Its pretty obvious that the gear ratio is different. The bigger gear obviously has the same gear pitch but more teeth since the diameter, and hence the circumference is larger. The motor will, I'd say be under slightly more strain when turning the engine of course, and we would hope it can stand the extra current, but assuming the motore is the same it will turn over the engine a tiny bit faster and have more teeth in contact with the flywheel gear at any one time, I'd have thought. Brian
I'd imagine its within the range of adjustment myself. Many moons back when I had sight and my Father was alive this same question came up on a much older car. I don't quite recall which, but this does beg the question that if this sort of issue was known back then, how is it that more modern cars designs still make the same mistakes and retro fit the same solutions? Brian
Surely straight cut gears ground to the same specification will mesh correctly regardless of their diameter.
Thinking back to my Meccano days all the gears would mesh successfully with any of the pinions, there were pairs that one used most frequently because the diameters added up to multiples of 1/2" but you could use different pairs without problems if you had shafts at odd spacings.
Isn't this why (straight cut) gears are ground the way they are?
Maybe they are wrong. Maybe the mounting plate has the necessary offset to compensate. I would have thought that just increasing the pinion diameter (which goes with adding another tooth, if you keep to standard profiles) then you would end up with the pinion teeth "bottoming" in starter ring.
But maybe not; perhaps there is plenty of clearance with the standard pinion, so that you can get away with increasing the pinion tooth count / diameter.
Various sorts of tip and root relief are used on different sorts of gears. Modern finite element analysis lets you play all sorts of tunes.
No you don't. You can just machine the tips off so that the 11 tooth pinion has the same diameter as the 9 tooth one. But, with a standard profile, you will now find that the tips of the 11 tooth ones are too wide to fit into the gap at the root of the flywheel pinion. So you also have to make the teeth of the 11 tooth pinion a bit thinner.
The contact ratio (the average number of teeth in contact through a cycle of one pitch) depends on other parameters, like clearance, which is likely to be different if the centre distance is the same.
A good way to think of this is to start with a rack, with straight flanks. A gear of infinite diameter, if you like. If it is symmetric, it has three parameters: the flank angle, the tooth height, and the tooth spacing. For involute gears with an arbitrary number of teeth to mate with this successfully they must have the same circular pitch (circumference at the pitch line divided by number of teeth) or module (pitch diameter divided by number of pitch). This is how you make gears with any number of teeth mate with each other.
The pitch line is the point where the width of the teeth is the same as the width of the gap.
There are standard values for module, all gears with the same module will mesh. The addendum (radial distance from pitch line to tip) and dedendum (radial distance from pitch line to root) are usually fixed multiples of module and this works for gears with, iirc, 9 or more teeth. For fewer teeth, something needs tweaking.
Involute geometry is not particularly sensitive to the spacing of centres (provided of course the gears are not interfering) and gives better performance than (for example) the peg and lantern wheel geometry that you see in medieval water wheels, windmills, etc.
This is not a bad article, which also shows something of the geometry of "conformal" gears like the Wildhaber Novikov.
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Conformal gears are *very* sensitive to the spacing of centres.
For an engineering product of true beauty, I recommend the main gearbox of the Lynx helicopter but sadly I have not been able to find any images of the internals on-line. (In the 1970's I used to run across people from Westland and Imperial College, who collaborated closely on gears and bearings).
Absolutely no need. The unit has instructions on how to rotate it within the adaptor plate if needed - which would also involve drilling new holes. This might be needed in a kit car etc fitted with this engine to clear the exhaust or whatever. If there were an offset, they'd have made this plain in those instructions. The fixing holes, adaptor plate to engine, are 180 apart, and assuming clearance to other things, the unit could be mounted upside down.
I think it's fair to say, as someone already has, that a starter motor under good charge can produce a lot of torque. I have heard of friends get the car to a garage on a starter motor.
So the engine gets turned 11 teeth per starter gear rotation and the extra torque generated by the extra 2mm radial length is eaten up. A faster engine turnover is what you get.
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