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Site updated
20 March 2011

How to do it

by James Mather

MG Midget 1500 5 Speed Conversion

Instructions. How to do your conversion

Please read this in conjunction with a works manual and looking at the pictures on the other pages of this site.

Midget

1: Remove original Midegt engine and gearbox.
2: Split engine and gearbox and unbolt bellhousing.
3: Remove clutch slave cylinder and bracket from bellhousing. The bracket is not needed. Keep the cylinder.
4: The gearbox, mountings and lever can be sold or disposed of.
5: Drill the centre bellhousing hole out to 1Ē or use file to enlarge it so that it will slide over the Sierra input shaft. There isnít much metal to be removed so it can, with patience be done with a file. Accuracy isnít required.
6: The clutch operating arm and pushrod is needed in total. Remove for refitting later.
7: Remove clutch and flywheel. The clutch driven plate is not needed.
8: Remove spigot bush from rear of crankshaft. Drill or ream or bore to 16.05mm internal diameter.
9: Replace the bush using some thread lock or bearing fit liquid. Do not push it all the way in. When refitting the flywheel allow the flywheel to press it home. It will now be slightly further out than when fitted before. This slight extra length is needed because the Sierra input shaft is shorter than the Midget one.

Sierra Gearbox

1: The rear sliding output shaft is not required as you will be using a different one from a Cortina. I toyed with the original shaft for ages machining it to fit a Hardy Spicer coupling. The whole lot went in the bin :-( If you unbolt the rubber coupling and cut the 3 legs off the sliding shaft you can reinsert it into the rear of the box to stop oil spilling out and stop dirt getting into the seal.
2: The Sierra rear gearbox mounting rubber is needed.
3: The bellhousing can be unbolted, but retain the bolts. You can use the rear face as a drill jig if you
cut it off with an angle grinder.
4: If you are drilling your own adapter, you can use the Ford bellhousing (see 3 above) as a drill jig. Otherwise it is not required.
5: Remove the Sierra Gearbox input shaft sleeve (retained by 4 x M6 screws) and cut as shown on the picture. Do not damage the oil seal. Refit after cutting and cleaning. Note when refitting that the small cast cutout inside it goes to the bottom.
6: The Sierra clutch release arm is not required.

Conversion

1: Bolt the adapter loosely to the Midget bellhousing using 3 M10 bolts in the bottom 3 holes. The top 2 original holes are not used but 2 more holes need to be drilled. The small spigot on the adapter rests in the recess in the rear of the Midget bellhousing.
2: Using an 8 mm drill, mark through the 2 x M10 tapped holes in the adapter plate which donít have bolts in.
3: Remove adapter and drill the holes through the bellhousing rear face where you have marked them, 10.5mm or 11 mm diameter.
4: Grind inside the bellhousing casting around the 2 new holes to give the bolts a flat surface to bear down onto.I used square ended milling cutter in a drill but a Dremel type tool can be used too. If you are really posh you can stick it on a milling machine.
5: Bolt the adapter to the Sierra gearbox using the original gasket.
6: Bolt the Midget bellhousing to the adapter plate using 5 M10 bolts.
7: Reassemble the Midget clutch release arm.
8: Fit clutch slave cylinder with pushrod and new bracket.
9: Fit 1500 Avenger clutch plate and reassemble cover.
10: Reassemble engine and gearbox.
11: Shorten Sierra gear lever. If you do the following it may too short for you. It was for me. Dismantle the rubber anti-rattle bush near its base. Thread the end of the gear lever rod M10 to take the knob.
What I did was to get another lever and cut it and re-thread it 2Ē above the anti rattle bush.

Your assembly should now look like this (see below) , (but with clutch slave cylinder fitted). Follow this link for the drawing of the slave cylinder. Ignore gearbox out put shaft in this pic.

Remember that the Type 9 gearbox uses special synthetic gearbox oil.

Converted

Midget Body

Cut out gear box crossmember as shown in the picture. Insert reinforcing pieces inside the cross member until flush with cut end, they may need slight knock with a hammer. If you knock them in too far they can be knocked out using a long bar inside the front 2 jacking point holes.
Cut out hole for gear lever. This needs to be larger than you think!

Lots of details are elsewhere on the site.