Wrist pin and bearing modification on 820's

[steve welte]

I use a belt sander when I grind the end of the needle bearing shell/case down. It is still in the rod. The needles are in place. I put a cut off (threads removed) 1/2" bolt in the bearing and grind the side away. This also grinds the end of the needles down. Then turn the rod around and carefully remove the bolt (all the bearing need to remain in place. Install the bolt from the other end but this time be sure to slide a washer to thrust washer over the bolt before putting it through the bearing. When you grind away the outer bearing shell you need to firmly keep pressure against the side/thrust washer, you already ground down. This will keep the bearings from moving over when you grind the shell away and your bearings will be the same length as the shell. You need to be very careful. Do not grind into the rod eye. Stop a couple thousands short of flush. You then go to a surface that you know is flat. I like to use 6" DA sand paper with sticky back in 180 grit. You still have the bolt/thrust washer/thru the rod eye. You lay the rod on the paper and sand to get the outer shell and bearings flush with the rod. Note that the big end of the rod is on the surface area laying flat. When you have that side done you can carefully remove the bolt and thrust washer from the rod eye and put it in the other side. Repeat the process. If you did all this correctly your bearing shell and bearings now are the same dimension as the width of the rod eye. Remember you must always keep pressure against the thrust washer to keep the bearings in place. If you make a mistake you can start all over with another new bearing. It takes about 3 to 4 hours to setup one piston and rod properly. Remember I am doing this at home with limited equipment. Maybe someone else can do it faster. Faster means nothing until you get on the track. I just took apart and ole 820 that had been running on a kart a long time without bearing failure but I doubt in stock form it ever turned more that 8500. I hope this info helps.

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You also need to be sure the wrist pin boss on the inside of the piston is 90* to the wrist pin. In most cases you may have to remove a bit of materiel from the piston/wrist pin boss to get it square.