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 Post subject: Lucas 29d springs
PostPosted: Mon Jun 05, 2023 7:45 pm 
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848cc
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Location: Brisbane Northside
Does anyone have the part numbers for the springs in a 29d for a 1968 998 matic.

I know this is a bad idea, it isn't me wanting to know. I am asking for someone who can't be convinced that what was specified in 1968 is not good in 2023. It has previously melted a piston which I say is because of a worn out 29d and original spec carb (both poorly maintained and tuned)

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 Post subject: Re: Lucas 29d springs
PostPosted: Tue Jun 06, 2023 3:30 pm 
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Location: near Baulkham Hills, NSW
29D is an orphan now, was made by Lucas Australia, who sadly are no more.
Even Bosch made rotors and caps for them are NLA now. Can still get points, which are same as a 25D.
I've just refurbished a 29D as a spare it's what I have found recently.
Good luck finding any springs here. There is a distributor restoration place in UK which sells Lucas springs I will find a link.

https://www.distributordoctor.com/

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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. :mrgreen:


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 Post subject: Re: Lucas 29d springs
PostPosted: Tue Jun 06, 2023 4:20 pm 
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drmini in aust wrote:
29D is an orphan now, was made by Lucas Australia, who sadly are no more.
Even Bosch made rotors and caps for them are NLA now. Can still get points, which are same as a 25D.
I've just refurbished a 29D as a spare it's what I have found recently.
Good luck finding any springs here. There is a distributor restoration place in UK which sells Lucas springs I will find a link.

https://www.distributordoctor.com/


That is where they are trying to source springs, the problem is that distributor doctor doesn't know what a 29d is so needs the part numbers.

Out of interest I did recently search for 29d caps using at least the Bosch and Beru part numbers, nothing came up. The Bosch catalogues that I have seem to give the wrong cross reference for the Repco numbering so I can't search for NOS that way.

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 Post subject: Re: Lucas 29d springs
PostPosted: Tue Jun 06, 2023 5:00 pm 
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1098cc
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Give the place who took over mini kingdom online a call about the caps John had a few on the shelf before he sold it

Other than that there like hens teeth or rocking horse crap to find new

There was a bloke getting around the swap meets in NSW with them but haven't seen him at a few ive been to lately may be passed away too


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 Post subject: Re: Lucas 29d springs
PostPosted: Tue Jun 06, 2023 5:37 pm 
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My 70 Mini.Matic had a 45D in it, I'm pretty sure it was original. These 99H prefix 998 motors and auto transmissions were imported assembled.

Why not send the dizzy to UK and get DD to restore it? They can select whatever springs to get the proper advance curve. (Or was proper back then for super grade leaded fuel).

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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. :mrgreen:


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 Post subject: Re: Lucas 29d springs
PostPosted: Tue Jun 06, 2023 5:51 pm 
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There’s also plenty of places locally that can recurve it to any advance curve you need.

They can also test your existing one and tell you how inappropriate it is now that the springs are all stretched and the fuel is different

You can map the advance curve yourself easily enough with a dial back timing light too

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 Post subject: Re: Lucas 29d springs
PostPosted: Tue Jun 06, 2023 6:40 pm 
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848cc
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Hi, if the springs are stretched, most likely the whole distributor is very worn and not worth messing with.(bush, weights, shaft) Apart from the distributor doctor in Uk, it must be almost impossible to find quality points with a fibre rubbing block (NOT PLASTIC LIKE MOST), let alone a condensor /capacitor .that actually works.
that auto as standard is a low compression engine, and in my own road cooper S which is Rover auto, I run 20 degrees base timing, total 32 degrees with one of my own distributors. It goes very well, mind you the mixtures have been set accurately with a gas analyser.
I doubt if stretched springs caused your meltdown, as they will tolerate reasonable timing as you cant load up the engine a lot. I suspect its is way too lean, or way too much total timing., or both, and if using ULP98, flat aged fuel.
I use a 43D special , as 23d/25d. have very poor cam shape, and get early points bounce, and 29d suffer badly with weights wear, and lack of parts.
I do have people tell me you cant run 20 deg base timing. Unfortunately they do not understand ignition systems. This also helps the auto torque convertor multiplication factor, and it increases vacuum at idle, which in turn gives better carby response off idle.
Cheers Lindsay Siebler

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1970 Colt 1100F SS restored
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1948 Allard M coupe Olds 215 v8 project
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 Post subject: Re: Lucas 29d springs
PostPosted: Tue Jun 06, 2023 7:51 pm 
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848cc
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Joined: Thu Apr 07, 2016 10:07 pm
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The 998cc Mini Matic in Australia has a high compression engine running at 9.0:1. The H designation at the end of the engine number prefix indicates "High" compression. The centrifugal and vacuum advance characteristics are completely different to the 998cc manual tranmission power unit. The details can be found in my Engineering Series Deluxe book, but I have prepared a simplified version of the data so shown in the graph below. I am sorry I cannot tell you the part numbers of the individual springs, but using the advance data (which has come from a Lucas drawing), you should be able to use a distributor tester to find out how close or far you are with the present distributor and then you can make some meaningful decision about whether to keep it, repair it or replace it. regards, Tony


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 Post subject: Re: Lucas 29d springs
PostPosted: Tue Jun 06, 2023 9:34 pm 
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848cc
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Hi, thanks to Tony for that graph, as it made me realise I was talking 1275, as I had not read the original post clearly.Sorry.
From the graph I see base timing under 2 deg, 16 deg around 1700 rpm, and total mechanical at 25 deg.at 3200- 4000 rpm, at lower revs than manual. We would still set base idle at around 18 deg, . The vacuum adv I dont quite understand, but under full load total is still 25, which is very low.IMHO. I presume the vacuum advance at light throttle was meant to give some peformance with careful driving .If someone advanced it up to get better higher revs performance, then low end timing would be well advanced , contributing to possibility of piston failure.
In the old days we would steal the 12g295 head off 998 autos, and I do not remember flat top pistons, so it must have been a bit of a battle to get 9.0:1 comp ratio.
ULP burns differently to leaded fuel.
A 998 auto would probably be driven a bit harder these days to keep up with traffic, and that dissy would not help.

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1959 Austin A40 Farina fun car
1965 Mk1 Cooper S restored
1970 Colt 1100F SS restored
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


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 Post subject: Re: Lucas 29d springs
PostPosted: Wed Jun 07, 2023 7:48 am 
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848cc
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Location: Brisbane Northside
Unfortunately there is no point commenting, the owner (my sister) doesn't want to listen. I have tried again and many times before. I had always said the advance was wrong and was able to prove it. It was only improved by her installing the shortest springs from a few 29ds. That was only done after doing things club members had suggested such as installing an aluminium radiator and removing the thermostat with no improvement. It was a similar story with worn advance plates and faulty ignition coils proven with my engine analyser.

I really need to stop assisting and just work on my own minis. If anyone has the part numbers that will be the only thing that gets listened to unfortunately.

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 Post subject: Re: Lucas 29d springs
PostPosted: Wed Jun 07, 2023 11:00 am 
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848cc
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While the actual circumstances of the case are what they are, the discussion is interesting enough a topic in general. The Mini-Matic head has less height than the normal 998cc head by about 30-40 thou but both auto and manual engines use the same pistons. This decrease in head height increases the compression ratio to 9:1 over standard. There is a graph in my BMC Engineering Companion book which shows changes in compression ratio as a function of head height for those interested in more detail.
The part number 12G295 referred to by Lindsay I believe is for a high compression Morris Cooper 998 engine which also has 9:1 compression ratio but is a different part to Mini-Matic and this head appears to have the same head height as standard –achieving 9:1 by piston shape (cavity volume 4.09cc compared to 5.69cc standard).
The issue of petrol composition is interesting and it would be reasonable to assume that the combustion characteristics of unleaded fuel is different to that of leaded fuel of past years with the same octane rating. Since Lindsay reports better performance with an increase in ignition timing, the inference is that ULP burns at a slower rate than leaded fuel, and this is consistent with higher compression ratios of modern cars (often 10:1) since flame velocity is greater at higher pressure (hence the need for vacuum advance at part throttle where combustion pressures are lower compared to WOT). Maximum mean effective pressure has to still occur at the same crank angle (everything else being equal) so more advance is needed for a slower burning fuel to achieve this.
The Mini-Matic has a rather tall final drive ratio which is offset by the characteristics of the torque converter. However, it is obvious from the HS4 carburetter and the higher compression ratio that BMC intended to increase the power output of the Mini Matic to minimise loss of performance through the transmission.


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 Post subject: Re: Lucas 29d springs
PostPosted: Wed Jun 07, 2023 11:18 am 
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848cc
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I am still very interested myself in details on ignition timing for the autos although my own ones are both A+

I don't yet worry too much about my 1986 998 as it still has the original distributor is good condition. I would though like to know what the timing should really be, I assume 32 degrees max. I have been running 98 in it however if it is unnecessary I would like to change that. It would have been sold in Japan as being unleaded capable but I don't know what they actually changed.

I also have a 1991 1275 which was an spi. Once I fix its transmission it will be running a programmable ignition system (CB performance black box) as I was unable to source a good distributor for it so it is running a 998 Ducellier. To get it running to find the transmission was bad I was using a basic curve that I specified. Using the guess-works engine lookup this one specifically says 95RON so I assume there should be no problem running 95.

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 Post subject: Re: Lucas 29d springs
PostPosted: Wed Jun 07, 2023 11:39 am 
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Also the original engine the topic is about (the 1968 matic) has had the block skimmed significantly and has dished pistons. I don't know the specs myself and they have possibly been lost by now, it was done in the process of fixing a crack between two cylinders. It is actually a different engine to the one which melted a piston but it has the same distributor in the same mini.

It was having heat issues at highways speeds and a little bit in traffic.

The timing seemed to be at full advance by 2500rpm (engine) before changing the springs. I haven't checked it since as I am "not allowed" to rev it to 4000rpm etc in order to test it properly so I try to not be involved in the timing. Obviously you can't just change springs and not test the advance at all rpms.

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 Post subject: Re: Lucas 29d springs
PostPosted: Wed Jun 07, 2023 5:52 pm 
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The 12G295 head was used on the 1098 automatic Morris 1100. The 998 mini matic got the standard 998 head as eightfifty says. I had one and confirm the pistons were dished and the head was decked.

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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. :mrgreen:


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 Post subject: Re: Lucas 29d springs
PostPosted: Wed Jun 07, 2023 6:07 pm 
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848cc
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The Mini-matic pistons are the same as manual transmission pistons with a dish of volume 5.69cc. THe drawings show cylinder head height (i.e. thickness from top face to bottom face) 1/32 smaller for the Mini-matic head taken off the bottom which is equivalent to 31 thou. I wouldn't like to go beyond that so who knows what the compression ratio was on that engine you mention that was repaired. I can have a look for A+ specs, but I doubt if I would have anything for an automatic since this was never made here.


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