This instructable is for the mechanically minded and should be done with extreme caution as you will be working with heat, high pressure and high precision. This is applicable to both two-stroke and four-stroke crankshafts for single cylinder small engines ( dirt bikes, motorcycles, ATV's and snowmobiles.The first step is to measure the width of the crank webs so you can have the same distance when you finish.
Step 1: Checking Out the Crankshaft.
Mark the crankshaft webs as a referance to put them back in the proper alignment. also make sure there are no bends or imperfections on the webs since those will not be replaced. On this particular crankshaft (which is a four-stroke ATV crank) the pin is covered partially by the bearing and gear. ""Important"" YOU MUST LINE THE GEAR TOOTH BACK UP TO THE KEYWAY OR YOU WILL NOT BE ABLE TO TIME THE VEHICLE!!
Step 2: Removing the Bearing and Gear.
For this step you will need a torch, bearing puller, and a shop press ( I use a 20-ton press). The best way to pull the gear off without damage is to heat the gear with the torch. I put the bearing puller under the bearing then started to heat the gear while tightening the bearing puller. This started to pull the bearing and gear off but you will still need the pres to finish the job. Once you transfer the crank over to the press put a socket or some othe protecter onto the end of the crankshaft so you won't damage the end. Apply constant pressure to the crankshaft end until the crankshaft seperates from the bearing and gear. ""Important"" Make sure you hold the bottom of the crank so that it does not fall on the ground!!
Step 3: Seperating the Crankshaft.
In this step I seperated the crank webs from the pin. I put the crankshaft into the press while using a vaiety of press pins to push the pin through the first crank web. When the pin was almost fully out I held the crankshaft so it would not fall on the graound. I then removed the old rod and bearing and put the aside. Then I flipped the crank web over and pressed the pin out of the remaining web.
Step 4: Comparing the New and Old Parts.
This is a required step that makes sure that the crankshaft will have no issues when reassembled. On crankshafts that use an oil feed for the rod bearing you have to make sure the oil feed holes line up on the pin and the crank web.
Step 5: Pressing the Crank Back Together.
Once you have made your alignment marks you will start by putting the crank pin in the coinsiding web. Once the pin is flush with the other side of the web you will need to place the first washer onto the pin the goes the rod bearing and after that you install the rod ( you may have to spin the rod back and forth to get it to fully seat since there are very close tolerances) then you install the last washer and set the second web onto the pin. make sure your alignment marks are as close as possible so that there will be as little realignment necessary. When you get the webs close to the rod you need to keep a close eye on the measurement between the outsides of the webs it needs to match the original measurement.
Step 6: The Final Steps.
Once you have the correct measurement you will need to make sure the crank webs are aligned. You will need v-blocks or a lathe with live centers to measure the runout. If the alignment is off you will need to adjust them with a copper hammer to realign. You will need to litterally whack the webs back into alignment ( my crank was dead on with zero runout so this was an uneccesary step).