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MG Midget and Sprite Technical - 1275 dimensions needed.

Been away from board for a fair time as I've been up to other things. However I'm now trying to fit a Maestro engine into the frog. Hopefully I've done 90% of the necessary work but I would like some confirmation on one of the critical measurements.
I need the distance from the surface of the engine backplate to the gearbox facing side of the flywheel, Alan A has done this for me on an engine that he has but I want to check that neither of us got it wrong! So if anyone has an engine out, with flywheel on, could they please let me know the dimension from the back/flywheel side of the backplate to the clutch side of the flywheel.
thanks, Graham.
Graham P


it's 1 7/8" but note there's a step in the flywheel about 3/4" in from the outer edge. I've measured to the outer edge so add the depth of the step for the clutch mounting face dimension.
David Smith

I did this measurement last week for a friend and it is 1.15/16ths from backplate to working face of flywheel, which supports David's measurement.

Bernie.
b higginson

Graham, I've got a Maestro engine to go into a Frog sometime (but not soon)and got to the stage where I need a flywheel solution. I have a 1275 flywheel that has been machined for a Marina engine but the Maestro crank is a bit bigger than the Marina so need some more machining. Also bolt holes are different on Maestro crank.

What flywheel solution have you got? Also, backplate solution?

Rob
Rob aka MG Moneypit

Grahem
You are welcome to drop in and measure my spare engine.
Alan
Alan Anstead

Thank you chaps for the measurements, I should be getting my flywheel back from the machinists tomorrow, so I can check against your figures. Fingers crossed it should be OK.

Alan, you already measured it for me, but thanks, I might well take you up on that just to be nosy :+)

Rob, using a 1275 flywheel you will find that all but one of the holes line up but are centered on a slightly smaller radius than used on the maestro crank. The holes need to be slightly slotted, the one hole that is way out has to be plugged, I made a tight plug (around 9mm I think) and stuck it in with JB Weld then re drilled the hole in the correct place. The machine shop is turning out the locating ring on the back of the flywheel from 3" TO 3.25" approx so that it will fit snugly on the crank.
As for the backplate, that is the hardest part. You need a maestro backplate and a cast iron spridget one (or alloy if feeling rich)and make a hybrid backplate from the two. You also need to use the sump from the maestro due to the sealing system on the engine. If you do not do it this way then you need a spare rear bearing cap, a spare crank, spare sump and all the sealing parts for the rear scroll seal, or you could use one of the rear crank seal kits from sundry suppliers. The rear cap would have to be line bored to enable you to use it with the new crank and block.
I wanted to avoid as much swapping of parts as possible as the engine I bought is brand new never used!
I will try to provide a "how to" at some time if people are interested and it works!
Graham.




Graham P

Looks like I have somewhat of a problem!! The picture shows the measurement I was asking for and if that is what you guys measured then my flywheel will be roughly 1/2inch too far into the bell housing!!!!!!!!!!!
I guess that this would compromise the clutch operating angles but I'm not sure, any bright ideas out there? Please ignore the poorly fitted ring gear, it was like that when I got it and I'm sure it'll work fine.
Graham.

Graham P

Must be mostly to do with the crank spigot. The flywheel on the midget runs very close to the tin can covering the oil pump, the back of the flywheel is only 3/4" from the backplate.
Is the Maestro crank longer, is the spigot thicker?
Is that a Midget flywheel? Looks thicker towards the centre (I guess the chamfer is where it's been lightened).
Depending on what clutch you are using you may need to relieve the inside of the bellhousing. I think you can get the clutch throwout back to where it needs to be by using a 1098 thrust brg.
David Smith

Dave, it is a 1275 spridget flywheel that was lightened when I got it.
The flywheel boss on the crank is definitely thicker than the spridget one.
It would seem the maestro crank is longer, which is really annoying as I thought I had measured it to be the same as a spridget.
Next problem, I have a type 9 gearbox to match it to, along with a roller release bearing and a 6.5" clutch. I wonder if it may be easier to fit a concentric clutch release to get the correct throw.
Trouble is I need some measurements on the type 9 conversion bellhousing to see what needs to be done. In theory it should work by just shortening the slave push rod perhaps?
Graham.
Graham P

Graham
Next Monday / Tuesday I'll have a Spridget in my garage for another T9 conversion. Bring a tape measure?
Alan
Alan Anstead

Graham, this is what I have done so far shown in the image. A 1098 backplate/Maestro alloy housing sandwich. The bolt shanks you see will have alloy spacers fitted to fill the gap and ensure that the alloy housing is evenly pressed. There are other spacers on 5 or 6 other bolts hidden behind the backplate.

I have a 1275 flywheel that has been modded for Marina crank which I think is 3 1/8 diameter but as you have done needs taking out to 3.25 inch to fit the Maestro crank. Also, for some reason it has been machined inwards so the crank flange sits deeper into the flywheel. Not sure why but the friend I got it off reckoned the Marina/Ital A+ crank flange was thicker hence the machining was to get the backplate to flywheel face dimension correct.

Rob



Rob aka MG Moneypit

Rob
Presumably the heater tray will have to be cut back to facilitate the engine / gearbox fitment?
Alan
Alan Anstead

Not sure Alan. The Maestro gubbins adds about 1 Inch to the length of the Engine/Gearbox. Either the engine moves forward to retain the GB mounts in the standard position or the GB mounting moves back to leave the engine in the standard position. Either way I think the heater tray is (just) safe.

Still early days yet.

Rob
Rob aka MG Moneypit

Rob, I've seen it done that way before, not the nicest looking adaptation and also difficult to fit properly in the engine bay! Also with a standard 1275 front pulley/damper fitted the engine would not fit but would have to be moved back by quite a bit.

As you can see from the picture, I've cut the two backplates together to form a new hybrid one which keeps the engine position the same as previously, unfortunately with the crank being 1/2" further in to the bell housing. :+( I don't think I could have had anything but a very small amount removed from the rear of the flywheel as it would make the mounting surface too thin for safety.

Alan, might well be able to make it on Tuesday, but my wife is having a cataract operation on Monday so don't know whether I'll be able to or not.
Graham.

Graham P

Hybrid backplate from the "block side".

Graham P

Graham, I must admit I never thought of doing that. Looks like a neat way of doing it but as you say you need to loose a bit of excess clearance.

Using the 948 or 1098 clutch release bearing will give you more clearance but not sure how the bellhousing will react with the flywheel pushed so far backwards.

How about using a 1500 bellhousing with Canley Classics adaptor to get to Type 9 gearbox. It would gain some flywheel diameter but a Marina/Ital backplate would be needed.

Rob
Rob aka MG Moneypit

Unfortunately I need some more dimensions. Below should be my "excellent" cross section of a bellhousing fitted to a type 9 gearbox for an A series engine. I need dimension A (the measurement from the tip of the 1st motion shaft to the backplate/steel rule across bellhousing).
With this measurement I can get the spigot bush in the right place in the crank/flywheel.
So if anyone has a type9 box with an A series bell housing fitted could they please take that measurement for me?
Graham.

Graham P

This thread was discussed between 16/03/2014 and 19/03/2014

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