Distributor curves.

[RobThomas]

Alta specify the 40251 dissy with the suffix 'E' or beyond. I found several of the earlier 40056 and a 40251D but none of the ideal spec ones. Looking through the list of distributor curves I made a list of curve figures and then plotted them on a piece of graph paper.

In short, the 40251 seems to have about 2 degrees less advance over the 40056 throughout the entire curve apart from the first 800rpm. The 40819E (Cooper S 23D4) has a similar curve, within 1 degree, to the 40056 until about 2000 rpm when it continues advancing more rapidly, although stopping at 15 degrees instead of 18 (30 crank degrees instead of 36) so if you start the timing at a few degrees btdc it will sit constantly advanced all the way through. The 40056D from the 803 is an almost identical curve shape to the 40251, stopping at 18(36) degrees again, but has the added advantage of vac advance to help with fuel economy. Having plotted all this out I set the 40056D at TDC. It runs beautifully on an EK needle. I now will play with advancing the ignition progressively to take advantage of the better fuel available now over the 1949 spec 'Pool' petrol that had an octane rating in the 80's.

I hope this info will be of some use to others playing about with the MM engine. Lambda 14.5 idle, 12.8-13.3 pretty much all the way through the acceleration.

Happy to have anyone add amendments wherever necessary!

[mike.perry]

Any A Series distributor will fit the side valve engine which gives the option of connecting the vacuum advance to see if that has any effect on the performance.
The USHM3 head has graduations marked around the distributor shaft. These are at 5 deg. intervals.
If a water pump is fitted you cannot see the crankshaft timing marks, if the engine is out of the car it is easier to set the dizzy before dropping th engine in.

[tortron]

I'm currently using the mini cooper one from accuspark (no vac)
however I came across this article a while ago about tuning your distributor. So you get the correct advance for your engine.
It is a very good read
http://www.firstfives.org/faq/timing/ti ... ngines.PDF

As for not being able to see the timing marks. you can now get usb/plu into your phone endoscopes for very cheap. They have quite a few uses on cars

[RobThomas]

The thing that surprised me was the advance needed at low rpm. Because the car has such a massive stroke you need to fire the ignition early so that the flame can chase the rapid piston down the bores. The max advance is quite high, too. Do you know what static and max advance you've used?

The 18(36) degrees that you get from setting TDC static with the standard MM dissy seems rather conservative, nowadays.

I bought one of those endoscope cameras last week. Good little tool.

PS. Glad to see you back on here!

[tortron]

What I have been doing recently is setting the timing at high idle, about 2000rpm, this lets a bit of advance in already.
you are right with needing it expecially on a sidevalve due to the flow the fuel mixture takes. Fortunately the SMM head is about as advanced as sidevalve heads go so theres no need to run twin plugs.

I haven't had a chance to work out what the replacement distributor is actually doing (lots of stories about crazy advance from them, but perhaps that's not so bad on our engines, I don't think I could get it to knock if I tried)

I plan on working it out and adjusting it as per the link I posted, but not until iv got a reground camshaft in

[RobThomas]

I got some graph paper and plotted several advance curves I downloaded from the Starchak website. It made sense that the longer stroke engines such as the 1098 had more mechanical advance built in to chase the piston whereas the 1275 has less. The (now very untidy) chart made it so much easier to comprehend.

Have you got any details on the camshaft regrind? I'd be interested to know what you've worked out. Another Aquaplane Ford profile?

Cheers

Rob

[Nickol]

I would assume that my 1947 Austin 8 with its 803cc side valve engine is very similar to the early Morris type MM. I have also had a Play with the Timing on the distributer lately as I was not convinced that the full power was being obtained.

As mentioned above, to get smooth idling, the dist. is advanced right up, almost as far as it will physically go and even beyond the scale. This allows for a significant increase in power Output - I can climb some of the hills here in third instead of second. I should mention here that the dist. is not original - but do not ask me from whence it came!

Does anyone think though that advancing the timing to his extent is a desirebale thing to do, i.e cause any Long term damages?

[smithskids]

As long as it doesn't pink under load or run on after it is switched off it should be alright.