tooth count on starter

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daimlersteve
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tooth count on starter

Post by daimlersteve » Tue Jan 09, 2018 6:47 am

men of great knowledge out there.---- tooth count on sp startyer pinion , is it 11 ? we have an aftermarket unit with ten and its not engaging well.

steve

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Vortex O'Plinth
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Location: Gloucestershire

Re: tooth count on starter

Post by Vortex O'Plinth » Tue Jan 09, 2018 10:04 am

The correct starter motor pinion and sleeve for the SP is a Lucas 255194. As you see from this chart, it has 11 teeth.
Nick

Pas d'elle yeux Rhône que nous.

daimlersteve
Posts: 276
Joined: Wed Mar 09, 2016 11:20 am

Re: tooth count on starter

Post by daimlersteve » Tue Jan 09, 2018 11:24 am

Just as i thought, the aftermarket hi torque uk starter sold as for an SP has 10 --- saloon fitting. - never has engaged correctly in ten years it seems.
steve

silverdart
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Re: tooth count on starter

Post by silverdart » Wed Jan 10, 2018 12:20 pm

If the starter pinion for the sp. has been designed correctly, it could have either 10 or 11 teeth and this would not affect the engagement to the starter ring gear.

Dave.

daimlersteve
Posts: 276
Joined: Wed Mar 09, 2016 11:20 am

Re: tooth count on starter

Post by daimlersteve » Wed Jan 10, 2018 8:29 pm

In this application when the pinions (either) are rolled around a ring gear the 11 has a better engagement . -- same dia for both. If the sp backing plate is overlaid with the saloon version the pcd difference is seen
steve

daimlersteve
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Re: tooth count on starter

Post by daimlersteve » Thu Jan 11, 2018 10:49 am

Think about it, the pinions are the same diameter. with ten teeth the profile will be fatter than with 11 teeth. I'm just putting together a new t5 to SP jig using a saloon backing plate so will measure the starter pcd on both that and the SP unit tomorrow.
steve

silverdart
Posts: 125
Joined: Sat Feb 13, 2016 10:49 am
Location: West Midlands

Re: tooth count on starter

Post by silverdart » Thu Jan 11, 2018 11:30 am

Just a thought, the SP ring gear was designed by Daimler and the v8250 by Jaguar.
The gear rings may not even be the same pitch.
Car manufacturers often used completely non-standard gear pitches to prevent copying by industrial gear suppliers.

Dave.

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Vortex O'Plinth
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Re: tooth count on starter

Post by Vortex O'Plinth » Thu Jan 11, 2018 11:57 am

If they're involute gears (which they most probably are) then pinion teeth with a fatter pinion tooth profile can mesh correctly with the ring gear but not on the same pitch circle. With 11 instead of 10 teeth and the same diameter, the pinion would need to be moved further from the ring gear. There are applications where different pinons can be used on a starter but in this case the pitch circle diameter would be modified to suit. More teeth without changing the pitch circle or modifying the profile reduces the effective addendum of the tooth which can lead to increased wear or noise. Some high torque starters offered as an alternative to original units include pinions with more teeth to increase the cranking speed while still maintaining high torque. To retain the correct involute profile and strength in the teeth the mounting flange is machined eccentric to the motor shaft to offset the pinion further from the ring gear.
Nick

Pas d'elle yeux Rhône que nous.

daimlersteve
Posts: 276
Joined: Wed Mar 09, 2016 11:20 am

Re: tooth count on starter

Post by daimlersteve » Sat Jan 13, 2018 4:25 am

and, for the final word on the subject,---- the jag/saloon c/l pinion / crank c/l radius is 12 mm more than the SP.

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