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MG Midget and Sprite Technical - My engine specs so how to set up

Alan Anstead has very kindly put my engine back together and along with Gary Puxty they have done some proper measurements. So after four years, I have an accurate CR figure.

Head is stamped 22cc which is correct (ish) a mean figure of 22.5 across the four chambers.

Piston dish is 8.4, gasket 4, ring land 0.78, piston clearance 0.21.

All 'adds up' to CR of 10.26:1.

So my question is on my 1330, with a peter may fast road head, slightly played around with hif44 with K&N, Maniflow manifold an RC40 box. 123 dizzy and NGK BPR7ES plugs.

I really need to know best set up.
Timing?
123 dizzy setting(it's an early one)?
Plug gaps?
Tappet gaps?
And anything else which you think may be useful.
With runs to Le Mans and the Netherlands, I would prefer to sit on the side of reliability rather than squeezing every last hp out of it.

many thanks in advance

Gary
G Lazarus

Rolling road is the only way to be sure its right. Aldon is probably best down your way.
john payne

if the cam and rocker gear are standard then use standard tappet clearance.
Plug gap 30 thou.
David Smith

thought Aldon are in Birmingham? I recommend Novatech in Slough, they do Rae Davis' cars...
David Smith

Sorry, forgot to add. Standard rocker but 276 cam.
G Lazarus

Gary....if you come to my event to make a weekend of it...I could dyno you on the Thursday 22nd May.

Peter
Peter Burgess Tuning

Sorry Peter, I'm so tempted but I will be at work.
G Lazarus

Set mix correctly as per SU manual

Check valve clearances - Personally I have found them to be more critical than first thought. 16 thou both I/E for me also with 276 cam.

Timing - Yes rolling road for it to be absolutely spot on, but for me, also with 123 fitted, fine tuning by rotating the dizzy CCW/CW and a bit of trial and error up a nearby hill works just fine - 7/16 spanner for the clamp is all you need. I have a slighly modded head and from memory it is on setting 5 - in the 30 deg max advance curves I think, but if your max is different then clearly your setting will be different.

Plugs - as yours - curiously one went duff almost the moment it went in. Took ages to find!

Carb - a wise choice, check it thoroughly for any leaks and ensure the dreaded timing case PCV - if fitted, and I recommend it - is operating correctly
Mark O

Gary

yes its best to get it on a RR

Suggest 16 thou for the tappets to start with. I use that setting and its fine. Timing, try 7 degrees btdc static to get you going. I use this and am running about the same CR. I don't have a 123 so can't comment on the dynamic setting

I use Slark's rolling road as its got one of their heads but they are in Amesbury.....

Bob
Bob Beaumont

Don't forget the old fashioned road test. For years and years (on mechanical systems) I set ignition timing by static light then roadtest, advance, roadtest, advance until pinks on roadtest then retard a tad or till performance suffers then advance a tad. For carbs I used a similar approach for mixture - adjust between too lean and too rich and road test several times. Dynos are wonderful but one's sensory perception is also pretty darn good.
Nick Nakorn

what HP are you expecting. . .I have modded my engine and have no idea what to expect, cooper s head, high lift roller rockers, cant remember the cam, twin 1.25 S.U. Aldon Yellow Dizzy, performance exhaust and K & N filters. . . reckon it should be 65BHP but like you I need to set it up properly. Sounds like a sewing machine at idle !!
P Bentley

I should add its had a rebore, but again so long ago I cant remember the given size, but it was a 1275. . .must learn to write things down, or rebuild cars more quickly ! :)
P Bentley

Gary...

+.060 = 1330

It sounds almost like my engine... aside from the whole running vs non running argument LOL

I think your safe on all the above....

I just have 2 comments

1. Noisy valves are happy valves (trevor jesse quote), its better to be to loose then to tight....I think .015 is a good call to start with

On the dissy timing... 2 options,

1. have a pro recurve the dissy to fit the engine

2. Time the dissy from the other side of the rpm scale.... 4200 to 4500 rpm at 28 to 32 degrees

Youtube has some really good videos on how to tune in.a.dissy ... your looking for general concept not so much specific A series 1275 engines

Id also set the carb up a bit richer for tunning it all in, it makes the valves a bit cooler

Also... ive found, its easier to tune an engine.by going broad spec. And narrowing the range of the spec over several attempts.... similar to torquing a head...

1st attempt getting running,.2nd attempt get everything in a general ball park, 3rd attempt fine tune it in detail

Valves, ignition, then carbs...in that order.

Prop

Prop
Prop and the Blackhole Midget

Gary
Your spec sounds almost identical to mine (although I have a P & P MG Metro head (not sure what yours is) and I have hi-lift rockers. I also think my CR is higher than yours (around 11.2 to 1).

I set my 123 dizzy to the most conservative advance curve on the max 30 degree family of curves. Plug gaps 25 thou although I'm not convinced this makes a difference, High power coil. Tappets at 16 thou. HIF44 needle is BDL.

The car has been on a rolling road twice (at Hi Tech in the West Mids). I set up the timing using the 123 standard procedure and the mixture by 'feel'. The guy on the rolling road set the timing by adjusting the dizzy slightly 'this way and that' until it was producing the best power and torque. He did not seem keen to change the advance curve so it remains as I said above. He is an expert in mini and A series so I trust him to get the best result. The car went really well at a Silverstone track day recently so it seems to work well.

I am reluctant to quote a bhp figure since there was a 20 bhp difference between the fist rolling road and the second with the only difference being the new RR equipment being used the second time (the spec of the car was the same!).

Not sure if this helps but it seems to me you are pretty much there with your set up but the final tweaks do require a RR as others have said!

Chris
Chris Hasluck

This thread was discussed between 16/04/2014 and 17/04/2014

MG Midget and Sprite Technical index

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