Using Banshee pistons in your air cooled RD350/400

A few days ago my pistons and cylinders came back from the machine shop. Here is how they went together. The only company making true rd350 pistons now is wiesco big $$. Banshee pistons on the other hand are a dime a dozen and are available in a wider range of oversizes. With a small mod you can use the more plentiful banshee piston in the rd motor. Most places are charging $12-25 to modify this piston for your air cooled. Here were going to do it with no more than a few sharp jewelers files and some patience. There is a small tang under the piston ports you must remove. In the banshee intake there is a bridge in the center to allows this tang to ride. The rd has an open area here and the tang will catch on the bottom of the intake runner, break off and cause all sorts of damage  to the top end. I started by marking with a sharp pencil where I wanted to file off to. I CAREFULLY filed down to this mark just making contact with the scalloped areas to ensure it was flat. When you have it smooth all the way across, use a fine file to bevel the edge as not to catch on anything. As a side note I held this in my hand to do this NOT in a vise. It probably took me longer to write this post than modify both pistons. Make sure to thoroughly wash the pistons with hot soapy water to remove any contamination.

This is how the pistons come stock, notice the small tang on the bottom of the piston under the intake ports

Now with the tang removed

Now to install the rings, there are 2 pins in the ring lands to capture the rings and keep them from rotating into the ports. Look at the rings, notice that the end gaps have a section to correspond with the pins in the pistons. Install them this way. I should also mention you should check the end gaps by installing the rings only in the cylinders and checking the gaps according to the specs listed in your shop manual.

Notice the small pin in the ring land, this is to keep the rings from turning and catching the ports in the cylinders

Since I was working alone this night I decided to try something to install the jugs more easily. It can often be hard to hold the jug and try to compress the rings and assemble it all even with a helper. I know some of you know what I’m talking about. This time I put the pistons in the jugs while they rested on the bench. This allowed me to only have to push the wrist pin in while suspending the jug with one hand, worked pretty well I thought.

Piston in just past the rings.

Paper towel to keep the circlip from falling into the case when I drop it

All together and at TDC

Later that night I put the heads on and did some measuring of the squish band, and started on some major rear suspension upgrades. Come back later in the week for more on that, promise you’ll be impressed.
-DAN

2 thoughts on “Using Banshee pistons in your air cooled RD350/400

  1. Pingback: Ring land | Kedewang

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