5 Speed Marina Conversion
The background to this conversion started before I did the overdrive gearbox conversion, I had read up a lot about gearbox conversions and from the reading it all seemed a bit expensive with custom bellhousings, complete kits at £1,000 plus etc. As it turned out the Overdrive conversion was about the same cost as doing this conversion (nowhere near £1,000!) so I should have done this first. The other key factor was the ability to share my thoughts with someone else who wanted to do the same thing - Steve Green has a Marina engine Marlin Roadster and between us we have pulled something together that has worked straight out of the box. There is a pre-cursor to this in that Brian Viney had done a Type 9 conversion, but started with a 4 cylinder box and as a result he had to make several engineering decisions that I wanted to engineer out. Steve and I set out to make something as bolt-able as possible.
I started by sourcing a V6 Type 9 gearbox, it had to be a V6 type as the standard version doesn't have a long enough input shaft to accommodate the adaptor plate. My favorite 24 hour shop (eBay) came up trumps with a used box for £72.00, anything under £100 and you are laughing. The V6 gearbox is more than strong enough for the 'B' series (or 'O' series) engine; as it is capable of handling the 2.8i / 2.9i Ford V6 engine which produces way more power and torque than a tuned B series is ever likely to. Some of you will recognize the description below from the www.5speedmarina.com website. Steve and I have had some plates made up and assembled a kit of parts to allow other Marina modders the opportunity to switch to a 5 speed gearbox.
This is the finished product prior to fitting to my Coupe. When I bought the Ford gearbox it was already painted black and so after I got the Marina bell house back from the engineering shop, I fitted it all together and gave it a once over with black engine enamel. This first page relates to the engineering part in mating the components together, page to relates to fitting the gearbox into the Coupe and making it work.
Ford Gearbox to the Marina Bellhousing
When comparing the Ford gearbox to Marina bellhousing fixings inevitably nothing lines up. The top two mounting holes are about 5.5mm out of alignment (roughly half the bolt width), the lower and outer Marina fixings are inside the Ford box face, the lower centre Marina fixing conflicting with the Ford lay shaft. Finally the lower Ford fixings are outside the Marina bell house face. The solution we adopted was to lightly modify the Marina bellhousing and do all the difficult stuff on the adaptor, our kit includes an engineering drawing for drilling dimensions on the Marina bellhousing.
Drilling the Marina bell house for the top Ford fixings was fairly straight forward; but first I plugged the existing holes with 'plastic metal' to give a more secure final fixing. I used the adaptor plate to position the new holes. The lower three Marina fixings have been tapped straight into the plate with M10 threads for the socket head screws. The M10 socket head screws are marginally longer than required and needed shortening so that they do not protrude beyond the adaptor plate otherwise they wouldn't have locked home on final installation.
When viewed from the inside of the bell house the metal around the top left hole required relieving slightly to provide a flat surface for the socket head bolt to mate against (see picture below). This was done ‘carefully’ with an angle grinder or could be machine faced by the engineers if used for the other work required above.
On different 'B' & 'O' series engines there seems to be a variation in the depth of the crank shaft spigot bush hole . As many engines will have been transplanted over the years it is difficult to be specific. On mine I had to shorten the Ford input shaft by 13mm. Ideally when assembled the input shaft should not protrude more than 8mm past the Marina bell house, the same as the standard Marina gearbox.
The standard Marina spigot bush was changed for one with a larger bore to accommodate the Ford shaft (supplied in the kit).
Whilst our design allows you to keep the Marina clutch mechanism, a little work is required to make the Ford bearing retainer sleeve take the place of the Marina one. The Ford bearing retainer sleeve has a slightly larger diameter than the Marina version, I had the Ford sleeve machined to reduced the outside diameter to 33mm for a good fit for the Marina release bearing assembly. It is worth measuring the diameter of your Marina bearing retainer sleeve first to confirm the dimensions on your gearbox. The Sierra sleeve is longer but does not foul the clutch or release plate.
The base of the Sierra sleeve is also substantially larger than the Marina equivalent. The adaptor plate was bored to suit its major diameter to allow the bearing retainer and its fixings to be enclosed. Owing to Ford's production tolerances; I found that I had to do a small amount of fettling of the adaptor to fit cleanly over the sleeve base.
The Marina bell house centre bore needed opening out slightly to clear the oil seal boss on the Ford bearing retainer sleeve, opening the Marina centre hole out to 52mm cleared the Sierra oil seal boss.
The Marina clutch release pivot post remains fitted in its' machined hole in the bell house, butting against the adaptor plate. I Loctited the pivot post into place.
The Ford gearbox front has a central selector rod at the top that protrudes around 24mm into the Ford bell housing, the Marina gearbox also has a similar rod, it is however off-set from the vertical by about 5%. The adaptor plate had to be machined to clear the Ford selector rod, I bored the mating face of the Marina bellhousing with a 16mm bit to a depth of 12mm to accommodate the end of the Ford selector rod, this partially broke into the Marina selector rod hole, see picture below, the kit includes a drawing for the engineering shop to work to. It is advisable to fill the selector shaft hole with epoxy metal before machining.
This hole must form an oil seal around the selector rod. This is achieved by using a liquid gasket compound on the gaskets on each side of the adaptor and gaskets.
The shape of the adaptor plate was determined by the Ford gearbox gasket, with allowances made for the Marina lower fixing holes. The adaptor plate does not fully cover the hole provided for the Marina selector rod. It is important that this hole is sealed but still allows movement of the Ford selector.
Before starting this conversion it is important to drain any oil from both the gearboxes. When dismantling the Marina bell house, the lower fixing has a copper washer to act as an oil seal. The Marina gearbox has three small springs trapped behind the bellhouse, when releasing the bellhouse be careful to catch the springs for the gearbox. The Ford gearbox should be drained prior to mounting, as the tailshaft oil seal needs the propshaft yoke in place.
Sequence of fitting
I measured and recorded the Marina gearbox output flange height. The new installation should be the same height or slightly less to maintain the standard propshaft angle. In a Marina the engine is canted back at an angle of 5 degrees, the new gearbox mounting should match this to avoid unnecessary strain on the propshaft UJs.
I removed the gearbox, bell housing and clutch assy (as per Haynes), also removing the BL spigot bearing from inside the crank/flywheel.
With the gearbox and bell house assembly out of the car remove the clutch release bearing assy, actuator arm and the pivot post and set aside for later. Now was a good time to remove the clutch release bearing from its assembly and replace with new.
I thoroughly drained the gearbox of oil .
I then undid the five hex head screws attaching the Marina bell housing to the gearbox. The lower screw has a copper washer and acts as an oil seal. Once the bell housing is separated, I put all the screws and washers back into the gearbox for safe keeping. Remove the three small springs, place in a plastic bag and attach to the gearbox along with the gear lever assy as you may wish to sell the gearbox on to another Marina owner.
I stripped and cleaned the bellhousing mating face of dirt and remains of paper gasket etc. I tapped out the bearing retainer sleeve and attach it to the gearbox to keep dirt from the exposed input shaft bearing, there is an 'O' ring between the bearing retainer sleeve and the gearbox.
I arrange for machining of the bell housing as per the drawing and for machining of the Ford bearing retainer sleeve to match the Marina sleeve.
Once the machining work has been done on the Marina bellhouse, with the Ford bearing retainer sleeve in place, I loosely mount the Ford gearbox, 5SpeedMarina adaptor, gaskets and Marina bellhouse and measure how far the gearbox input shaft extends beyond the bell house. As mentioned earlier the correct dimension is an 8mm extension, you may need to remove up to 13mm from the end of the input shaft. This is hardened steel and will need an angle grinder, preferably with a slitting wheel. I made sure that a slight taper was ground on the nose of the shaft as per original to ease installation.
With the bearing retainer sleeve and bell housing machined, assembly can now start.
I ensured that the turned down bearing retainer sleeve fitted cleanly into the Marina bell housing and into the adaptor plate. I fitted a new oil seal inside the bearing retainer sleeve, then fitted the gearbox with a new cork gasket offered up the sleeve and torqued the four M6 screws to 10Nm. I made sure that the gasket was aligned correctly and the bleed hole in the sleeve was at the bottom.
I located the gearbox face Ford gasket with a little gasket compound around the selector shaft and lay shaft to help prevent oil leaks. I positioned the adaptor plate, checked for free movement of the selector rod and then fitted the lower two screws and lock washers (Ford originals), rechecked for free selector movement and finally tighten to 70Nm, bottom bolts only.
I then selected 1st gear on the Ford gearbox, this moved the selector rod out of harms way inside the gearbox. I the fitted the special Marina face gasket to the adaptor plate (supplied) and applied a little gasket compound to ensure that there are no leaks. The next step was offer up the bellhousing and fit the top two M12 Cap Head bolts and lock washers, torque to 70 Nm and then fit the remaining three M10 Cap Head screws and lock washers and torque to 50Nm. I checked again for free movement of the selector rod by selecting 2nd and 4th gears - no problems.
I refitted the clutch release post, clutch lever and release bearing. I used a good quality thread lock compound for all threaded sections and for the final fitting of the clutch post.
Careful preparation and machining meant that the whole thing went together in less than 30 minutes. That completed the gearbox and bell housing build up, the next web page covers the installation in the Marina.