1963 MG Midget - Nissan CG engine & 3D printed manifold

Great work on the Midget. I was surprised you even tried to retain the original gearbox, but it seems to run pretty nicely anyway! Someone has recently fitted a Suzuki Liana 1.6 engine to a Minor Traveller (avoiding any hacking up of the bodywork), mated to a Suzuki Jimny gearbox and MGB 3.9:1 diff; it allegedly does the 0-60 mph dash in around 9 seconds, rather than the standard 25 or so!

Here is the mx5 box I am preparring for the minor, gearstick is now in the same place as the minor / midget.





Once the gearstick has been moved the length isn't too much of a problem as the tail housing just goes where the prop would go, the chunk on the side for the mx5 powerplant frame and can be cut off if required.

That must be this build: www.morrisminorowners.co.uk/viewtopic.php?f=48&t=13154 It's a very neat build and has been done in very good time.

Otherwise I am at the stage of the project where a lot of time and effort goes in and very little seems to come out, certainly very little tangible that can be shown.

What I do have is a provisional CAD model of a rear gearbox mount which will pick up on the original Midget carrier and uses the same mounting setup. I was keen to retain this as a lot more R&D will have gone into this design for NVH and load transfer (even in the late 50s) that I am ever going to manage. It picks up on the same bosses the Jimny mount attaches to so I am happy it will be strong enough.





The construction method is similar to that used for the engine mounts, laser cut 5mm plate, bent and welded with locating tabs so it is self aligning for welding. This saves on fixturing and means I can rely on the laser cutting which is repeatable and accurate.

I spent a long time measuring the bell housing to get the hole positions, this was a lot easier for the engine conversion as I was running a CMM as part of the day job then! Still, I got there in the end.



I now need to spend a couple of hours double and triple checking everything before getting the prototype parts ordered.

Clutch wise I think, but need to confirm, that the Micra pressure plate will work with the Jimny clutch plate and release arm. For clutch actuation I have looked at retaining the cable but cannot find a nice way to make it work with the pedal box without cutting anything and still having sensible routing.

I considered a concentric clutch arrangement but the guide for the release bearing gets in the way. Trimming it would not work because it would actually have to be cut back as far as the seal.



This leaves a conventional external slave acting on the arm. This was not my first choice because there is nowhere convenient to mount a cylinder near the arm. A very large bracket would be needed, the case would have to be trimmed and I am not sure how to mount it.



What I have pretty much settled on is a 'pull' type slave cylinder. These are pretty rare in OEM applications because it's an expensive way out of a problem you shouldn't be in - you'd just put another boss on the casting and be done with it. Thankfully Wilwood have just the thing, it isn't too expensive and I have confidence that being Wilwood it won't be rubbish. I am also happier having the slave accessible. While a concentric slave is completely normal practice and they are totally tried and tested I was also a little nervous having a hydraulic system that involved engine removal in the case of a leak or failure.



The final hurdle I am aware of right now is the speedo drive, or lack of. Being a 4x4 with a low range transfer box, the Jimny doesn't have a speedo drive on the gearbox, or provision to fit one. And I want to retain my original odometer. I have found clever looking drives like this www.speedhut.com/Speedbox.html but they seem pretty expensive for a stepper motor and a circuit board.



I am not ruling them out but would like a more elegant (and cheaper) solution. My current thinking is to modify a motorbike type speedo drive so the body and drive gear run on the prop shaft. It's not a huge priority but something I am working on in the background. I know that electric Smiths gauges are out there but I really dislike the digital odo display. Also, it should have Jaeger gauges being a Mk1 and that sort of thing really bothers me because I am weird.





Hopefully there will be a bit more to show next time... Thanks for reading!

James

As mentioned before, we’ve modified our Jimny box to use a conventional push cylinder. We used the Jimny arm but with a mild cut and shut to correct the ratios (we hope!) and improve the push rod angle. We also went to some lengths to tuck the cylinder close to the box, but that was driven by the need to miss the Spitfire chassis.

I’ll takes some pics next time I’m home in daylight.....

Nick

Thank you for the photographs vitesseefi, that looks like a very neat solution.

The engine is out and I have taken some measurements of the clutch and clutch arm this evening. Maximum travel of the clutch release bearing on the race is 12mm. This would take 50mm of cable travel to achieve and is well beyond the stroke of any hydraulic slave cylinder.

I need to confirm on the press how much the release bearing needs to travel to disengage the clutch, but I know that the concentric slave used with the A-Series box had ~10mm hydraulic travel. This would require 41mm of lever movement at the end where the cable would attach, or ~34mm travel for a slave fitted as per your design, which is fairly standard for a clutch slave, so I would be pretty confident it will work! I need to do a bit more checking but I think I may have to playgurise that setup, if you don't mind?

Speaking of playgurism, I must give credit to ettorebugatti who actually suggested a Jimny box in the first comment of the thread, clearly planting the seed that I shamefully forgot the source of.

The clutch plate is also causing a minor headache. I was running a 7,25" / 185mm 1098 Midget plate with a late 180mm Micra pressure plate which worked very well. For obvious reasons I cannot use the Midget plate with the Jimny input shaft so had picked up a Jimny clutch kit with a 190mm plate. This unfortunately is a just too large for the Micra pressure plate so a rethink is required.

My options are to either have the flywheel re-machined to accept the Jimny pressure plate so I can run a full Jimny assembly, or source an alternative clutch plate 185mm or smaller with the Jimny 20 tooth / 22,3mm hub. I believe that a Mazda 323 plate may be the answer and have one on the way but we shall have to see on that front.

Speedometer wise I have had no luck in finding a motorcycle speedo drive with the correct ratio or internal diameter so have got in touch with Smiths.

They are offering this delight for E-Types


www.smiths-instruments.co.uk/blog/new-smiths-digital-jaguar-e-type-speedometer

Despite appearances the odometer and trip counter are OLED displays replicating the 'rollover'. This looks infinitely better than the standard offering of an LCD



I am hopeful that they may be able to offer the OLED setup with a Midget gauge. I feel that this would offer the best of all worlds, standard appearance, digital accuracy and reliability with (legal) speed sensing from the propshaft or hub.

Next time I promise to remember to take some photographs...

James

Also loving this gauge, I tried but couldn't find a video of it working?

Advice as above, go all DW and get it bought!

With the gearbox mount and adaptor plate designs completed and on order I got a bit bored so put the engine up on the stand for a bit of a refresh. This was meant to be limited to a new crank seal but soon spiralled. The crankshaft seal in the front timing cover had a little bit of a weep, probably due to the the pulley coming on and off a few times. That and the seal being 25 years old... Anyway, to get the seal out the timing cover had to be removed. Simple enough. Only in doing so I managed to catch the head gasket where it seals the timing chain. What a shame. Of with its head!


Everything looks to be in good order


I had noticed on the last run that #4 plug was cleaner. I will check the carbs before it goes back in as it is a bit on the lean side I think.


The bores are however exceptional. This is a 100k mile engine. My Metro engine didn't look half as nice as that after 30k miles when I rebuild it.


The head was then introduced to the parts washer, and since it is no longer on the engine I did the right thing and sent it off for porting and a 2mm skim. That should go nicely with some Humphris Rallysport 774 camshafts...

Yesterday I got a highly anticipated delivery of the prototype parts.


Adaptor plate


And rear gearbox mount


This is an unmodified A-Series Midget rear gearbox chassis mount fitted with a pair of cotton-reel type AV mounts


I don't think that looks too bad


D'oh


Pain is temporary...




I am pleased with that


And here it is mated to my mockup CG block

Next steps will be confirming the clutch operation and a trial fit into the car.

Thanks for reading

James

Hi Nick,

The mounts are from AV Mounts Online

www.avmountsonline.co.uk/bobbin-mounts/male-female-bobbin-mounts

I am using 50 x 20 M10 male-female bobbins but there is a good range to chose from. Quality seems good but I am a little way off knowing what the NVH is going to be like.

James

This is fascinating work you're doing James, I'm interested in eventually doing a 5 speed conversion on my Cortina but the type 9 doesn't have the ratios and the prices are only going one way - I digress!

I don't know if this will benefit you but I have been leaning more on laser cutting stainless for work instead of rough fabrications and use the tab method for plate alignment. One thing I have done is apply a 2x2 chamfer on the edges of the tab to allow for a decent tack weld that can easily be finished back without affecting the flat surfaces. It's worked out well for us - please don't think I'm trying to tell you how to suck eggs!