Ipgo,
doesn't that depend on how accurately you want to set TDC?

On any engine, there's about 5 degrees of crankshaft rotation either side of TDC where the piston barely moves, so the 'positive stop' (or dial gauge) method is the only sure way of ensuring that it's right.

http://www.mopedarmy.com/wiki/TDC

ken

you need to use the "stop" method for accuracy as long as it stops the piston somewhere near TDC. There is too much dead travel as the crank goes over TDC to try to "feel it" with anything

turn the crank over till it hits the stop mark the flywheel then rotate the other way till you hit the stop and mark again, then TDC is halfway between the two - just make sure you mark the TDC not BDC

Made the tool and tested it. Variation between the 2 cylinders are less than half a tooth, no worries there.







I have 25 teeth between the 2 marks (numbers of teeth depends on length of tool) Marked middle tooth now TDC with 12 teeth on each side.



Now I need to work out the 10 degrees BTDC. Easy the original sensor tap is located at 10 degrees BTDC but where do I place the pistons in relation to points cam. Do I back off the number of teeth between TDC and the sensor tap (between 7 and 8 teeth, photo angle show 6) which is 10 degrees BTDC and then place the cam at 35 degrees (according to Perfect Product)

Cheers fellows.

Hang on a minute, am I missing something here.

If the flywheel pin (censor) is placed at 10 BTDC and each tooth is 2,75 degrees ( 360 degrees divided by 131 teeth) then I should be 3,6 teeth away from TDC but I am 7-8 teeth from my marks + why bother with the marking if the pin is correctly placed at 10 degrees BTDC. Wouldn't it be easier to count forward to reach TDC?

Finaly you get what i was saying in first place

edit ah you ve been back on while i stopped for tea,

each tooth is 3.36*( count the teeth 107 for m28 dont know what a visa is)

10* divided by 3.36 = 2.97 teeth so 3 teeth as near as damn it

make up a degree wheel and bolt it to the nose of the crank

print off the following stick it to some backing

Are you shure it is 131 tooth, Im not at home but when i remember right a 2cv ha s 107 tooth i cant imagine a vosa has that mucu more... Will do a counting later this evening

Now I have doubts about getting the TDC right. I'm to far off the 10 degree pin, if I calculate using the 360 divided by 131
I want to be absolutely right in setting the points box and cam spot on.

Since a Visa 652 starter ring has 131 teeth, the engine needs to be turned anticlockwise (131 x 10)/360 teeth from TDC to be set at 10* BTDC.
( That's 3.64 teeth. )
If you've still got the Visa gearbox or bellhousing to hand and offer up the engine to it, the flywheel stud should then be directly under the low speed sensor hole.

I don't know how this points cam is fixed to the Visa camshaft, but if it's the usual expanding bolt setup and the standard centrifugal advance mechanism is retained, I'd fit the points box 'horizontally' with the points gap correctly set, turn the points cam assembly until the points are just opening, then lock it off with the expander...

ken

Final approach

Just did A count at my Visa engine.... you are right 131 teeth (couldn't believe it first)...

I would do it like this:

Take a 2cv engine put a 6mm drill in the hole (or the Citroen special tool... whatever you like) make a mark flywheel/engine. Now turn the engine over till the 2 bars (from the points)on the camwheel are horizontal or vertical (what comes first) now count the tooth between the 2 marks. do the calculation thing (360/107) x tooth 2cv and you have degrees.

Now put the pickup in the Visa engine just behind the upper sensor hole (would be better if you put the sensor in and messure volt. at the moment the sensor start giving 7 volt the sensor 'sees' the pickup. Now do the calculation backwards
(degrees x 131) /360 = tooth Visa

Now you have to move the visa engine in the same direction as the 2cv engine the calculated tooth. Put on the plate (horizontal/vertical) like on the 2cv engine and your done....

You can put a ruler on the 2 bars then you can see if it is horizontal/vertical

good luck...