H4 Piston Change Procedure
I made a hook from 5/16" cold rolled rod. I made it 12" long plus the 5" handle. I then made a 90+ degree bend on the other end and ground a lip to hook the wrist pin. The little hook must be only slightly smaller than the ID of the wrist pin. I used 5/*" ID plastic conduit and 3/4" ID copper pipe for the dowels. Both were 8" long and ground to a taper to nearly the inside dimension. The tapers really line things up. Remove the access plug from the end of the block first. Now put the piston into the lowest point in the cycle. Using a mirror, you can now see the spring clip. Use needle nose pliers to remove the spring clip, insert the wristpin puller, lift it and tug until you are sure it is hooked. Gently pull, and if needed, give it a few taps with a small hammer, away from block. Once the wristpin is out, cycle the cylinder to push the piston to the top of the cylinder and then continue to cycle back the the lowest point. The piston will remain at the top. Tap the piston gently to rotate it about 15 degrees or so. Now cycle the engine again, and the rod will push the piston right out into your hand. That's the easy part. When you put the new piston in, make sure you put the inside spring clip in the piston, then use the ring compressor and slide it in a position that will accept the wrist pin, but only just into the block. Now you have to use a mirror and line up the connecting rod with the hole. I took the rod to the retracted position and then used an old rag from underneath, to hold the rod up. I then gently tapped the piston in until it started to line up. Now this is where the 2 guide dowels tha I made, come in. Use the plastic dowel on gently rock the prop and wrist pin until it fits in. Push the rag underneath to hold this position. Now use the copper dowel and repeat the procedure. DO NOT force anything. When the copper fit in, it is pretty well lined up for the wrist pin. Check with the mirror. If all looks good, lightly oil the pin and gently wipe off the excess. Slowly insert the wristpin. You will feel in start into the piston and if it feels like it is hitting something, gently wiggle the connecting rod up and down, while maintaining a gentle pressure on the pin. It should pop right in. Lightly tap it in until it bottoms out. Use the needle nose pliers and insert the spring clip. Make sure it is fully seated. There are photos under "Piston Failure and Replacement" in the Photos section. Now the disclaimer....... I have just now successfully used this process, and it worked for me. You mileage may vary. Good luck !!!! Randy R. C-GYOO
