Cam ring capers

[orabanda]

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

[dpaddock]

Very clever, Richard!

David

[a10 gf]

Nice setup!

& in case I have not mentionned it before, thanks for all your excellent posts !
e

[orabanda]

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!





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







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

[rocket man]

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



dave

[Brian]

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 !

[orabanda]

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

[tombeau]

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

I look forward to hearing your results.
Cheers,
Iain

[a10 gf]

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

[trevinoz]

Brian,
            32 degrees is close enough to 5/16".
Trev.

[Brian]

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.

[trevinoz]

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.

[orabanda]

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

[tombeau]

http://www.srm-engineering.com/technical/timing-figures

[Triton Thrasher]

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.