Topic: TDC? For CB400F?

[brandon]

I'm really sorry for the noobie question, please bare with me. This is in regards to valve adjustment and TDC:

I have a Haynes Manual and also a manual that I downloaded off this sight. The one I downloaded has the picture of a wheel on the cover and the colors are blue and white. Anyways, I set out to give my bike a full tune up today. First thing is starting with the valves. I was getting ready to get started and noticed something that I don't quite understand.

Per the directions of both manuals, the crank needs to be turned clockwise until the T 1.4 lines up with a static line. However, this is where it starts to get confusing. Per the instructions, I line up the T 1.4 line to put the #1 and #4 cylinders at TDC.

More specifically, the crank needs to be turned 360 degrees to put #1 cylinder at TDC on it's compression stroke, adjust the specified valves, then turn the crank another 360 degrees to put #4 cylinder at TDC on it's compression stroke and adjust the remaining valves.

My question is: How do I figure out which cylinder (#1 or #4) is at TDC to perform a proper valve adjustment? The manuals explain nothing.

Thanks for any help.

[mattcb350f]

Yes, this one can be confusing. With all the caps removed to adjust the valves, and the 1.4 mark lined up. One of the two cylinders either one or four will be at top dead center on the compression stroke. The trick is to now figure out which one. I do this by rocking the engine with the wrench on the nut inside the points cover, ahead and back a 1/4 turn in either direction. If you do this while watching the valves you will see either the #1 or #4 cylinders' valves begin to open. the valves that open indicate that that cylinder is NOT the one on TDC and you are on the TDC of the other cylinder. Now that you've determined which cylinder is at TDC, reallign the 1.4 timing mark and adjust the valves. Then after that, you can do the 360 degree turn to adjust the other cylinder.
 Matt.

[Bodi]

Cylinders 1 and 4 move together, as do 2 and 3. So when 1 is at TDC, 4 is also. One will be at the top of the compression stroke, the other at the end of the exhaust stroke. You want to adjust the valves on the one on compression, with both valves fully closed: the one on exhaust will be just closing the exhaust valve and just opening the intake valve, so the tappet clearance will be unpredictable and not settable.
Turning the engine "forward" - turning back is a bit nasty as you have to turn the starter motor - watch the intake valve tappet (I watch # 4 because it's on the end with the points nut used to turn the motor over). When the tappet moves down to open the valve, the intake stroke is happening and the piston is moving down: next time it comes to TDC it will be on compression, where you want it. If you watch #4 and want #1 on compression, just turn another full crank turn.

[brandon]

Thanks for the replies. Much appreciated.

Curious...can I also hear which cylinder is doing what by pulling the respective spark plugs and listen to the air escaping the respective cylinder as the piston comes up on its compression stroke?

Just to double check, on the compression stroke of say...cylinder #1, the rocker arms will be higher in regards to the rocker arms above cylinder #4?

[OldSchool_IsCool]

When I set valves, I pop off all the caps and the points cover.  I then rest a finger on #1 intake rocker.  I rotate the crank clockwise via the points nut, feeling for #1 intake rocker to open and close (careful to not pinch your finger as the rocker comes back up!!).  I then watch for the next time T1.4 comes around.  I now know #1 is at TDC of it's compression stroke. 

[mlinder]

Or, take off all the adjustmetn caps. Put it at 1.4 TDC.
Wiggle #1 and #4 rocker arm. If it wiggles at all, it's the one at TDC. The other one won't (unless there is something severely wrong with it...)

[brandon]

This was by far the easiest method. I couldn't believe how tight some of the valves were! Now all I need to do is the cam chain and sync the carbs.

Thanks to all that posted. All of your replies were much appreciated.

Or, take off all the adjustmetn caps. Put it at 1.4 TDC.
Wiggle #1 and #4 rocker arm. If it wiggles at all, it's the one at TDC. The other one won't (unless there is something severely wrong with it...)

[754]

I was wondering why it took so long to do the wiggle test, thought everyone does that...

I think is so blind people can work on bikes as well...

 The hard part about adjusting mine was getting the .014 feeler guage in there (have to put a kink in it)......... big cam...

[crazypj]

I was wondering why it took so long to do the wiggle test, thought everyone does that...

I think is so blind people can work on bikes as well...

 The hard part about adjusting mine was getting the .014 feeler guage in there (have to put a kink in it)......... big cam...

Even with a big cam I've never heared of tappets being set to points clearance?? ( 14thou, or is that metric which would be roughly 6 thou?)
PJ

[754]

Recommended clearance is .014..


 Dont have the sheet here but have it at shop

 300 + duration,  .360 or .370 lift..

 Will try to find specs to confirm.. sounds like a lot but depends on your lift.. not really that lood when running..

[crazypj]

Recommended clearance is .014..

 0.014..
 but is it inches or mm?
 There is a major difference. You'll probably punch through the hardening on tops of valves and mushroom adjusters at 0.014"
PJ

[754]

Actually I was wrong, it is .012 THOU....not 14

I listed some of the cam info on the Weber thread.

At over 300 deg duration it spends little time near closed, it is not as noisy as you would think... on a stock motor .012 would probably be louder..

Will look for my cam card today..

[crazypj]

WOW, I've learned something.
 I've never used a cam in a Honda that needed that much clearance. (even full race)
Any idea who made it?
PJ

[754]

RC  ENG 315

[crazypj]

Thanks, never used them. ( Piper and Yoshi)
PJ