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MG Midget and Sprite Technical - flywheel compatability / modification (1275)

hi all,

I have a few questions about flywheels. I have a an engine I got from ebay that is from a Morris Marina, it's a 1275. I'd like to fit this to my MG project (original engine is toast and needs rebuilding) However, the flywheels are different.

I had hoped I could just swap them over but the MG flywheel doesn't fit the Marina engine.

It seems the end of the cran on the MG engine is appox 2mm smaller in diameter than the crank on the Marina engine.

are there any issues with getting the MG crank machined out on a lathe to fit the Marina engine ?

some pics to help explain if I haven't been clear enough:

marina flywheel bore - approx 78mm
http://www.spiny.org/rr/mgoc/flywheel-DSC00606.jpg

MG flywheel bore - approx 76mm
http://www.spiny.org/rr/mgoc/flywheel-DSC00607.jpg

there appears to be enough metal on the MG flywheel to allow it to be 'opened out' ok

any thoughts ? or is there a part out there that I can just buy outright and fit ?

phil near bristol

Get a Morris 1098 flywheel, redrill the extra bolt holes for 6 bolt fitting (morris is 4 bolt, but 2 are in the correct position) or nip down to Bath where the Moggy shops are and get a pre-converted one for about £50. ESM are the moggy people who sell the most. For that price you even get a new starter ring!
rob multi-sheds thomas

yep, machining the midget flywheel to fit the Marina / Ital crank spigot is routine for this application...
David Smith

I have a 1430 witch stems form a stroked marina crank. I'm now planning to fit a frontline 5 speed conversion based on the ford sierra Type 9 'box. The spigot bush which is supplied with the kit is in a housing desinged to push with an interference fit into the end of the midget crank, does this mean that it won't be compatible with my marina crank?
Nick

I thought from the archives it was the Ital crank that didnt quite fit.....but the marina was fine ?

Phil - do you have a pic of the block itself ?
Dean Smith ('73 RWA)

Hi Dean,

I have this pic:

http://www.spiny.org/rr/mgoc/flywheel-DSC00610.jpg

if thats not clear I can pop out to the garage and take more.

I got the engine on ebay and was told it's a marina lump. It has the spin on oil filter and built in fuel pump.

rob: other people have suggested ESM, I have mailed them for more info, cheers :)
phil near bristol

Marina and Ital cranks are the same (for all intents and purposes), have 6 bolt fitting plus dowel and the OD of the flange is larger than the 1275 Midget crank. Either lathe down the crank (nope!), open out the Midget flywheel (possibility of getting it off-centre, Nope!) or use a Minor flywheel that fits flat to the crank but needs the 4 bolt fitting modified by drilling the extra 4 bolts at 60 degree spacing.
ESM seems the best option since they reface the flywheel, drill accurately and then fit a new ring gear. You can't do the job yourself for less money.
They do levy a surcharge, though. £50, I think.

Need a flywheel for exchange?
rob multi-sheds thomas

Rob,

I think the problem you create there is that the flywheel is not well located on the crank unless you add another dowel. IIRC the 948 and 1098 flywheel fit a spigot on the crank and the 1275 flywheel fits over the end of the crank which is the problem here in that the spridget and marina crank end differ in size. Fitting a 1098 flywheel to the 1275 crank would lose the location afforded by the flywheel fitting over a location diameter, the dowel will provide location but the flywheel can rotate about it limited by the slop in the bolts so balance, hopefully the assembly gets balanced, may not be repeatable.
David Billington

If anyone has both marina and 1275 cranks to hand, a side by side picture of the flywheel bosses would be very useful to me... Anyone?
Nick

will have Nick in a week or so.
Tarquin

I just happen....
marina engine on the right


David Smith

the marina/ital has a single dowel and a parallel spigot which is 3 1/8" dia.


David Smith

...while the Spridget one has a parallel bit and then a taper, the parallel part is 3 1/32" dia.


David Smith

Thanks david thats a great picture.

I'm most interested in the internal dimension differences as the frontline spigot bush holder is obviously specifically made for a midget crank, and I want to know if it will work with my marina crank, for a kickoff your marina crank appears to have a greater chamfer on the leading edge.


Nick

I was hoping you wouldn't ask that - but knew you would ;-)
Unfortunately I'm no engineer and I don't have any instrument to measure inside holes. The Marina does have a bigger leading chamfer, but the midget has a chamfer at least as big but a half inch or so down the 'ole. The midge spigot bearing is thin-walled and the marina one is thick-walled so the 'ole for the gearbox input shaft ends up about the same size. There should be plenty of spigot bushes available for different combos of crank and 'box, and I've seen needle roller bearings in place of the p-b bushes too.
David Smith

Nick:

I have these pics I took a few days ago, not exactly scientific but ... :)

marina flywheel - bore is approx 78mm:
http://www.spiny.org/rr/mgoc/flywheel-DSC00606.jpg

MG flywheel, bore is approx 76mm:
http://www.spiny.org/rr/mgoc/flywheel-DSC00608.jpg

side by side, but not very clear:

http://www.spiny.org/rr/mgoc/flywheel-DSC00609.jpg

I can take more pics if needed, I would measure the bore properly, but I don't have a vernier (is that the right word?) caliper.



phil near bristol

rob, yes I do need a flywheel for exchange :)

I'd like to keep my MG one as it's the original from the original engine, which although it toast, is rebuildable.

I just want to get the car on the road :)
phil near bristol

Nick, misread your post,

MG crank end:

http://www.spiny.org/rr/mgoc/flywheel-DSC00614.jpg

Marina:

http://www.spiny.org/rr/mgoc/flywheel-DSC00613.jpg
phil near bristol

Nick

does the Frontline spigot really fit the flywheel?

Reason I ask is I'm sure the MMC one fits in the hole in the centre of the flywheel itself, rather than the crank.

As I have never even seen the Frontline kit it may be worth checking before you start

(wanders off wondering if he was right....

but beggared if he is taking the engine out to look!)


But there exists this picture! In t'flywheel not crank.

(kept in place with Loctite "Stud'n Bearing Fit")


Bill

Phil,

In your last pics is it a trick of the light or does the midget crank end flange have a step in the outer surface and the marina crank not, just a chamfer.
David Billington

David, here are some better pics. the Midget flywheel does have a step:

http://www.spiny.org/rr/mgoc/flywheel_DSC00632.jpg

the Marina one just has a tiny chamfer at the edge:

http://www.spiny.org/rr/mgoc/flywheel_DSC00635.jpg

also, rob multi-sheds thomas I can't seem to find anyone remoltly close to me with a flywheel for exchange, so yes, I'm interested :)

email: phil AT spiny.org



phil near bristol

Phil,

That's what I was wondering and if the back side nearer the engine was the same size as the marina crank flange OD. Just idle curiosity really. Regarding the problem at hand I would probably have machined the crank down to take the midget flywheel as it doesn't need much machining.

On the subject of flywheels I think I have a 1098 sitting in my mothers garage in Bath so you're welcome to that flywheel.
David Billington

David - that would be fantastic :) let me know when would be convenient to pick it up, if you find it :) email: phil at spiny.org
phil near bristol

Phil,

You have mail. I noted that the flywheel shown on the EMS site only has 2 dowels and so would suit a 7.25" coil spring clutch ala 1098 but not a 7.25" diaphragm spring clutch that you would require for 1275 torque, that would require 3 locating dowels. May be worth checking with whoever does the work about getting that change done if required. BTW the guy that used to run the MM centre parts department in Bath and sold to EMS lives about 1/2 mile from me and works at EMS occasionally.
David Billington

This thread was discussed between 24/08/2008 and 30/08/2008

MG Midget and Sprite Technical index

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