Topic: Cam sprocket position and timing marks questions. now with pics!

[ntm1974]

I am reassembling my cb350F engine.  I am trying to screw the cam chain sprocket to the camshaft. 

I understand that I need the 1.4 mark lined up while the cam chain sprocket's marks are parallel to the the crankcase.  My question is: there are a lot of marks near 1.4,  including two lines to the right of it and a dot over it.  Which one do I line up with the "mark?"  Also, I have two options of how to orient the camshaft itself.  Does it matter which was it is oriented?  The manual doesn't specify and I don't want to screw anything up.

Thanks for any replies.

[bryanj]

As you rotate the crank in a clockwise direction looking at the points end you will se in order:-

two lines---these are for checking the advance

"F" with a line----this line is the static timing mark

"T" with a line----this line is the top dead centre mark

It dont matter which way up the cam is as, when talking about 1 & 4, one is on exhaust and the other on compression and the plugs spark together

[ak58lp]

Not sure what year your bike is, but on my 1982 CB650SC the one you want is the "T" at 1.4. When you line this up with the index pointer and make sure your cam notch is exactly horizontal with the front of the head, the bolts for the sprocket should go in. If not, leave everything like it is and just move the chain one tooth until it lines up. Put a marker line on both so you know which way to go. Here's a pic that might help.

[ntm1974]

Thanks for all the replies.  My confusion lies on what is the "exact" place on T 1.4. 

Should I line it up with the small dot directly above 1.4 in this picture (picture A):

Or should I line it up with the F mark near 1.4 (picture B)

Or is it the "T" mark (picture C)

This is my first time rebuilding any engine and while I am reading (and learning) a lot, it is tough to discern some of the subtle terms from the manuals that I have.

Thanks for you patience and replies! 

[ak58lp]

As I mentioned above, I would say it should be picture C. T is Top Dead Center (TDC).

Can you let us know the exact model and year of your bike?

[ntm1974]

As I mentioned above, I would say it should be picture C. T is Top Dead Center (TDC).

Can you let us know the exact model and year of your bike?

1974 CB350F

[ak58lp]

There is a very good shop manual on this page from this forum for that bike.

Honda CB350F - CB400F Shop Manual     http://forums.sohc4.net/index.php?topic=17788.0

The manual is huge but on page 158 there is a diagram that shows what I mentioned and you have shown in picture C. It sounds identical to the procedure to set my cam timimg on my 650 Nighthawk.

I didn't look through the rest of the manual to confirm the cam position, but this sounds like mine as well as as noted in my picture above.

[jpmire11]

As I mentioned above, I would say it should be picture C. T is Top Dead Center (TDC).

Can you let us know the exact model and year of your bike?

I just rebuilt my 750 and a local 750 guru told me it has to be lined up above the "T". So picture "C" is correct.

[Oddjob]

T is timing, F is firing. So T is correct, when strobe timing the bike you'd be looking to time it on the F mark.

[ntm1974]

Thanks a heap for all the help.  I'm going to owe a lot of folks on here a beer by the time I get this bike up and running!

[dave500]

you can also line the cam up "180 out"with the notch rearward,if you want.

[dave500]

T is timing, F is firing. So T is correct, when strobe timing the bike you'd be looking to time it on the F mark.

"T" is top dead centre.

[Oddjob]

As said T is for timing, F is for firing, you time the cam position by the T mark and the firing position by the F mark. So timing means cam timing not firing which is ignition timing

[ttr400]

Yes Oddjob you are correct but your terminology is incorrect.

Dave500 is 100% correct. the T mark means top dead centre. the F mark is for setting ignition timing at idle.
With the T mark lined up for 1/4 cyl, yes you would position the cam sprocket so the lines are lined up with the head surface. (no notch on 400F cam).
Plus you would also align the T mark (top dead centre) for 1/4 cyl to set the tappet clearance etc.

Kevin

[Oddjob]

The terminology I use was the same as Honda used on their courses. I was a Honda mechanic for a long time and I attended a number of courses run by Honda in the UK. We were taught that T was cam Timing, and F was ignition timing, remember this was in the 70s and maybe terminology has changed since but I still call them as I was taught.
You must remember that Honda made the mark not to mark TDC which to be honest you don't need as if you've got the head off you can see TDC, it was put there so you positioned the cam in the correct place, you'd only need this mark if you had removed the cam, even though you can use it for tappet clearance it only works for 1 and 4 cylinders, you'll notice there is no mark for 2 and 3 cylinders, mechanics used the position of the cam lobes to check tappets.
The marks further to the right of the F mark are the fully advanced marks for when checking the advance/retard mechanism with a strobe light.