View attachment 184673 View attachment 184681 View attachment 184682 View attachment 184684 View attachment 184687 View attachment 184688 View attachment 184689 Well that was easier than I anticipated. A GEMS 4.6l HP24 auto box fitted to a THOR 4.0l engine.
I picked up a know good working order GEMS HP24 gearbox for £150 to replace my faulty THOR HP22 box. There seems to be a lot discussions regarding lack of compatibility so decided to give it ago, what’s the worst that can happen!!!!!
To start with the overall gearbox length is identical as is the transfer box used on all P38’s, so no issues with length, mounts etc. The flywheel mounts on the crankshafts are also identical. The difference starts with the bell-housing length. The GEMS HP24 is longer to accept the larger torque converter. The input shaft on the GEMS HP24 gearbox is also substantial longer so the THOR HP22 torque converter WILL NOT FIT the GEMS HP24 box. To compensate for the longer bell-housing, a shorter rear section is fitted to the rear of the gearbox to maintain an identical overall length. The rear section also houses the crossmember mounting points, therefore all engine and gearbox mounts are identical for all engine / gearbox configurations.
The issue starts with the larger torque converter. The GEMS HP24 4.6l torque converter is larger in diameter and depth. This causes an issue when the gearbox is offered up to the engine. Basically there should be a 2mm clearance gap between the torque converter and flex plate with the torque converter pressed fully in to the gearbox and the gearbox bolted to the engine. The torque converter will be pulled up to the flex plate when the flex plate is bolted in position. This distance is important to prevent damage to the gearbox fluid pump, too small a distance will put mechanical pressure on the pump, too large a distance could cause damage to the locating slots. To overcome this issue, a thinner flex plate / flywheel is fitted to the GEMS HP24 4.6l engine. An easy fix would be to use the flex plate supplied with the GEMS HP24 gearbox as engine and gearbox dimension are identical (GEMS / THOR, 4.0 / 4.6, HP22 / HP24). Unfortunately the GEMS (Lucas) and THOR (Bosch) engine use a different crank-position-sensor pickup on the rear of the flywheel / flex plate, so that won’t work. After a bit of comparing between the flywheels / flex plates, I discovered a spacer between each of the flex plates & crank mounting bosses, problem solved. Swap the spacers between GEMS & THOR flex plates!!! With this done, gearbox moulted perfectly with the correct clearances between torque converter and flex plate.
One thing I didn’t notice, was the bell-housing / engine mounting bolts. The THOR engine uses an aluminium sump, the GEMS engine uses a pressed steel sump. The THOR engine has M12 mounting bolts all round the bell-housing, into the engine block and sump. The GEMS engine only has mounting bolts around the engine block. Due to the use of a pressed steel sump, no mounting bolts are available around the sump area, instead a cover is mounted to the gearbox using M8 bolts. Prior to fitting the gearbox, it would be a good idea to drill and tap the bell-housing to accept the correct bolts around the sump area of the THOR engine.
So I now have a THOR 4.0 engine fitted to a stronger GEMS 4.6 HP24 gearbox.
Hope the photos help explain........
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