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1982 Honda CX 500 TC Turbo
1983 Honda CX 650 TD Turbo


Weak Turbocharger Wastegate Spring

Over the course of examining several turbochargers, I have found that the amount of lift the waste gate delivers at the pressure specified in the manual is consistently at least double the specified lift. For example, I checked the lift on one of my Turbo's which has been my least perky Turbo. Specs say there should be 2 mm of lift at 18-19 PSI. Using a quality gauge and a digital micrometer, I measured the actual lift to be 3.5-4.5mm at 18-19 PSI, respectively. I decided to add a spring to help bring the lift back within spec. I purchased an assortment of springs at Pep Boys. The waste gate actuator is permanently mounted to a bracket on the compressor side. I drilled a 1/16" hole near the edge of this bracket near the actuator. For experimenting to find the correct spring/location along the shaft, I fastened a small, round electrical lug to the shaft with a tie wrap firmly fastened around it. This held in place strong enough to stay in position, but loose enough that I could slide it back and forth to take various lift measurements at various points along the shaft.

So finally I selected the Perfect Spring. It had a glowing aura around it and everything. The biggest dilemma in my mind has always been how to reliably fasten the spring to the rod near the gate lever. Plastics obviously were out, I could find no clamps small enough, and I would not trust any glue or epoxy to reliably hold a tab in place. So, I marked where the end of the spring should be on the shaft. I took a 1/16" wide file and filed a small flat on the top of the shaft. Upon this I created a divot with a spring loaded center punch. Into my Dremel tool I placed a 1/16" drill bit, centered it over the divot, and carefully drilled straight through the shaft. The 1/16" hole is small enough that I don't foresee it being a problem in the shaft, as the shaft is not really stressed at all. From the bottom of the new hole, I inserted a 1/16" cotter pin all the way through, with the eye facing down. Bent the legs and snipped them off at 1/8" long, leaving a neat little eye right at the shaft surface for the spring to snap on to. Really clean. Now the lift is exactly 2 mm @ 18.5 PSI, instead of 4 mm as before the modification. More significantly, the addition of the spring causes the wastegate to begin opening a full 1.5 PSI later, at 16.5 PSI.

So, how does it feel now? I could convey the difference in terms of how many additional pairs of clean underwear were needed on the maiden voyage, but that would be gross. The bike now feels MUCH stronger. The boost hits harder, and keeps hitting harder past 130 mph, where before acceleration was more sedate above 110. I would suggest next time any owners have a chance, to check the wastegate lift at the pressure specified in the manual. If it is opening more than the 2mm, add the proper spring. You will love it! The only down side is now I have to run the highest octane available. I could run 88 in it before with no detonation. Now it needs the 92 here at sea level. A price I can pay for the extra grins!


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