The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Lannis on 08.01. 2009 18:24

Title: Dynamic ignition timing - A10?
Post by: Lannis on 08.01. 2009 18:24
So here's the thing - Old PJ has built me this loverly A10 engine, which has done about 1600 miles around the UK pulling a 550 pound (yes, that's right - 40 stone - but I'm a vegetarian now, that will improve) two-up touring payload and done very well.

Now the bike has gotten off the ship, and is in my shop being adjusted and snugged down for American roads. 

I've read Old PJ's missives on the melted pistons, possibly an effect of too-advanced ignition timing due to worn magneto parts, and as a result am a little leery of just static-timing the engine with the auto-advance locked open, and setting the point gap, and hoping all goes well.  How do I know that, under running condtions, the mag is firing in just the right place to avoid disaster?

On my A65 and other bikes, I can check running timing at all RPMS with a strobe light connected to the spark plug wire, and be sure that it's firing right.

Has anyone ever used a degree wheel to make a mark on some rotating part of their A10, and used a strobe light in a similar way?  Is there some part that turns with the crank that would lend itself to this sort of thing?  Seems to me it would be a good thing to do?

Lannis
Title: Re: Dynamic ignition timing - A10?
Post by: LJ. on 08.01. 2009 18:43
There has indeed been a lot of worrying reading concerning the melted pistons and I also am concerned with my timing proceedures on all four of my bikes... Okay one bike is a sidevalve and I'll never have to worry about that, no chance of melted piston on an M21.

I've never used a degree disc or strobe light and I guess I'm put off by this because of mainly having to remove so many parts to be able to set it up correctly. Hopefully I'll learn more about this as the thread grows, but up till now I have had no problem whatsoever with the usual tried and tested methods.
Title: Re: Dynamic ignition timing - A10?
Post by: stratcat on 08.01. 2009 20:25
Without cutting holes in your primary casing, the only way I could see of you doing it is to take the primrary cover off. Then use blobs of paint on the nut on the end of the crank and some sort of pointer system.
Very "heath robinson" and not conducive to good health and safety, messing around with the primary chain whizzing around
Title: Re: Dynamic ignition timing - A10?
Post by: bsa-bill on 08.01. 2009 22:17
Maybe it could be done Stratcat
First off you could remove the chain - then you just have the crank to be aware of.
From memory I think there are a few spare threads on the crank, now there may not be room but the cushdrive bits could also come off, then a timing disc could be secured using two washers and the original cushdrive retaining nut and a spare nut ( remember it's a 20 tpi ) they are available from stainless scources.
Well that's the theory, wonder if anybody has used this method - bet its been done

All the best - Bill
Title: Re: Dynamic ignition timing - A10?
Post by: a10gf on 08.01. 2009 23:03
... and a Welcome onboard to Lannis.

e
Title: Re: Dynamic ignition timing - A10?
Post by: Lannis on 09.01. 2009 01:20
... and a Welcome onboard to Lannis.

e

Thanks!

I assume Heath Robinson is kin to Rube Goldberg, that legendary designer of impossible and overcomplicated mechanical contraptions ....

Maybe I'm over-worrying about it; maybe setting the timing once via the drive gears, and setting the points, and hoping the points cam in the mag is OK,  will assure that I don't melt a piston.  Just want to get some serious miles out of this bike before I have to do anything to it again !

Lannis
Title: Re: Dynamic ignition timing - A10?
Post by: twintom on 09.01. 2009 06:18

Hello, over the years i only needed one thing. My grandfather was with it very fast, too.
 *conf* cheers Tom
Title: Re: Dynamic ignition timing - A10?
Post by: stratcat on 09.01. 2009 16:49
Maybe it could be done Stratcat
First off you could remove the chain - then you just have the crank to be aware of.

You couldn't start it without the chain.


I would wonder what you would gain from dynamic timing, O.K. you could get it spot on. When you consider that most people set timing with a stick down the plug hole and a bit of fag paper I'm not sure its worth the effort.
Also as modern fuel is so different from the fuel the bikes were designed to run on it's a bit of a moot point.
I'd say as long as it's not pinking (pinging) I'd not worry too much.

One of Heath Robinsons wonderful inventions

Title: Re: Dynamic ignition timing - A10?
Post by: Richard on 09.01. 2009 17:19
Lannis
set the timing as per the book except I alter the timing to compensate for modern fuel so if the timing is 11/16 btdc I would set it at 5/8btdc and so on.
you can check the timing with a disc quite easily but in a static mode
What I did was to put a thread in the timing side of the creankshaft as the timing cover is still off at this stage and put the engine at true TDC then with a bolt with two nuts on it I attached the disc to this fitted a wire to use as a pointer and then checked the timing making a note of the degree's should be about 32 degrees.
But to be honest with the A10 if it does not kick back on starting and sounds and runs crisply you should have no worries
all the best
Richard
Title: Re: Dynamic ignition timing - A10?
Post by: bsa-bill on 09.01. 2009 17:31



You couldn't start it without the chain.

How did I miss that !!!! *red* *doh* *problem*

Oh well at 65 the occasional brain fart is to be expected I suppose.
I do like the idea of some form of micro adjuster on the Magneto though, and I know that has been done.

All the best - Bill ( who might just be a tad embarrassed )

Title: Re: Dynamic ignition timing - A10?
Post by: Lannis on 09.01. 2009 17:50
Lannis
set the timing as per the book except I alter the timing to compensate for modern fuel so if the timing is 11/16 btdc I would set it at 5/8btdc and so on.
Richard

All, good input and maybe I ort to quit worrying, but a mate who was also listening for pinking and whose bike started easy melted two pistons on his A10, and it looks to be a bad magneto ring, so I was trying to eliminate that from the equation.

Now about this static timing - maybe I missed it in my Haynes' Manual, but how do you convert the reading on the gage or stick that's in the spark plug hole to compensate for the angle of the hole?  If I want to do 5/8" BTDC actual piston movement, how do I find that through the hole (without removing the heads)?   If I knew the angle I could do sines and cosines and figger it out, I suppose, although school was a LONG time ago and getting longer!

Lannis
Title: Re: Dynamic ignition timing - A10?
Post by: Richard on 09.01. 2009 19:37
Lannis
one reason to convert the timing mesurment to degrees and fit a disc  to the timing side of the crank
It is easy to determine the actual TDC with the spark plug hole tool set the disc to zero then turn back 50 degrees then bring forward to the actual degree mark you require BTDC (Fully advanced) hey presto timing set.
Richard
Title: Re: Dynamic ignition timing - A10?
Post by: dpaddock on 09.01. 2009 20:37
All this talk about melted pistons and I haven't seen but one reference to it here. Is there an epidemic underway or just the fear of one? Anyway, . .
Make sure the mag is set up to have the breaker open at precisely 180o apart by attaching the degree disc to the drive end of the mag and manipulating the cam ring to achieve this. Then stake the cam in position (auto advance). For manual advance, make sure the ring rotates concentrically with the breaker assembly. The idea is to ensure that both cylinders fire at the same advance setting. You'll be amazed at the result!
I use a thin red straw (from a can of WD-40) down the spark plug hole. It's nigh parallel with the piston stroke and is easily marked for TDC and whichever advance mark you want. It's also long enough to keep from getting lost in there.
Finding TDC is a problem, but you only need to do it once. Here's what I do:
Remove the primary cover cap. Get the LH piston approximately 1/4 inch from TDC and make a mark on the exposed chain with a white paint. Mark the straw, too, where it's easily aligned with a fin edge. Now rotate the engine past TDC so that the straw mark is aligned with the fin edge again.
Mark the chain again with white paint and measure the linear distance between the chain marks. Half that distance is where you mark the straw for TDC against the same fin edge when you rotate the engine the other way.
Title: Re: Dynamic ignition timing - A10?
Post by: RichardL on 10.01. 2009 00:16
Let's suppose we could, indeed, establish a timing mark that could be viewed by a timing light. What then? It's not like we have a big distributor to grab onto for careful turning and adjustment. Instead, the part we would need to turn is, itself, turning and tightened down, else the engine does't run for 'dynamic' timing. I wonder what the thought process was when the Lucas engineer decided that the mechanic should try to detect and hold the smallest possible point opening while the cam follower is on the steepest part of the cam.

There are other threads here on the forum where we have discussed manual timing techniques at length. I think one useful idea back then was a light or meter, thus freeing up at least one hand. For me, it seemed that the most important thing was a gentle approach to tightening down the pinion. Since my head is about to come off (pick one), I will soon get more practice checking timing.

Richard L.
Title: Re: Dynamic ignition timing - A10?
Post by: groily on 10.01. 2009 07:01
Would be nice to be able to watch the advance and retard unit at work though, to see whether it really is fully advanced at whatever rpm, and fully back before tickover. For those with ATDs that is. Otherwise, the bulb/meter route should work fine for the points, and for the pistons I'll stick with a depth gauge if the head's off, a degree disc if the primary cover is off, or a prodder down the plug when it's all together.
Title: Re: Dynamic ignition timing - A10?
Post by: olev on 10.01. 2009 10:26
The attached article (for a commando) shows the advance curves for centrifugal and electronic ignition systems.
 
It would be interesting to see what the optimum curves for an A7 & A10 look like (off dyno readings)

http://www.captain.norton.clara.net/boyer_exposed.html#Top

Orabanda mentioned in a recent post the new BTH magnetos have slotted mounting holes so the whole magneto can be rotated for fine adjustment. sounds good to me.
Title: Re: Dynamic ignition timing - A10?
Post by: G/F DAVE on 10.01. 2009 12:26
I  Think the main thing is to make sure magneto is 100% ! IE; 180 degrees apart on points cam. I have a modified pinion for K2F magnetos that I can fit a degree disc to, once fitted to magneto taper I use a flexible drive from a battery drill and make up a pointer for disc bolted to mag body.Then zero the pointer when points start to open, doesnt have to be accurate as you adjust it when using strobe. Once you have set up your strobe you are ready to start drill to drive magneto. I normally just concentrate on one pickup to set pointer to zero then clip strobe to other pickup to check if its at zero reading IE; 180 degrees apart if its not you need to change cam ring or use oil stone/ flap wheel to grind ring untill both readings are correct. I also have timing marks on cam wheel & inner timing cover to set up the magneto once they are in line and using a buzzer to set points tighten ignition pinion and re-check with buzzer. Simple!!  *smile*G/F DAVE
Title: Re: Dynamic ignition timing - A10?
Post by: jfligg on 10.01. 2009 21:10
Hey Lannis

  What do the plugs look like?  Nice and brown?  Vegatarian??  Is that extra lettuce on the burger??  LOL
 Post a pic so we ca see the new bike.  Jeff