Topic: Setting Timing Plate -- From Scratch -- CB750

[RogueM3]

Hi All,

I have a 75 750F that I've been deconstructing and now rebuilding.  When I bought the bike it had a Dyna2000 ignition system that I removed a few years ago to recoup some $ knowing I wouldn't fully use it and a DynaS would be a fine replacement. Now that I am looking to get the bike back on the road I need to figure out how to install the DynaS and factory timing plate on a bike that has nothing but the timing shaft right now with a nut on the end = I have no way of knowing where the bike is on timing or in which cycle right now.

Is my best bet to just start rotating the crank around with plugs out until I can feel cylinder#1 come back up on the compression stroke? Open tappet cover and determine that way?  Both of those seem like ways to get close, but not to precisely know where the engine is currently.

Any pointers?

Thanks!

[willbird]

I found the instructions here........

https://www.mpsracing.com/instructions/Dynatek/DS1-1_1-2.pdf

There is also a youtube video where a guy does a decent job explaining the whole setup, I'm more of a read the instructions guy than a watch the video guy, not sure about you :-). NO harm in watching the video THEN reading the instructions ;-). They say to rotate the advancer to full advance by hand and static time that way.

If it helps it does not matter which cyl is at TDC they both get fired with our waste spark system. So when 1 and 4 are at TDC they both fire no matter which one is on compression and which one is on exhaust. Knowing which is on compression is important when lashing valves. Bad things happen if you use the Hex nut to rotate the crank with spark plugs in (and maybe with them out maybe?). The small dia shaft that the spark advancer mounts to can be bent easily.

One dude who showing how to lash valves put the bike on center stand and put trans in 5th gear and rotated the rear wheel by hand to rotate the engine...that might be a two human operation to do static timing tho, have not tried it myself.

The dwell on the Dyna S is super long as I recall ? Uses a lot more mAh of energy ?

Bill

[Floshenbarnical]

I ... did not remove the spark plugs to rotate crank. I didn't know I was supposed to. So, the outcome is a potentially bent shaft? How can I tell if its a little bent?

[willbird]

I ... did not remove the spark plugs to rotate crank. I didn't know I was supposed to. So, the outcome is a potentially bent shaft? How can I tell if its a little bent?

IMHO I think millions of owners did...I'm sure I have done so myself many years ago. People have detailed here how to straighten them so if you can search those threads you might see their setup to check runout.

[RogueM3]

Thanks Bill. Ironically, I just watched the above video and thought "Let me go back to the forum and see if anyone replied. "

I will give it a look this weekend and see if I can't make a bit of progress.

[BenelliSEI]

If you turned it slowly, you probably got away with it. If your system uses a central rotor and and fixed electronic pick ups, check the air gap as you rotate the crank (plugs out, with the kick start lever, or from the other end, with the cover off). If the gap stays fairly consistent, it will all work. If the gap shrinks and widens significantly, read the “how to straighten” posts.

[Floshenbarnical]

I rotated it extremely slowly as I have rotator cuff pain, but I will check it out regardless.

[HondaMan]

If it is bent, it will show up as "timing jitter" when you get it running, under the strobe light. The timing marks will appear to jump back & forth a little bit (or a lot if bent a lot) instead of sitting still under the light.

[PeWe]

Cut the advancer springs will make it better, run more evenly at low rpm.