Topic: How to replace the cam chain tenioner on a CB350F

[BlueThumb]

Hi,
can I replace the camchain tensioner blade on a CB350Four, by just taking of the head covers with the Engine still in the frame?
If Yes, what are the caveats?
Thanks and best regards
BT

[Bodi]

If the rocker cover will come off with the engine in the frame, then yes. It looks like there's room and the 400F cover comes off easily, so it should. The front blade (the guide) is then free, the rear one (the tensioner) is held in by a bracket with two 6mm bolts.
There's a rubber block in the bracket that the tensioner blade pivots on. The main thing to be careful about is not dropping the bolts, bracket, or block into the crankcase.
Once you have the top off and remove the bracket, undo the tensioner lock bolt and see if the internal mechanism is free. You should be able to push the rear blade down and have it spring back up with no problems. Any problem with movement means either living with it or splitting the main cases to get at the parts. Press the rear blade down all the way and lock the adjuster, this makes installing the blades a bit easier. Getting them in and seated correctly is a bit fiddly with the frame in the way but it can be done, mostly the problem is that you can't see down at what you're doing.
The rubber block has a notch for the blade to seat into. It isn't exactly centred but I haven't seen any instruction as to which way it goes... probably it doesn't matter but try and take a look at it when it comes out and get it back the same way. It might come off with the bracket and might stay with the blade when you lift the bracket off.
Use some medium (blue) loctite on the 6mm bolts. You need to clean the oil off the threads and out of the holes for it to work properly.
Loosen all tappets and ensure that none are stuck on a valvestem when you reinstall the rocker cover! Be very very careful with the rocker cover bolts, get them back in the same holes they came from (you want the right thread engagement - mixed up will have some too deep but not a problem unless they bottom out - and some just holding by a few threads... guaranteed to strip) and tighten with great care. The head threads strip easily! Loosen the adjuster lock once the cover is on, and slowly rotate the engine forward a turn or so. Lock the adjuster and it should be tight enough to start and check for noise. Maybe the adjuster springs weaken with age or something, but several 400s I do work on need manual pressure on the adjuster rod to tighten the cam chain enough so the motor doesn't sound close to self-destruction. Set the tappet clearances and you're good to go.

[bryanj]

Caveats:- The rubber block can fall out of the horseshoe tensioner; The horeshoe itself can be stiff; the tensioner can be siezed finaly if the tensioner is worn out the cushion probably is too and the camchain worn

[BlueThumb]

Dear friends,

Thank you very much for your help. Your advice is better than any workshop manual! I will try to get the spares now and start the work later as a winter job.
Another question: Do I have to losen the tappets bevore removing the rocker cover?

Best regards
BT

PS: It may sound pathetic but I adhere to it: We live in a better world, if those who know help those who don't. Thanks again.

[SteveD CB500F]

Do I have to losen the tappets bevore removing the rocker cover?

You don't have to but you sure as hell won't get it back on again without bending something (like a valve).

Best to loosen them.

[Bodi]

Like brianj said, there's another rubber block at the bottom of the tensioner blade that might stick on the blade and come out with it. You don't want to lose it in the engine either. So be careful lifting the blade out, if that block is stuck on don't knock it off.
When you undo the rocker cover screws, the valvespring pressure will be pushing it up. You should leave 4 bolts near the corners snug and undo them one at a time a little bit at a time so the cover comes straight up.  If you loosen all the tappets fully there will be less spring pressure but still some, I would loosen them all before removing the mounting screws.
If the cover has been on a long time it might be stuck on, if so remove all the bolts and then pry it lightly and it should spring up. There are locating pins on the front leftmost and rightmost bolts between the head and cover and that's where it will be stuck most likely, take care not to drop them in the motor.

Try and get a full set of 8 tappet cover O-rings and a replacement 12391-333-000 cover gasket (long squiggly O-ring thingy). You probably won't need the big gasket and it's a bugger to replace, but I like to have one on hand in case it's damaged. After 30 years in there it can get really stuck to the head and tear on removal. The tappet cover O-rings will be completely flattened and should be replaced by now, with new ones you can tighten the covers gently without leaks and be able to remove the covers easily.

[BlueThumb]

Hi,
The weather is still quite acceptable here, so I am still riding the CB350. But as a provisional preventive measure I have tried to adjust the cam chain according to the Honda shop manual. No success, still same clatter as before. Then I have tried  to remove the spring screw and have some manual pressure (with a long screwdriver)  - as Bodi suggests.  I could not feel the slightest movement. Does this mean the horse-shoe is stuck somehow?
I have expected that the two springs would come out of the crankcase when removeing the collared screw, but the didn't.
Any ideas, what happened?
To Bodi : What means  "live with problems of the movement" ?
Thanks for your help
BT 

[Bodi]

I meant that if the tensioning lever is damaged as in the picture above, or the rod is seized in the cylinder block... you have a choice of either doing nothing and accepting the noise or dismantling the engine to do a proper repair.

You can try and free the tensioner if you accept the risk that you can make it much worse, you would need to dismantle the engine to fix it then.

Probably the chain is now just loose enough to make a lot of noise, and if it's rubbibg the tensioner pivot then it's done as much damage as it can. This is not a good thing but it won't destroy the engine immediately; if the cam chain snaps (and being loose puts a fair bit of stress on the chain as it slaps around and wears against the tensioner pivot) you have an expensive repair job as valves, pistons, and maybe connecting rods will be damaged severely.

To try to free the thing:
Remove the starter motor. This is pretty easy, remove the wire and the attaching bolts and it comes right off with an O-ring sealing into the engine case. This lets the engine turn "backwards" freely.
Loosen the chain tensioner screw, remove the cap bolt and get a nail ir thing screwdriver to touch the top of the rod.
Remove the alternaltor cover.
Remove all 4 spark plugs.
Put a 14mm wrench on the alternator rotor holding bolt. Put the nail/screwdriver against the adjuster rod. Give the engine a sharp quick turn backwards (CW on alternator bolt). This puts a lot of pressure on the tensioner unit - trying to loosen the chain. The rod should pop up a bit. Press it down firmly and repeat a few times to work whatever is stiff a bit, turning the motor forward should make it easier to push the rod down.

You can adjust the tensioner using the static method and a moderate force on the rod then start the bike with the starter motor and alternator off, the battery won't discharge immediately and little or no oil should get out of the starter hole.

The risk is that you'll pop the rod up but be unable to press it back down. The chain could then be slack enough to start jumping sprocket teeth, bad news. If that happens (unable to retension chain) you need to take the engine apart.

[BlueThumb]

Hi,
Again, thank you very much for your expert advice !

Best regards
BT