The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: LJ. on 24.08. 2018 11:21
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One of these arrived today, any Good?? I would like to hear and learn of any tips that you can give in their use.
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ahhh, a professional version of my concoction > https://www.a7a10.net/forum/index.php?topic=368.msg10533#msg10533
and it's use https://www.a7a10.net/forum/index.php?topic=368.msg10538#msg10538
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The only problem I can see, and this has been discussed before, is that the plunger is not at right angles to the piston crown so the marking will not be accurate. This doesn't matter of course if all you want is TDC. I suppose if that tool was designed for our bikes it may have been graduated to take the plug angle into account.
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So my "tool" wins :O) it's 90 deg to piston.
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Everybody has their own way of setting the correct piston height and Greybeard is correct in what he says about the angle of the plug hole in relation to the piston crown, I did once measure the angle and draw it all out on paper and there is a difference in relation to the angle of the plug and the vertical drop of the piston. How I overcame this was to use an old plug break off the ceramics and modify the center of the plug to accept a 8mm dia rod, tighten the plug in the head then bring the piston up to TDC then using a junior hacksaw blade mark the rod take rod out put a decent groove in the rod using the junior hacksaw then measure your timing distance accurately from the bottom of the groove put another groove in the rod so that your correct distance is to the bottom of both grooves when you set the piston at TDC take it down to the top of second groove this then compenstes for the angle of the plug hole. As I said earlier everybody has their own way and this works for me. Also as an addition I was told many years ago that when setting correct height of the piston you should always take the piston down past the correct level and then bring it back up to the correct mark this I was told eliminates any wear in the timing gears. In regard to the original post you only have to look at who makes it to make me doubtful look at the width of the timing grooves if you used the bottom of one and top of the other you could be off with your timing.
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Hi LJ, I got one of these years ago. It has been very useful. There are so many worn out parts on my bike that i just glad it starts and runs and i'm sure my timing could be better but she runs at mo. *smiley4*
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I 'aquired' this tool when I was working on Puch mopeds. It's not long enough to use on an 'A'
If anyone has a need for this let me know.
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I like BikerBob's idea..so what is the correct BTDC for an A7SS?
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...what is the correct BTDC for an A7SS?
I have the W. C. Haycraft, 'BSA Twins' book here. It says; A7 Standard 5/16", A10 Golden Flash 11/32", All sports type engines with High compression pistons, (7.5 to 1) 3/8"
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I did what Bikerbob did, works a treat! The moving pin on my one is hexagonal, so I have different bikes' settings marked on a side each.
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a handy tool for getting TDC, you can get a measurement by setting a rule up against vertically, might need thre hands tho
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Why not just use a tdc finder and degree wheel? Using A10 stroke=84mm=3 5/16 inches=53/16 x 2 for a complete revolution, 3.4 degrees= 1/16". Don't recall what the advance should be in inches, but a conversion to degrees rotation should be easy enough, and simpler than trying to ensure that you are truly perpendicular to the piston? Am I missing something?
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Why not just use a tdc finder and degree wheel? Using A10 stroke=84mm=3 5/16 inches=53/16 x 2 for a complete revolution, 3.4 degrees= 1/16".
That’s wrong.
Am I missing something?
How many inches piston travel is a crankshaft degree at TDC?
How many inches piston travel is a crankshaft degree when the piston is halfway down the bore?
Are those two the same number of inches? No.
This might work.
http://www.dansmc.com/mc_software2.htm (http://www.dansmc.com/mc_software2.htm)
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This is better
http://www.a7a10.net/forum/index.php?topic=195.0
Beezageek had it all worked out in 2007
Col
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Hmmm. I see I way oversimplified. Accel/decel of piston depending on crank position easy to visualize. Struggling a bit to figure how rod length factors into this. Good brain exercise.
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Draw it on a sheet of squared paper .
If you consider the engine to be a right triangle with the con rod as the hypotenuse it will all make sense.
If you plot piston drop vs degrees you end up with one of those nice sine curves they tried to teach you about in high school.
See even way back then you wee being preparred for a future fixing motorcycles.
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Struggling a bit to figure how rod length factors into this.
With a shorter rod, the piston changes direction more suddenly, to put it simply.
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Went for a nice long ride and thought about it (no traffic) and was able to picture it more clearly.
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Everybody has their own way of setting the correct piston height and Greybeard is correct in what he says about the angle of the plug hole in relation to the piston crown, I did once measure the angle and draw it all out on paper and there is a difference in relation to the angle of the plug and the vertical drop of the piston. How I overcame this was to use an old plug break off the ceramics and modify the center of the plug to accept a 8mm dia rod, tighten the plug in the head then bring the piston up to TDC then using a junior hacksaw blade mark the rod take rod out put a decent groove in the rod using the junior hacksaw then measure your timing distance accurately from the bottom of the groove put another groove in the rod so that your correct distance is to the bottom of both grooves when you set the piston at TDC take it down to the top of second groove this then compenstes for the angle of the plug hole. As I said earlier everybody has their own way and this works for me. Also as an addition I was told many years ago that when setting correct height of the piston you should always take the piston down past the correct level and then bring it back up to the correct mark this I was told eliminates any wear in the timing gears. In regard to the original post you only have to look at who makes it to make me doubtful look at the width of the timing grooves if you used the bottom of one and top of the other you could be off with your timing.
I bought the same timing tool but the graduations made it a little difficult. the fit was a bit sloppy as well. I did exactly what is described here using the sparkplug with ceramic broken out, they machine easily and makes a more accurate reading.
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My timing plug. Now I have Boyer on both I just use it to find TDC on the degree disc. Turn crank one way till stops, mark disc, turn other way till stops, mark disc. center between two marks is TDC. Use timing light to get 35 degrees on the A7 and 32 on the Cafe.
With the magneto I had the plug set at the right distance before TDC and brought the piston up to it to set the points.
Cheers
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I too have that tool and yes it is a bit floppy to say the least, plus the graduation lines are pretty much useless. So having fitted 3 small rubber grommet rings over the lower inner part section and then brought the piston up to TDC it was then simple to measure and fit another ring on the top section at the right height (3/8") and drop back the crank and slowly bring up the piston until just touching the tool. Yes it might not be 100% accurate but it seems okay to me. You can of course check the position using the old pencil method afterwards, something I have done, not much difference.
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Ha, I used the pencil the first time and worked spot on, using that graduated tool similar to Muskys gave the same result , Im not an expert but the engine will tell you
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I bought this tool a while back and found it quite useful however beware of the o ring which luckily broke in my hand and not while in the plughole. *eek*
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Next time your in Costa or other coffee shop grab a handful of the slim wooden stir sticks, they're thin enough to go vertically down the plug hole, and long enough that you can use the join between the rocker box and the head as a reference point to mark TDC and you preferred timing point
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I really prefer TDC with the head off and using a dial gauge to find TDC..in conjunction with a timing disc on the primary. Then work backwards to find BTDC for the setting. Luckily the manual adv/retard on A7SS's means even if using the TDC tool mentioned that is not at 180 degrees to the flat-top piston, you'll have a 'sweet spot' you can manually set when underway to give the best timing. Those ADV/RETARD ;levers had a purpose!
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I really prefer TDC with the head off and using a dial gauge to find TDC..in conjunction with a timing disc on the primary
No argument there, dial gauge gives much more accuracy as to TDC, but for those occasions when timing is required and the head is on and staying on, I'll forgo a bit of accuracy, always a bit of remedial adjustment via the points gap ;)
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.... Then work backwards to find BTDC for the setting. .....
Ok, but as far as I'm aware, general thinking is to go back past the timing mark and come up to the mark, which takes any slop out of the gear train
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hi Peter, whilst I think your attention to detail is admirable I think you are over complicating our engine. It was after all mostly a commuter bike and as such needed to be "fixable " at the side of the road and whilst i take time to time it properly i certainly wouldn't take the head of to do it . As i keep saying I (SORRY ) set mine with a pencil and a fag paper ,always a new one ! My bike as always been a 1 to 2 kick starter even after the winter lay up.
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My bike as always been a 1 to 2 kick starter even after the winter lay up.
A quick start will be handy when the bikes all pull away for your local DGR this weekend!
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I agree with the comment on the advance retard lever, makes it easier to start by retarding a bit and when hot you can find that right spot, using the old fashioned ear. Retarding a bit on a hill seems to work as well.
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@ Topdad, totally agree..except mine is a rebuild from scratch and so, the head is not even on!
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Sorry Peter thats what you get from jumping into a post half way through *sad*