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MG Midget and Sprite Technical - 1500 engine and tuning guide

After a number of threads referring to 1500 engines and the odd reference to a lack of info on this site; I have at last found a reference I have read up in the past that has given me insight and help.

This further refers to: Triumph Tune Spitfire guru TERRY HURRELL

Please remember I am not an expert, simply an enthusiastic amateur, I am still working the day job. I use my midget as a get by day car. So anything I put on here is from my own limited personal experience.

Just trying to be helpful and build up a greater depth of 1500 engine stuff.
Dave Squire (1500)

am I missing the point, this is more about as the page title says 'Building a Reliable Spitfire Engine for High Performance' track use rather than road or 'fast road' use
Nigel Atkins

yes you are missing the point...
David Smith

I pinched this from here,,844853,page=1 but it's good advice!

My intention here is not to get into the minutiae of how to do everything, just to give a recipe which will achieve what you want

100 streetable horsepower is not a difficult thing with your 1500 spitfire. I am assuming that you have, or have access to the knowledge to put a standard engine together, as your new thing will not be much different to standard.

The 1500 in European spec came with 9:1 compression, the US spec with 7.5, the torque figures being 81, and 69 ft lb respectively.
If you could maintain your 81 ft lb at 6500rpm, you will make 100 hp. 6500rpm is too much for reliability with a 1500 engine, so Torque must be increased. If you can achieve 90 ft lb, then your 100 hp will happen at 5800 rpm, which is OK.

Essentially, you will build a mk3, standard spec engine, with a few subtle improvements.

At least 9:1 compression, is required, so use standard euro pistons, a standard mk 3 camshaft (25 65), or slightly bigger (30 70) is all that is required. 9.5 is better, and is just fine on 98 octane fuel. The crank should be checked and reground if out of spec. The factory balance is pretty good, and hardening or balancing can often create more problems than it solves at this state of tune. Buy the bearings before you get the crank ground, measure them, then, using clearances in the manual, specify the finished size and finish to the crank grinder. If he will not accept this, find someone who will.

I am not familiar with the US low comp head, it may be the same as the euro head. If it is, the valve sizes and ports do not need looking at, but a small amount of material should be removed from the chamber wall where the inlet valve is masked. This just requires a ball end grinder to give a curved wall allowing a better flow at low lift around the inlet valve. I have not explained this particularly well, but it is really easy to do at home, and quite self explanatory with a picture or two. Others can advise you if obtaining a euro head is a better start than the US one. Do not port/polish the head, just clean up any dags.

1.25 in SUs will not support 100 hp, so a 1.5 in setup adapted to a mk3 manifold is better, as they will support about 120 hp. Use a #4 needle and heavy spring as a start (probably 1 too rich). Finish setup on a dyno and if the SUs and particularly the linkages are rebuilt, they will hold their tune for a long time. Your existing exhaust is probably fine. The best distributor is a Mk3, rebuilt to standard spec, and use points not electronic at this stage. Points are reliable, can be fixed on the side of the road, and just require checking every so often to keep them in spec.

The most important part of this build is to be thorough. The motor should be stripped and all castings hot tanked. It is worth while looking into the oil and coolant galleries and smoothing any casting flash, removing sharp edges, etc. Many engines do not perform as they should because of hot spots caused by scale, flash etc resulting in localised steam traps, hot spots, and detonation. The water pump you use should have a cast impeller, the tin ones do not pump water, they just make milk shakes.

Invest in a set of micrometers, dial gauges, calipers, and learn how to use them, ensuring the cam, crank assemblies are all smooth, round and square where they should be, the rocker arm, bearing clearances and ring gaps are correct, the bore finish, valve seat concentricity etc.
There are several items on these engines that are set by shim, measure and set everything as described. If for instance, the distributor end float is incorrect, a few thou can cost 15 HP, and cause inconsistent idle and rough running.

Follow the Triumph manuals, be thorough, and pay attention to all these little details, and the results you achieve will far exceed any number of bolt ons. Your aim is a low speed engine, 6000rpm max, with 100 ft ib of torque, and will comfortably exceed 100 HP, and pull seamlessly from 1300-5500 and will not leak oil. The bottom end and oiling is more than adequate for this application.
a highfield

what David you're agreeing with unsolicited threads that don't ask a question

as long as they're something to do with racing ;)

I see the general point but not that particular link Dave put up, I can see with the last post

but it matters not if I follow it, or not, just nice to see David converted to proactive information :)
Nigel Atkins

The thing with these pieces of info as posted by AH is that it gives background to the engine, its history, limitations and also capabilities. (Which contrary to the impressions given on this site can be considerable). It allows understanding and insight to a piece of engineering that is in the minority in threads on this site yet has been installed to a lot of midgets.

I am not anti A series in fact I loved them back in the 70's and 80's but I don't have one now. They are tolerant bricks that are easy to work on and keep going through thick and thin at high revs. They generally, in road going form, top out rather than break. They are from a time when engines were for reliability first and British engineering was not about design and modernisms. I applaud that but have a 1500 in my midget.

If anyone has more 1500 posts that would be useful pointers for us amateurs please carry on.

Dave Squire (1500)

The Triumph 1500 engine is the worst bit of engineering I have ever come across - to the point that I now point blank refuse to rebuild them.

I certainly would not consider increasing the power of the engine without addressing the poor crankshaft location - two half thrust bearings are just insufficient and prone to wear and dropping out of place, leaving the crank free to destroy itself and the block.
Chris at Octarine Services

This thread was discussed between 18/06/2013 and 24/06/2013

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