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MG MG Y Type - Flywheel follies...

Can any one help me with this query..I have a YB fitted with an early replacement XPAG engine - the flywheel is 10 1/4 in Outside Diameter and has a ring gear (Internal Diameter 7 1/4 in) with 93 teeth and it uses the M418G (larger) starter motor. I understand that later YA flywheels were 10 3/8 and the late YB at 10 3/4 both ring gears having 120 teeth with a later (smaller) starter motor (M39). Can I fit a 120 teeth ring gear to my 10 1/4 flywheel so I can use the later starter motor or am I geting confused.
The Octagon CC offer 3 ring gears at these diameters but the 10 1/4 is 93 teeth. Lawrence's book on page 66 states that later YA ring gears were thicker to take up the difference but is he correct as YAs were 10 3/8 OD inch flywheel surely??.
Octagon part numbers are :
SBI026
Starter ring gear id 10.1/4" 93 teeth TB.TC

SBI027
Starter ring gear id 10.3/8" 120 teeth early TD/YA

SBI028
Starter ring gear id 10.3/4" 120 teeth late TD/TF/YB

D MULLEN

If my last message was confusing then I'll try again. I need to confirm that there are 3 different flywheels that can occur on XPAG engines:

early type: 10 1/4 inch OD (93 teeth on ring gear) and requires M 418 G starter and 7 1/4 inch clutch
and:
10 3/8 [7 1/4 clutch]and 10 3/4 inch [8in clutch](both with ring gear of 120 teeth) using later M35G starter.

can anyone confirm/explain this?
D MULLEN

Your interpretation of the three ring gears in your second post is correct, and NO, there is no 120 tooth ring gear that will fit your 10 1/4" flywheel.

SB1026 fits TB, TC and early Y.
SB1027 fits early TD, late Y and early YB.
SB1028 fits TD, TF, late YB and W4/44.

Obviously engines and flywheels have probably been swapped around a few times by now, so checking is necessary. Hope that is of some use.
Roger Wilson.
R A WILSON

This thread was discussed between 03/11/2009 and 05/11/2009

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