The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: LJ. on 15.09. 2009 11:45
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I've noticed recently my blue A10 to be sort of sluggish & juddery when in third gear at 30mph. I've been wondering if this might be a dirty air filter or weak carb etc... But on removing the outer timing cover to investigate a noise in there that others have heard. I found the breather cork to be undersized and in need of replacement. Further on, removing the inner timing cover I notice the timing wheels to be out of sync as you can see in the picture below.
Now then... What should I do here? move the wheels around to line up the dash and dots or leave well alone as it had been running mostly okay. I'm wondering if lining up correctly will allow the bike to run smoother than it is presently running.
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LJ
They don't line up all the time.
Rotate the engine & they should eventually line up once every few strokes.
Should add, if they are misaligned engine would not run!
Rusty
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LJ,
Rusty is correct, but it is more than every few strokes, like, every 98 revs. Look here http://www.a7a10.net/forum/index.php?topic=789.msg5039#msg5039 and at the rest of the thread for similar discussion. And, yes, in my "o'pinion", you must start with the marks in alignment, but, as you well know, others here have their "teeth" deeper into the subject.
Ricahrd L.
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A "timely" piece of wit!
I remember turning mine over to see how long it took.
Don't think that many for my longstroke, would have got bored & gone off for a beer long before that.
Think I only had to turn it over a dozen or so times max.
Rusty
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Hi Just come back in from the shed, excuse the oily hands...
Thanks guys!
Rusty... I got up to 49 turns and the dots n' dashes once again lined up. How good a feeling is that?? lol.
Richard... That is one thread that I missed, it was too mathematical and technical for me but was an interesting read in relation to my query. Such is the joy of our forms information and of you guys too!
Many thanks! (Now looks for the next problem) *lol*
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Sorry, I guess I need to check my math. The fact that no one objected at the time made me think I was right, so I moved on.
Hide your children, I will be back with more on this, probably a display of how one can walk with tail between legs.
Richard L.
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Your an honourable chap Richard... I'd have just re edited my post. *lol*
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Sitting on the bus, thinking. No matter how we slice the math, the cam must do one rev for every two of the crank. Hence, 49 crank revs yields 24-1/2 cam revs and the cam dot is 1/2 rev out of position. LJ, is it possible you started your count with the crank and idler marks aligned such that the next 49 turns got everything aligned?
I await the fall of the guillotine, but, no matter, the head in the basket had long forgotten numerical analysis and differential equations.
Richard L.
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I was informed that when positioning the valve timing idler pinion, the engine is automatically positioned at TDC and this can be used as the basis for setting the ignition timing at the same time. Can anybody confirm this.
Beezageezauk.
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It doesn't matter where the marks line up after revolving from the initial timing setting (BSA Service Sheet 215). The idler can be as big as a wagon wheel because the timing will be correct since the cam pinion has twice the number of teeth as the crank pinion. Period.
David
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The original point, I take it, was to determine if LJ's crank and cam are in the correct relationship regardless of where they are at at any given time. The only way to know this, as I understand it, is to initially line up the crank and cam timing marks with respect to the idler. My point was to give an idea (really, the exact idea) as to how many turns one would have to rotate the engine before the marks once again line up. Assuming gear timing is correct, and the crank mark is lined up with the idler mark, you are either right on the marks or 49 turns of the crank away from them. When you are 49 turns away, the cam gear mark will be 180 deg. away from its rightful location opposite its corresponding idler mark. If you are not timed correctly at the gears, you might learn this by turning the crank over 98 revs and seeing that the marks never all align, but that would be ridiculously tedious versus just repositoning the idler and cam.
Richard L.
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I'm begining to wish BSA had made the Idler Pinion the same size as the camshaft Pinion.....
;)
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. . . However, the philosophy of the 'hunting tooth' - whereby an idler is nearly always a weird number of teeth - is standard practice. What we don't want is the same too/eeth on the idler always taking the load every time a valve opens. So, by giving that gear a prime number's worth of teeth (or at least, like 49, a number not divisible by any of the numbers that divide into the number of teeth of the driver and driven gear (in this case 2 and 11 and 22)), we get to a situation where the load is shared equally between all the teeth of the idler and it, theoretically, lasts a very long time. With consequent benefit to the other pinions in the train, which are not having to mesh with the same ever more worn teeth.
This bit of knowledge from Groily, which was most enlightening (to me, at least), explains why not.
Richard L.
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Ok for the Idler, but what about the camshaft pinion, teeth on that would take a "regular" load ?
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A good answer coming from me would be "dunno."
Groily was careful in saying that the idler teeth were conserved, and, in turn, did not wear the teeth of the other gears.
Richard L.
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Can't have everything . . . the cam pinion teeth will indeed always be loaded at the same points - as the lobes whack the followers. But if the idler teeth which bear on the cam pinion are constantly changing because of the idler's funny size, then the overall wear on the gear train will be much less than if it was the same idler tooth contacting the same cam pinion tooth every time for each follower. That's the theory anyway. BSA, Triumph and AMC twins followed the same practice in their different ways, successfully I'd say. Norton and Royal Enfield twins of the same era preferred chains for their single and twin camshafts respectively (hence their clockwise rotating magnetos - no reversal of direction en route).
Not sure whether chains/sprockets suffer from localised wear or not (suppose they must to some extent), but they are certainly more of a pain to set up than a gear train, there are 2 of them (one for the mag/distributor/whatever), and then they need periodic maintenance as well to keep them tensioned. And that's without thinking of how to turn the dynamo, if there is one.
Cars are pretty much the same: setting chain driven twin ohc engines is a fiddle; gear driven is in principle a lot simpler - although as anyone will know who's played with a set of helical timing gears, they can be a fiddle too.
And while we're on, why did only AMC have the wit to use steel mag pinions? I have now seen no fewer than 4 fibre mag pinions fail in the last 18 months or so: my A, a Sprung Hub Speed Twin, a Vincent Twin and a Venom. That's a high rate of attrition, albeit on some very well-used bikes. The A and a local friend's Speed Twin now have alloy gears. Now, right back on point, they probably DO need swapping around on their shafts from time to time to even out the wear!
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You lot have got me a bit baffled, not hard, I've had my idler pinion off, forgot and turned the engine over while doing something on the clutch, do I move the engine around until I can slot the idler pinion in with the Marks lined up, or do you have to have the engine in any particular position? I think you must do otherwise wouldn't the pistons be in the wrong position to the camshaft???
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Yes turn everything around until marks line up and slide idler pinion in to align marks, this is the safe way.
If nothing else had moved ( crank or camshaft ) you could just slide the idler pinion in but can you be sure???
IIRC with marks lined up engine is at TDC
All the best - Bill
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Tone, The answer is both.
To avoid a valve / piston interface situation, take out the plugs and carefully set the pistons at the bottom of their stroke. Then turn the camshaft until the dot points to the center of the idler, then turn the crankshaft so the pinion dot is also towards the center of the idler pinion. Then slot the idler back in position with the marks correctly lined up.
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Tone, The answer is both.
To avoid a valve / piston interface situation, take out the plugs and carefully set the pistons at the bottom of their stroke. Then turn the camshaft until the dot points to the center of the idler, then turn the crankshaft so the pinion dot is also towards the center of the idler pinion. Then slot the idler back in position with the marks correctly lined up.
That's a good answer which I did not know. Would Tone also then have to re time his magneto? or would that still be correctly timed? Probably a good idea to re check it of course.
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No he wouldn't as the camshaft and mag haven't been separated.