Benefits of a Midget crankshaft?

[millerman]

I have a Midget 1275cc engine in pieces ready to re-build to replace a Marina engine in my Trav.

Philthehill staed in another thread that:

The 1275cc Marina A+ crankshaft is not the best of crankshafts and whilst reliable for normal duty - any tuning of the engine will reduce the reliability of the crankshaft. To overcome the deficiencies in the Marina crankshaft you can with a straight swop fit the 1275cc Midget crankshaft/flywheel/clutch assy and rear engine plate.
I have a 1275cc Marina A+ block fitted with a 1275cc MG Midget crankshaft fitted in my Minor so can speak from experience regarding the use of the 1275cc Marina A+ engine in a Minor.

So, what has been done to the Midget crank to make it more reliable and, in case I come across another, what are the identification marks/part numbers?

Many thanks

[bmcecosse]

I don't see any particular problem with the Marina crankshaft - it uses the larger (1.75") big ends and con rods, and there are various different conrods in that size - some heavier than others. But I have never heard of a problem with the rods provided good quality bolts and nuts are used... - and the larger big-end means there is more 'overlap' with the mains in theory giving a stronger crankshaft - although heavier. The Midget crank only has 1 5/8" big ends - and uses 'Cooper S' type rods - although they are made of slightly inferior material and are NOT the genuine (AEG 177/8) S rods. AEG 625 is the Midget conrod part number, I have a brand new/unused set ..... Again - never heard of a problem... The crank is not EN40B and so the bearings are unfortunately not nitrided - although they 'may' be tuftrided?? Perhaps Phil will know about that? So overall there is absolutely nothing wrong with the Marina crank (except perhaps the greater whirling mass) that I can see!

[les]

Yes I was a bit puzzled by that remark, Incidentally I thought the Marina became an Ital with the introduction of the A+ engine not sure if the crank differed though. Perhaps late Marinas had A+ engines as well.

[philthehill]

Les
The term Marina (1971-1980) or Ital (1980 - 1984) is/can be used as a generic term as basically only the body of the Marina changed when it become an Ital. There were a few minor mechanical changes but nothing major.
The Midget/Sprite crankshaft is made of a much better better material than the Marina/Ital crank.
Early 1275cc Sprites and MG Midgets had nitride cranks.
Later cranks were made of EN16T and tufrided. The last of the Midget/Sprite crankshafts (1974) were EN16T and non heat treated.
Whether the crankshaft has been heat treated or not it is recommended that Midget/Sprite crankshafts should not be re-ground by more than 0.010" without having the heat treatment applied/re-applied.
Whilst the Marina/Ital crankshaft had bigger diameter crankpins than the 1275cc Midget/Sprite the increase in size was more to do with the use of an inferior crankshaft material i.e. it was cheaper to increase the crankpin size to 1 3/4" than to continue using EN16T/EN40B in the manufacture of crankshafts for 1275cc engines. So by using the Midget/Sprite crank shaft even with the smaller 1 5/8" dia crankpins the better material and additional heat treatment gives you a much more reliable crankshaft. The flywheel is located by two dowels and not one as on the Marina/Ital engine.
The part No of the 1275cc Midget crankshaft is 8G2741. To find a 1275cc Midget/Sprite crankshaft In good condition on its own is now quite rare but 1275cc MG/Sprite engine assemblies are available for around £400 -£700 in a running condition which is what I had to do to get a spare 1275cc crankshaft.
To improve reliability some Marina/Ital cranks (and other 1275cc non Midget/Sprite cranks) had a Rolled Fillet radii in the corner between the bearing journal and the crank web, there is a possibility of the crankshaft failing by breaking through the fillet radii. When BMC/BL put the rolled fillet radii into production many of the cranks did not have the rolled fillet radii correctly applied and consequently the situation was made worse until production techniques had been improved.
To repeat my post quoted above - the Marina/Ital crankshaft for normal use is adequate; but for use in a tuned Marina/Ital A+ 1275cc engine it is better to use a Midget/Sprite 1275cc crankshaft. You can then use Cooper 'S' rods

[bmcecosse]

Totally agree - although not aware of any EN40B Midget cranks....unless they were maybe a Special Tuning part?

[millerman]

Thanks for very comprehensive reply.

Other than measure the crank journals, one thou ovality, I've not washed it off to see part numbers. It will be a while before I do so but I will endeavour to post my findings

[philthehill]

BL Special Tuning listed the 1275cc Midget/Sprite competition crankshaft under Pt No: C-AHT326 and it is shown as Nitrited but it does not say what material it is made from.
I have a quotation from Farndon Engineering dated 15 Jan 2002 for the manufacture of a MG Midget crankshaft fully nitrited made from a EN40B billet at a cost of £1000 plus the usual.
The quotation also includes for the supply of qty 4 MG Midget con rods fully machined, shot peened made from EN24V at a cost of £145 with ARP bolts plus the usual
I did not take up the quotation as I got Oselli to fully rework my MG Midget crankshaft (at not much less including the purchase of S/H crankshaft) and Manx Racing fully reworked my MG Midget (possibly 'S') con rods.
It should be noted that nothing comes cheap when modifying even the humble 'A' Series if you want to get serious power out of it.

Over the years BMC/BL gradually down graded the specification of metals used in their engines for example con rods:-
Cooper 'S' ................EN24V
MG Midget/Sprite...... EN21
1300GT/Innocenti..... EN19
1300......................Originally EN19 but latterly EN16
'A' plus...................EN15

All in a downward trend

[bmcecosse]

Only an EN40B crank can be nitrided.... So it does look like the nitrided Midget crank was a Special Tuning option.

[millerman]

Crank washed off ready for installation:
[frame][/frame]

Any observations on part numbers?

I have got new big ends and mains bearing shells to be fitted!

Cheers all

[philthehill]

The crankshaft looks very good.
The most important number on the crank is the EN16T.
BMC put various numbers on crankshafts and other parts over the years and it would not necessarily be the part number it was listed or sold under.
Personally I would fit a new first motion shaft bearing (Pt No: AHU1026A (MOSS) late 12CC/12CE & 12V engines) in the end of the crankshaft before refitting.
Phil

[millerman]

Phil, thanks for reply and advice.

I am using a Ford type 9 gearbox so do you know if the part number you quoted will give a bearing the correct size for that gearbox?. I know "Google is my friend" but a second opinion is always very useful

[bmcecosse]

Unless the engine is being modified to high output - I would SELL that crank - it's worth GOOD money !! Do you have matching conrods for that crank ? The Mini lads use the equivalent standard 1275 crank (EN16T etc) and rods for well over 100 bhp with complete reliability.

[philthehill]

The part number quoted above is for use in a standard 1275cc engine/gearbox arrangement.
My 1275cc Midget/Ford RS200/Quaife SC/CR gearbox arrangement has a needle roller bearing fitted.
Firstly the rear of the crankshaft is counter bored and a machined insert fitted into which the roller needle bearing is fitted.
I would suggest that the/a gearbox conversion kit supplier should be able to supply whatever you need.
I will try and post a photo of the rear of my spare 1275cc Midget crankshaft.
Phil

[millerman]

Phil

I look forward to seeing the photo
Be careful Roy might persuade you to sell

[philthehill]

Pictures of my spare Oselli fully re-worked 1275cc Midget/Sprite crankshaft.
The crankshaft has been cross drilled, wedged, balanced both statically and dynamically and finally tufrided.
To enable the Ford RS2000 4 speed gearbox to be fitted the rear of the crankshaft had to counter bored and a insert fitted and the needle roller bearing fitted inside that.
I do not know if there is any difference between the 1st motion shaft of a Ford RS2000 gearbox and Type 9 1st motion shaft.
This conversion was one of the first if not the first where a Ford gearbox was fitted to a 1275cc Midget/Sprite engine so it was all suck it and see and it took many a trial assembly to get it right. The adapter bell housing used was from CS Autoclassics and which I subsequently improved the working relationship between the gearbox and the adapter bell housing with extra bolts and locating dowels. This upgrade was done as the engine/clutch/bell housing and gearbox were to be subjected to high rev standing starts and I did not want it to all fall to pieces.
Anyway you can see from the photos the insert into the rear of the crankshaft and the needle bearing.
The Marina/Ital has a needle bearing in the rear of the crankshaft and it may be that the front of the type 9 1st motion shaft will fit into the Marina/Ital needle bearing. No doubt someone on here will tell us.[frame][/frame]

[philthehill]

Photo of the rear insert and needle bearing.[frame][/frame]

[philthehill]

End on photo of insert and needle bearing.[frame][/frame]

[philthehill]

Another photo of insert and needle bearing.[frame][/frame]

[philthehill]

Another photo of the crankshaft.[frame][/frame]

[philthehill]

If anyone persuaded me to sell one of my three Oselli modified crankshafts they would have to have very deep pockets as the crankshaft shown cost me a fortune to find, purchase and for Oselli to carry out the modifications.