Vacuum unit on distributor ???

Moderators: scimjim, philhoward, erikscimitardemon, Roger Pennington, Lukeyboy46

Post Reply
jvasabra
Posts: 26
Joined: Tue Nov 09, 2010 7:43 pm
Been thanked: 1 time

Vacuum unit on distributor ???

Post by jvasabra » Wed Jul 19, 2017 8:16 am

Hello,
On Sabra/ Sabre4,
Do we really need the vacuum unit on the distributor working? On 4808 it sems it is not working, but the car runs fine in all ranges of revs ( till 4500, never tried more)?

Can anyone confirm we have a Lucas 25D distributor. On mine there are other numbers (DM2/P4 ????)
This because there are several models of vacuum unit available. 


On 4808 the vacuum unit was "tested" by sucking at the vacuum line at the carbs and it seems the distributor's points plate does not move.Is there another or better way to test.

I would like to be sure about this before buying a NOS one or an aftermarket one . Here too , anyone has an idea if the afremarket ones are ok, they are cheaper than NOS ones.

Thanks for a reply.
Jacques



User avatar
philhoward
RSSOC Member
Posts: 23346
Joined: Tue Aug 29, 2006 5:41 pm
Location: Staffs, UK
Has thanked: 37 times
Been thanked: 457 times
Contact:

Re: Vacuum unit on distributor ???

Post by philhoward » Wed Jul 19, 2017 9:09 am

I would class the "suck" test as proof that the vacuum advance test works in total; if it doesn't hold vacuum then the diaphragm is gone but if it does, then the advance mechanism may well be siezed (centrifugal advance may also be effected but you can only see that with the engine running and a strobe light).

A working advance mechanism on a road engine improves its part-throttle driving and response, as well as fuel economy.

If it's a 25D (that rings a bell - or is it a 23D?), they are usually rebuildable anyway - the base units are the same with just the engine fitment changing (fitting into the block, weights and springs in the advance mechanism and the vacuum advance). I've not tried an aftermarket one - might be OK for something mainstream like BL cars (MG. Triumpg etc) where there's a large market but for something like the Ford Consul engine you may be best either rebuilding your own or getting it rebuilt (if it's not beyond repair).


Phil Howard
Scimitarweb Forum Admin
SS1 1600 Rooster Turbo; Sabre Mk1.5, Sabre Mk2
Previous: SE5/5a/SS1 No.1/SS1 Rooster/SS1 1800Ti/SE5a 24 Valve
http://www.ss1turbo.com
Never try and argue with an idiot. They drag you down to their level, then beat you based on experience.

User avatar
Roger Pennington
RSSOC Member
Posts: 19013
Joined: Tue Aug 29, 2006 9:43 pm
Has thanked: 106 times
Been thanked: 432 times

Re: Vacuum unit on distributor ???

Post by Roger Pennington » Wed Jul 19, 2017 1:35 pm

The Distributor Doctor is a name I've heard mentioned and recommended a lot in connection with rebuilding Lucas dizzys (not used him myself, of course, because my cars are later). Might be worth contacting him?


....Roger

RSSOC member (since 1982)
- - - - - - - - - - - - - - - - -
Image

"Condition can be bought at any time; Originality, once lost, is gone forever" - Doug Nye

User avatar
peter freeman
RSSOC Member
Posts: 8942
Joined: Thu Aug 31, 2006 12:12 pm
Location: Newcastle
Has thanked: 9 times
Been thanked: 273 times
Contact:

Re: Vacuum unit on distributor ???

Post by peter freeman » Wed Jul 19, 2017 1:47 pm

A guide to dizzy repair can be found here - https://www.scimitarweb.co.uk/~nenoggin ... ibutor.htm - not for your dizzy but probably similar in many ways.



User avatar
Old and Slow
RSSOC Member
Posts: 636
Joined: Tue Jan 20, 2015 6:37 pm
Location: East Berks
Has thanked: 2 times
Been thanked: 29 times

Re: Vacuum unit on distributor ???

Post by Old and Slow » Wed Jul 19, 2017 2:35 pm

AFAIK The Zodiac engine has the Lucas 25D6 as standard, so I assume the Consul engine used the 25D4. the 23D6 distributor doesn't have the vacuum advance.
On 660XYB with the 25D6 the vacuum is not connected; I believe the main advantage of having the vacuum advance connected is the extra 10-12 degrees of advance will be brought into play when the throttle is shut off at reasonable revs (i.e. on over-run / engine braking) as the unburnt fuel drawn into the engine makes the mixture over-rich and will take longer to burn, so an earlier spark stops all the popping and banging that I get.
With the throttle open there is little or no vacuum created so under normal acceleration the vacuum advance is ineffective.
The static timing should be 8 deg BTDC and the centrifugal bob-weights will come in around 1500 rpm, and linearly add advance up to 20 degrees at around 5000 rpm. The total advance including any vacuum advance shouldn't exceed 35 degrees, to avoid pinking, valve and piston damage etc.
To check the centrifugal movement, if you take off the distributor cap it should be possible to turn the cam a bit by hand, and it should spring back although the return is usually a bit sloppy, which is OK as the engine only rotates one way and all the slop is taken out.
A strobe is much better though, as you can see the advance in operation.
Hope this helps,
Philip N


Philip Needham
Ashley-bodied TR3; '54 Ford Consul; '55 AC 2-Litre Saloon;'65 850 Mini; '70 Ford Zodiac MkIV; XR3i
'81 911SC Targa, '64 Sabre Six

User avatar
Old and Slow
RSSOC Member
Posts: 636
Joined: Tue Jan 20, 2015 6:37 pm
Location: East Berks
Has thanked: 2 times
Been thanked: 29 times

Re: Vacuum unit on distributor ???

Post by Old and Slow » Wed Jul 19, 2017 4:25 pm

You might find this article informative; unfortunately the original URL doesn't work, so it is probably better to download a copy from there before it disappears again:
http://www.vitessesteve.co.uk/PDF/lucastuning.pdf
Also, DM2/P4 appears on this list, (17 pages of Lucas distributor part numbers!) near the top of page 5 is listed 40631A for 1961-2 Consul, giving various levels of advance vs rpm.
http://www.sterlingbritishmotoringsocie ... _Chart.pdf
Good luck!
Philip N


Philip Needham
Ashley-bodied TR3; '54 Ford Consul; '55 AC 2-Litre Saloon;'65 850 Mini; '70 Ford Zodiac MkIV; XR3i
'81 911SC Targa, '64 Sabre Six

jvasabra
Posts: 26
Joined: Tue Nov 09, 2010 7:43 pm
Been thanked: 1 time

Re: Vacuum unit on distributor ???

Post by jvasabra » Tue Jul 25, 2017 7:34 am

Hello,
Thank you for the info. The link to the list, well, what a list, of Lucas distributors was very welcome. Now I know that the DM2 PA, which I Always looked at a bit suspicious, is in fact the Original one for a Sabra with the ford consul 1.7l engine. Most cars hav D25 nowadays.

I ordered a Lucas vacuum unit, not an aftermaket. Hopefully it will work correctly.No one could give me the Lucas specifications as there were no numbers on the item??? Aftermarket, no brand , are a one for all.
Thanks again.
Kind regards,
Jacques



Post Reply

Return to “Early Sabre”