MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - 3synchro to 4-synchro conversion

I am converting my 1966 MGB-GT from a 3-synchro to a 4-synchro + overdrive transmission. I’ve read lots in the archives (plus the magmgb.com technical discussion of the swap), and I learn that I’ll need the following from a 4-synchro car: a rear engine plate, a flywheel, and a pre-engaged starter. My question is this: is the flywheel replacement solely to accommodate the pre-engaged starter? If I cut a hole in the bell housing for my original Bendix starter, can I use the original, 3-synchro flywheel? Thanks in advance for your comments!

Mike
M.E. Whalen

You can cut a hole for the old starter, but when I did the conversion on my '67, I had access to all of the parts that you mentioned above. This made installation much easier. Also, the later starters don't abuse the flywheel's ring gear as they don't begin to turn until they are engaged with the ring gear. Getting the old starter to align just right, using the 4 synchro trans, is also a pain. If you can get all of the later parts that are needed, it will make the installation a breeze. RAY
rjm RAY

Mike, I assume you know the gear lever comes in a different place??

CP
Colin Parkinson

You need the backplate to marry to the gearbox and this places the starter further out from the crank, so you MUST use the bigger flywheel which has its ring gear fitted to suit the later pre engaged starter.

There are no shortcuts - just do it right!
Chris at Octarine Services

The easiest way to do this is to drill the hole in the bellhousing of the 4 sync and keep all the rest the same.

Using the later backplate and starter will require some clearacing with a hammer to make it all fit around the starter area. Nothing serious, but a reality to deal with.

You also need to do something about the lower starter bolt. Either weld in a chunk of Alloy so you can drill and tap, or just use a nut and bolt like I did.

The shifter comes out a few inches further back. Most people do a bit of minor surgery to deal with it and adjust the carpet as required. Myself, I ended up using a shifter extension housing that was shortend to fit the original hole. The work was done with a MIG and alloy wire.

Very worthwhile modification in my opiion. My experience is that the three synch units have the lifespan of an ice cube in the sahara.
p p

When I installed the 4 synchro/od trans in my '67 B, I didn't have to modify anything around the starter. I used the backing plate and starter from a '68 GT that a friend had bought for parts. The area where the od lives required very minor hammering and the re-location of the shift lever, 2" rearward, was helped by installing the shift lever backwards. The biggest improvement that I made to the car, followed by adding a supercharger in 2003.RAY
rjm RAY

As a slight aside, but it can apply here. What does the membeshipt think of these alloy or aluminium back plates you see advertised? is there any advantage appart from weight? Are they stronger? Mike
J.M. Doust

Just lighter, for the racing crowd. RAY
rjm RAY

This thread was discussed between 01/12/2010 and 14/12/2010

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now