Speed 25 distributor

For Speed 20, Speed 25, 3.5 Litre and Crested Eagle cars
NeilWillatt
Posts: 23
Joined: Sat Jun 16, 2012 7:35 pm
Name: Neil Willatt

Speed 25 distributor

Postby NeilWillatt » Wed May 15, 2019 7:10 pm

I have found that there is about 5 to 10 degrees of free rotational movement of my rotor arm before the timing springs come in to play. Surely this can't be correct as it will cause random changes in the ignition timing. Testing with a timing light does indeed seem to show such changes. Attempting to investigate I tried to remove the bakelite base of the distributor from the metal pedestal beneath but in spite of removing all visible fastening screws (2 on opposite sides at the outer edge, two retaining the spring arm for the points, and one retaining the condenser) I couldn't move it at all. I was very fearful of cracking it so the force applied was limited. Can anybody shed any light on what might be causing the free play and how I might correct it.

Also, two devices protrude from the pedestal whose function I don't understand, a knurled knob protruding towards the offside of the car, and a longish 3/16 whitworth bolt head protruding forwards. These are in addition to the locking nut which protrudes towards the nearside. Can anybody shed any light on what these are for ?

Delighted that my post about pressure relief valve in the radiator has prompted such an interesting discussion !

johnlayzell
Posts: 164
Joined: Mon May 21, 2012 2:44 pm
Name: John Layzell

Re: Speed 25 distributor

Postby johnlayzell » Thu May 16, 2019 11:03 pm

Will have a butcher's tomorrow. Does anyone other than Brits still use offside and nearside? Confusing to this long-transplanted Brit! Left and right seems so much easier. Is your car offside drive or nearside drive?
1925 SC12/50
1937 SP25 VDP Saloon
1970 Peking to Paris Rally VW Beetle

johnlayzell
Posts: 164
Joined: Mon May 21, 2012 2:44 pm
Name: John Layzell

Re: Speed 25 distributor

Postby johnlayzell » Fri May 17, 2019 7:13 pm

Same, or at least some, free play in my rotor arm. Here's what the base of my dizzy looks like:

SP25 distributor base.jpg
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1925 SC12/50
1937 SP25 VDP Saloon
1970 Peking to Paris Rally VW Beetle

NeilWillatt
Posts: 23
Joined: Sat Jun 16, 2012 7:35 pm
Name: Neil Willatt

Re: Speed 25 distributor

Postby NeilWillatt » Sat May 18, 2019 3:32 pm

Thanks John, I don't think I have the same distributor as you. I have attached picture of mine, taken from directly in front and showing the various parts mentioned in my original post.
Distributor.jpg
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johnlayzell
Posts: 164
Joined: Mon May 21, 2012 2:44 pm
Name: John Layzell

Re: Speed 25 distributor

Postby johnlayzell » Sat May 18, 2019 4:45 pm

Yes, quite different.

Alvis SP25 JD6 distributor.jpg
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1925 SC12/50
1937 SP25 VDP Saloon
1970 Peking to Paris Rally VW Beetle

DeaneHarding
Posts: 15
Joined: Fri Aug 09, 2013 9:18 pm
Name: Robin Gilbert

Re: Speed 25 distributor

Postby DeaneHarding » Sat May 18, 2019 10:44 pm

Neil, it appears that you have the "coil only" ignition of the later Speed 25, not the combined magneto/coil system of the earlier version. The "Mystery knurled nut" is in fact the dust cover on the lubricator tube for the distributor shaft bearings. It has a cut-out at the base of its circumference which, when it is rotated, reveals a corresponding cut-out in the tube leading to the bearings. Use an oil can to squirt lubricant in. This saves wear in the shaft and its bushes, another cause of wandering timing.
The "mystery 3/16" Whit. bolt" is the screw which retains the distributor in its mounting. It should be 1/4" BSF with a spigot end to engage in the groove machined in the distributor body shank, allowing the distributor to rotate when the hand advance lever is moved. Removing this bolt allows the distributor to be lifted out of its mounting. It is frequently lost and replaced by any handy 1/4" BSF screw with the end filed down. 1/4" BSF has the same measurement across the flats as 3/16" "old Whitworth" and old spanners marked 3/16 Whit. will fit. "Modern Whit." has the same A/F measurements as the hexagons on the corresponding BSF thread diameter.
Lastly, the "locking nut" tightens the clamp holding the manual advance/retard plate in position. This must be loosened to set the timing or remove the distributor. Many, but not all, of these plates have two slots through which project bolts holding springs and washers arranged to push the whole assembly downwards to promote consistent timing.

NeilWillatt
Posts: 23
Joined: Sat Jun 16, 2012 7:35 pm
Name: Neil Willatt

Re: Speed 25 distributor

Postby NeilWillatt » Sat May 25, 2019 6:04 pm

Robin, many thanks for your comprehensive reply. Can you shed any light on the 5 - 10 degrees of free play ? Should it be there, and if not is there anything I can do to fix it ?


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