Author Topic: CB400f cam chain tensioner problems (Read 15135 times)

Dennis316 · « **on:** May 10, 2012, 08:48:35 AM »

So i purchased a cb400f without knowing anything about the cam chain issues. it was kind of loud on the ride home and had no top end power. It need a few things since i bought it from an old guy who couldnt ride, he used to drag race bikes when he was younger and still builds/rebuilds them. Anyways, i put on all new cables and everything works fine but there is a loud clacking coming from the engine, builds with revs

i figured it was the cam chain and was seemingly correct. i read everything i could find about them and still cant figure out whats wrong with mine. the bike has 14k miles on it. so i started inspecting and found that the locking bolt was broken off inside. looks like someone tried to remove it but had no luck. so i figured the adjuster was locked in place and thus couldnt adjust the cam chain tension. i tried some easy outs and had no luck. i ended up drilling it all the way through successfully.

here is where the head bashing began. i took off the top bolt (actually adjuster bolt) it was just screwed in, didnt look like it was doing anything, just seated all the way down and no touching that little platform. i took a flat screwdriver and with the bike running pressed down into the tensioner bolt hole. NOTHING, got no movement at all and the sound never changed. i tried pressing down with as much force as i could manage and still got nothing.

could the assembly be stuck? any help would be appreciated, im stuck at the moment and this weekend is going to be 80 degrees and perfect! (atleast i have another bike to ride)

flybox1 · « **Reply #1 on:** May 10, 2012, 09:58:35 AM »

Welcome Dennis316
read this, all the way through.
http://forums.sohc4.net/index.php?topic=69468.0

jessezm · « **Reply #2 on:** May 10, 2012, 10:05:17 AM »

Probably the joint of the tensioner arm is seized due to the loose chain eating into it... Probably will need to split cases to fix....

camelman · « **Reply #3 on:** May 10, 2012, 11:18:03 AM »

Quote from: jessezm on May 10, 2012, 10:05:17 AM

Probably the joint of the tensioner arm is seized due to the loose chain eating into it... Probably will need to split cases to fix....

Agreed. You could force it to move, but you risk splitting the tensioner arm apart. If that happens, then you'll wreck some critical engine parts. Splitting the cases actually isn't too bad. It will take some time, but is very doable.

Dennis316 · « **Reply #4 on:** May 11, 2012, 11:31:38 AM »

im not really afraid of splitting the cases...i broke the starter idler gear on my honda valkyrie (6 carbs, 6 cylinders) and had to take the engine out and apart. wasnt bad at all to be honest, just took lots of pics if i got stuck putting it back together. just trying to avoid it for one main reason.....if i take it apart ill start finding stuff to upgrade and spend money on!

is there a way to check if its just stuck or super worn without taking the engine apart? the bike has 14k miles on it, i got it from the second owner

Dennis316 · « **Reply #5 on:** May 11, 2012, 12:15:14 PM »

ALSO. would it save me any time to buy a cam chain with a master link instead of an endless one? can i replace it without splitting the cases, assuming the horseshoe, tensioner etc are fine of course

and is it possible to replace those without splitting the cases?

Trevor from Warragul · « **Reply #6 on:** May 12, 2012, 05:51:22 AM »

Quote

is there a way to check if its just stuck or super worn without taking the engine apart?

Take the cylinder head cover off (aka tappet/valve cover). Undo the two bolts holding the rear camchain slipper holder. It should "pop up" a little. Take off the slipper holder. Put a screwdriver down the hole at the front of the motor. Now, gently push on the slipper while maintaining a little pressure on the screwdriver. Does it move? If it does, the tensioner is not seized. Gently push on the screwdriver, gently push on the slipper, etc. If you're lucky this will free up a slightly sticking tensioner...

Your problem may actually be a knackered camchain and the tensioner is at the end of its travel. Replace the camchain using a soft rivet.

Dennis316 · « **Reply #7 on:** May 12, 2012, 06:42:14 AM »

Quote from: morini on May 12, 2012, 05:51:22 AM

Quote
is there a way to check if its just stuck or super worn without taking the engine apart?

Your problem may actually be a knackered camchain and the tensioner is at the end of its travel. Replace the camchain using a soft rivet.

im praying it is this!, how far do i need to get into the engine to replace the cam chain?

robvangulik · « **Reply #8 on:** May 12, 2012, 12:49:10 PM »

Quote from: morini on May 12, 2012, 05:51:22 AM

Quote
is there a way to check if its just stuck or super worn without taking the engine apart?

Take the cylinder head off. Undo the two bolts holding the rear camchain slipper holder. It should "pop up" a little. Take off the slipper holder. Put a screwdriver down the hole at the front of the motor. Now, gently push on the slipper while maintaining a little pressure on the screwdriver. Does it move? If it does, the tensioner is not seized. Gently push on the screwdriver, gently push on the slipper, etc. If you're lucky this will free up a slightly sticking tensioner...

Your problem may actually be a knackered camchain and the tensioner is at the end of its travel. Replace the camchain using a soft rivet.

I think you mean "take off the valve cover"? (quite a different amount of work...)
The rest of the story is absolutely correct!

jessezm · « **Reply #9 on:** May 12, 2012, 01:24:03 PM »

Yeah, just the valve cover! You just have to take off the tank and coils, then you can easily get the valve/cam cover off and follow instructions above to see if the tensioner will still pivot freely on its hinge.

Trevor from Warragul · « **Reply #10 on:** May 12, 2012, 10:44:19 PM »

My bad - cylinder head cover (aka tappet/valve cover)

Obfuscate Freely · « **Reply #11 on:** May 16, 2012, 06:28:36 AM »

I just bought a '75 CB400f, and it seems to be in pretty good working order (the PO restored it to rideable condition).

However, I have noticed a bit of a clattering noise coming from the engine, and after seeing lots of references to problems with the cam chain tension, I figured I would see if I could reduce the noise by adjusting it.

I started by following the procedure in the owner's manual, which didn't seem to work. In fact, I believe that loosening the adjuster locking bolt may have created a different, harsher sort of rattling (maybe the cam chain isn't the source of that clatter I heard initially?).

Next, I tried removing the blank bolt, and applying pressure through the hole with a small screwdriver. With the engine off, I couldn't budge anything this way, so I figure I may have a seized adjuster. When I tried this with the engine idling, I felt quite a bit of vibration through the screwdriver, and when I applied some firm pressure to it, the rattling seemed to diminish (even though I still couldn't discern any movement in the adjuster). I was able to tighten the locking bolt and nut while applying pressure to the screwdriver, and the harsh rattle is gone, but the clatter remains.

I apologize if any of this doesn't make sense, but I would really appreciate any thoughts you all have about what I'm experiencing. Does it sound like I have a cam chain issue, at all? If so, my next step is probably to try replacing the blanking bolt with a filed-down 8 x 35 bolt, as was suggested in the thread flybox1 linked to.

What else could be causing the clattering, and is it something that needs to be addressed? Could it be valve clearances? The PO claimed to have adjusted the valves regularly. I understand that poorly-synced carbs can cause the engine to make funny sounds, as well. Is there a best way to diagnose this, or is it just trial and error for someone who can't easily identify engine sounds?

Thanks for any help you can give me.

hoodellyhoo · « **Reply #12 on:** May 16, 2012, 09:14:43 AM »

Sounds like you have a good grip on the cam chain adjustment. If you got the harsh clattering to go away with preasure on the bolt then it sound like you have it adjusted correctly. Out-of-synch carbs tends to give you more of a "chugga chugga chugga" clucth rattle at idle, not what I would call a clattering noise. Based on your description it sounds like you should check your valve clearances and see if that helps.There will always be some degree of valvetrain noise. Despite what your PO may have said, it's always a good idea to go through a full tune-up when you buy a bike.

Obfuscate Freely · « **Reply #13 on:** May 17, 2012, 08:43:31 PM »

Thanks for the info, and for the encouragement!

I went ahead and adjusted the valve clearances this afternoon. I'm sure it wasn't a perfect job (I'm not very experienced working with feeler gauges), but it seemed to me that none of them were off much, if at all.

After putting things back together, the engine is making all the same sounds (and the bike rides fine, just as before). Without any way to know better, I'm ready to chalk those sounds up as normal valvetrain noise. It all gets nicely drowned out above 2000 rpm, anyway.

hoodellyhoo · « **Reply #14 on:** May 18, 2012, 08:54:46 AM »

I know in some of the period road tests they talked about the mechanical noise being more noticeable just because the rest of the bike is so quiet.

Hablo · « **Reply #15 on:** May 18, 2012, 03:46:28 PM »

Could the noise O.F. is hearing be the rocker arm rods/shafts?

Dennis316 · « **Reply #16 on:** June 05, 2012, 08:55:44 AM »

Where do i press down to see if the tensioner is seized?

Ernest T · « **Reply #17 on:** June 05, 2012, 06:09:27 PM »

Not in that pic.

It's down in the front of the engine just above the oil filter.

This is the best pic I have of it. You are going to remove the blanking bolt and push down on the other end of that rod with the square end. This is the upper case upside down.

This is a better pic of the blanking bolt, it's below the cam chain.

Make sure you loosen the lock nut and back off the cam tension bolt before you push down on the rod. Mine was frozen hence the engine teardown.

jessezm · « **Reply #18 on:** June 06, 2012, 12:37:58 PM »

Quote from: Dennis316 on June 05, 2012, 08:55:44 AM

Where do i press down to see if the tensioner is seized?

Not sure I agree with Ernest T--

In your picture, there are two 10mm bolts holding down the tensioner itself. They are directly behind the cam sprocket. Remove these two bolts and be careful not to loose them (it's under tension), and also do not lose the little hardened rubber cup that should stay put in the underside of that holder. Now you can remove the tensioner by just pulling it straight out. Now with a flat head screwdriver you have direct access to the tensioner arm. First loosen the locknut in front of the engine and then push down through the top on the arm where the tensioner you just removed should seat. The action should be nice and springy without hitches or hesitation returning to its position.

If you try to push down from the blanking plug, since there is very little leverage at that point, putting pressure on the arm likely wont result in any noticeable movement. But the fact that you feel a lot of vibration there with the motor running and the locknut loosened is a good sign the the arm is not seized. Performing the test I described above will confirm that.

Bodi · « **Reply #19 on:** June 06, 2012, 01:12:27 PM »

Yes, the front slider is fixed, the crank pulls the chain down at the front of the engine, slack is at the back. The picture of the top case shows the springs and pusher plunger, this pushes down (up in the picture since the case is inverted) on a horseshoe assembly that ends up pushing up on the bottom of the rear slider blade. This bends the blade, taking up the slack.
The pivot in the horseshoe thing gets bashed by a really loose cam chain, damaging it so it's locked and no longer pivots. If you can feel vibration I doubt if it is locked up.
If you can press on the plunger (under the blanking screw) with the engine running, you should be able to push hard enough that the chain gets quiet then tighten the clamp bolt. Too tight and the sliders will wear rapidly, too loose and you have the chain rattle. Even if the pivot is stiff, a mild tap with a hammer on a bolt or nail touching the plunger will usually tighten the chain enough to quiet it until you have time to open the cases and investigate. It's better to open it up and have a look if it doesn't act normally. I would at least remove the rocker cover and check that the chain looks OK and isn't so stretched that it's close to failing. That is an expensive experience.

Ernest T · « **Reply #20 on:** June 06, 2012, 05:37:42 PM »

This is what happens when the chain gets loose and can't be tightened.

Kwality · « **Reply #21 on:** June 06, 2012, 11:45:50 PM »

I have one of those photos $:-\$ !

oldbob · « **Reply #22 on:** July 09, 2012, 01:18:33 PM »

No problem with a rattling chain, but I hear a whine that sounds as if it is coming from the center of the cam shaft. I suppose it could be the guide or the slipper for the chain adjuster, but I'm not sure.

Any thoughts?

Thanks.

Bob

friday · « **Reply #23 on:** July 08, 2017, 06:23:08 AM »

I have the same problem.. broken cam chain tensioner bolt.
my tensioner is not moving a bit. I have already split the two cases. Drilling is the only option I see..

I was wondering if anybody has solved the problem and how did you do it?

Bodi · « **Reply #24 on:** July 08, 2017, 12:07:11 PM »

Try a left twist drill, about 5mm or 3/16 is close. You drill "in reverse", usually with stuck bolts the bolt stub catches and unscrews before you bottom out. Might be different as this screw does push against the bar?
Check where it snapped. The bolt has a 6mm end thread then an 8mm thread to the head where the locknut goes. If it snapped close to the case surface maybe you can slot it with a dremel then get it out. Heat around the area might help. A racing engine shop should have an edm system to get snapped stubs out if all else fails - not cheap but racing engine heads are $$$$ so it is worthwhile.

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Author Topic: CB400f cam chain tensioner problems (Read 15135 times)

oldbob