Adjustable Cam Timing?
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Adjustable cam timing
-Edited to start a new thread -Admin
Someday I'd like to try the longer chain in a 400 and design an idler gear so I can vary cam timing externally while the engine is running.
Someday I'd like to try the longer chain in a 400 and design an idler gear so I can vary cam timing externally while the engine is running.
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From: Minneapolis, MN
adjustable cam timing
Brian, how about two idler sprockets (think gear drive but with clearance for the chain) mounted on a bar that can be adjusted from side to side, possibly with a screw adjustment. It would have to use a roller chain 'cuz the factory "silent" type doesn't like to bend backwards.
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Pros and cons
Originally I was thinking 2 idlers but space is tight if I use factory size gears. I think if I use a rubbing block on the non tension side of the chain, that should work OK. The rubbing block would be mounted to the same moving device as the idler gear.
I agree, a double roller is much better otherwise the idler has to be on the inside of the chain. Most likely the movement would be controlled by a screw type device with a servo motor. I'm not sure how much kick back there could be from the chain.
Linear or rotational movements? I'm not sure yet. Rotational would be easier because I can use the crank or cam as the pivot point. Linear would require more fabrication but it would allow me to compensate for chain stretch at higher speeds.
A hydraulic cylinder could work too but I was thinking about hydraulic controls for the other idea about varying valve lift by moving the pivot point on a rocker arm. A canted valve head makes it harder because I can't figure out an easy way to link the rockers together.
I agree, a double roller is much better otherwise the idler has to be on the inside of the chain. Most likely the movement would be controlled by a screw type device with a servo motor. I'm not sure how much kick back there could be from the chain.
Linear or rotational movements? I'm not sure yet. Rotational would be easier because I can use the crank or cam as the pivot point. Linear would require more fabrication but it would allow me to compensate for chain stretch at higher speeds.
A hydraulic cylinder could work too but I was thinking about hydraulic controls for the other idea about varying valve lift by moving the pivot point on a rocker arm. A canted valve head makes it harder because I can't figure out an easy way to link the rockers together.
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You have oil pressure to use for power and a small hyd valve is easy to control. A spring loaded plastic rubbing block would work well. The cam timing could be varied directly with engine rpm with simple controls.
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Hydraulic controls
I agree with what you're saying and I haven't ruled it out yet. I'd like to use something more like a tension release on a spring loaded mechanism. At lower rpm there isn't as much load on the timing chain so that's when I'd like to have the most tension against the idler sprocket. At high rpm I'd like the chain to be straight with a fairly light or no load from the idler. Oil pressure doesn't vary consistent with engine speed. If I use a hydraulic set up a solenoid still needs some electronic controls to vary the amount. I haven't decided if I want to advance the cam based on just the rpm, or if I need something more sophisticated like throttle opening, mpg, engine load or a combination of several things.
