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MG MGA - MGB Clutch Conversion

Hello,

Trying to get pprepared for an MGB clutch conversion. With 18 fingers on an MGB clutch, compared to the A 6 point pressure and 3 point release system, thi sshould be good.

Question for anyone - When moving to a 3 bearing B engine with an MGB clutch,MGB 3 bearing flywheel, 3 synchro clutch fork and front gearbox casing for piviot, using 10 spline gearbox shaft and hence the MGA drive plate too, why should I use an 18G/GA rear engine plate?

Do I need this plate to use an MGB starter (N418G) rather than a MGA starter (M35G)? Why can't I use a High starter plate or low starter plate from an MGA with an MGB starter in, if the starter is pourely for a better torque on turning an 1800 engine?

I've tried scouring the archives here, but can't see much.

Regards,

Martin
Whitehill
Hants
UK
Martin Smyth

You'd use the MGA backplate that matches your starter position. Why do you think that you have to use the MGB backplate? I don't know for sure that an MGB starter will bolt in because I've never tried it. FYI, the MGA starter has no problems whatsoever turning an 1800. I use the A starter on my 5 main. Just make sure your brushes are in good shape.

Mark
Mark J Michalak

Thanks for the quick feedback.

I've been reading Tech Sessions by Mike Ash (North American Register) and page 130 seems to suggest in a table written by John Twist that an 18G/GA rear engine plate is required.

I think I'll just use the plate that matches my starter position as you say and continue with the A standard starter.

I have seen some discussions on fouling of the MGA gearbox bellhousing with certain MGB pressure plates and perhaps some pressure plates requireing greater than normal clutch pedal force to engage. Has anyone experienced this with any particular pressure plate manufacturer. Therefore I'll be able to avoid potential dangers.

Regards,
Martin
Whitehill
Hants
UK
Martin Smyth

Try this site for info


http://mgaguru.com/mgtech/clutch/ct_102.htm
Kris Sorensen

Martin,

You need to use the MGA backplate when installing a 5-main, so I don't know why it wouldn't be the same for a 3-main.

I doubt there is enough info out there concerning exactly which brands foul the A gearbox. You can test fit it before you install it in the car, If it doesn't clear, just use a grinding wheel to take off some material near the starter hole.
Mark J Michalak

Martin,

I had my mga engine rebuilt by Doug Jackson of British Automotive who lightened my flywheel (well worth considering)and put an mgb clutch in at the same time. His site is MGBMGA.com - he has a number of interesting articles about modifying mg's and I found him very approachable. Maybe an email to him would help answer your questions.

Good luck,

Randy Myers
'59 roadster, coupe
Randy

You don't need the MGB rear plate, you can use the MGA - neither have provision for a rear main seal, unlike the 5 main.

The MGB starter has a larger diameter spring than the older starter and may well foul the bellhousing, but all you need to do is remove a bit of bellhousing material to clear it or use the old style starter (it will turn the MGB engine with no problem).

I believe you may find that the 3 main MGB and late high mount MGA plates have a minor variance so that the wrong plate won't allow the starter holes to line up, but it's been awhile since I compared rear plates.

I also use the MGA plates when installing a 5 main MGB engine - I just have the plate machined to the correct diameter to take the 5 main rear seal.

Personally, I prefer the 3 main you are using.
Bill Spohn

I just updated and uploaded a new web page today showing the differences in a variety of rear engine plates (mostly compliments of Kelvin Dodd of Moss Motors). The key dimension locating the starter motor shows why you cannot use an MGB plate with an MGA gearbox. See here: http://mgaguru.com/mgtech/engine/cs200.htm

Always use the engine rear plate that matches the gearbox. If you are mating an MGB 5-main engine to an MGA gearbox, bore out the center hole in the MGA rear plate to accept the rubber seal for the 5-main crankshaft.
Barney Gaylord

This thread was discussed between 01/03/2008 and 05/03/2008

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