TABLE OF CONTENT
2 STROKE ENGINE REBUILD
INTRO : 2 STROKE ENGINE REBUILD
STEP 1 TOOLS AND MATERIALS
STEP 2 STRIPING THE CRANKCASE BARE
STEP 3 THE BUILD (replacement and Tuning)
STEP 4 BOLTING UP
STEP 5 ASSEMBLING THE BLOCK
STEP 6 OTHER BITS AND PIECES
STEP 7 START UP
INTRO : 2 STROKE ENGINE REBUILD
*****Please note that following this instructable can be dangerous and can cause bodily harm. Basic knowledge of how a combustion engine works must be a must have for anyone trying to replicate this work safely. Stay safe and remember don’t always rev the engine so high in idle mode and don’t squeeze down hard on the throttle in hill climbs. *****
This instructable was written as a sequel to my final build. I have always wanted to be mobile having my own means of getting around and this need gave rise to my love for ebikes but traveling with them was out of the question. In my country the epileptic power supply meant charging the bike was a problem even if I managed to buy or build one (high cost of purchase or accessories to build one) hence I shifted my attention to motorized bikes. There was still another problem which was the funds to buy the cheap knock off chinese kit engines to build my bike, hence the need for me to build my own engine. This engine build was done bearing in mind the availability of materials and built on a budget. We have a lot of generators actually 2 stroke engines precisely, the 4 stroke are costly to buy and serviceable parts aren’t pocket friendly (IN MY COUNTRY). After much research 3years actually, I think its time to let you guys see what am up to and I hope to inspire someone out there.
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Step 1: Tools and Materials
The tools you will need will differ depending on the materials at your disposal if you have a full engine you want to repurpose fewer tools if your scavenging then you need alot more like me. the full list of my tools are given below since i am scavenging to do this build(had to repurpose a pin nose plier as a clip remover).
- Pin nose pliers
- Philips screw drivers
- Spanner nos 8, 10, 12, 14,
- 10ml/ 20ml syringe
- Sanding machine
- 1/2 rod
- old screw driver
- A piece of waist belt pin
- And losts of spare time
The materials you will need will depend on what you have around you in your locality. You will need
- A scraped up Tg 950 generator as your donor engine, you could buy half an engine, you could use the one you have at home or you could buy ckd parts (completely knock down)
- All the gaskets for 2 stroke generator
- Rags or old clothing for wiping away
- flat washers
- old electrical plug
- cleaning fluid (pms,kerosene,carb and choke)
Step 2: STRIPING THE CRANKCASE BARE
I decided to repurpose one of the TG 950 2 stroke generators in my house which fried its coils and has been ckded (completely knocked down) during its lifelong servitude in our home. Starting with the crank case, removing the governor was quite difficult but in the end it came off. I pried the clip locker for the bearing off using a pin nose plier which I had filed down for that purpose.
Using an old screw driver to bang the oil seal of and a piece of ½ inch rod to ram the bearing off too, Inspecting the two crankcase, I noticed a little disparity in the two casing (this is as a result of the difference in moulds used by the Chinese makers. The newer engines are lighter and thinner while the older ones are thicker and a bit heavier) sizing them up visually I decided to proceed because the two case lapped accurately. Cleaning the casing up a bit wiping the smog’s and oil deposits off, then it was time to install the old and some new parts.
Step 3: THE BUILD (replacement and Tuning)
First to go in was the engine seal rubber followed by the bearing. Banging them in using a ratchet adapter for my plug. I use this always because it fits snugly at the edge of the rubber seal and my bearings too. I replaced the governor arm (speed limiter) rubber, broke of the fingers of the governor and filed and smoothened it out. Then it was time to re-attach it back with the screws after installing the governor arm. I installed the bearing on the crankshaft and crank case using my ratchet plug adapter then the gaskets went in.
I want to note here that this engine models come with a mechanical (centrifugal) governor or rpm controller. A flyweight mechanism driven by the engine in this case its actually on the crankshaft is linked to the throttle and works against a spring. the centrifugal design is more sensitive to speed changes and hence is better suited to engines that experience large fluctuations in loading. This mechanism, as good as it sounds is also problematic when there are deposits on the crankshaft rod on which its mounted. these deposit accumulate from residues or contaminats in the fuel oil mixture. when it sediments in the engine. Over time it causes the engine to run too high or bug out in low rpm's.
If you have one of this engines take time out to break it down and wash all the deposits out especailly on the crankshaft. Many people complain that the engine dont idle or steam after servicing, changing new carbs and installing new gaskets or seals but this will likely be what your missing out.
I removed my governor because i wanted more rpm which is dangerous i dont have a tachy to check or keep track of my revs so i will possible install a throttle limiter as a reminder to use it for short burst of speed.
Step 4: BOLTING UP
Cleaning up my bearing locker and installed it back where it should be and It was time to put the piston back and close the casing I didn’t have to worry about the governor accessories because I had removed them (if the governor was present you should be careful not let it slip out of sync with the crankshaft). After series of banging the two lips of the engine came together and were bolted down finger tight;
HINT: if you have been working on engines you will know when it’s good old tight. The next step is to install the engine block bolts. I like to use 4 long bolts, the reason being that over the years I have had to re-bore the engine block sitting holes over and over. The trick to installing the bolt firmly if you don’t have a wrench is to use a lock nut approach. Bolt 2 size 10 nuts onto the long rod lock them againts each other using a ring and a flat no 10 spanner. The fly wheel key pin which is usually a small magnetic bar of metal got lost in storage so I had to improvise. I had an old belt head pin which was broken so I used it to replace the missing key pin. After a lot of filling and marking it was ready to go in, installing the 2 in 1 ignition coil and voila came on the fly wheel. Oops…… I failed to install the wire guard for the ignition coil so I went back and put it back on I don’t want my engine leaking current everywhere due to wear and tear on the wire when the fly wheel is bolted into place.
Step 5: ASSEMBLING THE BLOCK
Placing the base cylinder gasket at the base of the engine block bolts (using the empty engine block to push it down the pins where skewed a bit) cleaning out the piston rings and maneuvering it into place on the piston head. Oiled the engine block and pushed the piston into place.
N/p young engineers or home mechanics or wanna bees please pay close attention when installing your piston. There is an arrow which should point downward toward the exhaust and the ring pin which is at the top. If you don’t have a piston clamp please do the following:
1. Align the rings rightly to the top and the arrow mark on the piston crown facing down towards the exhuast port.
2. Apply some lubricant inside your block
3. Squeeze the rings with your fingers from the side with the arrow facing downwards towards the exhaust port and push into the engine block.
With the piston in position inside the block guild it into the engine block rods, insert the piston bearing followed by the piston pin rod. Since this build is on a budget and a diy I decided to fabricate my own pins (the spare I had was missing in storage yet again). I took the fuel hose clips cut grinded and bent away till I got myself a new set of clips actually better once because the metal was thicker and stronger.
HOW TO: To achieve this cut one of the legs of the clip using a wire cutter, use a nose plier to bend the cut end into a 'G' the cut the other end off sand it down, and there you have made a piston clip for yourself.
Step 6: OTHER BITS AND PIECES
After installing the clips, I put the top gasket and the top cylinder on but when I started bolting down I noticed the nuts where chewing away at the top cylinder head, so I put some washers there.
The danger associated with this problem is that the top cylinder can get partailly fused to the block. Those small aluminium shavings can get into the threads of the nuts, and running the engine over time can fuse it together making it hard to open the block.
The next step was to oil the engine up. Then it was time to install the intake manifold the valves and gasket but as you can see I have some caked gasket parts on the engine so I plugged the hole and scraped away with a blade and also sanded a little. I had to also cut away the excess part of the center gasket which was protruding excessively and could hinder a smooth seal of the air intake port. Assembling the reed valve was easy, just make sure that the reed valves plates are straight and Then I screwed it down to the port attached the gasket alittle more oiling and bolted the entire unit onto the engine. Install the carburetor rods just the way the engine rods are installed and then the exhaust can follow.
Step 7: CARBURETOR CLEANING AND ASSEMBLY
Unscrew the cup nut remove the floater pin, valve, the pin jet screw and the steamer screw. Wash with a brush in pms or carb and choke cleaner or whatever works best for you, reassemble the carburetor back pay close attention to the jet pin screw;
WARNING: DO NOT TIGHTEN IT ALL THE WAY DOWN, your engine will run very lean, remember that you have not broken in the engine. This applies whenever you carry out major repair in the form of replacing parts ie: changing the crank shaft piston or bearings........*****IT IS NOT WISE TO RUN YOUR MOTOR ON LEAN SETTING YOU ARE HARMING THE MOTOR ALTHOUGH ITS SAID YOUR SAVING FUEL.
Mount your carburetor and adjust the throttle connecting rod. Now install the carburetor joint gasket and bolt the carburetor down.
Step 8: STARTER REPAIRS
Many atimes the starter fails because it recieves alot of banging during repairs.the motor is usually turned on its side when working on the armature or its bearing or as a result of improper tightening of the bolt and eventually the threads were lost. The starter failed in my case because the center bolt lost its thread. To fix this problem, If you dont have any form of welding equipment, is to drill a hole right through it and use a long bolt to screw it down.
- simply drill a hole on the back of the case
- pass a bolt through and bolt it down.
- It would be wise if you used a small drill bit to mark out the center by drilling through from the front then use a bigger drill bit to widen it to suit your bolt. You can also use a punch to mark from the inside too(***remember to ask for a second set of hands when punching or drilling so that u don’t have to go through the stress of recoiling the starter coil afresh***).
- After drilling pass your bolt right through and lock with a nut i used a lock washer to prevent the bolt from coming of you can also use a double nut or a nylon nut those will work too.
- remember to hold the head of the inner bolt in position when you tighten.
Step 9: Throttle Assembly
Having taken off the governor meant that the engine rpm and gas control were gone so it was time to make my own regulator. so i used the governor spring, the lug nut from a socket, 1inch m13 screw and two washers. I inserted the 2 washers into the M13 screw and screw it into the lug nut i ripped of the socket. Pass one end of the spring through the eye and bend into a tear drop using a nose plier and attach it to the key sitting used in aligning the coil.
Step 10: START UP
The last bit to go in was the starting coil and testing for sparks using a spark plug.
After squirting some fuel into the carburetor and a few priming the engine came to life hurray now u know how to take the limits off your two stroke engine.