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Hi All. My first timing belt change having acquired my '77 3½ last year as a non-runner. I've watched Paul Compton's video (https://www.youtube.com/watch?v=rvqPVx3ZlBw) a dozen times and, of course, mine wasn't quite so swift! Getting the old belt off took an hour and I wondered if I might just have well cut it off instead. Sadly, the cam pully has now moved and, although I'm pretty happy about lining the top and bottom marks up, I'm a little anxious about the result of getting it wrong. The cam pully has two potential marks which are 180° apart, but am working on the basis that the one that is uppermost when the "A" mark on the pulley is the right way up (towards the front of the bike) is the right one. What really throws me is that, with the mark lined up with the mark on the crankcase, the pulley won't stay in position and keeps wanted to rotate back (anticlockwise) by about 30°. I'm guessing this is a valve spring acting against a cam. Is this to be expected?
On the crank, there is a hint of a mark in line with the woodruff key on the crank and a good mark on the case, so I think that's good.
Given that the "A" pulley ought to be on the smaller side, I'm also concerned that my new belt doesn't exactly go on easily. I've seen mention of talc/french chalk to ease the process.
If anyone has any advice to help a newbie, I'd be most grateful.
Cheers, Harry

The "A" should be upside down and on the left.

Is there not not a punch mark on the periphery of the crankshaft pulley which lines up with a mark on the crankcase, around the 2 o’ clock position and then a single punch dot mark on the cam pulley which lines up at the top with the mark on the case? As per diagram 117b on P68 in the blue book?
If it has not turned all the way it should work. If in doubt you could check valve movement in relation to piston movement I guess.
John

The A, B or C mark has nothing to do withe the timing.
It´s the punch mark that counts.

Thanks to all for the swift responses, especially 70sbikes who, I reckon, has cracked it. I HAVE got a (faint) punch mark on the crank that lines up with a mark on the case at approx 2 o'clock. I've also now confirmed (by removing the plug) that this corresponds to TDC on the front piston. The problem with the cam pully is that there are TWO marks on opposite sides and I think it has somehow got 180° out (which might explain the difficulty getting it to stay in position).

I'm sorry I missed this question - next time, follow these four simple steps:

1. Get a scalpel/Stanley knife.
2. Carefully slice the old belt lengthways in two and cut the front half off.
3. Slide on your new belt halfway and then carefully cut off the remaining old half.
4. Slide new belt fully home.

Works a treat.
Cheers,
DD

Brilliant ...like all ideas so simple and makes me think why didn't I think of that ! It's things like this that make MRC such a great riders club. Thanks

Another picture of the marks aligned

That’s a very clean looking set of pulleys.
John

vapour blasting and zinc plating, makes old things look new