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3LW ring gear


Maudesmaster

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I have a 3 LW in a new build narrow boat and want to know if anybody knows how many teeth on the ring gear I have just fitted a reconditioned 12 volt Starter motor doing away with 24 volt starter I tried to count the teeth turning the 14" pulley I have fitted by hand but it was too jumpy Thank you in advance

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Why do you need to know if you have fitted a starter (just curious). I have a couple of parts manuals but they do not give the no. of teeth, Neither does the Tools and Workshop Equipment handbook (but does give fitting instructions for the ring gear.

 

However I am sure someone more knowledgeable will be along soon!

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Those numbers don't fit the standard formulae. OD =N+2/DP

SO at 8DP the OD should be 22.125 in or at 10DP the OD should be 17.70 in.

Alternatovely for a 20.00in OD there should be either 198 teeth or158Teeth.

 

Since I am sure the info given is correct, I suspect that the ring gear tooth form is not a standard involute gear

 

You live and learn. Is this common to other ring gears?

The odd tooth form will also apply to the pinion and means that cutting a new pinoon is a rather more ticklish job than it first appears.

N

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Those numbers don't fit the standard formulae. OD =N+2/DP

SO at 8DP the OD should be 22.125 in or at 10DP the OD should be 17.70 in.

Alternatovely for a 20.00in OD there should be either 198 teeth or158Teeth.

 

Since I am sure the info given is correct, I suspect that the ring gear tooth form is not a standard involute gear

 

You live and learn. Is this common to other ring gears?

The odd tooth form will also apply to the pinion and means that cutting a new pinoon is a rather more ticklish job than it first appears.

N

Its a stub profile not standard involute ( 8/10 Fellow Stub to be exact). This is fairly standard for British engines of this era, Listers/Gardner's etc etc however the 20" which I think caused the confusion mentioned in my fathers post is the ID not OD wink.png.

 

The DP is expressed as a fraction for example 3/4, 10/12, or in this case 8/10. With the Fellows Stub tooth system, the numerator determines the pitch diameter only. The denominator determines the size and configuration of the teeth. OD = No teeth/Numerator + 2/Denominator = NUMERATOR/DENOMINATOR

 

also for the OP what model starter are you fitting? as there are a couple of different types fitted originally and depending on which one yours has(if original) it will have 11, 12 or 13 teeth on the starter pinion. If the 12v unit you have fitted is the same basic model as the 24 you have removed you need to make sure the pinions match

Edited by martyn 1
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Thank you all very helpful The 12 and 24 volt starter both 11 teeth the 24 volt used to skip there was an O ring between the shouldered plate I assume is for lining up tooth to tooth as the hole the motor fits through is not central When I took the 24 volt starter out half of the pinion was scuffed and inner half clean. measuring in to ring gear from plate and measuring pinion depth there was about 13mm difference so removed 8 mm O ring now catches every time

I need to know teeth number for magnetic RPM sender

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Thank you all very helpful The 12 and 24 volt starter both 11 teeth the 24 volt used to skip there was an O ring between the shouldered plate I assume is for lining up tooth to tooth as the hole the motor fits through is not central When I took the 24 volt starter out half of the pinion was scuffed and inner half clean. measuring in to ring gear from plate and measuring pinion depth there was about 13mm difference so removed 8 mm O ring now catches every time

I need to know teeth number for magnetic RPM sender

 

It may be easier to take a tacho feed off the alternator

 

Richard

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I have the hole drilled and tapped 5/8 to 5/8" UNF and ordered the sender so would like to go down that road

Thank you though This is my first owned boat as been one of them there hirers for the last few years because we had a time share thingy We are hoping to be CCers come next summer when all fitted out

Regards Rich

Edited by Maudesmaster
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Those numbers don't fit the standard formulae. OD =N+2/DP

SO at 8DP the OD should be 22.125 in or at 10DP the OD should be 17.70 in.

Alternatovely for a 20.00in OD there should be either 198 teeth or158Teeth.

 

Since I am sure the info given is correct, I suspect that the ring gear tooth form is not a standard involute gear

 

You live and learn. Is this common to other ring gears?

The odd tooth form will also apply to the pinion and means that cutting a new pinoon is a rather more ticklish job than it first appears.

N

Thanks to Martyn for the tooth designation description.

 

Having looked it up in Machinery's Handbook it becomes a little easier to understand, the OD is calculated as an 8DP standard involute tooth as per the calculation, giving the OD as 22.125"

As I have one to hand I measured it at 22.080, so give a little bit of manufacturing tolerance is correct.

The tooth form and depth is calculated from the 10DP giving a narrower tooth form.

The pressure angle is 20 Degrees as with current convention

 

Interestingly my 26th Edition of Machinery's Handbook published in 2000 refers me back to the 18th edition for further details saying that it is a seldom used tooth profile.

The 18th edition was published in 1969, so it has been out of general use for some years now

 

Maudesmaster is the sensor that you have ordered one specifically for picking up the edge of tooth profiles?, most sensors have a specified target size, if it is to large then it will not be able to detect the gap between the teeth and will give you a constant output as it will see the next tooth before the last one has passed.

 

Steve

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  • 2 months later...

Thank you Steve I think so it has a pin like detector on the business end I don't know how to put pictures on here it's a Murphy Magnetic Tachometer Sender 76mm x 5/8-18 UNF

 

A.S.A.P Part No. 708855

Richard

Steamraiser2 All these calculations went way over my head and could not measure fly wheel anyway

I went to Gardner marine in Canterbury and they let me count the teeth on a new one You were correct 175 teeth Thank you

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