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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - New 25D4

BPNorthwest has a new 25D4 dizzy. Has anyone had any experience with this one yet? Is there any advantage of a 45D over the 25D? I have AUD 405's with the vacuum port on the carb body but I could easily use manifold vacuum source. Jeff, I know you must have some thoughts on this.
M.A. Barrera

I just got one of these from BPNorthwest and it looks great..perfect new 25D4 with perfect new vacuum capsule. Came in a new Lucas-TVS box. This is for a new engine I am building so it is still untested. Great price, I may buy a second one.
Cliff

Cliff Maddox

Are any specifiactions on the mechanical and vacuum advance included in the instructions? If no instructions the vacuum capsule should be marked with something like 10 15 5 as an example.

Clifton
Clifton Gordon

Thanks for the input, Cliff. Sounds like a winner. I e-mailed BPN to ask for specs on the unit. Cliff, did you get the pertronix-equiped unit?
Mike Barrera

Both the vacuum capsule are marked Lucas- TVS "Made in India". Dist body is marked "25D". The Lucas box has label which reads "fits all MGA, MGB to 1974, Sprite, MG midget to 1974 and Triumph TR3, TR4 and TR4A". It is still in the box so I cannot say what advance may be. Seems to be nice and smooth, I have my fingers crossed.

Cliff
Cliff Maddox

I think we all keep our fingers crossed when we by parts from any of the suppliers. I just bought a driveshaft from Moss. Looks ok, but there is a little too much play in splines, shaft to yoke. It came from India also. My old shaft had less play and its >30 years old. I think I'll call Moss and ask then to check out the other shafts they have in stock, mine could be a reject.
M.A. Barrera

I doubt it will be the only one!
Dave O'Neill

45D4s are slightly smaller than 25D4s and the bolts securing the clamping plate to the block can be undone to remove the distributor complete with clamping plate. This makes it easier to get the distributor back in close enough to start and dynamic timing, also avoids frequent slackening and tightening (usually overrightening) of the clamp bolt which destroys the distributor body. Later 45D4s also came with sliding points, which reduces spiking and pitting. 45D4s don't have the vernier adjustment, though, which makes small adjustments in timing more arkward.

Any 45D4 or 25D4 will 'fit' any MGB block, but the important thing is the curves. Any curve can be set to give no pinking, but the further the *shape* of the curve is from the correct curve for that engine, the more performance and economy you will be losing.

Even if you get distributor body and vacuum capsule with the correct reference numbers for your engine stamped in to them there is no guarantee that the curves are what they are purporting to be, there are a lot of charlatans out there, even the big suppliers get caught out.

Finally even if you *do* get the correct curves they are irrelevant to a greater or lesser degree unless you run the engine on the original fuels they were specced for, i.e. high octane leaded for most.
Paul Hunt 2

M.A., I actually bought one of these from a company in England a while back. The first thing I did was disassemble it and check it out!

I found that the hardware was metric for starters. The advance assembly looks like they used original leftover parts! The cam assembly and shaft are virtually identical to original in every way! They are NOT well curved for perfomance though! The vacuum advance is actually smaller than orignal and an old vacuum advance cannot be fitted without some minor machine work to the housing (10 minutes work). Otherwise the fit and finish are good! Its a good alternative to a rebuild, but it would definitley not offer great performance! A recurve would really wake it up and make it a steal of a deal for a new dizzy! First things first though - throw away the clamp bolt and install a 1/4" x 1 1/2" bolt so you don't have to use metric tools on your B!!!
Jeff
Jeff Schlemmer

Sounds like one I bought - only one spring, incorrect cam stop-plate with the advance number filed off, incorrect vacuum advance capsule. Apart from that the rebuild was great ...

The company claims to supply many of the big parts houses.
Paul Hunt 2

This thread was discussed between 20/01/2007 and 28/01/2007

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.