dynamo rotation direction ?

[Brandis]

Yes, the pest is back again. 
I just got a good looking dynamo from the UK.  Backwards rotation so probably out of a Matchless.  But it is the shorter E3H and they are hard to find so I have to make this work.  I assume that all I do is to reverse the connections between the coil and brushes? 
Low voltage so I'll have to go through the usual check list. 
I'm getting my magneto rewound by a specialty shop.   Amal sent me the wrong slider for the carb. 

This business of putting together a bike from a pile of parts with the key ones missing, is a test of human patience.  And clearly a test of all your patience as well.  Thanks again.

[trevinoz]

Rotation is anti-clock looking at the drive end.
If it is out of a Matchless then it is no good for a BSA.
The number on the body will tell what it was originally but bodies can be interchanged.
Pictures would help.

[Brandis]

If I connect it to the battery with the + on the motor case, and F and D to the - it motors anti-clock at the sprocket end.  I want it to motor the same direction it will be driven, right?  My experience with brushed motors is that you reverse the relationship of the field and armature, the rotation will reverse.  Any danger in doing this?  I can put a fuse in series to cover my dumb ass.

The Lucas # on the case is  E3HAC 33-0

[groily]

If it were off a Matchless/AJS single it'd be an E3AR or E3N, with a tapered drive end for a sprocket.
An E3H is what went on the early A7s, presumably also with a tapered armature for a sprocket like other pre-unit Beesa twins? Lucas part # 200303 or 305. E3AR is 200370 and the N is 200802. The N version is easily available new, as is the E3HM (for magdynamo) version with parallel drive end for a pinion and keyway. I don't know if either could be persuaded to suit your dynamo (with some machining work on the M) if push came to shove.
Nor do I know if the drive end bearing retainer plate is the same on yours as on the later twins with E3Ls.
Nor if the later more powerful and relatively easy to find  E3L would fit on your machine or not. If it would, it's what I'd do!
Pix would indeed help!

You can bore yourself half to death reading the Lucas dynamo lists and what went on what if you want. Here's one link to them:
http://www.brightsparkmagnetos.com/library/Parts%20lists/Lucas%20motor%20cycle%20parts%201936-57/A03-34%20Equipment%20specification%20by%20machine.pdf. That shows the early A7 as having the E3H.
Or here for the even more boring Lucas dynamo parts lists themselves:
http://www.brightsparkmagnetos.com/library/Parts%20lists/Lucas%20motor%20cycle%20parts%201936-57/E01-11,15%20Dynamos%20and%20supersession%20chart.pdf

Basically, rotation and polarity are up to you, regardless of any arrow on the body. It needs to motor in the same sense as it is driven, yes.
As you say, you can reverse the rotation by swapping over the field coil wires, one of which goes to earth along with one brush, the other of which goes to 'F', if using an original type regulator or a modern one like a DVR2 which regulates on the live side. Alternatively - on most dynamos bar some very early E3s where one brush is permanently to earth because its holder isn't mounted on a mica insulator - by swapping the brush tail connections over. Not both though or you end up where you started. No danger at all in doing this. Motoring it the direction you want will also polarise it for whichever earth you choose.

You say you've got 'low volts'. Hope the armature is actually OK after all the hassle of getting it, and I'd suggest you hide a decent regulator in the old Lucas MCR1 box you should have on there, to give the system the best of chances going forward.

[Swarfcut]

      Early A7 with the shorter E3H dynamo had a domed pressing to the drive side front engine mounting plate. This covers the dynamo end cap. Later models have the usual big hole in the mounting plate for the longer E3L unit, which will fit straight on with the correct plate. The profile of both mounting plates are unique to the Longstroke ......later rigid and plunger engine types will not fit, the crankcase profiles differ.

 Early models were negative earth. From the description simply reversing the battery to give positive earth system, as on later models, should give the result needed.

 Dynamo drive sprocket remained the same for all models. Dynamo driven sprocket is a BSA part, not Lucas. See later observation by Trev, two different teeth sizes used. Chain is the same type from start to finish, but the Longstroke chain is shorter than the one used on later  shortstroke models.

 Lots on the Forum about testing and reviving an old dynamo, a good clean and check of the electrical connections has brought many back from the dead, but this one looks to be in reasonable order.

 Swarfy.

[groily]

Sounds as if it needs the short one then to retain the look and the correct engine mounting plate.
Fingers crossed the puppy you've got can bark OK without surgery to its vocal chords  . . .

[Brandis]

Will do.   And the modern regulator idea makes sense.  I've revived the later units so I'm sure I can get this one pumping electrons.  The fact that it motors tells me I can sort it out.

Thanks as always.   Maybe I'll give all y'all next weekend off.   What will you do with your time ??

[trevinoz]

Swarfy, the E3H has a 13 tooth sprocket and E3L 11 teeth.
Consequently there are different chains to suit.

[Brandis]

Popped out the brushes and put them in backward.  Motors in the correct direction. Polarity correct.  All installed in the bike.  Waiting to blow some smoke.
Thanks to all.   
Next week I'm asking if there is any way to measure oil pressure temporarily, what with me having drilled the con rods and all. So get some rest.

[Rex]

Popped out the brushes and put them in backward.  Motors in the correct direction.

Well, it is April 1st..

[Swarfcut]

Thanks Trev, I got the fine detail slightly wrong. Looks as if an easy way to boost E3H output is to fit the later 11 tooth dynamo driven sprocket. No problem with the chain, both types use the same one when fitted to the Longstroke.

 For comparison.....67 727   11 Teeth, used on E3L Dynamo,

                            67 725   13 Teeth, fitment to E3H

                           29 2199   Drive chain, used with both size sprockets, Longstroke A7

  Source...Forum Parts Catalogues, Literature Section.

 Swarfy.

[berger]

Brandis i made this up , i put the rubber seal over the holes to stop the pressure relief up to the cam etc and then took the seal off to see how much pressure it was letting go up to the cam trough

[Brandis]

Looks like genius to me.  What numbers did you get?

[berger]

 Brandis it was years ago when i did that but with a gauge of over 100 lbs and the relief holes covered it maxed the gauge out and ballooned a clear plastic pipe so i stopped the engine before i got covered in oil, can't remember what it gave when relief was on

[Brandis]

Dramatic description.  I think I'll assume all's well.  I'll just do a visual in the oil on the valve rockers.  The oil pump seemed very tight.  I was just wondering because I had drilled 2 1/16" holes to get some oil on the flywheel and hopefully up into the cylinders.

I also opened up the holes at the banjo fittings.  They were about the size of a human hair.  And yes, I know that has no effect on the oil pressure.

Given that I've never seen an A7 intact, I'm impressed at what a great looking bike it's becoming.

On another note.  I heard a rumour about a weird guy in the bush about an hour's drive from here who used to be the Brit bike guy in the area about 30 years ago. A barn full of stuff, I'm told. He's dead and his kin will shoot you if you walk up the driveway. A challenge I can't resist. I'll do my bible salesman act.  I'm depressingly good at breaking out in instant prayer on a stranger's front porch. No hint of a Canadian accent.
I believe this area is one of the last ones for old Brit bike finds because, "if it ain't a Harley, it ain't worth shit".