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MG Midget and Sprite Technical - 1275 V 1500 engine

I am sure that this question had been asked before but i have a couple of reasons for lifting the engine and gearbox out over the winter and am considering various options whilst it is out one of these would be should i consider replacing the engine with the 1275 is this seen by the learned body as a good move and what are the hidden implications, accepting that i would also replace the gearbox and possibly prop.



ps thanks to all with the cluch judder issue.
df mccabe

a really good and well maintained Triumph 1500 is always going to be better than an A series 1275

a question like that could cause a riot on here!!!
Nick Sayle

Nick. "Not arf". Really good and well maintained, you say. They don't like and can't take the abuse that an A series can though can they? Thrust washers spring to mind.
Just playing "Devil's advocate" you understand.

b higginson

Having had both, and both tuned to much the same sort of degree I would say that the 1500 certainly had more low rev torque, but somehow never seemed to be as lively in response. Both had lightened flywheels and balanced cranks but the 1275 just seems to have a "snappier" response. It just feels a happier car.
Guy Weller


With the old iron engine out, ou have the perfect opportunity to replace it with the one designed for the midget in the late 80s; the K Series. Somone's done a conversion for 130, so this has to be the cheap option.

Anthony Cutler

LOL Anthony - you shouldn't make ALL midgets in k-series - otherwise there will be none left ...!

Both have their own advantages and disadvantages, so, to be honest, it really depends on what you really want out of your car. Perhaps the question you should be asking is what you want out of your midget - and then decide which would suit you better.

If you decide on the 1275 though - one other option is to replace the 1500 in this car and sell it - and buy a 1275 :)

no-one ever mentions what a real heavyweight engine (and box) the 1500 is. Sure that cast iron bellhousing can be replaced along with the cast iron water pump, water pump housing, alternator bracket, etc. But that not be cheap. Does all that alleged extra 1500 engine torque do anything after it's accelerated all that extra weight?
Daniel Thirteen-Twelve

I like it when I say, "it's not the bored out Moggy Minor engine, it's a TRIUMPH"
Nick Sayle

1275 vs 1500

Ummm, the 1500! ... Its a nasty godless heathen, dog rapist, child hating, old people killer, girlyman panty wearing "TRIUMPH", Hello!!!!

Just ask Arie... its the devils dill doe


MG to the end! Not my opinion btw, thats from Jesus Christ himself!

Prop....Hollow be thy vizard
Prop least my glorious 1500 Triumph is RUNNING!!
Nick Sayle


My 1500's running too, I was on vacation this past week & enjoyed driving it everyday!

Here's an interesting thread from another forum:,1456030

The debate goes on...

Dave :)
Dave Rhine ('78 1500)

Dave, you did see my thought on that thread.

"Why not slip this little beauty in instead?

Aside from it's anvil-like weight (which does nothing for handling), the single biggest bugaboo in creating a high-output Triumph 1500 engine is its weak connecting rods. They don't like high engine speeds, and that's the principle reason that there are so few custom camshafts for this engine. However, custom headwork from an expert such as Peter Burgess can help power output a lot.

On the other hand, the 1275cc A Series engine can be tuned to a fare-thee-well, a plethora of proven power-enhancing parts being available from a large number of sources. The only limit is your bank account and your determination.
Stephen Strange

"Aside from it's anvil-like weight (which does nothing for handling),"

Just like the A Series then...

"the single biggest bugaboo in creating a high-output Triumph 1500 engine is its weak connecting rods. They don't like high engine speeds, and that's the principle reason that there are so few custom camshafts for this engine."

Absolute rubbish, the rods are good for outputs of 120bhp, especially if you use early TR5 rods. At that sort of power output it isn't really a Street Motor anymore anyway because it would be a PITA to drive (as indeed would an A Series). The rod weakness is actually in the big end bolt which can be replaced with an ARP item or a Ford Cosworth item.

The MAJOR "bugaboos" are:

1.) A heavy crankshaft that saps a lot of power to accelerate it.

2.) Poorly supported big ends (bearings too narrow), although this CAN be cured if you are in the know.

3.) Crankshaft flex at higher rpm starts to become a problem leading to oil film breakdown, especially at the centre main resulting in a con rod (usually number 3 making a bid for freedom at high speed through the side of the crankcase. Again this is curable if you know what you are doing. The flex is the result of having a heavy crank in an inferior steel.

4.) Detonation in tuned motors as a result of the recessed head gasket design.

5.) Poor piston skirt design (slotted skirts).

As usual people jive talk about the Triumph 4-pot when they don't really know what they are talking about.

Oh and there are plenty of good cam profiles around for the motor if you know where to look.
Deborah Evans

Hi Deborah

Your expertise on the Triumph engine is clear.

So the rods aren't weak if you replace them with TR5 items; and the heavy crank flexes and this can lead to rod failure; plus the b/e's are narrow and this can lead to over-stressing. Finally, the crank washers are also liable to fail when worn.

All these weaknesses can be improved by people in the know, as you say.

But it would seem that the Aseries had its faults (and there were some!) ironed out in competion in the 60s.

I think the arguement by those of us with limited experience is that the Aseries is more robust in standard form. It's therefore good for tuning to 1.5+ times more power with only breathing upgrades (manifolds, head, cam, carb), not structural improvements.

Hence it's a better engine for the average DIY.

In answer to the original question... AIUI the swap from 1500 to 1275 is relatively easy; the other way round is more difficult (but there are those here who've done the swap and may comment with more authority).

Anthony Cutler

It was bound to create a "discussion" but the fact is that Douglas didn't ask about the tuning capabilities of either motor - just if the switch was do-able and what the implications would be. I took that to mean could the switch be made and how would the driving experience differ on the road - rather than which engine could be best tuned for the track.
Guy Weller

Aside from my earlier comment made above in jest.

if you do convert from a 1275 to a 1500, Id hope you take a lesson from BMC and upgrade the structure of the car to resemble that of the 1500 car, for the reason of strength and struture


as ever it's horses-for-courses.

My 12CC engine was fitted in 1967 and is still in the car. Much like the gearbox and axle and seats and door cards etc etc...

I guess that's why I get [some may say deserved to be!] "tailgated" [see other thread] but all I want is a quiet little drive down the The Fish
David Cox

Having owned both in standard tune, I'd say the 1500 was more powerful and the 1275 felt sportier.
Contempory road tests (Motor) gave the following info.

Weight 702 kg
0-60 14,1
max 94

Weight 780 kg
0-60 12,3
max 101

If you remove the massive weight of the 1500 rubber bumpers, a 1500 engined car should be much quicker still and handle much more like a 1275.

Strangely, my 1500 also proved more reliable than the 1275 but it was also newer and in better condition.

I think that we shoulf value both vehicles.
s baker

A couple of questions for Debs expertise... :o)

I understand that you can use MGB shells to provide a stronger main bearing and do the "teardrop" oil flow mod to help lubrication but is there a stronger/lighter steel crank available at all?

I've also had a conversation with a local tuner that has used VW Polo/Golf pistons in an overbored 1500 (1560cc) to great effect. He used to race Spits a while back and reckons this was a favourite mod. Do you know any more about this?

To comment on the thread - I think a 1500 is just as fun and sporty an engine as a 1275 (if you ditch the bumpers!). Sure the 1275 is a little more free running but if you love piling on the torque pulling out of corners a 1500 will have the edge and will produce more top end power than a 1275 too. To my mind if you have a 1500 car with a decent engine and want to do some simple tweeks stick with the 1500. If you want a faster/sportier car you won't get much change swapping to an A series and may make it worse. If you want an easy and worthwhile performance engine/gbox swap try a K series ;o)
Bob T


It is possible to use MGB BIG END bearings on the Triumph 1500 crank with the requisite grind (the Mains aren't the problem, especially if you use Tri-Metal ones). These are wider than the stock Triumph bearings and give better support for the B/Es. However they do require a certain amount of 'fettling' to make them fit the Triumph rods and the crank fillet radii DO need to be checked!

I do this on all the 1500s I build because, not only are wider bearings a good thing, using MGB ones gives you a greater range of options for sourcing Tri-Metal bearings.

Tear-dropping the crank oil feeds is a good idea on a tuned motor. For higher revving motors it is possible to cross drill the crank, thus preventing high rpm oil starvation (especially to the B/Es) owing to centripetal force stopping oil flow into the crank oilways.

I have heard of using VW pistons but unfortunately I don't have the details of such things as deck to gudgeon pin heights and whether the pistons need decking / can be decked.

There is also a Ford piston as can be used (on around a 45 thou overbore). ;)

As far as uprated cranks go, Farndon Engineering certainly did a forged EN40b one (essential for racing but not so in a fast road motor). However it was uber expensive at around 2-3000 GBP! Personally if I was racing on a Triumph 4-pot I'd use the earler 'small crank' 1296cc unit and overbore it since this unit will always produce more bhp than the 1500 and is much more reliable (as a race motor).
Deborah Evans

If you want an A-series engined midget buy one
If you want an 1500 midget buy one
If you want a K-series fit one

But do not throw a A-series engine in a 1500 or vice versa.
That is just wrong
A more fitting midget is available buy that.
It is like fitting rubberbumpers to a chrome bumper car or vice versa
Onno Könemann

Hi Deborah

>>For higher revving motors it is possible to cross drill the crank, thus preventing high rpm oil starvation (especially to the B/Es) owing to centripetal force stopping oil flow into the crank oilways.

Surely there would be 'centrifugal' force pulling the oil along the throw of the crank?

Anthony Cutler

centrifugal and centripetal forces are different.

read this
Nick Sayle

I was always taught in Physics that there was no such thing as 'Centrifugal Force'.

So called 'Centrifugal Force' is in fact not a force at all, but a reaction to Centripetal Force.
Deborah Evans

being strange i googled centripedal to see if it was centripetal to the power of a 100, but it isn't, shame.
B Richards

Thank you Deborah for stepping in for the 1500! Truly a breath of fresh air for the 1500 crowd.

Pics...for your enjoyment.

Ron Koenig


Ron Koenig

and another one running.

Ron Koenig

RON!!! that engine in porn!!!
Nick Sayle


I see you've got the anchor chain attachment on the front of the engine still!.

Joking, but I'm more of an A series fan. Nice work, hopefully the engine bay is as tidy to do it justice. My experience with the A series is the main components are relatively light compared to other iron block engines I've played with but a mate and I moved my 1420cc A series into the shed the other weekend and it felt like a lump even with the 2 of us moving it. It was the full engine with backplate, flywheel, clutch, and alternator fitted, no starter.

Bit of a difference to a Rover K series, years ago I went round the production line and they had the main components there. I could pick up the bare block at arms length with one arm, no liners fitted IIRC. The K I have here is complete and easy to move single handed.

Seeing your photos reminded me how nice it is to have a simple engine electrical system that you can wire up for testing with a handful of wires.
David Billington

"Thank you Deborah for stepping in for the 1500! Truly a breath of fresh air for the 1500 crowd."

YW. I've been working with these engines off and on since 1983 so I guess I know them pretty well!

Ooops! have i given my age away there? lol

Nice, tidy looking engine there Ron!

Is that a single 40 or a single 45? may i ask why the single Weber and not twins? oh and whose manifold is that?
Deborah Evans

Thank You!

That is a single 45mm, as I believe it would provide better low-end power than twin 40's. The manifold I'm not sure, I picked it up second-hand. Custom linkage, a cross between used Stromberg and aluminum bar stock bent and bolted in place.

The engine has a mild 270 grind cam, bored 40 over, it has a silicone valve cover gasket, and a Janspeed 4-2-1 exhaust manifold. Other than that stock. The engine will be going into my one of two 76 midgets, this one I've been saving parts for and working on since 2003.

Deb, I've been carefully following your posts about 1500's, and I will implement several worthwhile modifications for road reliability ( including oil cooler and mating the 4-speed to a J-type overdrive and 3.7 diff. for better cruising )

Ron Koenig


My Scottish phys master would blow his top if anyone mentioned centrifugal or centripetal force - it's the 'force required for circular motion'.

So the oil is being forced down the crank throws with pressure from the pump. However, when the crank is rotating v quickly, the oil in the throws is spun out to the big-end, since there is no force to keep it in circular motion.

Hence oil is sucked from the main bearings and spun out of the big-ends. At v high revs, the oil flow into the big-ends can exceed the flow into the mains, which are starved (since oil is sucked straight along the groove and out down the crank throw, instead of onto the shell journal and being squeezed out side-ways); the combination of air and oil sucked into the main and then b/e's causes a breakdown in lubrication.

So oil flow down the crank throws isn't stopped, it tends to be increased with high rpm.

Cross-drilling the b/e journals reduces the crank radius seen by the oil column, and so puts off the above effect to higher rpm.

Anthony Cutler

dear all,

i will be very careful which car of worms i open next time thanks to all for the cracking comments and i am happy to say that i will no longer consider the switch but will look for ways of improving the power output, starting with the very basics.

But to cover this i will start a new thread and would love all comments


df mccabe

First, let me say that I don't wish to start a long-running arguement. You pointed out that the engine suffers from "Poorly supported big ends (bearings too narrow)". You also said that "the rods are good for outputs of 120bhp, especially if you use early TR5 rods." True, but I was talking about the Original Equipment connecting rods. Certainly machining the crankshaft to lighten it and the big end bearings of a B Series engine are great ideas. I'm sure that almost any engine can be improved to the point that it could be a reliable race engine, if one is willing to spend the money for the modifications necessary to do so. However, I have to stand with Anthony Cutler's statement "the A Series is more robust in standard form." My point was that the A Series engine is a simpler and more straightforward tuning propostion with a wider range of parts variety and availability for the home builder. Of course, if a race-winning engine is what's needed, the owner can always turn to a professional tuner like you to overcome whatever design weaknesses the standard engine may have.
Stephen Strange

Also not wanting to court controversy..
But I think the true comparison would be between the 1275 A series and the 1300 triumph lump..
I know the later was never fitted to a midget, but I think in this form the triumph engine was at its apex of development. The drive for more power by going to a 1500 pushing some of the components over the edge..
I know certainly amongst spitfire owners the early narrow journal 1300 is the engine of choice (if you can find one!).
Surely the 8 port design of the head stands for something?
My own experience of the 1500 (in a spit) was also a good one,, twin webers, extractor exhaust and 80 hp at the wheels. Even managed to keep the thrust washers in place!
However I have yet to trial the 1275 in my midget, so I wait to be impressed..
(can't wait as it happens!)

T Dafforn

This thread was discussed between 06/06/2010 and 12/06/2010

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