[Mgs] MGA 180 out Distributor Mystery

Max Heim mvheim at sonic.net
Mon Oct 22 18:54:30 MDT 2012

It's the vacuum advance position. The limits to rotation are the starter,
the heater valve, and of course how much slack you have in the vacuum hose.
With the gear 180 degrees out, the vac advance knob will be in an awkward
position, and you may not be able to dial in all the advance you want
because the pot is hitting something.

I struggled with this for some time before finally sorting it out. There was
a reason for the factory orientation.


Max Heim
'66 MGB GHN3L76149
If you're near Menlo Park, CA,
it's the primer red one with chrome wires

on 10/22/12 4:40 PM, Clayton Kirkwood at crk at godblessthe.us wrote:

> Correct me if I am wrong please, but it seems the only reason to set the
> distributor up "right" with the rotor pointing to the 1st cylinder (1
> oclock) is so that everybody does it the same way and nobody gets confused
> like this. If the distributor is 180 degrees out, one only need change the
> wires around. In fact, you could technically put the distributor in in any
> orientation and as long as you get cyl 1 tdc on the compression stroke and
> turn the distributor body to line up the rotor with the cyl 1 ignition wire
> you would be ok. Of course, you may have problems with the vacuum advance
> alignment but that is a different story. I think it basically comes down to
> everybody agreeing to one convention like driving on the left side of the
> road is wrong:>)
> Clayton
> -----Original Message-----
> From: mgs-bounces at autox.team.net [mailto:mgs-bounces at autox.team.net] On
> Behalf Of PaulHunt73
> Sent: Sunday, October 21, 2012 3:20 AM
> To: Robert J. Guinness; MG List
> Subject: Re: [Mgs] MGA 180 out Distributor Mystery
> As the points weren't opening on the original distributor, that was the
> original problem.  You then fitted several distributors.  If you didn't
> remove the plug leads from either the plugs or the original cap (did you
> reuse that with each of the replacement distributors?) then the assembly of
> the rotor and the drive shaft of the original distributor was 180 degrees
> different to the others you tried.
> Whether it is right now or not is another matter.  Static timing with the
> pulley mark by the appropriate pointer will show the points opening when
> No.1 *or* No.4 pistons are at TDC, but only one of those will be on its
> *compression* stroke.  You determine that by removing the plug from No.1
> cylinder, putting your thumb over the hole, and turning the engine until
> compression pushes your thumb off, then turn to TDC.  If the rotor is now
> pointing to about 2 o'clock, then either drive gear and distributor assembly
> are both correct, or both 180 degrees out.  If it's pointing to about 8
> o'clock then one or other is 180 degrees out.  Whether it is worth doing
> anything about it is another matter.
> PaulH.
> ----- Original Message -----
>> ... Two sets of newly installed points would not open when fully
>> adjusted out.  A club member suggested that the distributor bearing
>> was wearing out. I took the 1800's original 25D distributor and base
>> clamp and installed it.  ... I got used another DM2 with the same
>> result.  I installed a new Lucas 25D, same result. Then I switched the
>> wires replacing #1 with #4 and # 2 and # 3 figuring it was 180 out.
>> Bingo, it purred like a kitten.  Mystery.  How could the distributor
>> drive gear get 180 out when I never touched it?

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