Topic: Cam chain tensioner noise

[77_f2]

So...I know I should've set the cam chain tensioner and checked the valve clearances back when I got my bike last year, but I didn't. The valves definitely are not too tight, maybe a tad loose, and the engine has been running ok, if slightly rattly at idle. So I hoped the chain tensioner would fix the noise at idle.

The chain tensioner should've been easy, right? Now I've read different methods of adjusting the "automatic" chain tensioner. [1] set #1 to TDC and loosen & tighten the locknut & bolt. (from internet gossip)  [2] set #1 to 15 deg. past TDC, same. (from Clymer manual) [3] run the engine at around 1K rpm idle, loosen & tighten. (from alleged Honda factory manual reprint)

Well, so I tried method (2) because the idea of messing with it while the engine's running scared me. I heard and felt nothing, could not tell if that meant it was already perfect, or something in the mechanism is frozen, or what.

So then I started the engine up to try method (3). Initially, it sounded just as usual. But when I loosened the locknut and bolt on the tensioner, it *immediately* changed the sound. But not for the better. The rattley overtone sounds considerably sharper, more "metallic" now. Worrisome to my ear anyway. I tightened the bolt on the tensioner and the locknut, hoping they themselves were the source of the noise, but it wasn't.

Now I don't know how to interpret this. Maybe the tensioner *is* adjusted and I'm hearing the loose valves now because the chain is fettled? Or maybe the cam chain is looser because the spring is weak enough the idle method didn't work and I need to try method (2) above, again to get back to where I started. Or maybe the tensioner has failed, and there's nothing for it but to take *everything* apart.

The engine seems to run well otherwise, at least in neutral on the centerstand, it starts instantly, idles correctly, responds instantly to the throttle.

It has a little over 30K miles, for what that's worth.

[scottly]

[2] set #1 to 15 deg. past TDC, same. (from Clymer manual)

#2 is the proper method! #3 is asking for disaster.
BTW, when I adjust the tensioner, I check the depth of the end of the rod both before and after loosening the pinch bolt; it usually only moves a very small amount, like .020" over several thousand miles. You wouldn't notice without measuring.

[bryanj]

Would help to know what bike you are talking about

[BenelliSEI]

#2 method for sure. Assuming you have a SOHC cb750, don’t be afraid to remove the tensioner and make sure it clean and operates smoothly. Retract it when reinstalling and then release and do #2.

Valve adjustment, set the timing and doing a good carb sync (with vacuum gauges) will go a long way to silencing your “rattles”. Because the cb750 using a dry sump lubricating system it will always be a bit noisy. Cb400F of cb550 have their sumps full of oil, so they will generally be much quieter.

[77_f2]

Would help to know what bike you are talking about

1977 CB750F2 (super sport, sohc)

[77_f2]

[2] set #1 to 15 deg. past TDC, same. (from Clymer manual)

#2 is the proper method! #3 is asking for disaster.
BTW, when I adjust the tensioner, I check the depth of the end of the rod both before and after loosening the pinch bolt; it usually only moves a very small amount, like .020" over several thousand miles. You wouldn't notice without measuring.

There's a fairly good chance it was never done in 46 years and 30K miles.

I had the idea of measuring the difference from a youtube video, but there didn't seem to be enough room to get my caliper in there straight.

As I wrote, method 3 - while idling - is the method in what is purported to be a (copy of) a factory manual. Maybe UK, and maybe the factory manuals differed over time or in different markets. ¯\_(ツ)_/¯

While, respectfully, you may be correct about "asking for disaster", and Honda publications may not always be right, if someone on an internet forum expresses horror at what the factory instructs, I take it with a big grain of salt.

But at this point, I might as well attempt the second method again when I get a round tuit.

I ordered a used spare assembly to examine since there was one for $12 on ebay that didn't look in terrible condition. If it is possible to take off the spring and pusher bar assembly, without disassembling the whole engine, then if say the spring is no good I might be able to substitute it.

[77_f2]

#2 method for sure. Assuming you have a SOHC cb750, don’t be afraid to remove the tensioner and make sure it clean and operates smoothly. Retract it when reinstalling and then release and do #2.

Valve adjustment, set the timing and doing a good carb sync (with vacuum gauges) will go a long way to silencing your “rattles”. Because the cb750 using a dry sump lubricating system it will always be a bit noisy. Cb400F of cb550 have their sumps full of oil, so they will generally be much quieter.

Thank you for encouraging me to remove it and check! I found a used assembly for spare parts and education.

I do have a sohc cb750, F / supersport not K, as my picture and user name suggest.

I checked all the valves (cold, before I messed with the tensioner) and they were all at least 0.003. So the intakes could be tighter for sure. The locknuts on the adjusters were tight enough I was afraid to escalate the amount of force I was using and was cautious of fixing what isn't broke. So I haven't reduced the clearance to spec yet. I also didn't have a .004 to use the go/no-go method on the exhaust side. As you know, some people think more clearance than the official .002 and .003 is appropriate anyway.

The carbs I think are in good shape - Mike Nixon rebuilt/reconditioned them for me. He also advised me to check the timing, which I did statically, with the engine off, and that was probably the biggest improvement in how it ran so far - it was noticeably off and now it starts in like half a revolution.

It's full of fresh 10w40 motorcycle oil.

[newday777]

[2] set #1 to 15 deg. past TDC, same. (from Clymer manual)

#2 is the proper method! #3 is asking for disaster.
BTW, when I adjust the tensioner, I check the depth of the end of the rod both before and after loosening the pinch bolt; it usually only moves a very small amount, like .020" over several thousand miles. You wouldn't notice without measuring.

There's a fairly good chance it was never done in 46 years and 30K miles.

I had the idea of measuring the difference from a youtube video, but there didn't seem to be enough room to get my caliper in there straight.

As I wrote, method 3 - while idling - is the method in what is purported to be a (copy of) a factory manual. Maybe UK, and maybe the factory manuals differed over time or in different markets. ¯\_(ツ)_/¯

While, respectfully, you may be correct about "asking for disaster", and Honda publications may not always be right, if someone on an internet forum expresses horror at what the factory instructs, I take it with a big grain of salt.

But at this point, I might as well attempt the second method again when I get a round tuit.

Don't wait to for 'round toit' to happen....... Do it before you run it again.

[newday777]

From the manual

[scottly]

I ordered a used spare assembly to examine since there was one for $12 on ebay that didn't look in terrible condition. If it is possible to take off the spring and pusher bar assembly, without disassembling the whole engine, then if say the spring is no good I might be able to substitute it.

Just make sure you position the crankshaft at the 15 degree point before removing the adjuster assembly, and don't turn the motor until after it's reinstalled. Also, if you go past the 15 degree point, DO NOT turn the engine backwards to the mark! Turn the engine another turn forward until it's in the proper spot.
The only thing that tends to happen is that the rod can get stuck in the housing, so it doesn't move when the pinch bolt is loosened.

[bryanj]

When the chain gets worn the rod gets to the point where the lip at the end of the flat surface the lockbolt bears on stops the rod moving in.
Before removing the assembly try adjusting the chain then when assembly in your hand loosen the lockbolt and see if the adjuster has more movement

[Phoenix]

Last time I set it I idled it at about 1500 and adjusted the rod in and out and set it at the point of less noise.  I don't remember where I read this but it seemed to work.  Would like to hear what your thoughts are.

[scottly]

The point of setting the crank at 15 degrees is that it puts slack at the back of the cam chain. The spring applies the desired amount of tension. When the engine is running, the slack is trying to change as the valve springs are being compressed and relaxed. The proper way is to set the tensioner statically.
Have you ever changed the timing belt on a car engine? The ones I have done also use a spring-loaded tensioner, where you position the crank and cam in a certain place, un-lock the tensioner, then lock it after the spring has applied tension.

[scottly]

As I wrote, method 3 - while idling - is the method in what is purported to be a (copy of) a factory manual. Maybe UK, and maybe the factory manuals differed over time or in different markets. ¯\_(ツ)_/¯

Where did you find this purported copy of a factory manual?

[PeWe]

My owners manual to my CB750 K6 also have that crazy description of adjusting the cam chain tensioner. Release while idling. Horrible

I was lucky it did not ruin the engine the only time I followed the manual when stock. It just made it worse.
A friend shown me a way to adjust when using the kickstart. A thin screwdriver stucked inside tensioner rear hole. Kick around a little to feel when screwdriver or pin has reached its most inner position. Tighten and lock there.

It must be same as the recommended safer and  easier15 degree position.

I have been close to ruin engine when I had forgotten to tighten the tensioner locking screw. Hotter cam.
Chain jumped when starting the engine.

Real luck it jumped so valves did not hit pistons. More than one tooth, several. The jumping chain could have damaged the crank teeth too.
An additional check-up inside.

Photo show 15* ATDC 1:4
The tower with adv spring has just passed case mark.

[Quattrocilindri]

Last time I set it I idled it at about 1500 and adjusted the rod in and out and set it at the point of less noise.  I don't remember where I read this but it seemed to work.  Would like to hear what your thoughts are.

That's what the service manual stated on my 350F. My used bike was making a slight rattling noise while idling, shortly after I bought it. I set the idle at 1200 rpm, loosened the automatic tensioner lock nut and bolt above the oil filter housing, and immediately the rattle was completely gone. I never touched the spring loaded rod inside the case. Tightened the bolt and nut, and no more noise ever since.

[77_f2]

[2] set #1 to 15 deg. past TDC, same. (from Clymer manual)

#2 is the proper method! #3 is asking for disaster.
BTW, when I adjust the tensioner, I check the depth of the end of the rod both before and after loosening the pinch bolt; it usually only moves a very small amount, like .020" over several thousand miles. You wouldn't notice without measuring.

There's a fairly good chance it was never done in 46 years and 30K miles.

I had the idea of measuring the difference from a youtube video, but there didn't seem to be enough room to get my caliper in there straight.

As I wrote, method 3 - while idling - is the method in what is purported to be a (copy of) a factory manual. Maybe UK, and maybe the factory manuals differed over time or in different markets. ¯\_(ツ)_/¯

While, respectfully, you may be correct about "asking for disaster", and Honda publications may not always be right, if someone on an internet forum expresses horror at what the factory instructs, I take it with a big grain of salt.

But at this point, I might as well attempt the second method again when I get a round tuit.

Don't wait to for 'round toit' to happen....... Do it before you run it again.

I did apply the TDC + 15 deg. method again, sprayed a little wd-40 in for good measure, but decided not to take the entire push bar assembly off, seeing as the third bolt is obstructed by (what I think is the) oil pressure sensor boot.

I tightened the bolt itself just barely snug with a 10 mm wrench, and then tightened the locknut down firmly.

When I started it up, it sounded just like it originally did, not *tight* but not with a scary metallic edge like the chain was flapping in the breeze.

So my conclusion is that following the idle method made it looser, but now I am back to where I started, and probably any further improvement will have to involve adjusting the valve clearances a little tighter.

If I adjust the valves to be spot on and it doesn't make it sound a lot better, I may consider taking the tensioner off and seeing if the spring is tired or something. Next week I will have a spare for reference and parts.

[77_f2]

As I wrote, method 3 - while idling - is the method in what is purported to be a (copy of) a factory manual. Maybe UK, and maybe the factory manuals differed over time or in different markets. ¯\_(ツ)_/¯

Where did you find this purported copy of a factory manual?

A UK purveyor of classic honda parts. It is a physically (re)printed manual, and whether/how it was authorized I don't know.

In some respects it looks like a real Honda manual and in others it doesn't quite match pages I have seen from the/a factory manual. But I kind of assumed that was likely due to differences between UK and US.

For example, it does have the method for valve adjustment where you set the position and do 4 values, rotate and do the other 4. As opposed to the third party manuals that have you keep rotating it for every cylinder.

[77_f2]

From the manual

That looks like the Clymer manual I have. That may be the correct method, but I noticed that the drawing of the T/F marks is not quite accurate.

Nevertheless, following those directions undid the *new* noise, so at least I'm not going backwards.

[madmtnmotors]

These engines are noisy at idle. A good carb sync can make them sound (and run) a bit better. 

With a fresh carb sync mine will idle smoothly all the way down to near 800 rpm.

[scottly]

it does have the method for valve adjustment where you set the position and do 4 values, rotate and do the other 4. As opposed to the third party manuals that have you keep rotating it for every cylinder.

Lots of manuals have the 4 valve, then the other 4 procedure, but the one cylinder at a time method is easier, at least for me.

[PeWe]

I have tried the valve adjusting by 4+4 valves described in the CB750 shop manual. I think it was easy to get it wrong.
See photo from my CB750  Shop manual. Paper copy from eBay UK.

The better method described in the Owners manual I got with bike. Same manual with wrong cam tensioner adj.

Rotate engine, start with 1:4.
If #1 are not in position, rotate another turn to 1:4.
Adjust #1 valves, rotate to next 2:3, do #2, next 1:4 do 4, 2:3 do 3.
I continue to turn 1 more time for double check, if nut is tightened too.

Fine thread steel allow relatively high torque for the size.

[scottly]

With high performance, long duration cams setting the cylinder at TDC insures that both rockers are sitting on the base circle of the lobe.

[PeWe]

With high performance, long duration cams setting the cylinder at TDC insures that both rockers are sitting on the base circle of the lobe.

I prefer that method, valve cover off to see the rocker against base circle.

That need a frame kit

[scottly]

My Seeley frame allows removal of the valve cover, but I never bothered just to set the valves for normal maintenance.