Flywheels and cranks

[andypocock]

Hello Chaps

Hope some of you can throw some light on what I have here. I've just picked up an MG 1098 engine to use as a replacement in a friends 1960 saloon that has a horrible rattle after she holed her sump. The old saloon has been fitted with a 1098 at some point in it's life and this is mated to the original smooth case gearbox using the old flywheel with the old style clutch.

Having a few bits here I thought I'd start getting the 'new' engine ready - twin carbs in my parts cupboard (she won't want them), off with the flywheel to fit one of my spares from a 948 so that it mates up with here gearbox. Oh dear, it doesn't fit. Bore in the 948 flywheel is 1.75in with 2.5in bolt centres. The one I've just taken off is bored 2in and has bolt centres at 2.75in. I'm sure I've swapped flywheels in the past to fit later engines to earlier boxes and vice versa.

So does the MG have a different crank? If so it looks like I'm going to need to find a bigger lathe than the ML7 in my workshop.

Thanks in anticipation

Andy

[philthehill]

Does the MG/Sprite engine I.D. Plate have the 10CC prefix or 10CG prefix?
If it is the later 1098cc/10CC engine fitted to the MG Midget/Sprite it had 2" dia crankshaft mains and was Part No: 12G429 and its associated flywheel Pt No: 12G483.
The earlier 10CG 1098cc engine crankshaft fitted to the MG Midget/Sprite was Pt No: 8G2737 and had 1.75" dia crankshaft mains and its associated flywheel was Pt No: 12G180.
So to sum up the later crank will not fit the 1098cc Minor block with 1.75" mains.
Why not fit the whole 10CC engine/flywheel/clutch assy and back-plate (same as the Minor 1098cc) as it will fit without any problems and which incidentally is a much better engine for having the larger mains.
You are quite right to assume that the 1098cc Minor and early 1098cc Midget/Sprite engine parts are interchangeable but unfortunately not all parts are between the 1098cc Minor and late 10CC engine Midget/Sprite and vice versa.

[andypocock]

Thanks for the clear answer Phil. I must have the later 10CC setup. It came from a 1966 Sprite but there is no telling if it's original. The block is a 12G432. I'd happily stick the lot in but as I have the early smooth gearbox I thought I was going to need the 948 flywheel and clutch (which btw seems a lot heavier than the MG item)

Thanks again

Andy

[philthehill]

Andy
Is there not a engine number plate on the front o/s of the engine block. That will give you the engine number.
Unfortunately to fit the 1098cc clutch you will need the 1098cc ribbed gearbox as the bell housing has extra clearance to suit the larger 1098cc clutch.
The 1098cc 10CC engine was introduced in 1964 so your engine could easily have come from a 1966 MG Midget/Sprite.
The 1275cc 12V or 12CC engine was introduced in 1966 as well so your 10CC engine could be one of the last produced.
There are a few reasonable 1098cc gearboxes available on this forum or on 'e' bay if you want to go the whole hog which is what I would do.
As I said earlier you will end up with a much better and drivable car with the 10CC engine and 1098cc gearbox.
Phil

[andypocock]

I've just been down to the workshop for a look I do have the 2in mains. And the 2in hole in the flywheel.

I've laid the MG flywheel on the bench with the MG diaphragm clutch on top and next to it the Minor 948 flywheel with a Minor spring clutch on it. A quick measure suggests that the MG assembly is about 200thou deeper. However the MG back plate is about 300thou and the Minor back plate about 150thou so the MG would hold the box back 150thou which would take up much of the difference putting the release contact face in about the same place.

So it looks to me now as if the bigger MG clutch will fit the early gearbox so long as the MG backplate is used.

Hope my rambling so aren't too boring but if I think aloud somebody can stop me if I'm barking up the wrong tree.

Andy

[andypocock]

I posted after your last reply Phil. Engine number gone but it has to be a 10CC.

If I had time to play now I'd certainly go ribbed box. As the car is needed quickly it is looking like a quick machining job on the 948 flywheel so that I can get the engine in. Then I'll grab a ribbed box and overhaul that ready to put in with the MG flywheel and clutch.

Not ideal but sometimes in the real world...

Andy

[bmcecosse]

I don't understand why the 948 flywheel won't fit - even a 1275 flywheel fits ! Are you sure it's not a 1275 engine ? But even then...the flywheel should fit - but only two bolt holes will line up... You will need to use the thicker backplate - and if you persevere with the smooth box - you will likely have to grind the casing near the top - to make the 'hole' that is there on the later ribbed box to give clearance.

[andypocock]

It definitely doesn't fit! Minor flywheel has a 1.75ins hole. The MG one is 2ins. They are both 4 bolt but the spacing a are different.

Fits perfectly with Phil's explanation but it did come as a surprise to me that there were two versions of the 1098 MG engine. What did we do before the inter web?

Andy

[andypocock]

Ps. I'll use the Minor backplate with the Minor flywheel, clutch and gearbox so it should all fit.

Andy

[philthehill]

If you have a diaphragm clutch fitted it must be a 12V or 12CC 1275cc engine as the 1098cc either of 10CC or 10CG persuasion has a coil spring clutch.
If it is a 1275cc engine it is no wonder you have such differences in diamensions. The 12V or 12Cc has 2" dia mains as well and 1,625" dia crank pins.
Does your engine block have cam follower chest covers on the N/S of the block or is the block a solid casting in that area.
That will be the clincher.
The 1275cc flywheel has 6 bolt holes and two locating dowel holes so if you only have four holes and no dowel holes it is definably a 1098cc flywheel.
Picture of the front (pressure plate side) of a 1275cc Midget/Sprite diaphragm clutch flywheel attached. The hole through the centre of the 1275cc flywheel is 43.2mm.
Note the difference between the 1098cc and 1275cc flywheel.[frame][/frame]

[bmcecosse]

Can we see some pictures please? I'm not aware of any bolt pitch variation - not even with the Marina /Ital engines. The stronger crank etc was fitted to the Spridget 1098 to eliminate (well - at least minimise...) the crank breakage often suffered by hard run early 1098 engines. This to allow competition in the 'up to 1100 cc' classes which were popular at that time. It's essentially a version of the Cooper S engine of that time. So it still had cam follower covers. The blocks were then redesigned and strengthened by eliminating these covers - making 1275 engines for NS and EW vehicles and the 'S' block was dropped.

[philthehill]

bmc
You make it sound so easy to change over flywheels but it is not so simple as that.
The bolt/dowel holes are different in their location around the crankshaft flywheel flange and a 1275cc flywheel (Marina or Midget/Sprite) cannot be JUST installed on a 1098cc crank or vies versa without some work being undertaken.
The flywheel register on a 1275cc Marina crank/flywheel is different by (approx 1mm) to the flywheel register on a 1275cc Midget/Sprite crank/flywheel so again they cannot be exchanged.
Whilst all things can be done/overcome it is not just a question of undoing a few bolts and bolting a replacement flywheel in its place.
The easiest way to overcome the differences is to purchase a modified flywheel from ESM Pt No: 10M001. That will allow the fitment of a spring 1098cc clutch onto a 1275cc engine.

[bmcecosse]

Yes Phil - I know all that BUT the bolt pitch remains the same for them all...I now suspect this may be a TRIUMPH engine that has been 'acquired' !!

[philthehill]

Yes I agree the pitch for the bolt holes/dowels remains the same but their location/arrangement around the crankshaft flywheel flange is different as well as the flywheel registers; and yes you and I may know the differences but not everyone does and that is where we have to be very clear in our deliberations.

[andypocock]

It's definitely an A series BMC

The diaphragm clutch is obviously a later addition but the flywheel is a good old 4 bolt fixing to the crank just like the Minor. The register on the end of the crank is 2ins as opposed to the Minors 1.75ins. Perhaps co-incidentally the same size as the crank bearings. As a result of the large bore being needed it seems the bolt centres needed to be moved out 1/4 in.

Andy

[philthehill]

The 1500cc (Triumph engine) had 4 bolt holes and 1 locating dowel so if the fly wheel was from a 1500cc it would have 5 holes in it.
Attached is a diagram of the various clutches fitted to the 1098cc/1275cc & 1500cc MG Midget/Sprite.
Note:- There was no 1500cc Sprites only 1500cc Midgets.[frame][/frame]
Rear end of 1500cc crank. Note 4 bolt holes and 1 dowel.[frame][/frame]

[andypocock]

Looking at that Phil I'd say that I had a 1 and a 2

[philthehill]

Andy
All I can say is that if you can make it fit all well and good and it sound as if you have the will, skills and the tools to make a good job of it.
When I did my Ford 4 speed RS 2000 gearbox conversion it had not been done to a 1275cc at that time only to a 1098cc engine so there were no parts available to help me fit the box including the flywheel/centre plate/clutch cover and first motion shaft bearing in the rear of the crankshaft. All had to be done from first principles and a lot of trial fittings to get it all right.
The point being that it can be made to fit but you must be able to make it fit in a workman like manner.
Having a flywheel come loose is no walk in the park.
Any problems please come back to the forum.

[andypocock]

Thanks Phil. You help has been invaluable.

I can't see any problem in opening out the centre of the flywheel by 250thou. I'm happy to drill 4 new bolt holes between the existing ones. The pitch is different and the fact that BMC were drilling 5 or 6 or 7 holes suggests that there is enough metal there. The bolts will be wired.

I'll take some photos tomorrow. Let's hope they aren't too busy at the local engineering shop

Andy

[LUR759H]

sorry to change the subject lads but you guys seem to know what your talking about, i know impressions are not always factual... anyway can you advise me as to what i need to do to please the mot man a im tying to get my m trav back on the road and i have no ideas whats required.
And at the time of writing you were on line, where have you gone??

alan