Buy a shop manual and study the drawings carefully for several days. Get familiar with the part locations and the names of the parts you’ll be dealing with. Read especially the section on Ring Gaps and Gap orientation, this is very important. Read the disassembly and the assembly instructions over and over.
- Order your piston kit and make sure you order cylinder base gaskets, cylinder head gaskets, and Rocker arm base gaskets. If you have had your valve covers off before, order the upper and lower valve cover gaskets. If you haven’t taken them off yet, and the bike is low mileage, you can probably re-use them. You can replace the pushrod tube seals if you’d like but they are probably reusable. I did not remove my pushrod tubes for this piston swap.
Keep the parts associated with the front and rear cylinders separated according to their respective locations.
Place your bike on a stand to lift the rear wheel off the ground. Check out Mr. Tidy’s Tips for instructions on making a cheap stand.
Remove the battery. (at least disconnect it!)
Shut off the petcock, remove the fuel line from it (hold a rag under it to catch any fuel that might leak out), unplug the green connector at the back of the tank.
Remove the gage dash from the top of the tank. Put a towel over the tops of your handlebars and lay the dash over the top of the towel so you won’t scratch the bars or headlamp. If you’d rather, you can unplug the two connectors and remove the gage dash from the bike. Remove the tank vent hose.
Remove the cross bolt at the rear of the tank, lift the rear of the tank slightly and wiggle it side to side slightly while holding the front of the tank and pulling the tank gently to the rear of the bike. Lift off the tank and set it aside.
Unplug the plug wires and wrap them over the top of the frame rail. Leave the plugs in. If you have Dyna coils they will need to be removed.
Unplug the connector for the TPS (you may have to cut a cable tie), remove the fuel line from the carb (again, the rag for the gas). Loosen the two nuts at the ends of the throttle cables. Remove the choke cable from the bracket under the fuel pump (unscrew the hex portion completely). Remove the idle adjust cable from the bracket below the Carb. Unplug the two wires to the carb. heater at the bottom of the Carb. Loosen the carb. clamp on the manifold. Pull the carb. forward and remove the two throttle cables from the carb. Set the carb aside.
Remove the socket caps screw that hold the valve covers on. A ball socket hex-driver will be handy to remove the screws that are under the frame rail. If not, cut a short piece off the Allen wrench and stick it in the end of a piece of plastic tubing (Thanks Mr. Tidy!) Remove the two vent hoses from the rear valve cover. The valve covers are in two pieces (layers). You will have to remove one layer at a time. Be careful not to damage the gaskets if you may want to re-use them.***********. Each piece of the valve cover has two dowel pins on it. The pins can fall out during removal and go down the oil return holes and into the crankcase. The pins are located front and rear on the valve covers and both pieces have them (refer to the shop manual for locations!)
Remove the rocker arm bases (4 screws). Do not remove the Rocker arm shafts! **********!. The rocker arm bases also have two dowels on the bottoms. Don’t drop them into the motor. Remove the pushrods and keep them with their respective cylinders. It may be necessary to use a block of wood and a mallet to separate the parts. Don’t bang on the fins, they WILL break!
Remove the intake manifold
Remove the cylinder head bolts (6 total on each) by loosening them in stages (read: a little loosening at a time!) using the criss cross method shown in the manual. ************If you loosen one bolt at a time completely, you will run the risk of warping the head!
Remove each cylinder head. They have rather large dowels that align them to the cylinders. If you have to pry the heads, pry evenly on both sides a little at a time to raise the head evenly. Be careful not to damage the fins or the mating surfaces for the head gaskets. Wood and mallet can be used here also.
Put the bike in 3rd or 4th gear and rotate the rear wheel in the direction of the bike moving forward to position the pistons in the lower half of the piston stroke. I did mine this way, the pic shows how it is done by removing the left cover. Remove each cylinder and maneuver it around to get it from under the frame rail. *************** be careful not to let the dowels at the base of the cylinder fall into the crankcase (two of them) and don’t let the cylinder studs get inside the cylinder bore or mar the base gasket sealing surfaces.
Take some clean lintless rags (preferably tee-shirts) and stuff them into the cylinder openings on the top of the crankcase. You don’t want the piston circlips falling in there!
Take a 1/8” pin punch, put it in the notch next to the wrist pin hole and pry out one circlip from each piston. Don’t worry about losing them as you will not re-use them. Be careful of your eyes, these things really fly! Push out the wrist pin with your finger and remove the piston. The pics show how to make a tool to remove the wrist pin if it is stuck.
Clean out the carbon ring at the top of the cylinder. Use a fine Scotch Brite pad and WD-40
Send the cylinders out for a light honing to restore cross-hatching inside the cylinders. This insures that the rings will seat properly. EDITORS NOTE: Honing the cylinders is rarely needed, in fact, IT SHOULD NOT BE DONE. At the time this article was prepared, it was standard procedure. Since then we have found that the ceramic coating Yamaha uses for these bikes is extremely durable. If the crosshatching is still intact, we recommend that you clean your cylinders with hot soapy water and a scotch bright pad. Honing cylinders that still contain a good ceramic coating and the original crosshatching may do more harm than good.
When you get the cylinders back you will have to fit the rings to their respective cylinders. Insert one ring into the top of the cylinder. Take one of the old pistons and remove all but the second compression ring from it. You don’t have to be careful, as the rings won’t be used ever again. Take your piece of Scotch Brite and clean the carbon off the top and sides of the piston. This can be done in Hot soapy water. Rinse in very hot water and dry the piston thoroughly. Take the newly cleaned piston and push it pistondome first into the cylinder until the old piston ring is sitting flush on the top of the cylinder. This is approximately the correct depth the new ring should be at for setting the ring gap. The main thing is to get the depth of the new ring even all the way around. Get a good set of feeler gages and measure the gap between the ends of the ring. Mine had no gap at this stage. Refer to the shop manual for the correct gap. If the gap is too tight you will have to file the ends lightly until the correct gap is achieved. File equal amounts of material from both sides of the gap, keep the end square with the ring surface and most importantly “File a little and check often”, you’ll be surprised at how fast the material comes off. If you take too much off you’ll have to get a new set of rings. I set mine at .016”. All the rings need to be checked this way in the cylinder that they will be installed. The oil expander ring (the squiggly one) needs to be checked to make sure the ends do not overlap each other, if they do, trim the ends with a pair of side cutters. The gap on these is not critical but should not exceed .028”. After you are finished gapping the rings, deburr the ends of the gaps with a smooth stone. You don’t want the rings scratching up those freshly honed cylinders. Keep the rings separate according to which cylinder they go to! Stones may be used instead of a file if you have them. Just don’t spread the ends of the ring too far apart and be careful not to scratch the rings.
- Now we have to bench fit the Pistons and rings to the cylinders. This is done to make sure it is going to go together on the bike. Wipe out the inside of the cylinder and place the cylinder on a rag on the bench with the bottom of the cylinder facing up. Notice the large bevel at the bottom of the cylinder and the two crescent shaped cutouts at the base of the cylinder skirt. These are to help in compressing the rings during assembly. Wipe off a new piston (no rings yet!). Coat the piston with motor oil and slide it into the cylinder. If it slides in OK (and it should) remove it and wipe the oil off.
Install the oil expander ring into the bottom groove of the new piston. Take one of the oil scraper rings (they are the two thinnest rings in the set) and put in on from the bottom of the piston. You should probably go buy a cheap piston ring expander to do this but it can be done with your fingers if you are careful to not pull the ends apart any more than you have to to get the ring over the piston. If you bend the ring it’s toast! Put the other scraper ring on from the top of the piston. These rings actually fit over the outside edges of the expander ring. What you’ll have when you are done is a scraper ring at the top and bottom of the expander ring. Install the second ring (thickest one) from the top of the piston in the second groove on the piston. Now install the top ring.
Orient the ring gaps according to the positions in the Shop manual. Look at the illustrations in the book and you can determine the front and back of the cylinder. The key here is the large oil return holes. There are two of them that run the length of the finned portion of the cylinder. Remember that six holes are for the studs. The two larger of the four crescent cutouts on the tops of the piston domes are clearance for the intake valves, The large cutouts will face the Vee of the motor when installed
When you have determined how to orient the pistons in relationship to their cylinders, you are now ready to test fit them. With the cylinder upside down in front of you, take the piston, orient the valve cutouts properly and place it on the end of the cylinder. Take some motor oil and coat the rings liberally and the surface of the chamfer at the end of the cylinder. Push down on the piston while trying to compress the rings with your fingers. The crescent cutouts on the Cylinder sleeve aid this. Keep the piston nice and straight and it should slide in with minimal effort. The rings do create a lot of drag but it shouldn’t take more than a few pounds of force to move them up and down in the cylinder. Once you have done this, remove each piston and keep it with its’ respective cylinder.
Clean the gasket mating surfaces on the top of the crankcase and the bottoms of the cylinders to remove any traces of old gasket. Make sure the rags are still covering the openings in the crankcase.
Take the new wrist pins and coat them with oil. Test fit them in each piston then try them in the connecting rods. They should slide easily.
Install one of the circlips into each piston. If you have not removed the pushrod tubes, install the first clip into the right side of each piston so the wrist pin and the remaining circlip can be inserted from the left side.
Install the pistons onto their respective connecting rods. Check to make sure that the large crescent shaped cutouts on the tops of the cylinders are facing each other.
Make sure that the rags are still covering the openings and install the remaining circlips in each of the pistons.
Remove the rags from the crankcase slowly and watch carefully as you remove them to make sure that nothing falls into the crankcase.
Place the two dowel pins into the top of the crankcase (for each cylinder)
Install the cylinder base gaskets
If you are alone (try to get an extra set of hands for the next step) cut a couple of pieces of hardwood to place under the piston skirt to keep the piston steady.
Take one cylinder and coat the inside liberally with motor oil. Put some motor oil on the pistons and rings also. Lower one cylinder over the studs. Be careful that the studs do not damage the inside of the bore or the base gasket-mating surface. As the cylinder comes in contact with the rings, take your free hand (if you are alone) and try to push on the rings with your fingers. You can wiggle the cylinder around with the other hand while applying slight downward pressure. The rings should slide in with not a lot of effort. After you have the two cylinders on, you can begin to reassemble the rest of the parts. Mr. Tidy recommends using blue (removable) Loctite to hold the dowels in the bottom pieces for reassembly. Just double check all of your steps before proceeding to the next one and torque all the parts down according to the manual specs. Be sure to clean out the insides of the combustion chambers before installing the heads. I used a small bronze brush and some WD-40. Don’t worry about the plugs because you’re going to put new ones in before you try to start the motor.
If you decide to reuse the valve cover gasket, they should be cleaned with a good degreaser and be given a light coat of Permatex (or some other type of gasket material) to insure a that they seal properly
Good luck! If you have any questions you can E:mail me at firstname.lastname@example.org
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