Topic: CB400F Cam Chain Tensioner Stuck - Question

[jakec]

Hi, I have this new 400 that has a loud cam chain. I followed the manual adjustment procedure and loosened the adjustment bolt with the bike idling at 1200 rpm. unfortunately there was no movement on the adjuster shaft, at least not as far as I can tell because the noise didn't change. I have a video below of the noise. It's quiet at idle but gets louder with higher RPM. I've already adjusted the tappet clearance.

I read on here that I can manually adjust it, provided that the horseshoe mechanism is just stiff and not seized/broken. Basically remove the bolt and press down on the area with the red circle to add tension. If you go too far, you can remove the valve cover and press on the green circle to relieve tension. How do you safely add tension by pressing on the red circle, and how would you know if you went to far? I want to attempt this procedure tonight or tomorrow.



Image of the bike for your viewing pleasure. Thanks!

[bryanj]

Unfortunately there is no specific method, its all down to "feel" If its been rattling a while chances are the horseshoe pivot areas have been burred by the chain and to sort it is a vrankcase split job!

[jakec]

Well, that would suck. I'm already in the middle of a crankcase split job.

[jakec]

Ben, You really should have removed the push rod when you had the motor open, and yes the push rod can seize up in the case..Try and spray some WD40 down on the top of the push bar. Or the best way to check that all is working or not working is as follows.

1. set 1&4 to tdc and remove the tappet cover.
2. remove rear slipper top holder, make sure the lockbolt at the front of the motor is locked.
3. Put your finger on the top of the slipper. loosen the lockbolt. release the pressure off your finger, slipper should come up. now you can push down on the slipper and feel it want to push back up under the pressure of the springs on the push bar.
4. If this is working as described. proceed to 5. if not then the push bar is seized. try and spray some wd40 down the top push bar hole and at the same time push down on the slipper with you finger to try to get it free. If all this fails, then you will have to open the motor again.

5. Assuming all is moving as it should. turn the motor forward to the 15 deg ATDC. with the lockbolt still loose, install the slipper top holder. push down to start the bolts evenly. screw down the bolts until the holder is +- 1 to 2mm off the face of the head. tighten the lockbolt. then tighten the holder all the way.
Job done.
6. Turn back to 1&4 TDC. install the tappet cover, making sure the rockers are up and contacting the valve correctly. check tappet clearance and adjust as required.

Well I hope you managed to understand my explanation, as it's easier to do than explain...

Kevin

So I can spray penetrant in the hole at front to free up the spring, if that is what's stuck. You're saying if the chain chewed the horseshoe joint enough then it's just never going to rotate.

[Tim2005]

Take the rocker cover off, and see if pressing on the pushrod is having any effect whatsoever on the chain's tension.

[Nurse Julie]

If the cam chain is knackered and beyond spec, it makes no difference if the adjuster springs are weak, or the pivot seized, you won't be able to adjust the chain as no adjustment potential left.

[awrawr]

I had this in about 1979. If the pinch bolt has been over tightened in the past, the adjuster push rod can get slightly squished, causing it to jam in the tunnel. Remove the top bolt and put a small screwdriver down the hole and tap gently to see if anything moves. If it does, the rattling noise will change. Pinch the bolt up again to lock itin the dsired position. It will make a different sort of noise if you go too far. And if it is a tight fit in the tunnel, you might not be able to get it to back off. So caution required.

If the bolt has been seriously over tightened then there may be a dent in the adjuster push-rod in which case you may have trouble ever getting it to go anywhere else than back into the same dent.

It worked for me back then. Bought a new push rod and replaced at the next strip down.

[jakec]

I have the valve cover off right now. I tried pressing on the aft slipper piece (green circle above) but realized I that by nature it's supposed to bend, so now way I would be able to push a stiff horseshoe back that way (relieve tension). Maybe if the slipper was was out you could use a stiff rod to push down, but the slipper wouldn't come out with engine in frame.

Anyways I will put the retainer pieces back on and then tap on the pushrod to see if I see movement in the chain or the slipper arm.

Has anyone ever added something at the top end of the slipper to add tension, when the bottom won't move? this is assuming that you have more room for adjustment but the horseshoe is stuck.

[Tim2005]

The slipper will come out with the engine in frame. The tiny packing piece at the bottom of it hopefully will stay in situ, there is a risk there though.  Once the slipper is out you can use a long screwdriver to press on the horseshoe. Take the cam out to give you a bit of space and vision.

[awrawr]

Can be done (the tapping thing) with the engine running. Big risk if that isnt the problem, though. But you do get instant audible feedback on the results. (And burnt hands).

[jakec]

I reinstalled the retainer on the trailing end of the slipper (green circle), and pressed down on the spring-bolt (red circle). I didn't see any movement in the slipper (didn't bow out or anything). I also didn't see any movement in the chain of course. I am not sure I want to try Tim's suggestion right now as I don't have time to jump into a full rebuild right now, and I would rather button the engine back up than drop a part of the tensioner down into the case. Not sure what to do with this bike right now.

[jakec]

redline,

remove the front push bar cover bolt and place a thin punch inside to rest on the push par, it'll be protruding out of the hole in a resting state
Done

then when you push the tensioner slipper down, the punch will come up.
when I do this, the sluipper just bends, and the punch doesn't move

on 2 motors so far ridden a whole bunch, i used to think the tensioners were stuck or broken. and they both work like they're supposed to, the spring tension is kind of hidden by it can't move much, so it seems like it's weak, but if you have cam off and the chain now is only around the crank, and you back off the lock bolt
I have not taken the crank off - what does that help? I'm willing to try, just curious.

that pushrod will then become like a bullet. just make sure you tighten the valve adjuster nuts sufficiently! and then some.
are you saying that removing the cam sprocket and shaft takes enough tension off the chain that the push rod can extend more easily?

[jakec]

This is my fear, see camel man quote below:

[jakec]

I probed around at the tensioner rod with a pick and hammer, tapping lightly, but I am not seeing any movement. I don't want to break the horseshoe. I think the risk is too great considering best case scenario I adjust the tensioner for one service interval (1,500 miles?) and then i have to risk it all again. I think I will be putting the cover back on and getting it closed up/running again, so I have the option to sell. Kinda sucks cause I really wanted to ride this bike. But I don't have the option to work on the engine since I'm already halfway into a rebuild already. Such a nice bike too. It just needs an engine!

[jakec]

My fear is that since it's obviously not moving, if I do get it to move then I am risking breaking a small part off once it suddenly moves. Like best case scenario I move it a bit, and then maybe look down the shaft with a boroscope or something, confirm that the horseshoe is mostly all there, and then hope that it wants to move naturally once unstuck.

I already tapped on the plunger and didn't see ANY movement on the rear slipper.

[bryanj]

Its probably siezed on the pivot due to cam chain wearing into it so if you do get it move it wont move freely

[jakec]

That's exactly what I was saying going to get some rubber bands today to put the valve cover back on, then I will look into getting a bike cover for it and probably store until spring.