Breaking Down a China HT Engine in PICTURES

Discussion in '2-Stroke Engines' started by Al.Fisherman, Oct 9, 2009.

  1. Al.Fisherman

    Al.Fisherman Active Member

    I have made a 59 photo tutorial (each and every step) on how to break down a China 2 stroke 80cc (49cc same).

    The pics are located here:

    Text description for the pics is below:

    Photo 1 of 59 Remove engine from bicycle and place on an uncluttered, clean work area. Easier to keep track of both parts and tools.

    Photo 2 of 59 If you haven't already done so, remove the spark plug. You will notice that the pictures are posted in the wrong sequence as the engine was taken apart. Don't be of concern as to the way I did it or as the pictures show, both ok. There is NO set sequence in removing many of the parts. This is a what is this part and a how to disassemble.

    Photo 3 of 59 Remove the (4) cylinder/head nuts, washers, and lock washers. If not already done, I'd replace the OEM studs and acorn (not to be confused withAssociation of Community Organizations for Reform Now), nuts with grade 5 (8.8 metric) studs and lock nuts. Depending on model6mm (same as both the intake and exhaust stud sizes) or 8mm.

    Photo 4 of 59 Remove head and check for a true flat surface. I mill the head AND cylinder as little as possible (couple of thousands) with 200-320 grit DA self stick sandpaper. I stick a sheet onto my garage window and rotate head surface until I know it's true. And replace gasket with a thin gasket from SBP. If too much is shaven off the clearance will be too close and will close the spark plug gap.

    Photo 5 of 59 Remove these two 6mm bolts. These are 2 of 8 that hold the case together.

    Photo 6 of 59 After the head is removed pull cylinder jug up to expose the piston.

    Photo 7 of 59 Here you can see the set (2) rings on the piston.

    Photo 8 of 59 Finish removing the cylinder jug and set aside.

    Photo 9 of 59 Here is a picture of the wrist pin retaining clip. This has been already removed for a better view of what it looks like.

    Photo 10 of 59 Here is where one of two of the clips are located. Grasp the tab of the clip with needle nose pliers; pull into the center, rotate counter clockwise and pull toward you all at the same time. Only one needs to be removed. I always remove the clip from the drive (left) side, this way I don't have to mark which way the piston needs to go in when replaced. You want the piston in the same position as it came out.

    Photo 11 of 59 This is the backside, the clutch side. You will see another clip. Take a small tool like a screwdriver and push on the wrist pin enough so as to stick out the opposite side. This is not a problem with the clip still in the piston. The pin will slide easier then you thought.

    Photo 12 of 59 Pushing the wrist pin out through the wrist pin bushing/bearing in my case..

    Photo 13 of 59 The wrist pin prodding out of the piston. Grasp with needle nose pliers and pull and rotate at the same time. Pull only enough that the piston can be removed.

    Photo 14 of 59 Here is what the piston and wrist pin will look like.

    Photo 15 of 59 Remove the bushing/bearing by sliding it out of the connecting rod. When replacing I pack with a light type of grease.

    Photo 16 of 59 Close up of bearing.

    Photo 17 of 59 Removing the engine drive gear cover. After removing the cover the gear is exposed.

    Photo 18 of 59 SEE NOTE AT BOTTOM.....Here you see the engine drive gear exposed. There is a pin and ball in the center of the shaft, remove both. First the pin then the ball. This is used to engage and disengage the clutch along with other parts. The ball is used to cut down on the wear on the pin. Should you need to replace either for one reason or another you can made your own by cutting a drill bit shaft of the same diameter. Should you be where you can't find the ball just cut the drill bit longer for the time being.

    Photo 19 of 59 Photo of inside clutch arm cover. The arm can be removed by turning and pulling upward. This is how to grease the shaft. It can only go back in one way.

    Photo 20 of 59 Now to remove the coil cover by removing the (3) machine screws.

    Photo 21 of 59 Need I say anything?

    Photo 22 of 59 Here you can try and remove and save the gaskets. Should they get messed up, no problem. Use a small amount of silicone as a gasket. DO NOT use Indian Head or Permatex sealer.

    Photo 23 of 59 Here is a shot of the coil removed. The coil is held in with (4) machine screws like the one on the right.

    Photo 24 of 59 Now to remove the engine drive gear. As you can see we used the chain to keep the gear from turning while removing the nut.

    Photo 25 of 59 To remove the nut holding the drive gear on, you can use the supplied socket wrench (opposite end of spark plug wrench). That wrench supplied is such a poor quality that I choose to use a 19mm 3/8 drive socket.

    Photo 26 of 59 As you can see I had to use a little friendly persuasion.

    Photo 27 of 59 Here is the nut removed. There is a star lock washer behind the nut.

    Photo 28 of 58 Now is where a specialty tool is needed. To remove the gear I'm using the supplied (was in my second kit, not in my first) gear/wheel puller. NOTE
    All fourdrive gear, clutch gear, clutch assembly and magnet have woodruff keys. There are (2) different sizes. The magnet uses the one that is different in thickness.

    Photo 29 of 59 Removing the drive gear with the puller.

    Photo 30 of 59 Drive gear removed.

    Photo 31 of 59 Ok here is a way to make it easier to remove both the clutch and coil magnet nuts. I inserted a 3/8 drive extension (for nothing better on hand) through the connecting rod. As you turn the nut on both the magnet and the clutch the rod will bind on the case. A dowel rod of sorts would be better but I was careful as to not score the bearing surface in the rod.

    Photo 32 of 59 Removing the nut securing the magnet. Don't forget the key.

    Photo 33 of 59 Here you can see a washer under the nut.

    Photo 34 of 59 Removing the magnet. This was the hardest part as you don't have much room to get something under the magnet to carefully pry up with. As you can see I used an offset pair of needle nose pliers.

    Photo 35 of 59 Once broken loose I was able to work a screwdriver around the base.

    Photo 36 of 59 Note the washer beneath the magnet. Have fun with this washer when putting back together. PITA.

    Photo 37 of 59 Magnet removed showing key slot.

    Photo 38 of 59 Shot of keysecured to magnet... I placed all THREE keys on the magnet so easy to retrieve.

    Photo 39 of 59 Now to remove the clutch cover. There are (5) machine screws securing the cover on.

    Photo 40 of 59 Cover off, now remove the set screw that keeps the clutch adjusting star nut from moving.

    Photo 41 of 59 With a little help remove the clutch adjusting star nut.

    Photo 42 of 59 Clutch adjusting star nut removed.

    Photo 43 of 59 Notice a spring upon removing the flywheel.

    Photo 44 of 59 There is another nut below the spring.

    Photo 45 of 59 Remove the 19mm nut with either the supplied socket or your own as in previous step (photo 25). This is also where securing the connecting rod is helpful.
    Photo 46 of 59 Better tool to use.

    Photo 47 of 59 Here you will notice the star lock washer behind the nut.

    Photo 48 of 59 Lock washer removed. You will also see that the clutch pads can fall out. Easy to reinstall but be careful.

    Photo 49 of 59 Removing the clutch using the supplied wheel puller.

    Photo 50 of 59 Clutch disc removed..done..just set aside.

    Photo 51 of 59 Although this is out of sequence (clutch already removed), now remove the (3rd of 8) case machine screw.

    Photo 52 of 59 Remove (4th and 5th of 8) case retaining machine screws. These are located adjacent to the front main mount. These were a SOB as you will see.

    Photo 53 of 59 Here I HAD to use a pair of vice grips so I could not only turn the screwdriver but exert enough down pressure on the screwdriver. I twisted the tip of the first Craftsman screwdriver I used. Needless to sat these and the remaining 3 were tight to say the least. Arrowfront mount.

    Photo 54 of 59 Remove the clutch reduction gear nut. As you can see Vice Grips were also needed.

    Photo 55 of 59 Star washer behind the nut.

    Photo 56 of 59 Once again pry up and off the clutch reduction gear. Best to use the removal tool if it was included in the kit. My first kit did not have one. For detailed removal instructions, I added a new album titled "Small clutch gear removal"

    Photo 57 of 59 Remove the (3) of the 8 remaining case machine screws.

    Photo 58 of 59 Split case apart. You will need assistance with the use of something to help you. I used a WOOD chisel. Be careful as not to screw up a mating surface. Use the areas such as where the mounts are.

    Photo 59 of 59 This is what I used. Tap tap with a hammer two or three times and the case separated. Clean off gasket on both surfaces and as I said before you put back together, use Indian Head/Permatex sealer. Use a base gasket, as without the piston will hit the head. This is far as I had to go; I didn't have to split the crankshaft to remove/repair or replace the connecting rod or bearing/bushing. Easy to see how this is done. Machine screws are holding the (2 piece) crankshaft together much like the case.

    NOTE... Remove clutch screw and star nut before you remove the clutch arm cover. Disengage the clutch and pin at the clutch handle. This will give relief to the flywheel and make life easier.

    Hope this will help all those that need to see what it takes to disassemble a China HT engine. Mine is a 80cc but the 49cc is the same.
    Last edited: Oct 9, 2009

  2. Skyliner70cc

    Skyliner70cc Active Member

    Awesome post! I thank you for going above and beyond the "call of duty" for being a member of this website. This will help many folks who have to tear their engines down.

    One tip: Impact screwdriver from Harbor freight is awesome in removing case screws and other screws on the engine. Its very affordable and saves a lot of grief when tearing apart the HT engine.
  3. Al.Fisherman

    Al.Fisherman Active Member

    Yes it is, had one many years ago but not at the moment, and didn't want to drive 30 miles to Birmingham for a $10.00 tool at that time. I had all 5 large case screws out before one could get into their car and leave the suibdivision.

    Edit: Excuse me a $6.47 (inc tax) tool
    Last edited: Oct 10, 2009
  4. Pablo

    Pablo Motored Bikes Sponsor

    Good pictures!

    Hey you didn't do it in the right order.....JUST KIDDING!!:jester:

    Really -thanks for doing this. Many folks have asked.
  5. Al.Fisherman

    Al.Fisherman Active Member

    format.....I know. When I realized that I had it that way, "edit" time ran out. So don't use it....:devilish:
  6. Fabian

    Fabian Well-Known Member

    Al, your photo tutorial was excellent.

    Thankyou so very much for taking the time to document the process.

    Cheers Fabian
  7. moondog

    moondog Member

    Thanks for the pictures and info ! ! ! :D
  8. fetor56

    fetor56 Guest

    Norm has serious competition....well done Al.
  9. outrunner2

    outrunner2 New Member

    Very nice effort Al, I'm sure this will be a Big hit for anyone that attempts to disassemble their engine. Thank you for your time, effort andwillingness to share your step by step procedures.
    Last edited: Oct 18, 2009
  10. GreenPurgatory

    GreenPurgatory New Member

    Maybe I am missing something, but I am unable to see the pictures.
  11. srdavo

    srdavo Active Member

    Last edited by a moderator: Sep 20, 2017
  12. GreenPurgatory

    GreenPurgatory New Member

  13. MikeJ

    MikeJ Member

    Hi Al -

    Thanks for the pictures; they are good to have available.

    Can you advise me? I replaced my original 20-tooth drive gear (on the crankshaft) with a new 20-tooth drive gear. I made the mistake (a long time ago) of grinding out the original gear to an oversize diameter, and it became a sloppy fit on the crankshaft. Over time, the slop chews up the woodruff key and the gear keeps falling off every few hundred miles.

    The new gear is a couple thousanths of an inch too small in diameter. It is an interference fit at room temperature. I tried tapping it on with a hammer, but the gear will not go on straight nor bottom out on the crankshaft.

    I am thinking of screwing in the "approved" threaded extractor tool as a handle and heating the gear to really hot (maybe just below cherry red) with a propane torch and jam the gear on the crankshaft before the gear cools. I have to make sure the woodruff key lines up. (I want to keep that flame away from that vapor-filled crankcase. I am sure you understand why.)

    Any other thoughts how to jam that gear on the crankshaft?

  14. Al.Fisherman

    Al.Fisherman Active Member

    Just a thought..yes I'd keep the flame away from the engine, but if you must use heat and have no other way I'd pull the jug and take a hose attached to a tailpipe of a running car and insert into the crankcase. When the engine (HT) warms up any gas/fumes are dead and a flame can be put to it. Have done this on vehicle metal gas tanks to braze holes.

    What I'd do is run engine and turn the shaft down to size with emery cloth, checking fit often.
  15. Felipe perez s

    Felipe perez s New Member

  16. srdavo

    srdavo Active Member

    here ya go.....

    Last edited by a moderator: Dec 15, 2015
  17. gera229

    gera229 New Member

    Hey I can't seem to find the instruction manual you are talking about in this thread. But where can I download it from? (Couldn't find it on your profile with pictures.)

    Also I do not have my engine yet ordered, and would like to get suggestions from you on which engine I should get?

    What engine do you have?
    How often do you get problems with your engine?
    Is it a hassle?
    How far can you ride it daily without having problems?
    How many total miles are on your engine?

    I will ask about what should be done to an engine before operation later.
  18. Al.Fisherman

    Al.Fisherman Active Member

    That ought to take care of you for awhile.
    Last edited: Sep 6, 2011
  19. gera229

    gera229 New Member

    Thanks that's a very helpful post!
    I certainly have some experience with 2 stroke engines especially with the carburetor and the clutch, however not the cylinder and such.

    Anyway, when you ride your bike do you ever get caught? I mean isn't it illegal to just ride it? What's on your bike that makes it legal? Thanks.
  20. joeltrain

    joeltrain New Member

    I had to go a little further. My wrist pin bearing disintegrated causing damage to my cyl sleeve and piston. I decided to replace the whole crank b/c the piston on my 2009 skyhawk GT5 parts engine piston is different and tho it will fit on conn rod it bottoms out and crank will not go all the way around. To get the crank all the way out of the case i put a rag over my vise and positioned so only case was touching vise and crank was free. Hit a few times with a hammer and it came right out. The machine screws only hold the weights onto the crank. There is no reason to remove them. The 2010 gt5 crank is one piece. There are no removable weights

    SO a 2009 gt5 piston WILL NOT FIT on a 2010 gt5 crank. In addition, the 2010 crank has the bearings pressed on to the crank not pressed in the case. I suppose it would work if i had some way to remove the bearings, but i don't. I called gasbike, and they answered the phone quickly, and answered my question! I need a Superrat piston. $15 I would prob spend that trying to remove the bearings and no doubt destroy them. And who knows if they would even fit.

    I am going to attach some pix.

    Attached Files:

    Last edited: Sep 14, 2011