Timing Tool

[LJ.]

One of these arrived today, any Good?? I would like to hear and learn of any tips that you can give in their use.

[a10 gf]

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

[Greybeard]

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.

[a10 gf]

So my "tool" wins :O) it's 90 deg to piston.

[bikerbob]

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.

[BigJim]

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. 

[Greybeard]

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.

[Peter Gee]

I like BikerBob's idea..so what is the correct BTDC for an A7SS?

[Greybeard]

...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"

[roadrocket]

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.

[bsa-bill]

a handy tool for getting TDC, you can get a measurement by setting a rule up against vertically, might need thre hands tho

[jachenbach]

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?

[Triton Thrasher]

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

[Colsbeeza]

This is better

http://www.a7a10.net/forum/index.php?topic=195.0

Beezageek had it all worked out in 2007

Col

[jachenbach]

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.