The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: mikeb on 20.01. 2015 10:40

Title: timing differences - how bad and what to do?
Post by: mikeb on 20.01. 2015 10:40
I’ve been adjusting the timing on my ’61 Super Rocket and aiming for 5/16 inch BTDC (7.9mm) or maybe a little closer to 3/8 (9.5mm) as I have a manual advance/retard. I’m using the object vertically down the pug hole method and a buzzer. Problem is there’s a sizeable difference BTDC between left and right:

Left = 9.3mm BTDC = 0.366inches -> 36degrees approx., points gap = 0.012in
Right = 6.2mm = 0.244in -> 28 degrees approx., points gap = 0.013in (maybe 0.0135??)

(Degrees BTDC are taken from this table, if I’m reading it right- http://www.a7a10.net/forum/index.php?action=dlattach;topic=195.0;attach=16426;image (http://www.a7a10.net/forum/index.php?action=dlattach;topic=195.0;attach=16426;image) )

The right cylinder has a bluer pipe near the head which I guess suggests more retarded ignition. I’ve recently bought the bike – the timing was very retarded and the carb had problems (warped flange, pitted slide…) so I can’t get a read on the plugs yet, other than they are both very black.

First question is how bad is this?

Most of the threads about timing differences also mention differences in points gaps and then aim at the cam ring or its bearing cup.  As my points are about the same I guess that still leaves the cam ring as suspect. I assume the heights are the same so how to tell?

Are there other likely causes?

BTW if you've ever had a yearning to make a magento buzzer look at this -http://www.historicmotorcycle.org.au/magneto/MAGNETO%20TIMING%20TOOL.pdf (http://www.historicmotorcycle.org.au/magneto/MAGNETO%20TIMING%20TOOL.pdf) -  i made it without the kit mentioned and it works a treat. cheaper than taking up smoking to get a fag paper

Thanks
Mike
Title: Re: timing differences - how bad and what to do?
Post by: bsa-bill on 20.01. 2015 11:34
Quote
Problem is there’s a sizeable difference BTDC between left and right:

Hi Mike
To just clarify - are you talking about a difference in the measurement on the stick down the plug hole or the point at which the points open.
The first would suggest pistons are not the same (quite possible)
The second would as you say point to the cam ring, new cam rings are available but many seem to prefer grinding them to correct with a stone.
you could also split the difference and see how it goes
Title: Re: timing differences - how bad and what to do?
Post by: mikeb on 20.01. 2015 19:21
Bill - I meant the distance before TDC before at which points open. - height BTDC on the left being bigger so firing on left being more advanced.

if its the cam ring the lobe height must be about the same if the points gap is about even, so i guess one lobe may have a different angle of attack... ?? how would I grind that? would not facing the attack slope risk making the lobe lower?

any other suspects?

cheers
Title: Re: timing differences - how bad and what to do?
Post by: muskrat on 20.01. 2015 19:30
G'day Mike.
 *eek* I would have to agree with Bill on ODD pistons fitted. For the difference in timing to be that far out it's a wonder it ran at all. Do a compression test.
Cheers
Title: Re: timing differences - how bad and what to do?
Post by: mikeb on 20.01. 2015 19:47
muskrat - i did a quick test when i got the bike and both were around 145-150psi - can't recall which side was a little higher and it was a quick and dirty test. with torch down the plug hole i can see '060' marked on one piston so i guess that's oversize. actually idles in a lumpy rough but ok kind of way.
either way, the difference is between TDC and points opening is by each side, so i can't see how that would explain it. and the the pointer down the plughole was vertical so crown shape/differences wouldn't be a factor.
the only obvious difference between cylinders is the exhaust pipe on the right is darker/blue near the head.

???
Title: Re: timing differences - how bad and what to do?
Post by: chaterlea25 on 20.01. 2015 19:48
HI,
Quote
First question is how bad is this?
Not good !!!

Either the points pivot cam ring or magneto bearings need attention, maybe all 3
Usually as Bill said the points gap varies from one side to the other, but 1- 1.5 thou would not equal 6 degrees difference
Make up a timing plug from an old plug (nnock the middle out ) and thread the middle to accept a set stud (rounded inner end) and locknut
Firstly use this tool to set up the degree disc.
Then measure the timing difference setting the tool to stop the piston at the required position
( Use the tool on one side only to negate physical differences in piston / head etc)
This will give you an accurate degree setting to work from
There are several long topics on the forum about similar issues
Heres one, http://www.a7a10.net/forum/index.php?topic=3747.0

HTH
John

Title: Re: timing differences - how bad and what to do?
Post by: a10gf on 20.01. 2015 19:53
Camring eccentric vs armature shaft\points ? See http://www.a7a10.net/forum/index.php?topic=1375  for some findings\experiments > http://www.a7a10.net/forum/index.php?topic=1375.msg9862#msg9862

My test setup > http://www.a7a10.net/forum/index.php?topic=1375.msg9915#msg9915

Big gain in getting the l\r timing right, a well running, powerful engine, worth (any amount of :O) time and money.
Title: Re: timing differences - how bad and what to do?
Post by: wilko on 20.01. 2015 20:56
A mate has a v-twin cam ring that was worn so bad that one cylinder was firing 20 degrees late. Anew one fixed that. so they can wear quite radically if not lightly greased periodically.
Title: Re: timing differences - how bad and what to do?
Post by: beezermacc on 20.01. 2015 23:19
I deal with this issue all the time. Your main problem is the difference in piston heights when the fuel detonates, 9.3 mm on one side then 6.2mm on the other. Normally on an A10 a points imbalance of less than 0.002" is OK because the old girl (A10) is quite forgiving, particularly the iron head versions. The cam ring is not always the culprit, often its the machining of the cam ring housing which may be eccentric or bored crooked to the face. Your points gap imbalance is only slight, maybe 0.0015 which is tolerable. The points gap imbalance, in itself, is not a problem unless its enormous, but it usually indicates the mag timing is out as well. I would make sure everything is clean (cam, cam housing - particularly the face which mates with the mag body, shims, points heel, face of mag body) and check that the cam housing is a tight fit in the mag body, i.e. not capable of slopping about side-to-side. then set the mag up in the vice with a degree disc on it. Another point to note is that the automatic ones are easier to fix than the manual ones because the cams in the manual mags need to be loose to work! Check the firing moments with the degree disc; you'll probably find the imbalance is about 3 or 4 degrees which translates to 6 or 8 degrees at the crankshaft. It is very rare for me to have to stone the cam ring but, if I do (often on Vincents) I put a Dremel sanding burr ( not a stone as these wear unevenly) in a pillar drill and remove the smallest amount of metal off the leading edge of the overadvanced side of the cam ring. Be careful! You don't need to remove much metal to go too far!
Title: Re: timing differences - how bad and what to do?
Post by: beezermacc on 21.01. 2015 07:59
A mate has a v-twin cam ring that was worn so bad that one cylinder was firing 20 degrees late. Anew one fixed that. so they can wear quite radically if not lightly greased periodically.
It is more likely that the mag was fitted with the wrong cam ring. A Vincent is a 50 degree V twin but other cam rings can be set for different V's
Title: Re: timing differences - how bad and what to do?
Post by: muskrat on 21.01. 2015 09:34
My timing set up 1/2 way down this page http://www.a7a10.net/forum/index.php?topic=6011.msg41207#msg41207
Cheers
Title: Re: timing differences - how bad and what to do?
Post by: mikeb on 21.01. 2015 11:15
Thanks for the suggestions so far.  I made a piston stop (spark plug type), fix a laminated timing disk to the right hand end of the crankshaft (not easy that bit) and did some measuring. Basically the left fires about 7 degrees (at the crank) before the right (39deg vs 32deg).

On the cam ring pic below the green marks show where the cylinders actually fire – so the left is a few degrees ahead on the cam ring. (the black line is 180 degrees) The orange lines are the beginning of the visible wear tracks on the inside of the cam ring (from the points heel) and the red lines the end of the wear tracks. rotation is clockwise.

In case it’s a bent points plate I fitting a different one and the cylinder differences BTDC were the same, if not bigger.  As an aside, these points had a smaller gap as the heel is well worn… on the pic below note the orange mark (wear mark) and the green (firing point) are closer together on the left than on the right – so I assume the left lobe is steeper, and so a smaller points gap may be even more advanced on the left than a larger points gap. (? Does this make sense?)

In case it’s a mag bearing, shaft or cam ring housing I rotated the cam ring 180 degrees.In this position it won’t press in completely (coz the slot for the bottom peg is now at the top) but it was mostly in. obviously the heel will not be running fully in the same part of the cam ring. Doing this the right cylinder was now about 4 degrees ahead of the left. That’s a reversal (tho not of the full 6-7 degrees).. and if the housing, shaft, bearing and points haven't changed then it must be the cam ring... right???  for what its worth there's visible wear.

So the cam ring... Would you agree or am I missing something? At this stage I can’t see any reason to take the mag out form the bike for a bench test.... ??

If the cam ring is stuffed, I’ll get a new one. Given the forum posts talking of dodgy cam rings, who is a reliable manufacturer / supplier? I imagine they’ll be in the UK or US. This is a manual A/R.

And as parts take ages in this part of the world, I’m tempted to try grinding the current cam ring -  maybe facing the front of the left lobe with emery paper. In the photo I think I’m going at the bit at the end of the green arrows…. right?

Are you still reading all the way down here? Thanks for your help!

Mike
Title: Re: timing differences - how bad and what to do?
Post by: bsa-bill on 21.01. 2015 11:39
couple or more lads here might give you a price for a new cam ring Mike but as far as I can see your talking £70 UK plus any tax and travel.
Before parting with that or spending to much time with a stone/emery cloth or whatever I'd think about lifting the head and just confirm that both piston crowns occupy a similar and parallel position in time and space  *smiley4*

Anyway good luck with the honing
 
Title: Re: timing differences - how bad and what to do?
Post by: wilko on 21.01. 2015 20:07
A mate has a v-twin cam ring that was worn so bad that one cylinder was firing 20 degrees late. Anew one fixed that. so they can wear quite radically if not lightly greased periodically.
It is more likely that the mag was fitted with the wrong cam ring. A Vincent is a 50 degree V twin but other cam rings can be set for different V's
It was a very worn 50 degree cam ring off an AJS V-Twin. One of the bumps had worn down .
Title: Re: timing differences - how bad and what to do?
Post by: Triton Thrasher on 21.01. 2015 20:23
You can make quite a neat job with a Dremel type tool with a cylindrical stone. Keep it moving up and down the ramp.  As soon as you've visibly removed some metal, put the cam ring back into the magneto and check the timing. You may surprise yourself with the accuracy you can get.

You say it's a manual magneto. Is the fit of the cam ring sloppy in the mag?
Title: Re: timing differences - how bad and what to do?
Post by: cotterpinkid on 21.01. 2015 20:45
I had the same problem, running hot on one cylinder and cool on the other. I initially thought induction bias, but was advised to check the ignition timing. I purchased a bolt on degree disc and borrowed a timing strobe. Sure enough there was a big difference in ignition between each cylinder. The fault lay with the cam ring (which was 'new' replacement) and this was visibly evident just by comparing it with an original cam ring. Having replaced it with a BSA cam ring and re-timed the ignition both cylinders are spot on. Being able to check the timing with a strobe proved to be very worthwhile.
Title: Re: timing differences - how bad and what to do?
Post by: mikeb on 22.01. 2015 09:44
Triton thrasher - i can get a 0.002 inch feeler in on the sides between the cam ring and housing, but not at the top and bottom. there's a little side play but i guess it has to move.... how bad does that sound???? the ring does stick occasionally but i think this is about groove for the cable end adaptor (the next thing i need to look at).

bsa-bill - i don't quite follow why to the check piston crowns. there a couple in there somewhere and they seem to go up and down, with compression.  can you explain your thinking for me?

Some progress: so i've got the dremel out and have taken a bit of metal off so far. down to a 4-5 degree difference without too much effort at all. I think I'll get a new cylindrical stone in the morning (the current one is uneven) and have another go after that...

cheers

Mike
Title: Re: timing differences - how bad and what to do?
Post by: bsa-bill on 22.01. 2015 10:05
Quote
i don't quite follow why to the check piston crowns

Sorry if this is going over old ground , maybe I missed a post as I can't see if you've checked that both pistons are identical, yes they go up and down together but if not of the same make or compression rating the crowns could be of different heights, obvious one is not going to be too high but one could be lower than the other, this will upset timming to a degree (or two - pun intended ) and would also explain in part your blue pipe on one side although I've had a one pipe blues issue before which cured itself, think maybe a stuck valve.
Anyhow I just think if it was mine I would have the head off to check unless I had installed the pistons myself and knew what they were.
All the best with it though
Title: Re: timing differences - how bad and what to do?
Post by: mikeb on 22.01. 2015 10:30
OK thanks Bill - I get your point. I've got no idea whats in there really (other than some greyish metal bits) and will think this through - see if I can find the time and courage one day. or maybe I'll find a borescope and have a quick oil-free look for a start.

cheers
Title: Re: timing differences - how bad and what to do?
Post by: cyclobutch on 22.01. 2015 11:57
Roger at Cake Street did mine with a Dremel.
Title: Re: timing differences - how bad and what to do?
Post by: mikeb on 17.02. 2015 03:00
ok reporting back on this cam ring issue...
i ground it back to near equivalent to the other side with the rotary tool as per triton thrasher's encouragement. did it in 3 or 4 cautious steps, checking each one back on the bike. now within 2 degrees...

started second kick! idles! purrs!

this was easier that i expected especially once i marked up the cam ring so was clear about where to grind.
if your cam ring is similarly worn (and not a housing or shaft issue) I'd say give it a go.

Title: Re: timing differences - how bad and what to do?
Post by: muskrat on 17.02. 2015 08:41
Good on'ya Mike. Split the difference, one side adv 1, the other ret 1.
Cheers
Title: Re: timing differences - how bad and what to do?
Post by: RichardL on 04.04. 2015 21:19
Using this thread rather than starting a new topic.

Guys,

I might be losing my mind (perhaps reaching that age), but I can't seem to get my timing set for the life of me. Now, I've probably timed my A10 200 times and, at least three times correctly. Today, instead of using my traditional graticule stick down a plug hole I've actually got a dial indicator right on top of the piston. After several attmpts I'm not any to get closer than 70 to 100 thousandths. Usual deal: set the depth, adjust the points till the ciggy paper pulls out, smack the pinion home using a socket, tighten the pinion bolt, recheck BTDC. A couple of other things I do: wood wedge to create friction that stops points from sliding back down the slope when reaching "just open" position, wood wedge or screwdriver between points post and cam ring to hold points tight while tightening pinion bolt (while being real careful about hurting points or cam ring), solvent clean the pinion taper.

Even some consolation would help right now if this doesn't make sense to you, either. But, it HAS to be SOMETHING I'm doing wrong or missing. Just don't get it today, for some reason.

Richard L.
Title: Re: timing differences - how bad and what to do?
Post by: Triton Thrasher on 04.04. 2015 21:39

You shouldn't have to do anything with a stick at the points end.
Title: Re: timing differences - how bad and what to do?
Post by: RichardL on 04.04. 2015 22:06
Maybe not, but all I'm using the stick for is to provide a bit of friction so I can have the points fairly loose from the pinion taper when making the adjustment and preventling backsliding down the cam slope. Do you think it would better if the  pinion is somewhat snugged up while adjusting the points, so the friction comes from the taper?

Thanks for chimin' in TT.

Richard L.
Title: Re: timing differences - how bad and what to do?
Post by: duTch on 04.04. 2015 22:38

 A little ambiguous, but I think I got my head around it- am I missing/forgetting something? I'm not sure why you have the points plate loose on the taper..?
Quote
....., adjust the points till the ciggy paper pulls out, smack the pinion home using a socket,

 I'm assuming that means you've set the points @ ~12thou", and located the points plate relative to the cam ring, so the points are just opening...? (didn't you have some U-beaut doodad where you can hook up a meter to tell when the points are just open?..)

  I suggest maybe if the points plate is not snug in the taper, you may have a false points opening setting.
Also in "smacking the pinion, you may be moving the shaft a bit....I have the gear/nut close, but just free on the taper and push it snug with fingers, hold it in place then let the nut pull it on tight...

  I also took the opportunity to do a rough version of Orabandas slotting mod to make things a bit easier- didn't really take long with a rat tail file...!

Title: Re: timing differences - how bad and what to do?
Post by: morris on 04.04. 2015 22:56
Richard, like duTch I don't think "smacking" the pinion on is such a good idea. If the taper's a good fit, pushing it on with your fingers should give it enough grip for not to move while tightening. Giving it a smack will most probably disturbing it's position
Title: Re: timing differences - how bad and what to do?
Post by: RichardL on 04.04. 2015 23:33
Think you are all correct, because I've now got it within a few thousandths. First step was to be snug enough on the taper while adjusting the points. This made it so they did not slide easily down the slope when getting to the "just open" position. Also, the pinion didn't change positions so much between loose and tight. Then, sneaking up on tightening the pinion while bracing the points block.

Each piece of advice was a good building block to getting my head back in order. Thanks

Richard
Title: Re: timing differences - how bad and what to do?
Post by: chaterlea25 on 05.04. 2015 00:11
Hi Richard,
Musky posted a tip some time ago about holding the magneto in the correct position
remove the earth brush holder and fit a wooden dowel in place of the brush and spring
cut the dowel  to length so as it will hold the armature when screwed in partially
(or use a spare holder if you have one)

Once you have the timing set with the dial gauge ,(After fitting the cylinder head)
Make up a timing plug from an old gutted sparkplug tapped for a threaded bolt and locknut, round off the bolt end where it will meet the piston
remove the plug washer and screw it down fully into the head, then adjust the threaded bolt until it meets the piston then tighten the locknut
This tool will then stop the piston in the correct place anytime you wish to retime the engine in future

HTH
John
Title: Re: timing differences - how bad and what to do?
Post by: beezermacc on 05.04. 2015 09:07
A tip worth considering is the points gap, whilst ideally should be 10-12 thou the bike will run perfectly well in the range 9-15 thou. If you have set your timing and find the point of firing is a fraction retarded, opening the points gap has the same effect as retiming by taking the ATD off to advance the ignition, and vice versa of course.
The points gap limits are defined to prevent arcing and hammering. The lower limit is intended to be wide enough to prevent arcing should any fine particles find their way between the points. The upper limit is set to prevent 'hammering' - you have probably seen the impression of one contact on the other when the points faces don't line up very well - this is caused by the gap being too wide and the points crashing together, hence the term 'hammering'. The dwell angle (the amount of time the points are open/closed) is not critical as evidenced by the variety of cam rings for singles, twins and V's which have a variety of lift periods.