the timing again upon reassembly. You can then remove the 2 m4 screws holding the stator plate down and it should slide off as a whole around the rotor. I like to do this first so you can grip the rotor to keep it from spinning. Next remove the m5 screw holding down the rotor. The rotor itself is press fit onto the taper of the crank and you will need to pop it off. Conveniently and m8 bolt will do just this. Screwing an m8 bolt down into the center of the rotor will press in against the crank and push it free. Once it pops loose you can undo the screw the rest of the way and remove the rotor. Be careful not to loose the alignment pin (woodruff key).
My 225 stator had a CDI with an external flywheel. For this you will need to first remove the 17mm nut holding on the magneto (flywheel), which you should have done using a piston stop while the cylinder was attached, or alternately with a strap wrench or something to hold the magneto from rotating as you remove the nut. If you have a removal tool for a Jawa, use it. I don't have that tool and you probably don't either, so I just used a harmonic balancer puller with arms in the holes of the flywheel, but a 3 jaw puller should also work.
You will want to have the 17mm nut part way but not fully threaded on the end of the crank arm so that as the center of the puller presses against it the threads don't get crushed or ruined.
I didn't have the nut on the crank arm while pulling the magneto and it flattened some of the threads, but I was able to repair the threads using a pipe cutter tool. A tap and die set would also work to restore the proper threads.
Removing the clutch
Remove the clutch cover. You will need to first remove the 17mm nut holding on the front clutch bell, which you should have done using a piston stop while the cylinder was attached, or alternately using a strap wrench or something to hold the crank from rotating as you remove the nut. (Or an air tool if your fortunate enough to have one) This is also press fit and unless you have the proper removal tool, (a 22mm x 1.5 pitch flywheel puller) you can use a 3 jaw puller to pop it loose.
Again you'll want to have the 17mm nut part-way but not fully threaded on the end of the crank arm so that as the center of the puller presses against it the threads don't get crushed or ruined. Once it pops loose you can unscrew the nut the rest of the way and remove the clutch bell.
At this point if you needed to service the first gear clutches or lighten them to engage later, you can do this now by removing the 3 circlips on the outside of the clutch bell and pulling the 3 arms off. There will be a flat curved leaf spring underneath to limit the arms dragging against the drum and the rest of the clutch.
To remove the rear clutch gear you will need to hold the rear bell stationary. You may be able to hold it with a strap wrench, but I was able to jam a driver between the gear and the edge of the case to hold it still while I removed the 17mm nut.
At the same time you can remove the 17mm nut holding on the final drive front sprocket on the other side. Then pull the belt off. In order, you will then remove the round metal cover, a circular packing piece like a big washer, a sort of rounded lightning bolt shaped alignment piece, 1 or 2 metal washers and an o-ring, and finally the gear change shoes. I also had to pull these off with the puller; they're not press fit on but they can sometimes be difficult to pull. Sometimes inserting two screw drivers between the shoes and bell and gently prying and wiggling works. Should have a shaft going down into the case. Wipe them dry and keep them grease free. Then you can remove the rear drum gear itself which also has a shaft going down into the cases.
Splitting the case
With the clutches off, on the clutch side you should now see 10 m6 flathead screws. 2 will be outside the clutch housing toward the bottom of the engine, 3 under the rear clutch gear, and the other 5 around the crank arm under where the front clutch bell was. You will likely need an impact driver to remove these as they get very stuck.
With all 10 loose you should be able to gently and slowly separate the crankcase halves by tapping with the rubber mallet on one half while holding the other. Do not use a metal hammer. Do not bash it. Do not pry with a screwdriver or you can gauge the mating surfaces. Do not hit the ends of the crank.
The crank should come out on one side. You can then very gently tap it out from the crankcase half that it's still in. Again use a nut threaded onto the end of the crank arm so you don't damage the threads.
You can now pop out the crank seals using a screwdriver and remove the bearings (which should still be in the case) by taping against their center race with a socket and a rubber mallet.
You may if you wish remove the gears to clean them. There is a gear that likely fell out when you split the case which goes onto the bottom of the shaft attached to the rear clutch. You can replace the rear bearings and seals but these take much less wear and are much less critical to engine operation and I'd just leave them be as long as they're spinning freely and the seals aren't leaking.
This image is from a kickstart version and may be slightly different than yours.
Installing new bearings
The crankshaft bearings and should be all that needs replacing. You can press the new ones first into the casehalves, but I prefer to put them on the crank first. The bearings are both 6203, which is a pretty common moped bearing. Most bearings come with cover seals and you'll want to pop those off exposing the balls and cage. This allows for oil from your fuel mix to lubricate the bearings in use. To install a new bearing heat up the new bearing first. This will cause it to expand, making it easier to install. I hung mine in front of my heater that I had going at the time. note: these images are from an e50 rebuild, but the same principles apply.
Drop the bearing on to the shaft til it rests against the crank center. If it doesn't go on easy, take a seat post and tap it down pressing against the inner race of the bearing, not the bearings themselves or the outer race or you can damage it.
This is a e50 maingear bearing, but illustrates the idea.
Now you need to clean your cases. Using a razor blade gently scrape off any remnants of the case seal gasket and the base gasket. Be careful not to gouge the cases at all. Carb cleaner, Starter fluid, compressed air are good for getting out oil grease and dirt. You want the mating surfaces of the case to be especially clean, dry, and oil free.
Lube up the seals and install with the lips facing in. Make sure you have all the internal gears back in their original place before closing up the cases.
To seal the where the case halves join I use Permatex UltraBlack, but any case gasket sealer like Yamabond, Hondabond, or gas resistant RTV will work. Just squeeze the sealer out of the tube and apply a thin even coat to all the surfaces. You want a nice airtight seal otherwise your engine won't perform as desired. Alternately you can use a paper case gasket if you have one.
NOTE: there are 2 seals on the clutch assembly, one inside, for a total of 3 clutch side seals.
Press in the crankshaft assembly. You should be able to locate it in position making sure your clutch side and crank side arms are facing the correct directions. Be careful not to push out or scrape the seals. Once it's mostly in place you can start tightening the case screws to pull the case halves together and press in the crankshaft. You may need to use longer m6 bolts at first to start pulling it together. Go in a criss-cross star shape pattern in 1/4 turns so that you press it in evenly, bit by bit. Make sure your crank isn't dangling between the 2 halves and is properly facing where the cylinder will be. Tighten firmly.
The crank should spin. It may be a little stiff until everything is broken in, but shouldn't be difficult to turn by hand.
Reinstalling the clutch
You're basically doing the reverse of what you'd done before. Make sure to keep the clutch parts, especially the drums and pads, dry and free of oil.
Put in in order, the rear gear, the rear clutch, the round lightning-bolt shaped alignment piece aligning it on with the slots on the shaft, the big spacer washer, and then the cover and screwing it all tight. You can again use the screwdriver trick, or just hold the 17mm nut on the chain drive sprocket on the other side, and as you tighten it will tighten up both sides. Now reinstall the belt, the bottom part of the front clutch and the front clutch bell. Tighten the nut down now if you can, or wait 'til you have the cylinder back on to tighten it down with a piston stop. Then just pop the cover back on.
Reinstalling the stator
Line up the stator plate and tighten it back on with the two screws. Be sure that it sits neatly in it's groove or it can rub against the rotor and cause problems. Align the rotor with the woodruff pin, then tightening the screw on the rotor will press it back into place. You may want to wait until the cylinder is back on so you can use a piston stop. You can read how to adjust the timing from other sources once it is back on the moped. Timing the thyristor is most similar to ignition timing for CDI.
Reinstalling the top end
You'll first need to get the needle bearings back in and press or tap the wrist pin back through the piston to reattach it to the crank.
Make sure that the piston is facing the right direction. There should be an arrow pointing towards the exhaust (bottom). If not typically you can tell the exhaust side because it will have more darkening and discoloration and will often be more scored up.
Then reinstall the circlips. It's strongly advised against re-using the old circlips that you took out because they can bend and embrittle and are far far more likely to come out in use which can cause catastrophic damage to your cylinder. Make sure they seat properly in the locating groove in the piston, and give them a spin in there to make certain they're in the groove, and open end facing toward the base.
Place a new base gasket, either a genuine replacement one or one cut from gasket paper (don't use cork or rubber) on the cylinder studs against the base, making sure the cutouts line up with the transfers. Put a nice coating of 2 stroke oil inside the cylinder and begin to slide the cylinder (right side up) onto the studs and stop just before the piston. You will need to make sure that the gap in the piston rings aligns with the pin inside the ring's groove. The pins on a Jawa are atypical and should be at approximately 4 and 8 o'clock. This is imperative and if done improperly you'll break your rings. With the gaps lined up, squeeze the top ring together and gently work it into the cylinder. Once it's in, squeeze the bottom ring and do the same until the piston can slide neatly up into the cylinder. Set the cylinder all the way back, hold it with one hand and spin the crank by hand to be sure it's moving properly and the rings aren't binding up on anything.
Now just slide the head on over, there is normally no head gasket, but some rebuild kits come with one, your choice if you want it. Then tighten the 4 10mm nuts on the ends of the studs in a criss cross manner to ensure it all tightens on evenly. Don't use too much force, a torque wrench is good until you get the feel for it, or just use a very short socket wrench. Ideal tightness is 7-10Nm of torque.
You can now use a piston stop to tighten the clutch and rotor if you don't have an air tool.
Now that you have the rotor and electrical back on, the clutches reassembled, and the cylinder and piston on, you should be ready to put it all back on the bike. Put it in place and install the 3 engine mounting bolts (be sure that the one with a space for the kickstand spring is in the bottom hole with the slot facing the kickstand spring). Then reattach the chain, carburetor, exhaust, wiring and spark plug. Turn the engine over and check for spark.
Anytime you do a rebuild, it's a good idea to go a little heavier with the gas/oil mix to help break it in. Vary your speed and don't go full out right away. Let things settle in a bit.
Now is a good time to read up on porting and unleash the untapped power of your Jawa.