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MG Midget and Sprite Technical - core to build new racing engine

I am thinking of buying a 1275 core to use to build a racing engine. A friend of mine has one that looks like a 73 or 74 (late year 1275).

I was thinking that I could take my time building the next engine and then when I blow up the old one I can make the swap.

R Harvey

Good plan Rebecca. Sound 1275 blocks, heads and cranks are getting scarce so start collecting. I'm sure Prop could give you some sound advice.
Mike Allen

If you are looking for a good core, make sure it is a "thick rail" block. The flange on the bottom is what I'm referring to. There are 2 distinct different type. Sometimes on ebay you'll see one come up advertised as such. The thin rail blocks tend to crack more when they are used for a race engine. I'll measure the rail on our engine today when I'm at the shop and get back to you.
Tim Michnay

Conversely I know of a few long stroke race engines which have survived a number of seasons built on the 'thin flange' blocks. 1275 engines are not as common as they once were and I'm not sure people can be so choosy as previously

I'd rather advise you to try to get an assembled engine as opposed to a box of bits that someone has collected together - in particular using things like odd con-rods or crank from a previously blown up engine is a recipe for disaster...

When you come to build use the best components you can afford - Build for reliability rather than outright power (unless you're sponsored by Microsoft)

... Oh and treat anything Prop writes about tuning A series engines with a healthy degree of scepticism... ;o)
James Bilsland

Wise words I feel James. :)
Bob Turbo Midget England

There are 4 specific Sprite/midget block castings. There are books with this stuff in.... and they have pictures!

The block will be scarcest component followed by the crank. Rods are less scarce and heads are ten a penny, at least in the UK.
Daniel Thirteen-Twelve

you can get choice of blocks if you know where to go, I currently have 1 thin-flange and two thick sitting in my garage.
David Smith

luckly we sill have plenty of blocks here in the USA... so sorcing one isnt a big deal

Id give "Old Gray Norm" On ebay a shout he always has several selling for pennys on the dollar, and he is vary honest with his opinions... If he says its a good problem free part... you can take it to the bank, like wise if he thinks there might be an issue.. he will certianly share his thoughts with you just for the asking.

And he also has some good race parts as well... thats who I got my rare EN40B crankshaft from


>>>>>I'm sure Prop could give you some sound advice<<<<<


The biggest mistake I made was UNDER-ESTAMATING the complexity of building a modified engine,,, The more extreme, the more BULL SH*T you have to overcome.

There is vary little in common of Building a race engine compared to building a stock modification can have serious effects 7 steps later, the real fun begins when the entire engine is just a complete modification, just one modification built on top of the next modification and the entire build is that way

The best example I can compare building a race engine to is.... like trying to figure out how to adapt ford engine parts onto a bare chevy engine block and heads, the cool adverts say it will fit, but they rarely do, or they seem to always need extra extensive thought and further modification in order to fit some other modified part

I really belive you can do it yourself... your other post have proven your more then capable... your just going to need exercise several things... patience, imagination/creativity, focas (that one I dont have), time, determination, and a good sence of humor ! those will see you thur... (well thats what I keep telling myself anyway.)

And having at least 2 Good machine shops close by is an absolute God send. Make good friends with those guys esp in the shop area, cause your gonna need them. BIG TIME!

A huge BIGGY I learned this year ... Focas on the MATH as much as you do bolting on parts... thats just freaken BIG, dont fluff thur this area or you will pay a sad price tag.

If the above dosnt sound at least 3x times more fun then getting nasty with your husband on a friday night ... Then save yourself the grief and find yourself an "A-series RACE engine builder", notice I didnt say just an engine builder... someone like Hap waltrip of acme race shop or Deb evans of pristess race engine in the UK.... She does come to the USA frequently

BTW... If you do the fredenzia aluminum flywheel with a rivergate datsun 5 speed, conversion and a hi torque starter all 3 toghather... Give me a hollar off board, and Ill forward you my notes on several options for making it all fit and work togather.... cause there is nothing text book about that open head wound senerio.... on this one I can save you around 2-3 months of total head scratching and continually saying ... "WTF NOW", and "ARE YOU FREAKEN KIDDING ME" !


Also, there are a good few different types of race engine. Do you want a drag engine, a rally set up, sprints and hill climbs or endurance track stuff? All will have slightly different set ups and will require different cams and set up.
If you want to use it for road use at all then that will affect what you do too. Although I would strongly advise against using anything capable of being described as a race engine for the road. I built a rally-esque spec engine for my old mini and whilst it was fun for a while, having it come on cam at 3,000 and rev out to 8,750 at only 115 mph and doing 8 mpg did wear thin. Having said that, the engine was built for revs and top end power and not drivability.

Oh, and although it might seem a PITA, make sure you dry build everything! I spent a couple of hours trying to figure out why the crank wouldn't spin, only to realise I had the centre cap in back to front. Time is cheap, but there's also no need to waste it!
S Overy

Hi Rebecca,
Everyone will have there own ideas and advice on this. some more than others. I personally would suggest building a nice 1380cc or if you can fund a 1430cc even better. they give great torque and will also rev with the right bits in. I would also stay with the SU carbs as they give a cleaner lift than the weber, especially in autocross os solo 2 conditions. i have competed for several years in Colorado in midgets of various specs, but now back home in ireland. our cars are serious over here. The current engine choice is 14xx in size as it gives low end but will also rev to 8500 rpm. fabulous for those times you need to blast away from a corner or indeed hold gear, between two corners.

good luck on your decision!
WDT Corry

Not sure again what Prop means, the basics of an engine are ALWAYS the same!

The engine differs only in CR, head mods, bore Crank stroking (wedging strapping ETC.) and most importantly by a long long way CAM.

This is really basic stuff and with a straightforward approach is simple to do.
Robert (Bob) Midget Turbo

Having built a few race engines I know exactly what Prop is talking about.

The more exotic you get the more issues you will have getting it all to work together and probably the shorter the life of the motor.

I've had some friends spend some pretty large bucks putting motorcycle pistons in Spridget motors, etc.

I had a supplier send me a stroked crank by mistake and that caused me all sorts of problems (and money) to figure out I had the wrong crank. I eventually figured it out and sent the crank back and had to redo the motor completely.

After that, I just build my motors with stock cranks and rods, an aluminum flywheel, an off-the-shelf performance head and a vintage race cam. I still ran at the front (though not at the very front), spent about a 1/4 the money as the guy at the very front, and had a motor that lasts about three years, rather than three weekends like some.

Honestly, some of the folks that are spending all that money on engines need to put some of it towards a race driving school...
David Littlefield

Why would you want to put Motorcycle pistons in an A Series engine?
Bob Turbo Midget England

In our area we have seen entire cars going to the crusher as State Enviro Groups are forcing many yards to rid themselves of potential hazards leaking into the soil. The price of scrap steel and iron in recent years didn't help as engine blocks have been stolen from salvage yards for the scrap value. If you have a source, and have room to store these parts it might be good to do so.


Larry C.
Larry C '69 Midget

"Why would you want to put Motorcycle pistons in an A Series engine?"

I certainly wouldn't. But if you are a commercial racecar builder with a client that has a bottomless checkbook and doesn't understand diddly about motors and you like to experiment on someone else's dime, maybe you would.
David Littlefield

The one that I found appears to be a first run engine that spun a bearing (never overhauled). bearings and bore are still standard.
I will find out more after further inspection. I think that the data plate says 12V it is 1973 or 1974.

R Harvey

I bought it.
R Harvey

Since you mentioned a spun bearing: If you find that the crank needs to be turned, be sure to find a shop that can do it properly with a true fillet. Or maybe look for a crank that does not need to be turned and use it.
Trevor Jessie

I know a good shop. I will consider both options though.
Still evaluating what I have. I will report on it and post some pics.
R Harvey

There is no substitute for cubic inches
THINK BIG -- and go fast
Cheers Willy

according to the rules that I am using (SVRA) I can bore it up to .040 over but I cannot change the stroke.
R Harvey

Get them to change the rules

Rebecca you have set off down a very slippery slope which can consume huge amounts of cash, depending on how far up the front you want to be. Your rules for Group 1 allow a bit more freedom than ours, but as always, the trick is in the interpretation of the rules.
The cheapest performance you will find is in:
A) Weight reduction (driver and car). Make sure when the car gets on the grid that it doesn't weigh one ounce more than the minimum.
B) Driver skill. Amongst our group "I need more horsepower" is code for "I wish I could drive better".

When your +.040" engine needs a rebore, send it to me. We are allowed .060" overbore.
Mike Allen

Here are pics (starting here):

I will post more later when I take it apart.


PS: Yes. I know what I am getting into but for some reason I have to do it anyway.

R Harvey


I've been through all this:-

I bought a '74 Midget about ten years ago and turned it into a vintage racer, then raced it for ten years.

I did every bit of it myself, including the body and paint by enrolling in a community college course.

Of course, I had a machine shop do the short block work and I bought an off-the-shelf performance head, but I assembled the car and the motor myself, as well.

I learned a hell of a lot over that time and I'd be glad to share it with you. My car was built to race in CVAR in Texas, which has much less liberal rules that SVRA, but I'm sure much of what I did would be applicable.

You might also consider joining the MG Vintage Racers. There are a number of vintage racing Spridget owners that are members that are also happy to share their experience. Jack Woerhle, the SVRA head of tech, is on the MGVR mailing list and he is also very helpful in making sure cars are built to the rules to avoid problems later.

Good luck! Building the car is the least of the fun! Contact me if you have any questions.

Attached is a picture of me racing at Road Atlanta at the Walter Mitty.

David Littlefield

This thread was discussed between 07/12/2010 and 14/12/2010

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