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by Mal Marsden - 06/16/22 7:00 pm
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chainreaction, reverb, tdc
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Original Post (Thread Starter)
by Waterloo John
Waterloo John
Hello again. I am in the final stages of my 1970 Triumph bobber build. Exhaust is on and tightened up and now am just installing the Boyer rotor and timing. I am confused with where the timing mark should be in relation to the pointer on the primary cover.

I removed the plug at the rear of the cylinder barrels and found one of the notches, but not sure if there are two of these.

With the notch i found, the pointer on the primary is dead on the line in the raised pyramid block on the rotor.

Is this 38' TDC or is this TDC.
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by seanalex
I should also add,

Don't break off the timing tool in the plug. And when you rotate the stator plate to either advance or retard the timing, small movements of the plate work best. Like for me it was like a few mm in either direction made huge differences. The first time I did this with a friend, and it was really helpful to have someone hold the timing light, and keep an eye on the rotor mark.

The second time I did it by myself, and it was a bit more difficult. Had the timing light like duct taped to a chair. Ha.

And not sure if you know, but its more accurate if you run the timing light off a second battery, not off of the bikes own energy. Its also helpful to not melt the wires leading to the timing gun (this is where the friend also comes into play)
1 member likes this
by seanalex
@Waterloo I really hope this helps

When I did the timing on my 73 T140.

When your timing plug tool is in the slot in the crank, I used a small screwdriver) and the the pointer is aligned, this is TDC. I also used a pencil in the spark plug hole. As you approach the TDC you will see the pencil raise, it will be or should be at its highest point at TDC. Doing this along with the timing mark plug made this whole thing make sense to me.

1. remove your spark plugs, and raise the rear wheel.
2. rotate your wheel very slowly backwards, leave your timing tool in the plug and let it gently touch that crank journal.
3. it will fall into the next slot. This slot is the 38deg before TDC. I used small black paintbrush and drew a line on the rotor at the primary cover pointer.
4. this is now where you line up the Boyer rotor. I found it a helpful starting point to have the magnets at like 1 o'clock and 7 o'clock positions
5. line up the little holes on the stator plate of the Boyer. tighten it down, not worlds strongest man tight, but decently.
6. put in the plugs, and give it a fire. It should run.
7. now you do the static timing, and rotate the stator plate to then with the engine running you watch that black line you drew, and try to get it to line up with the pointer on the cover while you HOLD the rev at 4k.

if memory serves, rotating the Boyer stator plate clockwise moves the "timing mark" counter clockwise during the static timing.
1 member likes this
by L.A.B.
Originally Posted by DAMadd
The marks on the rotor are for timing light at 2000 rpm.

Assuming it's the usual "Boyer" Micro-MkIII/IV.
"Connect the strobe lamp and time with the engine running up to 4000 R.P.M."

Originally Posted by AngloBike
Not sure if you should have one or two slots in your 70 crank

Should be two (TDC and 38° BTDC) slots.
1 member likes this
by kommando
Crank flywheel not rotor, the crank flywheel has 2 notches, one at TDC and one at 38 BTDC, on the timing side crankcase is a plug which when removed you screw in the timing plug which will drop down into both slots.

[Linked Image from]
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by quinten
reverb , i re-read seanalex' post for the 4th and 5th time , and you are right .
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