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reverb Offline OP
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Hello;

Yesterday tried to start this engine and had kickbacks galore. I removed stuff and noticed that somehow the screw that goes into the cam (Hunt magneto fixed; unit engine) possibly did not doing the tight right because I checked the points at 38º and had 0.008 inches between its.
Now I have the taper corrected and somehow tight. I have the points opening at 38º with a cigarette paper (measured about 0.0015) I checked and a 0.002 gauge cannot enter between points but at TDC I have the points closed (I cannot remove the paper)
When I kicked I had no kickbacks but no starting too.

-Is 0.0015 too little of a gap at 38º? Is where the paper just can be removed...
-Are the points closed at TDC?
-How to check both lobes to confirm that I have the same breaking point?

----In any case I have strong spark; fuel goes into cylinders right. Compression feels good.

Thanks

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I think the paper thickness is good enough.


Did you set the points gap fully open first?

You check the timing on the other cylinder/other cam lobe by rotating the crankshaft so the other cylinder is on compression stroke and the other cam lobe is opening the points. Then check its timing.

Last edited by triton thrasher; 06/24/22 8:30 am.

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Hi TT; the points start to open at 38º (with that measure commented) then open more between 38 and TDC then close in TDC (the paper cannot be removed)
The gap I think is provided by the factory (Hunt) is a new magneto. Max gap is 0.012. I did not touched the point arm to change the gap due to change the internal timing too.
I think that the changing of the gap is when somehow the points are removed.

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Originally Posted by reverb
Hi TT; the points start to open at 38º (with that measure commented) then open more between 38 and TDC then close in TDC (the paper cannot be removed)
.


Ok if that’s what it does, that’s what it does. I didn’t expect that, but I don’t know my Hunts.


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If timing is fixed at 38 btdc then it will kick back.

Is the hunt mag a new addition to the bike or was it always on there?

If it was always atributed to the bike (whilst in your ownership and when it was running), have you done anything else to the bike like change cams or even reset the valve clearences, fit higher compression pistons etc etc?

The reason I ask is my 823cc A65 is a nightmare to start at present, when I first built it would start, but the pistons were just kissing the head - it didn't sound pretty, though once you polished the fuel residue off the piston you wouldn't be able to tell. I releived the head to give a 0.045"-0.05" clearance and re-assembled.

Since re-assembling, I have only been able to start the bike twice. Once was on points (though the AAU springs are the original ones and weak so it quickly went to full advance), tried a series of variables and nothing seems to work (long story short I am going to fit an A70 top end for now so I can at least use the bike)....

Apart from effectively lowering compression, the only other thing I did was change the valve clearance from .004" to .006", this will mean the valves open a degree or two later and close a degree or two sooner. The fitted cam being a softly tuned one will have a higher static compression than that of a full race cam.. wouldn't be a problem on a 650, but those extra CC's on an engine which is still a little tight make a huge difference. Like you, compression is good, so much you can stand on the starter and kickback is enough to break your foot.

I know nothing about mags, only they tend to work best with a 0.018" plug gap, and more likely to foul at wider gaps. But I do know that sometimes a fault like this might not be the ignition....

Last edited by Allan G; 06/25/22 6:25 am.

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Hi; the mag is new. I bought it several years ago and the engine is a rebuilt one that I did years ago too.
I managed to starts it but kickback in every try. Is painful.
Is a 750.
The carburetors are new out of the package.
Do not think that would be other problem due to as the title mention, I removed the magneto and installed again and obtained no kickback but a dead engine so I removed it again and checked everything perfectly and as mentioned is starting but kickback in every kick.
I have a damaged body so I do not have enough spirit right now to as you say stand on the kickstarter to affront that strong impact in every kick.

I bought it years ago, due to this bike is a bonneville but I never had the bike actually, I built it from pieces so no battery no coils etc hence the mag
I remember to ask in other forum to several guys with a unit and a hunt mag or Morris magnetos and all mentioned that their machines did not kickback.
I have a hunt in my pre unit and is a pleasure due to the auto advance. Never ever kicked back
With all that in mind I decided to buy it.

---I will increase the breaking of the points. I think that retards a bit but in that case is not anymore "points starting to break" is more like "points opening" at 38º

Here showing the rotor position of the magneto when "points starting to break" and then when closed.

opening.JPG close.JPG
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Point gap is .012 - .015, plug gap is .018 . When you put the cap on make sure it not pushing the points spring down and touching the mounting screw. It’ll ground the points


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Originally Posted by konon
Point gap is .012 - .015, plug gap is .018 . When you put the cap on make sure it not pushing the points spring down and touching the mounting screw. It’ll ground the points


Doh!!! Now I read it back that was very very wrong. My mind doesn’t operate half as good as it used to.


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looks like a 180 cam
but
cant quite tell from the quality of the image
¿ are both points-cam-tips... the same shape / profile ?
( should be same shape and 180° apart , from tip to tip , for a vertical twin )

¿ does this magneto use the impulse spring drive ? ( dont think so ? )

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Hi Quinten; if you click on the image you can enlarge it and you will see pretty good the details.
Is the same shape and the process is repeated in both parts. Wasted spark.

I put the points starting to break like the first image at 38º. Kicks strongly in every try
The magneto have side slots on a base where you can move it on his axis to fine tune a bit the opening of the points.
I tried to have more separation between points and obtained same kicking and may be slightly more difficult to fire up the engine.
I will try timing to 35 - 36º. In theory will kick the same because I need about 20º to have a good starting no kickback kick...

The other option but I am not electronic guy is to make a gizmo similar to what Morris sells to "retard" to start then move again that lever to ride. Kind of what the pre units have it.
I do not know exactly what they do to the points arm and how they lock the lever to ride.
May be one of you that know electricity or electronics can suggest me a way. I can try it.

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...hello; I put the alternator rotor at about 34-35º with the points just breaking. I obtained the kickbacks but may be with less aggression. When started sounded a bit not so "rounded".

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Is there a way to know if I am 180º out? do not see how with a 360º crank and wasted spark but may be I am wrong
In those photos showing when points start to break and when just closed, I set it in CW rotation and that could be the error? May be I needed to rotate CCW

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Triumph is CW. BSA is CCW


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Hi Konon; yes. The EX camshaft with Triumph turns CW but my question is regarding the magneto cam movement to set the points to start to break.
The strong kickbacks; the backfiring and some flame in the exhaust besides a possible close ex valve, indicates mag 180º out I think but if the camshaft turns CW and I moved the mag cam that way how I can be out 180?

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Might not be as much as 180° out, but are your mag points just opening or just closing when you set your timing?

It’s been a long time (10+ years) since I timed a mag but from memory the points were just opening for correct operation. We accidentally tried timing it points closing once and couldn’t work out why the devil wouldn’t start.

To be certain, you could disconnect the drive from the cam gear and rotate the mag in the normal operating direction. Plugs rested on the head and magneto earthed in some way to the engine. And watch the plugs spark, at what point of the points position do the plugs spark?

Just looking at your photos again, I would think that the mag cam wants be be more like horizontal, this would be the point where the points start to open. Least thats how it looks.


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Hi Allan; the points were set when just opening not closing. Closing is the bottom photo.
I cannot disconnect the cam gear with a Hunt magneto just installed.
So at 38º (or at 34 - 35º that I tested) and the magneto like the first photo; If I move the kick lever the mag cam moves CW and the points continue to open passing the TDC then close as the second photo.

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Another thing to ask, is the mag the correct type, as in I’m pretty sure they only work in one direction of rotation. Might be way out of the park with that question but I think it’s worth asking.


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Hunt have 2 types for Triumph and the only thing to change is the base plate; rear pieces; etc. I have both,

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Originally Posted by reverb
Hunt have 2 types for Triumph and the only thing to change is the base plate; rear pieces; etc. I have both,

Yes the unit uses a different setup than the pre-unit .

but I'm guessing the ( same Magneto body )
"unit" BSA Magneto is set up differently than the triumph "unit" Magneto ?

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Originally Posted by reverb
Hunt have 2 types for Triumph and the only thing to change is the base plate; rear pieces; etc. I have both,

I’m thinking that you could have been sold an A65 magneto instead of the triumph magneto which would rotate in the opposite direction.

I’m no expert on these, but I don’t like to see people struggle either.


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Originally Posted by Allan G
I’m thinking that you could have been sold an A65 magneto instead of the triumph magneto which would rotate in the opposite direction.

When you rotate the armature by hand, you can feel the drag of the magnet. The points should open a few degrees after maximum drag, when you can feel an “over centre” effect.

Running a magneto backwards would usually give you no spark or a very weak spark. It sounds like Reverb’s problem is not a weak spark. It sounds like he’s trying to start it without any manual or auto retard and having problems that are somewhat inevitable.


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I actually have the same Hunt magneto on my pre-unit Triumph. Everything seems correct from the photos and descriptions so far. The magneto direction is correct (clockwise looking at the points cam) and should be just opening at the desired crankshaft advance position.

That being said and to Triton Thrasher's point: when I had a fixed gear on the magneto timed at 36 degrees BTDC, I had to position the pistons quite carefully (just after compression stroke) before putting maximum effort into the kickstarter otherwise there was a really good chance of kickback. Even then, sometimes I didn't have the carb mixture correct for cold start and it still wouldn't start so back to square one again.

Noel

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