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MG Midget and Sprite Technical - Timing Question

As you can all see, I'm in the final stages now, but timing is confusing to me. I printed out the tuning 101 website that was posted years ago and will follow it methodically, however, when presented with timing info I get conflicting info. (see picture)

So...who to follow?

Chris


Chris Elkerton

Looks like you need 10 BTDC to me...

A
Anthony Cutler

try both, one will be obviously wrong
C L Carter

Do you have a Californian or non-Californian car?
James B

I'm in Canada, so I'm assuming a non.
Chris Elkerton

Both are correct.
The Haynes one you have highlighted is headed "static timing" whilst the Handbook one is dynamic, "at idle speed". Three up from the bottom entry on the Haynes list shewn also reads 2 deg ATDC at 800 rpm idle speed, with vacuum advance disconnected
Guy

Guy, Yeah...I read that, but not being US I assumed 4 up from the bottom was me which would be 10 BTDC. Or am I reading wrong?
Chris Elkerton

See what you mean. Its ambiguous isn't it? I took 4 up from the bottom to mean home (UK cars). Apart from which, I always understood the 1500 cars to be simply designated as a midget 1500, Not a MK III 1500! Looks like another Haynes error!
Guy

The 2 deg ATDC figure (static and dynamic according to the Haynes reference) is for a Californian car

Your car should be timed at 10 deg BTDC

JB
James B

thanks everyone for all the input!
Chris
Chris Elkerton

Chris,
as most will guess I'd say start with the figure in the Driver's Handbook - assuming you have the correct handbook for the car, last Canda car we had here chap had the handbook for a MGB :)

Guy,
the Midget 1500 was still a Mk3 - Haynes isn't always wrong :)
Nigel Atkins

Canada cars are usually the same as US Federal cars.
The figure changes by year for US Federal not Calif cars.
The "year" of your car may or may not be the year the car was built or spec'ed for.
There is something wrong with those listings, as it is impossible to have 10 static but 2 at idle. The mech advance cannot retard the spark. Some of these have vac retard, but the listing says "vac disconnected" as is normal.
The definitive answer is the sticker under the bonnet, either ON the bonnet or the slam panel.

If any of the emissions stuff has gone missing, all bets are off. Timing was retarded to lower NOx and improve idle predictability. Retarded timing slows the idle down, requiring more throttle, making mixture control more precise. They usually run better (and cooler) with more advance, but you have to watch for pinging = too much advance.

FRM
FR Millmore

Emissions system has been gone since Reagan was president. I'll go back to the "official book" and start there. Keep ya posted! :)

Chris
Chris Elkerton

ok. From the Robert Bentley "The Complete Official MG Midget 1500 1975 - 1978" Comprising the official "Driver's Handbook" and "Workshop Manual":

I think I have my answer. See pic.


Chris Elkerton

Chris-
Pay attention.
"They usually run better (and cooler) with more advance, but you have to watch for pinging = too much advance."
Given that Reagan is long gone, might as well take advantage of the gains possible. If you have the original low comp pistons, you will be unlikely to encounter any problems at 10BTDC. Advantages are better power, mileage, and cooler running.
(TR6 of the time, which is just 1 1/2 of your engine, actually had a thermostatic vacuum switch to advance the timing when it started to overheat from the retarded setup.)

If you have the POS Delco distributor, you might look into getting it checked and recurved. They were known for wear to the point of self destruction. The mech advance comes apart and machines the body in half! Sometime before that I reckon the advance curve is pretty screwy.

What are you doing/have you done to this engine?

FRM
FR Millmore

FRM,
Nothing done other than putting it back on the road after 18 years. Replaced all the gaskets. Set the tappets to proper specs. Want to set timing right and go putter about. The original distributor was the 45DE4 Opus that is long gone. Old MG guy in the city got me an old 25D that works great. Points are good.

The car only had 40k original miles when she went off the road (long story) so I wasn't interested in crazy mods. I want to buzz about the country roads on week-ends and keep her cool in the summer.

I'll give 10BTDC a shot and let everyone know the results!

Chris
Chris Elkerton

'old 25D' - you need to investigate the total advance of your dizzy - if it comes off something like an 850 Mini then you'll have something like 35 degrees advance... Meltdown territory... :(
James B

Chris-
As James said. Different distributor means all specs are irrelevant. Remove breaker plate, find the number stamped on the advance weights - it could be anything from about 3 to 21, depending on what it came from. That is distributor advance; multiple by two for crankshaft advance. That plus your static is total advance. Around 30deg is safe, more might be better but watch it. Since you have low comp pistons, you can likely go higher, maybe up to 35 total. Best bet is to get the distributor checked for curve, and find somebody who has actual info on this rather bizarre combination of parts. Jeff Schlemmer might have some idea, and can certainly set the distributor to whatever is decided.

FRM
FR Millmore

Chris:

An adjustable digital timing light can give you the info about mechanical (and vacuum) advance parameters of your particular distributor. A worthwhile investment if your budget isn't too tight. FWIW my aftermarket distributor provides 16 degrees advance on my (stock) 1500 according to my timing light. I have therefore run the car with static timing set anywhere between 10 and 16 BTDC, the sweet spot seems to be around 12-14 for my particular setup, for a total advance at revs of 28-30 BTDC. I never had pinking or overheating issues when total advance was 32 BTDC, it's just happier a bit lower.

Richard
Richard Reeves

see...this...THIS is why I love the internet! I swear I'd never have been able to rebuild this car without the web and this BBS!

James and FRM... Good info on the distributor. THANKS! Will check out this long week-end and report back. Setting up some Twin SUs from the UK as well, so...in for a penny in for a pound right?! lol

Richard...I think the suggestion on the timing light is bang on. At this point I can't think about budget or I'll rip my hair out.

Stay tuned (up)...

Chris Elkerton

once you've got things set up, run in, settled, shook down personally I'd suggest for improvement dumping the old dissy and points and putting in an all new fully electronic 1-2-3 dissy, programable one if you've got a really hot car

after safety items and a good battery a 1-2-3 would be at the top of my shopping list - only based on my personal experience and opinion of course - with a road only, year round use, non-track use car and non-mechanic
Nigel Atkins

Not too impressed with the 123 I saw. A mismatch between the cap and the body meant that the cap moved of its own volition changing the timing of a race engine between 28 deg advance and about 35 deg...

That sort of timing change can kill race engines fast - it was a brand new 123 too - the owner has resorted to sticking the cap on with silicone...
James B

some caps have been adapted so this might be the reason (of course I don't know as I haven't seen the cap you're refereing to so I could be totally wrong) should not be the case if it's brand new but . . .

cap lugs could have been changed from outys to inys (non-track terms)

race cars are a different beast to a road cars

the cap on mine is fine, the 123 makes my car go better

perhaps I'll be wrong and it makes my engine go bang in the future if so I'll recommend that they not be used

always more than one source of information, advice and opinion which is a good thing
Nigel Atkins

James-
If you can explain that, I'll fall off my chair.
The cap has nothing whatever to do with timing, unless it is so far out of phase that the spark jumps from the rotor to the wrong cylinder, which would be far more than 7 degrees.
Any distributor would make a correctly timed spark with no cap at all, notwithstanding the fact that the engine would not run.

FRM
FR Millmore

Actually FRM now you come to mention it that must be right - not my car and not my problem, but that's how it was put to me, and I hadn't spent any time thinking on it...

The owner assumed he had fixed the wandering spark problem by fixing the rotating cap - perhaps he hasn't... Anyway, I'm still not too impressed with an brand new electronic dizzy that has a loose cap and a wandering spark...
James B

do you know of anyone else that has a 123 dissy with a loose cap ?

mine's fine
Nigel Atkins

Nope, its the only car I have any immediate contact with that has one - maybe its an abberation, but I know the dizzy is new and it has had a couple of new caps on it...

As for myself, I like my old technology 1970's Lucas RITA hall effect dizzy - designed for F3 Ford BDA's - Never had a single ignition problem since I started using it in 1995... Tens of thousands of road miles and over 100 races since... ;o)
James B

James,
I done a list of 123 right angle cap alternatives (in the Archives now)
Nigel Atkins

Update: distributor is a 45D4 (which was for the UK 1500s according to the Bentley book) so it seems I'm back to the 10BTDC. There is nothing stamped on the back on the back of the breaker plate. Stay tuned...

C
Chris Elkerton

Numbers are not on the breaker plate. They are on the advance weights (with the two little springs attached).

FRM
FR Millmore

This thread was discussed between 14/05/2012 and 19/05/2012

MG Midget and Sprite Technical index

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