Neville, Thank You!
I did some followup to correct my invalid theory... Spring Rate vs. Pre-load Explained Conversation with Gemini You said is this true? Yes, agree that shortening a spring increases the spring rate for a given displacement. However, a shortened spring in the same tensioner creates a much lower pre-load so the force on the cam chain roller is less for any given tensioner position. Gemini saidThat is actually
true, though it can feel a bit counterintuitive. You’re touching on the difference between the
rate of the spring (how "stiff" it is) and the
force it actually exerts in a specific assembly.Here is the breakdown of why that logic holds up:1. Why the Spring Rate IncreasesWhen you shorten a spring by cutting coils, you are essentially reducing the amount of material available to deflect. In a coil spring, the formula for the spring rate k is:k=8D3nGd4
- n is the number of active coils.
- Since n is in the denominator, reducing the number of coils increases the spring rate (k). The spring becomes "stiffer" per inch of compression.
2. The Role of Pre-loadThe force (F) exerted by a spring is defined by Hooke’s Law: F=k⋅x, where x is the distance the spring is compressed from its
free length. Even though k (the rate) has gone up, shortening the spring drastically reduces x (the compression distance) when you reinstall it into the fixed dimensions of a tensioner body.
- Original Spring: High x (lots of squish) × Lower k = High initial force.
- Shortened Spring: Very low x (barely squished) × Higher k = Lower initial force.
3. Impact on the Cam ChainIn a cam chain tensioner, the "tensioner position" is dictated by the slack in the chain, not the spring itself.If you install a shortened spring:
- At the same physical extension point, the shortened spring is much closer to its "relaxed" state than the long spring would be.
- Because it isn't being compressed nearly as much as the original, the resultant force pushing on the roller is lower, despite the metal itself being "stiffer."
