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MG MGB Technical - Pulley alignment

I have am MGB with an alternator conversion where the pulleys are not aligned properly. The alternator pulley is sticking out a good quarter of an inch or so in front of the water pump and crankshaft pulleys. This car has also had a new water pump in the past.

I think the water pump boss which the alternator bolts onto has got too fat over the years. Is it OK to take a quarter of an inch or so off the front of the water pump pulley or should I start on the alternator? Or, third possibility, are there different pulleys for the alternator and I simply have the wrong one?

Mike
Mike

There were several pulleys used on the MGB over its life span. It would help to know the year of your car, the water pump that is mounted to it and the type of alternator that is currently mounted to the water pump. RAY
rjm RAY

I fitted a new alternator yesterday.

There was a bush sticking out of one of the mounting holes in the alternator. I had to remove it then insert it in the other end of the hole. Then things lined up.

There is a saw cut along the length of the bush - it's possible to squeeze it a bit with a wrench to pull it out.
Geoff Everitt

Photo

Geoff Everitt

Mike. A photo would help. I am assuming, since you mention an alternator conversion, that you have a Mark I MGB. But, knowing if it has a three main or five main bearing engine might be useful. There are several water pumps, with different lengths of noses, for the five main bearing engines. All will, physically, interchange but the pulley alignment becomes a problem if the wrong one is used. I am assuming that you need to bring the alternator rearwards. Correct me if I am wrong on this assumption.

Geoff. The split spacer is present on all of the Lucas alternators I have examined. It corrects minor spacing issues. I have seen spacing issues sufficient that I had to machine a spacer our to aluminum (aluminium to you) round stock to allow secure mounting at the rear of some alternators on some engines. In theory, this should not happen. In practice, sometimes it does.

Les
Les Bengtson

Hi Les, thanks for your comment. Yesterday was my first time - it was lucky I still had the old alternator to compare with or I might have been scratching my head for a while.
Geoff Everitt

Geoff. Most of us have had a similar experience, a time or two, in the past. Much easier today, with the internet, to get good information when we run into a problem. Glad you got it sorted. Now, put a volt meter on the system and make sure you are getting 13.5 to 14.5 volts with the engine running. I had one "rebuilt" alternator which I did not check out after installing. It was "new". The 18.5 volts it was putting out fried the battery relatively quickly. Not a mistake I have made since then. We are all students here.

Les
Les Bengtson

If the alternator is forwards of the water pump and crank pulleys, then the implication is that it is the alternator that is wrong, particularly if it is a conversion. As such there seems little to be gained by altering just the water pump to (presumably) match up with the alternator, there would still be a mis-match with the crank. The split spacer is to compensate for small misalignments has been said, but to the rear mount, the prime reference is the front mount. If that is wrong then the split spacer is irrelevant. And in any case the rear mount on my 73 is slotted where the bolts into the crankcase goes, so the split spacer isn't really needed anyway.

I think the water pump issue is a red-herring, I've seen both long-nose and short-nose pumps on 18V engines for example, the thing there is to use the correct pulley, i.e. a deep-dish or a shallow-dish respectively. The alternator mounting point remains the same, and if you use the wrong pulley it becomes the water pump that doesn't match up with either the crank or the alternator. It is a lot more than 1/4", more like an inch, which is the thickness of the spacer for the short-nose to get the fan at the correct distance from both the block and the radiator. See http://www.mgb-stuff.org.uk/cf.htm
PaulH Solihull

Les ... you said,

"Now, put a volt meter *on the system* and make sure you are getting 13.5 to 14.5 volts with the engine running."

I'm afraid this is a wee bit vague, could you be more specific please about what "the system" applies to?

Thanks!
Geoff Everitt

Geoff. At the battery terminals, engine turned off, you should see 12.5 to 13.0 volts. Same reading on the outside of the battery clamps if the connections are clean and tight. Then, with the engine running, the alternator should be putting out 13.5 to 14.5 volts. Readings can be taken off of the brown wire circuit (the front side of the fuse box, lower fuse where the brown wires connect to it) or off the battery terminal clamps. If you see voltage readings above 14.5 volts or below 13.5 volts there is a problem with the new alternator which needs to be examined.

Les
Les Bengtson

Thanks Les!

I have 12.7V and 14.3V, so should be OK.
Geoff Everitt

I also fitted an alternator today and the pulley was misaligned by about 3mm , but the split bush moved fairly easily and it lined up. If it's a Lucas replacement and it still will not line up, it must be the alternator pulley wheel, and they are pigs to get off.
One problem I've got with mine is the replacement alternator has a different connection, the old one had the normal 3 pin plug, but this is the BSH terminal with the large + spade. I've rigged up a harness to test it but I cannot seem to source a BSH plug from the normal outlets. Anyone know where I can get one?
c cummins

The split bush will *automatically* move to line up with the rear bracket as the front and rear bolts are tightened. That's why it is split, it's a tight sliding fit in the rear alternator bracket, to compensate for differences in distance between the block brackets. The alternator position is governed by the front mounts, if the pulley is still misaligned when the front bolts are tight then there is some other problem.

With the ignition and everything else turned off you can measure the battery voltage at any of the places Les mentioned and they should all be the same, unless something is very wrong, which makes the brown at the front of the fusebox the easiest place. Nominally 12.8v it can be over 13v if the engine has only just been switched off, or less than 12.8v is the battery is less than fully charged.

But with the engine running and the alternator charging, i.e. the ignition warning light comes on with the ignition, and goes out again when the engine is started and revved to at least 1000rpm, the alternator will now be charging the battery i.e. current is flowing and you can get different voltages in different places. The highest voltage should be on the brown wire at the alternator, and as the acceptable voltage range for the alternator is 14.3v to 14.7v is is this latter voltage that should not be exceeded. But it is also important to measure the voltage at the brown at the fusebox and the battery terminals, as bad connections in the charging circuit can significantly reduce the voltage at these other points. Even at maximum charge i.e. everything turned on you shouldn't get more than a couple of tenths difference between the highest and the lowest.
PaulH Solihull

This thread was discussed between 22/07/2010 and 25/07/2010

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