1970 MG Midget - Suzuki Jimny 5 speed gearbox conversion

No mods, just bolt in on the original mounts. Gear stick is in the original position too. There will be 948 and 1098 versions to come if there is demand, it just means having different flywheels and spigot bearings made to suit.

James

Thanks rustymetal, I will keep the updates coming

The ratios aren't that far off the ribcase until 4th, with a 0.86 overdrive 5th. Jumping between the two cars I am hard pressed to notice any difference at all on the road, if there is any lost potential performance the Suzuki box more than compensates with much faster changes. My 5 speed car still has a 4.2 final drive compared to the 3.9 in this car, but still manages to be much more civilised on motorways thanks to the 5th gear.



barrattengineering.co.uk/r7me/

For more spirited / track use I have designed a close ratio gear set reusing as much of the original box as possible and retaining and full synchromesh.



James

IIRC, a 1098 Minor van had a 4.55:1 diff, for that very reason, compared to the regular Minor's 4.22:1. I have a feeling that the 948 Spridgets (& possibly Minor saloons too) were also 4.55:1.

The mm's had the 4.55 and the later saloons the 4.22, trouble with 4.55 is it's a bit short for modern road speeds, if the longer first allows you to fit a 4.22 it'd be better all round.

Looking good metroman  . Will keep an eye on your website for costs.

tofufi - I believe it will fit a Minor, it will certainly bolt up to the engine and crossmember, the only unknown at this stage is clearance to the steering rack. I should be able to confirm either way soon.

rustymetal - that's good to know, price wise it should come in less than an MGOC/Frontline Type 9 kit but probably not by as big a margin as I would have wanted. Material and machining prices are double what they were 12 months ago. That said it is bolt in so there is no labour / time spent cutting out chunks of chassis.

Ref the early vs late cars I took both out back to back today for some demonstrations which was interesting. The later car is better as a 'car'. I personally prefer the early car, there is more charm and it feels like more of an event to drive (powertrain aside). However, if I had to have one as my only vehicle, daily use 365 days a year it would be the later one hands down. Progress normally makes things better but something is often lost in the process.

The highly calibrated butt dyno says that torque curves are similar up to 3000/3500rpm, at which point the A-Series starts to drop away. The CG is only just coming on song at this point and things get fun! Both will be on the same dyno back to back soon.

Thanks for looking

James

kevins - there is a traveller that has been converted with a Suzuki engine and gearbox, the box went in with no mods to the chassis and cleared the rack. The unknown between this build and my kits is the exact positioning so the box may need some material trimming. I have several Morris owners interested and have some empty gearbox cases I can lend out for build trials.

Since the last update I've used the car a fair amount to make sure everything is in good order. Had a lovely blast over the downs in new years day with some friends



The engine was then serviced and checked over pretty carefully before both cars had some fun on a rolling road.





I was pretty pleased with the performance, although did expect the torque to hold up for another 500rpm or so. The car has been slightly modified with a nice K&N filter box with stub stacks and an LCB manifold, but I think the standard exhaust system is limiting their effectiveness at higher speeds. Torque beat factory numbers (if the rollers are perfectly calibrated!). The SUs do a great job of controlling the AFR.



The butt dyno wasn't far off in thinking torque would be similar to the CG13 car to 3000, after that it's a different story!

This wasn't really the point of the project though. After several months of design, supplier issues, redesign and a lot of time spent I finally got the first gearbox kit together. So this happened.

















I've got quite quick at this now! The weight of the A-Series definitely makes a difference though when manoeuvring the assembly out of the car.

The ribcase was then removed, along with the flywheel and steel backplate and the kit laid out ready for a dummy build.



This is always a bit nerve racking as one-off parts are no cheap and there are always things that are missed or not perfect. I'm nowhere near skilled (or lucky) enough to get this right first time, the objective is to get everything good enough that errors can be resolved and fettled rather than parts scrapped. The key is to record it all so the error isn't repeated!

The first error caused a bit of head scratching! Luckily workshop dog Ted sorted it out.



I had bought a 1275 backplate to take hole positions and profiles from, and been able to do a trial fit on a bare block without issue. So why didn't it fit over the oil seal? And why did the oil pump cover not fit in the hole? Simple - the plate I had copied was actually a 1098. D'oh. Thankfully it was a 'material on' problem so a bit of work with the powerfile got the clearance needed for the crank seal and a 1098 pump cover fitted just fine.



1275 plate overlaid onto the 1098 pattern new plate.

A lot of work has gone into the clutch and flywheel for this conversion. The A-Series crankshaft flange protrudes a long way out from the back face of the block to allow the flywheel to clear the oil pump, which sits proud of the back face. This is no issue with the original gearbox which has a deep bellhousing with lots of space for a high clutch and release mechanism. The Suzuki box however has a very shallow bellhousing. This makes the box compact enough to fit in the MG with a 5th gear but leaves very little space for a clutch.

The original clutch/flywheel is a no-go, and even re-drilling the flywheel for a more modern, lower profile clutch still leaves no space for a release bearing. Given the problems faced by MG owners the world over with failed release bearings this one was part I really did not want to try to design myself! The Suzuki part works and the Suzuki part stays!

This meant the only option was a billet flywheel. A bonus is that the flywheel can be lightened, ending up at 4.3kg. The standard one is over 7kg.

Space is at such a premium that I had to resort to countersunk screws to mount the flywheel. One of the locating dowels needed lightly dressing with a file but otherwise it bolts up just fine.





The assembly is a hybrid with a Nissan cover and 190mm Jimny disc and release bearing. The torque capacity is much higher than standard at over 150Nm so should be more than a match for pretty much any A-Series.

With a small amount of fettling to make clearance for the starter motor it all bolted together nicely. The original inertia starter was another no-go. The system is just too bulky to fit without seriously compromising the structure of the gearbox so a high-torque unit has been used.



More to follow soon...

Thanks for looking

James

What year gearbox is this for? I believe that the Jimny was branded as a Samuri in the US. Will this be available in the US and is there an estimated price yet?