Magneto removal, screw in timing cover

[vwphillips]

I have just removed the outer timing cover of my recently aquired A7 shooting Star 1959 bike 1951 engine

a small counter screw 14mm long 7 mm diameter fell out.

Any ideas what this may be?

The rear magneto pickup is not providing a consistent spark(1 in 50) so am removing the magneto for sevicing

I need to remove the magneto pinion(manual advance) and have ordered a puller

http://www.ebay.co.uk/itm/Lucas-MagDyno-K2F-Mag-Pinion-Puller-BSA-A7-A10-B31-B32-B33-M21-M21-M33-P108-/190823108451

It appears I do not need to remove the inner cover, is this correct?

I have never worked with magnetos and while I can turn a spanner I find the more technical jobs more difficult
I have marked the pinion so it can go back on in the same position but will need very simple instructions for the ignition timing when I refit the magneto

[terryg]

Sorry, don't recognise the screw but, just a thought before you dismantle any further... Try, if you haven't already, cleaning the slip ring in the mag.
Take either pick-up off the mag and with some brake cleaner, rag and a suitable 'stick' clean the ring 360 degrees where the pick-up carbon brushes make contact.  After reassembling try running the motor again.
It may be your brushes are a bit soft and contaminating the slip ring.

[terryg]

The screw... I didn't ask if all 4 inner timing cover screws are present and correct. It's not a rogue replacement that has come loose and out, is it?

[RichardL]

VW,

Welcome, if a bit belated.

Can you show us a photo of the screw, er, maybe you haven't reached the post quota for adding photos.

Richard L.

[muskrat]

It's probably the inner cover screw between the two dynamo sprockets.
Try Terry's suggestion first, check points gap both sides and check the points spring isn't touching the cam ring.
Cheers

[Billybream]

Hi.
Welcome to the forum.
Will try to help, the screw will not be metric (Well should not be), so would be best to identify the thread. As Terry states could be one the the four inner timing cover retaining screws, these will be of cheese head design(Screw Driver Slot)

Regarding the inner timing cover, confirm no need to remove it.

This link will provide BSA service sheets, and highlights the one to cover ignition timing. : http://www.bsawiki.co.uk/index.php?title=Chapter02

You are correct with the need of pinion extractor for your bike with manual advance.

[vwphillips]

Thank you all for the feed back

I have checked the inner caseing screws there are 4 which require an allen key and they are all tight.

the mystery screw has a very used slot countersunk head

I considered removing the problem pick up and cleaning the pick up slip ring

but as I understand there is only one slip ring so if it was dirty it would effect both pickups

Also the pick ups are attached by wire locked screws and access to one of the screws of the problem pick up is difficult(I can just touch it) and I doubt I could reattach it with out removing the magneto.

I guess I could remove the acceable pick up(the puller has not arrived yet) but there must be somthing wrong with the bad pick up as as I understand the mag ihas only done 350 miles since refurbish.

Also there has been mention of both sides of the points gap

there is one set of points which appear open once per revolution

I have assumed both plugs spark at the same time, is this correct

[Triton Thrasher]

Points on a twin cylinder magneto open twice per revolution of the magneto, sparking one plug at a time. Magneto turns at half crankshaft speed.

Unless some idiot has put a cam ring for a single cylinder type. If so, you'd better check that you have a slip ring for a twin too. That's one with a short brass segment in the base, not a complete brass ring.

A dirty slip ring can have random effects and it might affect one cylinder more than the other. One strange result of a dirty slip ring is plugs which will spark when sitting out on the engine, but when the plugs are screwed into the head, the HT current tracks around the slip ring to the wrong pickup and plug, so the plugs don't fire when under compression.

[vwphillips]

Thanks Triton Thrasher

any info is usefull as I have no experience of magnetos

Anyway an update

I took the mag off and took it to Ken at britespark. http://www.brightsparkmagnetos.com/

He reseated the points assemble and the rear spark improved considerable, Ken said that they were not seated correctly.
The bike had been starting and running well for some weeks since they were touched which is difficult to understand.

As the magneto was off he gave it a service anyway, the capaciter and one pickup were leaking.
The pickup was changed and the capcitor changed for one of his easy fit capacitors attached to the points rather than hidden in the body. Ken also adjusted the body shiming as it was tight.

I was able to watch while he worked on it which was very informative.

He was also able to establish that the cam for the rear pickup is at the bottom of the cam ring which was very useful
Ken also tested the mag a 50 degrees C as well as ambient.

I was impessed with Ken's attention to detail and testing.

I have now refitted the mag after some problem with the bottom fitting and must time it(gulp)

The was a post about the angle of the plug when useing an plug TDC tool

the book timeing is 3/8 inch(9.5mm) BTDC
if the plug angle is 45 degrees I make this 13.44mm at 45 degrees

I made this some years ago http://www.vicsjavascripts.org/Triangles/Triangles.htm if anyone is interested

I will let you know how I get on

[muskrat]

G'day Vic.
See here http://www.a7a10.net/forum/index.php?topic=6011.msg41207#msg41207  re timing. 3/8" is 35 degrees but with the crap they call fuel these days 32 degrees may work better.
Cheers

[chaterlea25]

Hi Vw,
Working out the piston position with trig will depend on the shape of the piston crown
If the piston is flat topped then the base line of the triangle increases as the piston decends the bore and vice versa

Its worth while setting the crank position with a degree disc and then making a piston stop from an old spark plug
gutted and bored and tapped out to take a threaded bar and locknut
Once the full advance position is set this way keep the tool in a safe place for future use, mark it L or R as the threaded in position can vary from side to side

A previous post  I wrote on the subject
http://www.a7a10.net/forum/index.php?topic=1274.0

HTH
John

[bikerboy]

Whats up with the good old method of putting a straw down the spark plug hole and turning the engine to get it in the right position?

BTW is that green A7 the one that was on the Reading toy run at Christmas it looks very familiar?

[vwphillips]

bikeboy

 my bike lives in Portsmouth and got as far as Wickam over Christmass

I have finally set the points(I hope after numerous attempts) but have not tried starting it

Silly question I am sure but

can I run the engine for a short while with the
outer timing cover
primary chain case
and rocker covers off?

[bsa-bill]

Primary ok  but I would pop the timing side case on - lots of oil flying about in there
and whirly bit spinning around both side - be careful