Vacuum advance replacement

Spinakerr

Spinakerr

New Member
Evening all - The vacuum advance on my P5B is seized and beyond repair.

I've been looking at replacement units - will any an advance from any Rover V8 (land rover, 3.9 etc) fit and work within the 1972 engine specs? While the engine is running relatively smoothly once warm I am keen to bring up to peak condition.
 
H&H ignition solutions will refurb or sell you a new one.

google them, they are good.

Colin
 
Hi Spinakerr,

The current Lucas vacuum advance modules for the Discovery and Range Rover possess the same vacuum points and total advance offered as some of the OEM modules fitted to the P6B. There were slight variations over the years, so the item fitted to your P5B distributor may well be one of them. From memory the current models function between 5"Hg and 17"Hg and provide 8 degrees (16 degrees at the crankshaft) of advancement.

Ron.
 
Thanks - I spoke to Lee at H&H Ignition and they have quoted an entirely reasonable amount for a rebuild. I will send it off shortly and report back.

Would the car run without the module? From various sources I have been tabulating there are wildly conflicting opinions of how much impact the unit has.

I suppose if mine has failed running without it can't be an issue in the short term actually...
 
They help economy mostly i believe but should also have some impact on performance i think? Also worth trying simonbbc - his prices and service are good. Worth emailing him about your specific application first though.

Rich.
 
Spinakerr wrote,...
Would the car run without the module? From various sources I have been tabulating there are wildly conflicting opinions of how much impact the unit has.
Click to expand...

With SU carburettors the biggest thing that you will notice is an increase in fuel consumption. I have known P6 owners to drive for years with a failed module, and other than an increase in fuel consumption, no other symptoms were observed.

Ron.
 
Right, I've had two hours of irritation today attempting the simplest of tasks - removal of the vacuum advance unit. Both external screws had corroded to the point they either broke when turned or required Dremeling to create a workable head. That done, I noticed the Lumenition system fitted by the previous owner included a large opening on the side. This is letting all manner of detritus into the cap and requires sealing (it's not too clear on the photo, apologies). Can I use liquid metal to patch this temporarily and seal the wires in place?

I ran short of time but I am guessing I can note the rotor's position, dissaemble and work my way down to the vacuum advance 'arm' that needs to be disconnected. Are there any other traps lying in wait for me? Also, the rubber grommet for the arm has rotted/solidified such that there are now two opening letting in the outside world. A cabriolet dizzy, if you will.

The arm and rotor itself looked tired so I've ordered new ones.
 
Hi Spinakerr,

Use a silastic to form a plug around the wires. It allows a degree of movement for the wires whilst preventing dust etc from entering the distributor. You could also source rubber grommets both for this job and on the other side if you prefer.

The distributor shaft won't turn with the advance module removed, but you can be almost certain that the ignition timing will need an adjustment once you have fitted the new module. The Lumenition choppers do succumb eventually to heat damage, so be very careful that one or more of the blades does not break off when lifting it clear of the cam. Also check once back together that the distance between the chopper and the optical eye at their closest point is 40 thou (1mm). If adjustment is required, wind in or out the dwell adjuster so as to achieve the required distance.

Ron.
 
Thanks Ron - 10 minutes of gently prising this morning has freed it. I have not have any experience with the optical ignition systems; thank you for the quick reply & advice. The 'chopper' is not a particularly hardy component as you say but luckily a screwdriver inserted underneath to the base gently working it up worked.
 
Received my reconned vacuum advance today from the boys at H&H - quite a difference:

IMAG0240.jpg


Should the arm be at that seemingly awkward angle?

Ill be attempting to fit this tomorrow. Unfortunately one of the screw heads twisted off and no amount of heat/WD40/dremelling or diplomatic brinkmanship will persuade the remaining thread to budge.

I am resorting to a self-tapping screw as there is no conceivable way I can remove the confounded remainder without having to retap the hole.

Does anybody have any suggestions? If the vacuum advance is only attached by one screw I doubt it will be fully effective...
 
Hi Spinakerr,

The arm should come essentially straight out though, not be pointed up or down. Are you able to drill out the remaining thread from where it remains in the distributor? Using a self tapping screw is not a problem, but the advance module must be attached at both points, else it will move with use and vibration against the distributor body which will shift the base plate and your ignition timing will be totally unstable.

Ron.
 
Thanks Ron - as ever your quick replies and experience are greatly received! I'll borrow a car tomorrow to head out to DIY shop for a small profile hand drill and small enough bit. Good thing I have a few days off work...

The arm is being pushed upwards by a round component in the unit, which assume to be part of spring mechanism for the diaphragm. This can be pushed down to make the arm level, but it returns to the upward position. Of course the true test will be if it all fits together. The refurbishers see these regularly so I hope nothing has gone awry their end & this is acceptable 'play':

IMAG0241.jpg
 
It is always a pleasure to help where possible,... :) By the look of it then, the upward cant of the arm is intentional so that should provide a contant pressure against the underside of the base plate when in situ. A touch of high temperature grease or a drop of engine oil should keep things sliding nicely.

Ron.
 
Success! After selecting a number of drill bits and sourcing a small-scale hand drill I managed to excavate the remains of the offending screw and drill a hole for a self-tapping screw.

IMAG0243.jpg


The rest of the distributor went back together without bother, and the Dow sealant & a new rubber adapted from loudspeaker grill holders ensures the cap is dust free. New Red Rotor from powerspark also went on, alongside some second hand Magnecor leads I was given recently. Unfortunately the new distributor cap, despite being advertised as for P5s, was too short - perhaps my original is slightly different due to the Lumenition addition... does anyone know where to source replacement in the larger size? My original cap is the black one below.

IMAG0244.jpg


Still, after a long crank the engine fired on (almost) all cyclinders for the first time in 6 weeks - phew! The timing will need adjustment but for now I am just happy it is all back together.

Very many thanks for everyone's assistance & advice - minor task that took a while...
 
Hi Spinakerr,

Glad to hear that the vacuum module is now sitting happily and securely onto your distributor. The reason that your new distributor cap won't sit down fully isn't to do with the Lumenition changing the height, but rather a combination of your new rotor and the cap. If you have a look at the keyway on your new rotor and compare it to your old rotor, are they the same? Are the electrodes within your new cap and your old one of the same design?

Ron.
 
You must log in or register to reply here.
Back
Top