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MG MGB Technical - Distributor in/out how to get close?

I need your assitance/knowledge/tips/methods. I want to pull out the distributor on my 1979 MGB. Looks to be the late replacement type (with the black box).

The purpose is to change out the clamp on the base, inspect rotor, inside cap, also check for cracks in the cap, wire conncestions. The clamp "bolt/nut" are both "very" rounded, and I not sure it is holding dizzy... but no problems holding timing. Plus, I want to CLEAN all the parts and areas around the dizzy too.

Looks like I need to change/replace a small rubber seal (when I look at the exploded view in Moss).

Could I simply place a piece of tape on the base of the distributor, and block, place a line on both. Then line-up the lines when I reinstall??

Any tips? Please let me know. I understand I will need to check/set the timing when I am done.... just want to make sure I have it "close enough" so it will run.

Note: MGB 1979 has 74,400 miles, set-up with Weber/Header.

Thanks for any help,

Geo. My website, has some tech articles which may be of use to you on the MG section. As to the rubber O ring, I have only seen this on one or two cars. Most distributors do not have the groove machined into them to accept the O ring and do not seem to be leaking oil because of it. From your description, you have the Lucas 45DM4 system which uses some of the GM HEI parts. There is information in the archives on this.

I run a points type distributor system in my MGs and cannot say whether it is possible to static time the "electronic" distributors or not. I would think it should be. If not, recruit an assistant, hook up your timing light and while they crank the engine over, shine your timing light on the crankshaft pulley and turn the dizzy so that the light is flashing when the timing mark is near the pointers. This is sufficient to allow the engine to start. Then, turn the dizzy until the light is flashing about 10 deg BTDC, have the assistant run the engine up to the desired/specified engine rpm and set the initial mechanical advance. Tighten the nut securing the distributor, reattach the plugged vacuum line (remove it from the vacuum advance at the distributor and plug it with a cross point screw driver before starting the engine), and you should be fine.

Ask if you have problems or need more information beyond what I have provided here and my website provides. Many willing people here, waiting to help.

Les Bengtson

My favurite way or doing this is to set the engine to the correct timming . This is done by lining up the timing marks on the front cover and pulley. Do this by rolling the car in gear if need be.

Now put the distributor in and put a plug on the end of cyl #1 wire. Rotate the distributor until you see a spark jump the gap. You should be pretty close at that point. Timing light is still a good idea once you get it running.


Les. I'll check your website, and wait for some more replies. Also, I'll see if there is rubber seal on the base. If not then I will not install one.

Pete. Is this the procedure to follow?

1. Set timing (with light).
2. Remove distributor (do all I want to do, check/clean)
3. Put cap on with coil wire and #1 wire/plug.
4. Turn on ignition, and by hand turn dizzy until I see a spark jump plug.
5. Put dizzy now in block, install other 3 wires.
6. Start engine and adjust timing.

Did I miss anything? sounds like a good method.


I'm assuming that your car is running now. Either visually or actually mark the orientation of your distributor (to engine block) before removal. You can use some white-out or scratch it with the edge of a screwdriver. Note the location of the plug wires and write (draw) them down. Remove your distributor and do whatever you want to do. Reinstall the dizzy (it only goes in one way) and align orientation marks. Start the engine and adjust timing (turn dizzy) as you see fit (whatever gives you best performance).
Steve Buchina


Close, but it is actually easier than that! A timing light is not required.

I use this when I build a new motor. The idea is to manually align the timing marks on the front of the engine. Make sure you are on the compression stroke by either putting your finger over the plug hole, or looking at the rockers. I find that putting the car in gear and pushing it is the easiest way to turn the engine. Since the engine is not running, it is possible to align the timing marks quite accurately. Set the timing to whatever spec the book says.

Now set the distributor in the hole and wire it all up. Put a plug on the end of wire number 1. Slowly turn the distributor until you see a spark jump. You are now very close to the timing you have set on the marks. Certainly close enough that the engine will run. You will also be certain that you have a spark.


Steve. That is how I used to do my first car (46 Plymouth 6 cyl), about 47 years ago! It always worked for me then. Just wasn't to sure about the MG with electornic ignition.

You said it can only go in one way. Is the drive dog offset?

If I draw the location of the plugs/cap, and scratch the dizzy/block, make sure the rotor is pointing the same way, I think (correct me if I am wrong) Everything should work good enough to run, and then if needed, reset timing.

Pete. If I have the time, my plans are to pull off the valve cover, adjust valves, pull dizzy (clean/check/replace cap/rotor if needed. I just might as well turn engine to timing marks, and use your method too, along with marking dizzy and block.

Looks like a good plan to me.

Thanks for your support. This is a GREAT way to gather information for projects.

Geo 1979 MGB

You said it can only go in one way. Is the drive dog offset?

Yes, it is offset. No need to make extra work for yourself (i.e., set timing at the end). Just be careful when you go into your dizzy. If it's your first time - careful notes, diagrams and digital photos should keep you out of trouble. As suggested, if your car is running now, you shouldn't have any problems.

One other suggestion - I converted the dizzy on my '80LE to the older style (points and condenser) model 25D4 distributor. You might think about doing the same. Join up (become a member) and search the archives on this subject.
Steve Buchina


When you changed to the older style dizzy (with points and condensor), what did you set your points too (gap)??, and did you set your plugs to .025 instead of the .035?

Looking at Brit-tech, they have a complete package available for about $250 (new dizzy/points/rotor/cap/wires and coil). When you changed your's what did you change besides getting the 25D4 dizzy??


Points are at .015 and plug gap is .025. Personally, I wouldn't spend $250 for an ignition kit. Good used 25D4 (or 45D4) distributors can be had off ebay for less than $50 (some less than $25). Rebuilt units on ebay range from $70 to as high as $150. Warning - some on this board have posted that many of these rebuilt units have incorrect advance springs and weights.
The distributor on my '80 LE is forty years old and works fine. Should add, however, that I reconfigured most of my engine bay back to the look of my original '66B. All pollution (emission) control items attached to the engine were removed and the Zenith-Stromberg carb and manifold/catalytic converter were replaced with the mid-60's setup (i.e., HS-4's, intake and exhaust manifolds).
Course, I live in Alabama and can do such things. Not sure what can be done in Virginia. Don't you have yearly inspections up there? Perhaps someone else can jump in and offer their comments.
Steve Buchina

Geo, if oyu disassemble your distributor, check and mark the orientation of the rotor to the offset in the drive gear. It must stay the same upon reassembly. I think Les's website shows that.

Jeff Schlemmer

Before I converted to a pertronix, when I changed the points on my car I did the following. I left the clamp on the distributor and removed the two bolts holding the clamp to the block and pulled out the distributor. After changing the points I would put the distributor back on, and before the two bolts where tight, I would rotate the distributor to the left all the way. The holes the bolts went through are slotted, once the distributor was rotated as far as it would go, tighten the bolts. Then I proceeded with adjusting the timming. The car would usually be fairly close, even with the new points. The only time I loosen the clamp is to adjust the timming.



As long as you don't alter the points you can simply make a mark on both distributor and block and align them and that will be close enough to get the engine running again to do a proper dynamic timing check afterwards. But if you replace the points, or even regap them off-car, and especially if you replace the points with another type of trigger you may have to do a static or semi-static time first if it doesn't start in the original position. With points a static time is easy, with an electronic trigger probably the easiest way is to remove the plugs, then dynamically time it while cranking to the static position, which should get it running with the plugs in, then dynamically time it to the dynamic position.
Paul Hunt 2

This thread was discussed between 18/09/2006 and 22/09/2006

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