Topic: CB400F "Rigid" Cam Chain Tensioner Adjustment

[PowerCat]

First post. Hopefully this makes sense. I recently purchased a 1976 CB400F with 23000 miles. It makes a noise at idle that I think might be a loose cam chain. When I went to adjust it, I'm reasonably sure that the factory setup using springs to apply the adjustment force has been replaced with a long bolt. I'm afraid to take it apart to see if this is the case and lose the existing setting without knowing how to set it. Is anyone familiar with this setup and how to adjust it? I've seen some references to something like this and hope someone can steer me in the right direction for adjusting it. Thanks.

[camelman]

The stock piece looks like a long bolt when it is in place.  My guess is that it has not be adjusted in a while, has been eaten away by the cam chain, and is stuck.  Actually a pretty easy repair if you are a good wrench.

Camelman

[Tim2005]

Do you mean the plug above the tensioner bolt has been replaced with a long bolt? If so there's 2 ways to accurately tension it using that, as over-tightening is the risk, - either by removing the rocker cover and observing the actual tension, or by doing it with the engine running & doing it by ear- which is a bit of a gamble.
 
If, as per other post, the bottom part of the tensioner is locked up you do have to pull the engine & split the cases  (you can leave most of the top end in place), although the part, if needed, is nla from Honda so you're best to get hunting on ebay.

[Industrial Rat400f Killer]

http://www.cb400f.btinternet.co.uk/cam.htm

[PowerCat]

Thanks all for the replies.

I think what I likely have is what Tim2005 described; that is, the plug (blanking bolt) above the tensioner bolt (locking bolt) has been replaced with a long bolt and a jam nut. I've been reluctant to fiddle with it if I didn't know how to adjust it. Maybe it will be obvious once I remove the rocker cover, but does anyone have advice on how to judge if the tension is proper by observing it with the rocker cover removed?

[HondanutRider]

That "blanking hole" where you now have a longer bolt held in place with a jam nut, is directly over a rod with a spring over it that bears onto the cam tensioner to adjust to the correct tension.  Its a complicated lever arrangement that would work in theory but rarely performed as it was intended.  The spring is supposed to provide the correct tension with the motor at idle, and then a forward facing bolt with jam nut would lock the rod (with spring having applied correct tension) in the proper position.  The spring rarely provides correct/enough tension when adjusting according to the "book" procedure, so it has been found by some that if the blanking hole bolt is removed during the procedure (it doesn't do anything - no oil or spring comes out with it removed for this procedure) and a screwdriver or some other rod is inserted into the hole, pressure can "carefully' be applied and more tension provided to correctly tension/adjust the cam chain while the motor idles.  With this method, you just have to be careful and not press too hard and also avoid burning yourself on the hot exhausts.   Replacing the blanking hole bolt with a longer one allows you to more carefully dial-in the correct tension, but it can still be over-done!  You just have to have a good ear and be able to discern when it is running "loose" and when it just starts to quiet with the correct tension. 

[bryanj]

Kevin (ttr400) was re-manufacturing those horseshoe tensioners last i heard