The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: orabanda on 09.09. 2009 17:06

Title: Cam ring capers
Post by: orabanda on 09.09. 2009 17:06
I am happy with the results of grinding a magneto cam ring. Just finished, so won't be able to run the bike until tomorrow (it's midnight!).

Originally there was 0.002" variance in the points gap, and 5 degrees in the timing.

Now the points are 0.012" each side, and the static timing is identical on each pot.

I used my Dremel, mounted up to their router table attachment.

Richard
Title: Re: Cam ring capers
Post by: dpaddock on 12.09. 2009 14:32
Very clever, Richard!

David
Title: Re: Cam ring capers
Post by: a10gf on 13.09. 2009 14:08
Nice setup!

& in case I have not mentionned it before, thanks for all your excellent posts !
e
Title: Re: Cam ring capers
Post by: orabanda on 13.09. 2009 15:28
Well, it was well worth the effort!
The cam ring was fitted to the maggie on my '51 plunger.

before this, I had the bike dyno tested, and the carburation was set up spot on!


I had the SRM timing wheel in place, and strobe checked the timing. However, it showed a big problem; LH pot was 34 BTDC, RH pot was 40 BTDC! The dyno run was abandoned at this stage, and I took the bike home to "sort 'er out"!

The frustrating thisn is that the maggie had been done up before the run (by others). I talked to them, and they confirmed that new bearings had been installed, and shimmed correctly. I couyld not measure ant run-out on the shaft, so decided to focus on the cam ring to get the result required.

I bought a NOS cam ring, but when installed, there was 8 degrees difference between the pots!

This was too valuable to modify, so I had a rusty old ring, and worked on it. It cleaned up nicely, but I had 0.003" points gap variance, and 6 degrees difference in firing points.

I kept grinding away the profile on the side with the wider points opening until both sides were 0.012", then focused on carefully advancing (removing) the lip which opens the points until, using a 0.0015" feeler gauge, both pots opened at the same point before TDC

It took me about 2 1/2 hours to get both pots firing identically.

I had the SRM timing disc set up on their primary drive nut.

Then I fired up the engine, and checked the timing with a strobe light; they were both firing at the same point BTDC! At idle, it was 6 degrees BTDC. . The full advance was 32 degrees BTDC

Now, back to the dyno!

On the previous run, we achieved 18.7 BHP(rear wheel). Now we had 19.7, and more torque!

We advanced the timing to 34 degrees; this was too much - power dropped off.

The best result was 31 degrees BTDC. It resulted in 20.2 HP, and the widest spread of torque.. This equates to 5 degrees BTDC at idle so if you install a SRM kit, you can check your bike easioly. Note that i slotted my 3 maggy mounting holes, and had a total of 18 degrees variance available just by moving the mag body!

(http://i302.photobucket.com/albums/nn82/orabanda/P1010165_resize.jpg)

(http://i302.photobucket.com/albums/nn82/orabanda/P1010166_resize.jpg)

Interestingly, the '54 GF produced 22.2 HP with a different curve profile. Both bikes have 365 cams, 7.25 : 1 pistons, and 276 carbs. The other point is that the '54 performed best at 30.5 BTDC

(http://i302.photobucket.com/albums/nn82/orabanda/54A10resizegraph.jpg)

(http://i302.photobucket.com/albums/nn82/orabanda/P1010168_resize.jpg)

(http://i302.photobucket.com/albums/nn82/orabanda/P1010170_resize.jpg)

The bikes are noticably smoother and more power ful to ride.

Stay tuned for the '51 Rigid, '56 Road Rocket, '61 RGS replica and '60 Super Rocket!

Richard
Title: Re: Cam ring capers
Post by: rocket man on 13.09. 2009 21:26
this is great a real deal carnt wait  for the super rocket result
and good pics as well nice one mate your doing a grand job
keep it up *beer*



dave
Title: Re: Cam ring capers
Post by: Brian on 14.09. 2009 08:26
Very interesting Richard. I was surprised that slotting the maggy gave so much variation, this is something I will do with the plunger A10 I am currently building. Do you happen to know what 31 degrees is in distance BTDC. I am running both my A10's at 5/16" BTDC as everytime I try to advance any further they ping (both iron heads), I use pump 98 octane unleaded fuel as its the best thats available where I live.

Also very interesting that the NOS cam ring you bought was so far out, obviously it pays to check everthing.

I cant quite see in the photos but are both these bikes using auto advance units ?

Good stuff !
Title: Re: Cam ring capers
Post by: orabanda on 14.09. 2009 08:41
Brian,
I don't believe that the NOS cam ring was out; rather that this is the result of machining inaccuracies in that particular K2F.

I could have taken a different approach and dismantled the maggie, and clocked the bearing housing relative to the cam ring bore (where I suspect the problem lies; the two bores are probably not concentric to each other), but it was much easier to take an old cam ring and modify it to suit the mag.

This is the reason i did not gring the NOS ring, as it is perfectly OK.

I don't know the relationship between degrees and vertical travel (I have a spreadsheet which will calculate for you), but when I build the Super Rocket engine in the next few months, I will set up dial gauge and degree wheel, and take the measurements down.

Both bikes on auto advance.

Regards,
Richard
Title: Re: Cam ring capers
Post by: tombeau on 14.09. 2009 09:34
This is great.
I didnt know about the SRM timing product.
I doubt it'll fit mine with the A65 primary drive set up.
After a 4 year "lay-off" (mag failure, nightmare job, redundancy, freelancing, new job, baby, emigration, house rebuild...) the bike felt considerably more gutless than I remembered it. I put it down to unleaded fuel. My bike is currently set at 35 degrees, with the pin-point accuracy that can only be achieved by sticking a twig down the plughole  and blu-tacking on a cardboard degree wheel *dunno*

I look forward to hearing your results.
Cheers,
Iain
Title: Re: Cam ring capers
Post by: a10gf on 14.09. 2009 09:57
Quote
I could have taken a different approach and dismantled the maggie, and clocked the bearing housing relative to the cam ring bore (where I suspect the problem lies; the two bores are probably not concentric to each other)
I choose that option, as the cam itself seemingly measured ok on both sides, although evaluated to grind it. If another need to fix the mag should occur, I'll probably get a new housing and hope i't ll be better than the one currently in use. Cam\points\housing, interesting to realize how critical the setup is, and how much it can impact performance even with the tiniest of misalignment. see http://www.a7a10.net/forum/index.php?topic=1375.msg9862#msg9862
Title: Re: Cam ring capers
Post by: trevinoz on 14.09. 2009 22:02
Brian,
            32 degrees is close enough to 5/16".
Trev.
Title: Re: Cam ring capers
Post by: Brian on 14.09. 2009 23:06
Thanks Trev, it would seem that by what Richard has found with the dyno and what I have worked out by trial and error that 5/16" is pretty much the optimum timing for the A10's in distance BTDC.

Unfortunately nobody near where I live has a dyno as I would like to give mine a run just for curiosity.

All good stuff.
Title: Re: Cam ring capers
Post by: trevinoz on 15.09. 2009 07:47
I am mystified as to where all the horses have gone.
Maybe they were a different breed way back when these engines were built and brake tested.
Maybe not as strong as today's horses so there were more required.
Trev.
Title: Re: Cam ring capers
Post by: orabanda on 15.09. 2009 08:20
Trev,
I must add that both bikes sounded "sweet as" when being run up.

The carburation was spot-on (achieved during the first phase of the run), and I know the timing was the same on each pot (on both bikes).

I have never subjected A10's to the sustained rpm that Ray did on the dyno; he held them on full load @ 6000 rpm for what seemed like forever (less than a minute)!

No con-rods came out, although my natural tendency was to hide behind a bench!

He did 34 runs on the black bike, and 20+ on the gold one.

There was another observer who was a long-time Triumph owner. He was suitably impressed, and said that there was no way he would have the confidence to work his T110 that hard!


They certainly sounded like 100BHP!

Richard
Title: Re: Cam ring capers
Post by: tombeau on 15.09. 2009 10:59
http://www.srm-engineering.com/technical/timing-figures
Title: Re: Cam ring capers
Post by: Triton Thrasher on 15.09. 2009 11:55

There was another observer who was a long-time Triumph owner. He was suitably impressed, and said that there was no way he would have the confidence to work his T110 that hard!



Yes, that's rather typical of old bike owners.
Title: Re: Cam ring capers
Post by: beezalex on 15.09. 2009 16:05
Yes, that's rather typical of old bike owners.

The owners being the old part, that is...
Title: Re: Cam ring capers
Post by: rocket man on 15.09. 2009 18:37
i will have you know im younger than my BSA by 2 years
Title: Re: Cam ring capers
Post by: duTch on 27.08. 2013 16:02


 I thought to start a new thread, but this is fairly relevant....good story Richard, I've seen it a few times when I first came along- in fact was one that often came up in searches before I new about the forum....now, on with my hijack

 When I was checking my maggie over to do the assembly timing, I noticed a points gap variation of about .005", but chose to leave it till I'd thought about it and researched a plan and Richards method was about what I had in mind, but with just the dremel, none of that other fancy stuff..!!

 Before doing anything drastic though, I had a thought that maybe the points plate could be sitting a bit askew on the taper(s), so pulled it off, and there was a couple of minor blemishes on the main one near the key.

  Gave it a light scrape clean with a blade, and back on the keyway, but rotated to where there's no pressure on the rubbing heel to offset it.
 Much better, but just fettled it a bit while doing in the tapered screw, and it's within about .001"(for now).
 Seems to be running more even, but still a bit rich.

 Not to say it's totally fixed, but thought it all worth a mention and worth looking at before doing any unnecessary grinding......?

 Cheers for now

Title: Re: Cam ring capers
Post by: Triton Thrasher on 27.08. 2013 19:25


There was another observer who was a long-time Triumph owner. He was suitably impressed, and said that there was no way he would have the confidence to work his T110 that hard!



Sounds like  he's just careful with his own bike, whatever make or model.
Title: Re: Cam ring capers
Post by: ianselva on 10.09. 2013 14:10
I have traced my problem of uneven running A7SS to the same problem ,but much worse. I cannot get the gaps nearer than .008 difference. I have tried two cam rings . I am thinking about replacing the whole lot with a Thorspark electronic conversion . Has anybody had any experience of them ?

Cheers

Ian
Title: Re: Cam ring capers
Post by: RichardL on 10.09. 2013 14:24
Ian,

Take a look at this topic showing a10gf's mag rebuild.  Work your way down to where he discusses and fixes bearing cup eccentricity. I'm not sure this is your problem,  but It may be somrthing you haven't considered.

 http://www.a7a10.net/forum/index.php?topic=1375.0

Richard L.
Title: Re: Cam ring capers
Post by: ianselva on 10.09. 2013 15:21
I did find the bearing cup was offset but it has just been centralised, and I dont think it be offset enough to correct the points gap differences.

Ian
Title: Re: Cam ring capers
Post by: duTch on 11.11. 2013 10:35

 With regard to my post on previous page- scraping the whatzit- it didn't work, can't even figure what logic I was using, I think someone slipped something in my tea.
 So I changed the needle jet and it's much better, but still the points have a ~0.005 variation, causing a difference in L/R timing, and a dark patch on the front of r/h plug which makes me wonder if it indicates a timing discrepancy?

 How is the cam ring held in place ? and is it intended to/should it remove easily?? so that I may inspect it properly
 Thanks in advance, duTch
   
Title: Re: Cam ring capers
Post by: ianselva on 11.11. 2013 10:59
The cam ring should just slide out once you remove the end cap and points.
I had to have my mag completely rebuilt into a spare housing as the points gap difference was too large even after having the bearing re-fitted.
I got a spare housing from Netley Marsh A/j and sent the whole lot off to BrightSpark magnetos. He had to use bits from one set of casings with bits from the other in order to get the armature central so the points gap at both positions was less than 0.002. This made all the difference as the bike now runs properly on both cylinders for the first time and both plugs come out looking the same colour.

Ian
Title: Re: Cam ring capers
Post by: Briz on 11.11. 2013 13:10
I am mystified as to where all the horses have gone.
Maybe they were a different breed way back when these engines were built and brake tested.
Maybe not as strong as today's horses so there were more required.
Trev.

Its the difference between crank horsepower and rear-wheel horsepower.
Title: Re: Cam ring capers
Post by: duTch on 11.11. 2013 21:52

Thanks Ian,
        figured maybe like that but mine seems to be held with some kind of goop, and I didn't want to force anything. I forgot to mention it's a auto-advance one, are they same-ish removal, or a 'snugger' fit ??

  (mine was rebuilt (condensor, rewound) a while ago by the legendary (in my area) Les McKiterick, only done ~2000 miles, but don't know if he removed/replaced cam- maybe not)
  cheers
Title: Re: Cam ring capers
Post by: trevinoz on 11.11. 2013 22:09
Dutch,
              They can be a bugger to get out. Should be a nice snug slding fit but they tend to get corrosion around them.
Usually a spell in the oven will get them moving but you have to take the end off to do it.
 
Trev.
Title: Re: Cam ring capers
Post by: duTch on 11.11. 2013 23:54

 Thanks Trev, I'll put a bit of thought into it...(a bit hard to believe I know!! *smile*)
Title: Re: Cam ring capers
Post by: duTch on 14.11. 2013 13:11

 Ok so I put some thought in, and then remembered the slide puller......!! a little suck here, and a little suck there...voila(that Italian thing) out it came, just the right amount of tongue lube.....!!
 Was held in with goop, and after a cleanup, found it to be a fairly sloppy fit, ring profile(thickness) ok, but a touch out of round.
Have packed it out with alfoil will see how it goes.

 for the record, it's a #42174B maggie