midget v marina

[les]

Reading the posts about the marina engine for sale had me wondering what the specific differences there are between these two. I know a couple, flywheel, filter. Can someone list them? I am contemplating starting to assemble my marine/ital lump but before I get in too deep, thought I'd weigh up whether to look for a midget engine instead. Knowing all the variations will enable me to decide if it's worth waiting. At the moment I can't imagine one being any better than the other!

[philthehill]

Les
In a nut shell the Marina has a different crankshaft and is of lesser quality than the Midget/Sprite crankshaft. The Marina con rods are lesser quality as well. The mounting of the flywheel is different on the Midget/Sprite 6 bolts and two dowels against the Marina 6 bolts and one dowel. The flywheel register is different between the Midget/Sprite and the Marina so you cannot put a Marina flywheel straight on a Midget/Sprite or vice versa.
Whilst the Marina crank and con-rods will be perfectly alright in a road car if you want to get the best out of a Marina engine ditch the Marina crank and con-rods and replace with Midget/Sprite crank and Midget/Sprite con-rods.
The Marina rear engine/gearbox mounting plate is also different but the Midget/Sprite back plate will bolt straight on.
The front engine plate is also different because the Marina engine mountings bolt onto the side of the block.
The bell housing locating dowel on the back of the engine is different on the Marina to the Midget/Sprite but easily overcome.
The Marian block to go for is the 'A' plus with the extra strengthening ribbing and it is the strongest of the 'A' series blocks.
I have a Marina 'A' plus block fitted with Midget crank and either Midget/Sprite or Cooper S' rods fitted in my Minor (the best combination you can get) but there again my engine is a real mix and match of components

[mike.perry]

The Midget is probably getting difficult to source but has the advantage of being virtually a straight swap and the 1098/1275 gear boxes are visually identical

[philthehill]

There are still plenty of 1275cc Midget/Sprite engines out there but at a price. A good bare 1275cc Midget/Sprite engine will set you back £700 +; at the other end of the condition scale £350 +.
Les
If you fit the Marina block make sure that the engine mounting bolt holes in the block are blind. Some mounting bolt holes are right through the block wall and can leak oil if not sealed with a bolt/plug.

[bmcecosse]

Even a Spridget crank will set you back several hundered £s - if you can find one..... and the rods are not cheap either (although I have a brand new set if anyone wants them...)! For up to 90 even 100 bhp the Marina crank/rods will be fine - but don't rev above say 7000......

[philthehill]

The last Midget/Sprite crankshaft I purchased and with a 0.010" regrind cost me £400 and it took me 6 months to find it but complete engines are available but of course cost more.

[les]

Thanks for all the replies and Phil for a comprehensive breakdown. Appears to be quality of components as the main consideration but the difficulty, and to some extent the cost of a midget bottom end will probably see me using the Marina parts. The block fortunately is the A+ type, with a standard bore, so I'm happy there. The pistons are low compression and because of this I had visions of fitting a supercharger that has been with me for a number of years. However, from this advise, unless I make the crank change that may not be a good idea! One more thing, have both blocks got the same number of head studs?

[bmcecosse]

Yes - same head studs, although you can add two more - but Rover didn't bother to do that when they fitted the Turbo! It still had just the 9 studs. The s/charger is a great idea! Because it works at all revs you won't be running at high revs, so the loads on crank and rods are not excessive. I would modify the main bearing caps to take the later 'MG Metro Turbo' shells - possibly your A+ block has that type already? There is no oil groove in the shell in the cap.... And also fit the Turbo oil pump, and possibly use the Turbo head with the sodium cooled exhaust valves.

[philthehill]

Les
Your are right - the main difference is the quality of the reciprocating parts of the engine. The Midget?Sprite parts are of much better quality. The later the 'A' series engine the worse the specification of the metal became. BL increased the sizes of the crank and con rods and incorporated rolled fillets (not always successful) on the crank webs to partly make up for the lesser quality materials used in the later 'A' series.
The 9 stud AFG 940 head fitted to my engine has been converted to 11 studs. At both ends of the head are pillars of metal that can be bored through. The Marina block will also accept the extra two studs. Use a cylinder head gasket with the 11 stud holes for positioning the drilling.
My head also has an extra water transfer port between the block and head to aid cooling at the back of the head and around No 4 exhaust valve.
If you use Vandervell main bearings Pt No: VPM91120 and which I use in my 1380cc Marina blocked engine they do have the oil grove in both the bearing in the cap and the bearing in the block.
My Marina wksp manual does not differentiate between the 'A' and 'A' Plus 1275cc engines but the picture showing the main bearing caps show the caps fitted with bearing with integral oil grove. Unfortunately I cannot make out whether the block is 'A' or 'A' plus.

[bmcecosse]

It's a simple '2 minute' job to modify the caps to take the 'plain' shells. MG/Rover first introduced this idea with the Turbo engine, and it worked so well that they quickly rolled it out over all subsequent 1275 Metro engines. I don't know if the A+ has them - although it would be logical. There is a special 'Turbo' gasket which is quite expensive - I would take a chance on a good copper /copper gasket and clamp it down at 50 ftlbf using the later studs and the flanged nuts. I think I would add the extra studs too - although as I said earlier - MG didn't bother on the Turbo engine. What type of s/charger do you have ??

[les]

Thanks again for the valuable info, not sure how far I am going with all the mods mentioned but you can be sure they are being noted. Roy the supercharger is a Shorrocks that had been previously fitted to a Mini.

[philthehill]

Les
When I worked in the BMC garage we looked after a 970cc Cooper 's' fitted with a Shorrocks supercharger and didn't that fly

bmc
In your post regarding the turbo crank shells you seemed to wander off the main bearings/caps/shells and though not directly mentioned appear to refer to the con rod bearings/shells. Can you clarify as to whether the turbo shells you refer to have or have not a oil groove in the Main bearing shells and an oil groove in the con rod bearings/shells.
My Vandervell crank shaft bearings/shells only have a oil groove in the main bearing/shells.
My Midget/Sprite crank is cross drilled to alleviate any oil starvation at the crank pin journals.

Less.
The Midget/Sprite 1275cc main crankshaft journals are the same diameter as the Marina 1275cc 'A' and 'A'' plus at 2.0005" to 2.0010" dia
The Midget/Sprite 1275cc crank pin journal is 1.6254" to 1.6259" against the Marina at 1.7497" to 1.7505".
The larger Marina 1275cc 'A' and 'A' plus crank pin journal was an effort to try and make up for the lesser quality material that the crank was made from.

[bmcecosse]

I didn't think I had 'wandered'...but these days...... The stronger MAINS shells only have a groove in the block half - the 'cap' half is plain with no groove. These cap shells are secured in the cap with a tang in the centre - not at the edge. So all it needs is a little location for the tang to be filed in the mains caps. MGRover seemed to think it was a good idea! The con-rod shells are unchanged - plain with oil entry hole only.

[philthehill]

bmc
Thanks for the explanation. I just could not follow your thread - not getting any younger here either
Reference the stronger cylinder head studs and flanged head nuts - they are already fitted to the 'A' and 'A' plus engine as standard and can be identified by either a dimple (large/small) on the top, a 'Y' stamped on the top or a tapered top. The flanged nuts are fitted as standard also.

[philthehill]

There is a gold seal Midget/Sprite on 'e' bay item No: 171341102964 for £450. Looks to be good for the price.
I would have it myself but have too many Midget/Sprite 1275cc engine spares already.

[bmcecosse]

Shorrocks if in good order is worth a lot of money. I would use it - with your low comp pistons - and possibly a general clean up of the head around the valves to drop the CR even more. You can of course adjust the amount of boost by varying the drive pulley size. It will make a really good engine ! I'm wildly jealous!!

[les]

Well I hope to make it happen but it will be a while yet, although half the fun is planning these things. I certainly won't be doing any more work that involves vehicles in bits all over the place and cutting out rusty metal, so small cleaner projects are now order of the day! ps: Clutch job went ok.