Topic: Using a bolt to manually set cam chain tension on CB400F?

[benmanuel]

Ok, here's the situation. I've got what I assume is a fairly loud cam chain rattle, it's there from idle until I hit approx 4K rpm (does this sound right?).

I've done extensive searching on the forums, and I've come up with some good suggestions, but I've pretty much run out now, so here goes. I replaced my tensioner with TTR's aluminium piece when I had the engine out this winter, so I know the tensioner isn't seized, but I think the pushrod may be badly stuck since I've tried all the recommended methods of tensioning, starting with the manual suggested method:

1. Let it warm up and idle at 1200 rpm, loosen the locking bolt and locknut, and then retighten. I heard no change in the rattle whatsoever.

2. Suggested by my mechanic, remove the timing cover, line up the spring pin with the timing window at 15 degrees ATDC and loosen and retighten the lockbolt, still nothing.

3. 1200 rpm, loosen the lockbolt and plug and manually apply pressure to the top of the pushrod, I tried this with varying degrees of pressure, even some taps with a hammer on the end of a screwdriver, would not budge, noise did not change at all.

So what I'm wondering is:

a) Is rattling that stops above 4K sound like a cam chain issue?
b) How much will the pushrod move when pressing on it manually? I know it would vary, but roughly, mm's, a cm?
c) if I'm careful and stop right when it starts to quiet down, can I safely apply the pressure to the pushrod with a longer screw and then tighten it all up?

Hope you guys can help.

[mattcb350f]

Ok, since I replaced all my tensioner stuff recently and and adjusted the cam chain I can tell you that if the push rod is moving freely, your screwdriver should vibrate and almost bounce on the end of the push rod when the engine is running.

If yours didn't then I'd say it's stuck. However, it won't move a whole lot even if it isn't free, but that depends on how loose the cam chain is.

If I remember right, you can actually see the cam chain through a couple of the valve adjust. covers but I forget which ones; I think the intake side. If you can see the chain, rock the engine back and forth to see how much slop is there.

 Matt.

[benmanuel]

Yeah, the pushrod doesn't move or bounce at all, it's like setting a screwdriver against a solid metal piece, I'm thinking I could use a bolt even just to free it up.

[ttr400]

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

[crazypj]

When you say you replaced the tensioner, did you have the crankcase split?
 The 'horseshoe' shaped piece actually does the tensioning and its real common for the chain to damage the pivot area preventing it from moving. As far as I can remember, you have to use a piece of rod about 1/8" dia to manually adjust and it may need a few taps. if you go too far you have to remove head to re-set it.
PJ

[ttr400]

Just to add, to use a bolt to manually adjust the chain. yes you can do this.  You will need an M8 bolt about 25-30mm long with the end turned down to around 6mm x length ? this you will have to check how far down the push bar is, there is aprox 10mm of 8mm thread.

When you use this method it is best to do it with the motor running and adjust chain by ear, as if you over adjust and make the chain to tight......well then the motor must come out..! screw the bolt in slowly until the chain rattle goes away.
This is presuming you have new parts installed.? chain, slipper, front guide etc.

Kevin

[benmanuel]

Thanks Kevin, I will check to see if the pushbar is free, and if so I will do the first method you suggested. My mechanic installed the tensioner for me since I didn't want to take on the task of splitting the cases myself, and he did it more quickly than expected, so I didn't have much input 

I'm gathering that setting it manually is only advisable when you have a new chain because an old one could already be stretched to its limit. The slippers and everything else were in good condition and therefore not replaced.

I'll let you know how it goes!