Distributor advance and retard

[RogerRust]

I have a ditributor in better condition than the one I have just taken off my 1971 1098 Traveller. The one that was fitted has a 13 degree advance cam. and the new one a a 16 degree cam.
I can't find any reference in my manual to the centrifugal advance for a 1098.

1) Does anyone have the correct figure.
2) I run on real leaded 4 star so will the extra 3 degrees make any difference.
3) With ref to 1 an 2 is it worth disturbing the little springs to change the cam?

Roger

[Alec]

Hello Roger,

to keep the advance the same, swop the rotor assembly to your new distributor. (The 16 degree will actually give you 32 degrees advance at the engine, i.e. 6 degrees extra)
I think that you will need to be careful to keep the rotor arm slot to the same relationship to the offset drive dog or your timing will be 180 degrees out. (I'm sure someone will correct me if that is wrong)


Alec

[bmcecosse]

Just use the new dizzy as is - and if there is any pinking noise, retard the static timing slightly. It's a common mod to INCREASE the centrifugal advance by cutting a wee bit off the advance stop on the bob-weight - you are lucky - it's been done for you!
Check the vacuum advance is working before you use the dizzy - suck on the little pipe - you should be able to see the base plate move and then relax - as you gasp for breath.

[Alec]

Hello Bmce,

the trouble with over advance at higher revs is that you cannot hear it and it is detrimental to the engine. 6 degees is a lot of extra advance.
For a standard engine, stick to the standard settings.

Alec

[RogerRust]

thanks folks.
In the end I played safe and changed over the rotors. Its running sweetly now.

[bmcecosse]

But BMC could never settle on any 'standard' setting for the centrifugal advance - hence there is a range of different units out there. Pinking will be noticeable under heavy load if it's there. The cent advance runs out at about 3000 engine revs - so going at that speed (45/50 mph) in top gear up a slight hill - foot to the boards and if it pinks then too much advance, so set it back a little.

[Axolotl]

According to the workshop manual I have (reproduction), there were five types of distributor fitted to the 1098cc engine. Three for HC engines, and two for LC engines. Max. advance for type 40849B (HC) is 30 - 34 degrees at 6,400 rpm (max vacuum advance 14 degrees). For type 41124 and 41148 (HC) it is listed as 22 - 26 degrees at 5,500 rpm (vacuum 6 degrees), and for 40899B and 41025 (LC) it is 32 - 36 degrees at 5,500 (vacuum 20 degrees).

So, as you say, BMC themselves couldn't make up their minds. It looks to me as though if you are the boy racer type that's going to use 6,400 revs very often, you should try to get the first type... Can't work out in my head what that equates to in road speed. I expect someone can work it out.

PS, if the plate doesn't move when I suck, does that mean it is knackered, or that I am?

[Onne]

But those 1098 aren't specificly Minor are they? I seem to recall other models that used the 1098. 6400rpm seems like quite a lot for the long stroke 1098, with only three main bearings

Onne

[Axolotl]

I agree, but the manual is specifically Morris Minor. Series MM, II and 1000, British Leyland, 1970.

[Stig]

So how do you tell what you've actually got? I assume the number (40849B, 41124 etc.) is stamped on the side, but what if it's a recon unit and someone's been swapping bits around? Are the cam weights stamped?

And does anyone know what a 1275 should have? OK I'll come clean, it's actually the engine in my Sprite I'm thinking of.

[Alec]

Hello Stig,

the weights are the same, the only internal differences are the rotor and the springs, the rotor is stamped with the degree of advance but springs are unmarked. Also it is possible that someone has shortened or lenthened the 'beak' on the rotor thus altering the maximum advance. Vacuum units are also stamped with a reference number as they too vary. If you tend to drive hard the vacuum unit will have little effect at all.

Alec

[Stig]

Thanks for that, I'll have to have a good peer inside sometime.

If you tend to drive hard the vacuum unit will have little effect at all.

To be honest the exhaust is so loud I tend not to drive it that hard any more as it's embarrassing - loud as you zoom past is one thing, but loud as you barely keep up is another.
I suspect it may be the vacuum not doing enough as it's "popping" a lot more when I lift off.

The Minor engine is far more civilised, but it's been good sports car weather recently.

[lowedb]

you should be able to see the base plate move and then relax - as you gasp for breath.

Or get a mouth full of nasty stuff when the diapraghm has gone, like happened in my mates avenger!