Alfa Pages

Serpent33 · Posted: Mon Feb 27, 2006 9:47 am Post subject: Differential interchangebility?

Dear all. Some ratios come in 9/35 some in 9/37. Is the crwon gear interchangable? 35 to 37. without changing the pinion(9)?
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Each time I speed I say, "Dear lord, make me fast and accurate..."

Vecchio Alfisti · Posted: Sat Mar 04, 2006 11:42 am Post subject:

Hi Serpent33
I cannot say for certain if you can change the crown wheel without changing the pinion, but usually the centre distance between the two gears is fixed and the crown and pinion are paired to fit that cd. Also there are tricks used during assembly such as shimming to achieve correct meshing to overcome errors made during manufacture to achieve the correct centre distance/meshing. The gear pitch will be the same but if the match is incorrect you could be driving only using the tips of the teeth, and they will fail quickly. Alternatively, you may end up with too deep a mesh in which case the teeth will interfere with each other and this will also contribute to a failure as well as a lot of friction.

Sorry I cannot be more helpful but good luck and tell us how you go.

John
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Alfa 33 1.7 QF I think maybe now I m not so sure

ZeNiTh-PbArM · Posted: Mon Mar 06, 2006 12:56 pm Post subject:

Hi,

no way you can interchange crowns.
number of teeth is not all.

take two normal (ie not conical) gears : if the ratio is 9/35, and distance between axles is D, the contact point between gears is at D*9/35 from one axle and D*(1-9/35) from the other.
if you have 9/37 ratio the contact point changes location, the gears change diameter. so there is no way to match a 9 teeth from a couple to another.

The same applies to conical gear with crossing axles, considering the angle at the contact point location

It also applies to hypoid gear, but calculations are a bit more tricky.
(i checked myself to be sure!)
By the way, did you notice, Alfa crowns have the ratios stamped on them, not only the teeth number. This helps at identifying unknown crowns.

regards,
zp

Serpent33 · Posted: Mon Mar 06, 2006 5:52 pm Post subject:

Thanks for the feedback guys. So even they do fit and have no problems meshing together(by turning with the hand) . You reckon It'll encounter problems running.

Bad news is I have assembled them already. I'll have to decide what to do with it.. Confused

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Each time I speed I say, "Dear lord, make me fast and accurate..."

ZeNiTh-PbArM · Posted: Tue Mar 07, 2006 7:25 am Post subject:

hi,

yes it'll turn "by hand" but you can feel serious rattling in the hand when you turn gearbox axle.
i never tried to apply 90+ HP to such an assembly but i strongly believe you'd blow everything to bits the first time you let the clutch in.

regards,
zp

Serpent33 · Posted: Tue Mar 07, 2006 5:17 pm Post subject:

Thanks. Now my day has gone really bad. Embarassed

_________________
Each time I speed I say, "Dear lord, make me fast and accurate..."