Miatav8,MstrASE,A&P,F wrote:
Turn them for a slight interference fit to ensure they are not loose due to imperfections in the shell but even a loose fit is more accurate than any bonded rubber of the same dimensions.
Suspension bushings are a compromise like anything else. Bonded rubber has been the standard for oem vehicles at least as early as the ‘60s. They work well and last a long time if not oil soaked or twisted too far, cracking the rubber, too old, or too many cycles.
They are compliant, allowing the control arm to float around under load on the center sleeve. How much depends on the size and shape for a given load.
The compliance causes all alignment specs to fluctuate dynamically but they are zero maintenance and have an outer shell that presses into the control arm so pitting in the arm has no effect.
Long ago, when there were no off the shelf options to oem rubber bonded or hobby machinist lathes, racers would drive small nails into the rubber so it would be less compliant.
According to Norm Garrett, the miata was designed with higher durometer rubber than is typical for oems to help compensate for this compliance.
Cost is another factor since some oem bushes cost a great deal more than making your own or the application is rare/old enough that replacements are not available.
For a tourer, oem bonded rubber makes sense to me, especially if the arms need new shells.
Poly bushes do not last forever either. They eventually crumble. Also, the EPA has required most plastics to be biodegradable.
I'm going to order that rod you recommended and give it a shot. Do you think these need a sleeve?
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