Hi, recently I was told about a newly built 1275 that was about to be dynoed and the tuner noted it was misfiring. Inspection noted a brand new distributor had been fitted , at around 12 degrees base timing, but total timing at 4000rpm was over 50 degrees. An inspection then noted it most likely had a melted piston.
This would have been caused by whats really known as abnormal combustion., where the spark or heat of combustion is trying to force the piston down well before its got to the top, and as it is still going up, the gas that is in there is being compressed much more than normal, and also gets super hot. Voila , blown head gasket , melted piston, broken rings, seized piston, softening of alloy head..... many of these disasters can occur.
Often people think its pinking, where you may hear a tinny rattle under light load caused by too much ignition timing. That can be a cause.
The cause is usually multiple things
Too high a compression ratio for the fuel octane rating available, or the one chosen because it was cheaper.
Lean or excessively rich fuel mixtures
A poor cooling system or running excessively hot
Often the major part of of the problem is ignition timing, not the base or idle amount, but the grand mechanical total , often checked at 3500rpm, but some distributors still advance to 8000rpm.
Generally speaking an A series (mini) engine likes a max between 28 - 32 degrees . Less is more efficient, more is not generally desirable.
So that total of 50 meant 18 degrees of crankshaft rotation earlier before top dead centre the plug fired. If it got the mixture burning then that gas got super hot and softened the alloy to the point it failed. It may also have had other factors.
The point of this conversation is when tuning the car, check the grand total, thats when the damage is done, not at idle, or light load.
And I can assure you there are distributors available that have too much total, and need to be modified
Also you may be able to check your dissy by removing the rotor button, fitting a 360 degree marked wheel and levering cam forward to measure its angular movement.
Cheers Lindsay Siebler

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1967 EX works rally mini restoration virtually complete OBL45F
1965 Mk1 Cooper S
1970 Colt 1100F SS
2014 Mitsubishi Imiev fully electric daily driver
1948 Allard M coupe Olds 215 v8 project
1971 Twin cam Escort ex Uk championship winning rally car project

Thanks for your comments about over-advanced timing.

Will this method work to check that advance is within safe limits:
-when the flywheel is off the crankshaft, calculate and mark where 32 degrees is, based on the distance around the flywheel using the distance between the factory marks;
-once the motor is running satisfactorily, using a strobe light, rev the motor to around 3,500 rpm and watch to see if the 32 degree mark comes into view.

The above method was recommended by a friend who used to assemble production motor cycles at a dealer and this was one of the factory tests, when bikes used distributors.

The problem is many of the new dizzys have around a 20° advance plate in them, this is dizzy degrees. This is 40 crankshaft degrees because dizzy runs at 1/2 speed.
If you stick one in a motor and set it to 32° btdc at full advance, its static timing is 8° atdc. Won't hardly idle, no torque, fouling plugs, etc.
And if you set static timing to 5 or 10° advance you get lomin's scenario above.

They need the advance stop lengthened, it's a pity the makers have NFI what works.

I've played with two.
For those playing along at home, I found welding the stop to limit it to 4mm travel works well.
Giving around 9° dizzy advance.
With its standard springs full advance was then reached at 3500 rpm..

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Run distributor on a test machine before installation???

I remember doing this with a new distributor about 30 years ago only to find that the results were nothing liker the specs provided.

Easy to fix at this stage.

Cheers, Ian

Hi Bill, yes that absolutely will work and a good idea. As I have got older I find immense difficulty reading the timing mark on the flywheel using a mirror, so while doing the flywheel, put a mark on the front pulley where you can see it, and another at 30 degrees. Make them different colours or easy to pick TDC. I make an engine pointer out of a gearbox lock tab, put a point on it, bend a right angle and use a timing cover bolt.
This problem is not so bad for experienced people, but a lot of people are having their first go at tuning, and need our help,
BMC would test and check every part for quality and meeting specification, but virtually every product you buy now DOES NOT HAVE TO MEET A QUALITY STANDARD.
If you are fitting new parts, check that it works correctly, assume nothing.
Cheers Lindsay Siebler

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1967 EX works rally mini restoration virtually complete OBL45F
1965 Mk1 Cooper S
1970 Colt 1100F SS
2014 Mitsubishi Imiev fully electric daily driver
1948 Allard M coupe Olds 215 v8 project
1971 Twin cam Escort ex Uk championship winning rally car project

I feel like the two values dizzy and crankshaft were confused in setup or measurement.
12+50 = 72,
6+25=31 degrees. Egzackery half.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Anyone wanting their Distributor set up properly with correct built in total advance and correct Curve you are welcome to contact me via PM. I have all the required gear and have been setting up mini distributors for road and competition use for over 25 years. Can do std points type distributors and Electronic Units
Dave

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A blast from the past!

Keep in mind also that there are sub-standard caps, leads etc out there..AND rotor arms!

http://www.distributordoctor.com/rotor_arms.html

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"Show me the Mini!"

what is the process to figure out the best advance curve for a given motor?

from reading this thread I suspect I'm running a bit too much advance..

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did I tell you that I won a trophy?

Hi Simon, a start to your answer would be. What is your total timing at 2000, 2500, 3000, 3500, 4000, 6000rpm. Still 1275 ? supercharged, weber, su ? Cheers Lindsay Siebler

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1967 EX works rally mini restoration virtually complete OBL45F
1965 Mk1 Cooper S
1970 Colt 1100F SS
2014 Mitsubishi Imiev fully electric daily driver
1948 Allard M coupe Olds 215 v8 project
1971 Twin cam Escort ex Uk championship winning rally car project

not sure I want it in public Lindsay! it's pretty ugly... I think I made this map when I took the blower off, I think did a basic setting and then I just added advance, it ran OK so left it. Going by what you've said above, 39.3° at 2700 RPM would be too much and way too early!

I built this engine to run the supercharger but I took it off a few years ago so now it's just running a HIF44, 1275 + 0.072" = 1340, and about 9.4:1 compression. I usually put 98 RON in it, but it runs fine on 91 too. It's overdue for a rebuild... blower isn't going back on but I'll go to .094" pistons and 10:1 ish compression

the vertical axis on this is load, 100 is atmospheric pressure, below that is vacuum, so the top line is all mechanical advance (in distributor terms) with vacuum pulling it towards the bottom line

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did I tell you that I won a trophy?

Hi, I agree, its fairly high. I am surprised you don't get pinking, esp low down. Sometimes higher up is not heard, but it is getting hot in the combustion chamber and eventually softening the alloy pistons or head gasket. I would definitely remove some timing when you are under load. and it should go better. You should not really need more than 32 / 34 under heavy load. Maybe your low compression ratio has saved you. cheers Lindsay Siebler

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1967 EX works rally mini restoration virtually complete OBL45F
1965 Mk1 Cooper S
1970 Colt 1100F SS
2014 Mitsubishi Imiev fully electric daily driver
1948 Allard M coupe Olds 215 v8 project
1971 Twin cam Escort ex Uk championship winning rally car project

okie dokie - I'll change it, at what RPM would you expect it to be reaching that 32-ish degrees?

looking at examples like http://www.csi-ignition.nl/bestanden/mini_tuned_curves.pdf they ramp up and hit their maximum at 5000-ish, is that about right?

how's this? (current is the blue line, new is the orange)

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did I tell you that I won a trophy?

Hi Simon, there are many variables as you realise , and I dont know enough about your set up to be precise, but the yellow line is far safer. Cheers Lindsay . I had not seen those csi curve pics before. That would be confusing to most people Certainly easier to get a proper professional to set your curve.

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1967 EX works rally mini restoration virtually complete OBL45F
1965 Mk1 Cooper S
1970 Colt 1100F SS
2014 Mitsubishi Imiev fully electric daily driver
1948 Allard M coupe Olds 215 v8 project
1971 Twin cam Escort ex Uk championship winning rally car project

thanks Lindsay, much appreciated - I'll put that yellow curve into the ECU and see what it's like. There's a fella in our local car club who has a dyno and is good with my type of ECU, I'll try to get some dyno time before and after the next rebuild

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did I tell you that I won a trophy?