Help - bike's gone bang!

[Worty]

This is really helpful fellas but: How and where do you attach the timing disc?

[duTch]

 I've never had fag papers, but a bit of tinfoil works as well, can easily tear so be careful to retrieve it all.

[muskrat]

G'day wortluck.
To use a timing disc (degree wheel) you need to drop the primary cover and cush nut and put it behind the spring. Easier if you have an SRM cush nut as it has holes to attach a wheel. At least it's not a job you have to do often, most owners never.
Cheers

[Worty]

Cheers duTch and muskrat.  What about those things you screw into the spark plug hole.  From what I can work out, the stroke of a Flash is 84mm which you divide by 180 (degrees).  This give a figure of 0.47mm (to two decimal places).  This means that for every 0.47mm the piston is moved, it is equal to 1 degree (BTDC in this instance).  As I need 32 degrees BTDC, 32 x 0.47 = 15.04mm, so I just move it back until this figure is reached and that should be 32 degrees BTDC.  If this is so, then no need for a timing disc attachment.

By the way, I've got my fibre drive and 20l of cheap oil (£34 inc delivery).  It seems a good spec oil for the price but my plan is to drain the existing oil, clean the gauze, filter and oil tank.  Refill the oil to about half a tank and run for a few miles.  Drain that off and repeat the process once more before filling with usual 20/50 - does this sound about right to get the missing teeth out of the engine.

One last thing, anyone know where I can get rivets for the ATD repair, otherwise I'll get them made by my engineer fella.

[duTch]

 

From what I can work out, the stroke of a Flash is 84mm which you divide by 180 (degrees).  This give a figure of 0.47mm (to two decimal places).  This means that for every 0.47mm the piston is moved, it is equal to 1 degree (BTDC in this instance).  As I need 32 degrees BTDC, 32 x 0.47 = 15.04mm, so I just move it back until this figure is reached and that should be 32 degrees BTDC.  If this is so, then no need for a timing disc attachment.

 I don't think it quite works like that...the piston travel is greater between 45º either side  of half way up/down, due to angular trigonometric geometry stuff, and Pythagarus theorum... ..
 There's a chart here somehere that calculates it all. Off the 'top of my head', the more realistic measurement is something like 5/16-11/32" before TDC -stick down de 'ole method  (TBC)

[duTch]

 Here's a link to a thread with the chart;

https://www.a7a10.net/forum/index.php?topic=195.msg795#msg795


   Tried to 'insert image', but copy and paste may not/ doesn't work

[Worty]

Got it, thanks duTch.  The instructions seem to indicate 5/16 which is 8mm in new money.  So to clarify, I find TDC and measure piston movement with rod down 'ole of 8mm and I have 32 degrees BTDC - please tell me this is right.

[dave55]

Have you tried Dixon Hall in Wakey for the rivets ? not much they don't sell ?

[Worty]

Cheers all.  It's just the size of the rivets I'm not sure about.  Also not sure if they'd be 'off the shelf'.

[duTch]

 

......  So to clarify, I find TDC and measure piston movement with rod down 'ole of 8mm and I have 32 degrees BTDC - please tell me this is right.....

 Yeah- fairly much...to find TDC, is easier to roll it one way down a bit and note the measurement, then back  the other way the same distance down and split the difference- if that makes sense ?

 I may be missing something in that due to when I do it is usually with the Primary off and looking at the crank.... an aside note - dunno if it's just the cranks I have, but have noticed that the split-pin hole in the end of all my cranks seems to align with ether the big-end pin or 90º (can't remember which but all the same)

  Don't forget to come up to the mark as I mentioned earlier ^^^
 


 **edit- my method may also be a bit vague due to 3am here drinking beer trying to figure out why my Macbook files are all saved/stored/created/logged 12/12/2018 (or whatever year)...and may have a call about 5 to go to work ...if anyone has clues I'd be grateful

[RichardL]

Guys,

Remember this? Enter stroke and rod length and Robert is pursuing canubial relations with your mother's sister.

http://www.a7a10.net/BSA/ignition%20timing%20converter.xls

Richard L.

[muskrat]

Ignition timing for the Long stroke is 0.313" for 1947-49 and 0.375" for 1950 btdc. I can't find figures for the con rod length to use the calculator.
Cheers

[Worty]

Cheers Musky, what's your take on the timing for a 1961 Flash.  I make it 0.3125 or about 8mm.  Seems to be a lot of variation as to how people set it up - quite confusing.  I reckon I'll have to get my mate to take me through it then I should be ok.  Any info out there to suggest the dimensions of the rivets holding the fibre drive to the ATD?

Look, I really appreciate all the info.  The skills for maintaining these machines lie with a relatively small number of 'older' people, so I think of myself as an apprentice really.  I don't have the confidence to do some jobs for fear of it costing me a fortune to put right if I screw it up.  On the other hand, if I don't do them, I won't learn and it may become harder to find people who do.

With this in mind, I'd like to thank you for your patience - long may it continue.

[trevinoz]

Talk to Andrew and buy the kit.
It comes with everything that you need.

[bikerboy]

I know those rivets were available from a place called Grove Classics. Ok its a velo dealer but thats where I got mine a couple of years ago