Topic: Rattle in engine

[J Hunter]

I Have 75 CB750 that I restored a few years ago. I crank it once a month to circulate the oil and keep everything lubed up. The last time it was sitting idling everything was fine, then it started rattling it sounded like under the valve cover . I shut it down immediately to minimize any damage. I was wondering if maybe the cam chain broke. I haven`t pulled the engine, I thought I would get some opinions on what I might be looking for.

[ekpent]

You could check the valves and make sure that an adjustment nut on the rocker hasn't come loose and migrated up the thread and is hitting the valve cover inspection cap. Seen and heard that before. Check under all 8 caps.

[J Hunter]

I will check that today and hope it is that simple.

[newday777]

I will check that today and hope it is that simple.

Reply back what you find on the inspection.

[J Hunter]

It will be after lunch but I will post results.

[J Hunter]

Checked the adjustor nuts and they are all where they should be. Is there a way to check the cam chain other than pulling the motor?

[scottly]

Check the oil level in the tank; when a 750 sits, sometimes oil leaks past the oil stopper valve, draining into the sump, known as "wet-sumping". If most of the oil has drained, the remaining oil can get pumped out of the tank before the scavenge pump can replace it. If the oil level is low, only add enough oil to cover the outlet in the bottom, lest the tank overflows once the oil in the sump is pumped back into the tank.
If the valves are opening and closing when turning the motor, the cam chain is not broken.

[J Hunter]

We have a WINNER  the oil tank was dry. Charging the battery and adding oil to the tank will start it later. Thanks for the info.

[scottly]

 

[Tracksnblades1]

I Have 75 CB750 that I restored a few years ago. I crank it once a month to circulate the oil and keep everything lubed up. The last time it was sitting idling everything was fine, then it started rattling it sounded like under the valve cover . I shut it down immediately to minimize any damage. I was wondering if maybe the cam chain broke. I haven`t pulled the engine, I thought I would get some opinions on what I might be looking for.

Hunter,
I read your post as it was still running when you shut it off..?
If the cam chain broke, I think it would have shut itself off..

Did you replace the valve springs, or valve spring retainers, or retainer locks..?
Did the rattling sound like something loose (tapping or clicking) or something ready to lock up ( pounding, screeching)?

You could peek,restrictedly, through the lash adjuster caps to see if it obvious. Like a broken spring, backed off or broken lash adjuster, bad retainer lock, etc.  It probably be hard to see that good through the hole though.

I’m afraid if the rattle was caused by the oil tank being empty….?
Then did it ever pick up oil pressure as it sat idling..?
Does the oil light work..?
Well I’ll keep my fingers crossed…?

[J Hunter]

Yes it was idling, as soon as it made noise I hit the kill switch. I have not done any valve work on it so hoping the oil tank was the problem. I will know in a bit.

[Tracksnblades1]

Yes it was idling, as soon as it made noise I hit the kill switch. I have not done any valve work on it so hoping the oil tank was the problem. I will know in a bit.

Does your oil light work..?
I’m worried whether it had oil pressure as it was idling…?
You’ll know soon enough…
Fingers are crossed 🤞

[J Hunter]

Ok I got it to crank over and still had a noise. I located where it is coming from, it is the clutch. I can pull the clutch partially in and the noise goes away. I guess some thing has gotten out adjustment. I can turn the motor over with the kick starter and it pops kind of like its jumping teeth.

[Tracksnblades1]

So if you put it in 2nd gear an slowly push down on kick starter, with kill switch on stop, will it jump or slip without using the clutch lever?

[Tracksnblades1]

You could pop the inner clutch cover off pretty easy and see if something’s broke or loosened up..?

[J Hunter]

That was my next move, I tightened the adjuster screw 1/2 turn and it doesn`t have the same sound but when it running it sounds like something is rubbing, when I pull in the clutch sound goes completely away.

[Tracksnblades1]

That was my next move, I tightened the adjuster screw 1/2 turn and it doesn`t have the same sound but when it running it sounds like something is rubbing, when I pull in the clutch sound goes completely away.

I think you’ve found it. Hope it’s not oil pressure related.
Maybe just a spring bolts backed out..🤞

[J Hunter]

I don`t think it oil pressure related, the motor sounds great. The clutch has always rattled but I did some research and found that was common. I`ll pull it apart tomorrow and hopefully find a spring bolt or some thing simple. Thank you guys for the help. I`ll post what I find.

[Tracksnblades1]

I don`t think it oil pressure related, the motor sounds great. The clutch has always rattled but I did some research and found that was common. I`ll pull it apart tomorrow and hopefully find a spring bolt or some thing simple. Thank you guys for the help. I`ll post what I find.

The primary chains and the clutch basket play their own special music when she idles real slow..😇

[scottly]

The clutch has always rattled but I did some research and found that was common. I`ll pull it apart tomorrow

I wouldn't take it apart based on your symptoms. The rattle is more likely related to slow idle, like Tracks mentioned, than any mechanical problem under the clutch cover, unless someone has messed with it and fixed it until it was broke.

[dave500]

dont just let it idle cold,hold a fast idle if your just starting it to keep it lubed etc and let it get quite hot.

[PeWe]

I have noticed that oil tank will not be refilled in time when bike is idling a few minutes on side stand. Not good idea to let it warm up in that angle.

Noticed the flashing oil lamp and switched off direct.
Tank empty, added some. Saw pressure was pumping when it came oil squirts.

I had to remove that oil later on after a ride when tank was overfilled.
Learned to not idle on side stand.
Same on both my CB750.
I place a 2" thick wooden plank  under sidestand making it almost straight up when idling for a while as carb sync.

Clutch rattle at idle will be silent when using the clutch.
Bad synced carbs, bad ignition will cause engine to rattle.
Cut advancer springs 1/2 turn will help ignition to be right all the way from idle to full. Points or electronic have same need as long as stock advancer is used.

This will make adjusting ignition much easier.
Set F line up with case mark for idle and done.
I prefer 1200rpm idle. Easier to ride in city and ensure oil pressure really hot days with a hot engine

My K6 with heavy duty primary chains have less rattle despite a harder pounding engine due to higher compression. Balanced crank migh help too.

[J Hunter]

I found the problem, a bolt had backed off on the clutch and was hitting the outer cover.  No damage other than a bent bolt.

[J Hunter]

All the bolts were loose, what do they torque too?

[newday777]

I found the problem, a bolt had backed off on the clutch and was hitting the outer cover.  I can't figure out how to post pics. No damage other than a bent bolt.

That'll make some rattling for sure. Glad it was not catastrophic.