Topic: 1975 CB550 engine knock/chatter

[Amann31]

Hello, I am a new 1975 CB550 owner. I have had the bike about a week and a few days ago I began to notice a chatter from the engine at idle after a cold start. It would go away completely when warm. The last few days it has gotten louder but still fades away when warm. Yesterday I did the valve lashes thinking it could be valve against piston knocking, but I am still trying to diagnose the problem. Rode today and the engine started to die at a stoplight. Made it home and soon as I parked I saw a fast oil leak from the rear of the engine that was new. The leak stopped as the bike cooled. Listened to the bike hot at idle and the chatter is far louder and present even when hot. First video is a few days ago semi cold, second is this morning all the way cold, and third video is hot after the most recent ride. My theory for the new oil leak is a plugged crankcase breather, but I still cant figure out the chatter. If anyone can help with the diagnosis I would appreciate it. Thanks!


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[HondaMan]

First, welcome to the fun!
Second: if you're trying to post pix or videos, you'll not be able to until you have a few more posts in the forums.

In the meantime: pull your sparkplugs and see what they look like: if they are black then you need to start there with new ones. When they get black they don't ignite the fuel very well, and this makes for uneven engine response in a big way. This makes things in the engine rattle, like the cam chain and primary chain, and they generate all sorts of sounds. You can put a long screwdriver up to your ear and 'probe' it around the engine's surfaces to try to locate where the sound is originating, which quickly helps narrow the search.

[Amann31]

Hey, thanks! I have been trying to post videos and it just won't work. I guess that is why haha! I will go ahead and check the plugs and I plan on doing the cam chain tensioner adjustment next. Thanks for the fast reply and I will post the videos as soon as it lets me.

[M 750K6]

Mine is a 750 and when I was researching, before buying, I came across a few videos. At low idle revs (around 1,000rpm), they all seem to chatter. A primary chain type of noise.

On mine, I've worked on carbs and ignition (running points) to see how good I can get it. Warm I can run at 1300rpm idle smoothly, but start to get rattly below that. So, I leave it at 1300rpm idle.

Cold, I don't idle it, I start on choke, bit of throttle and choke straight off, then go. In my experience, they're not good at idling until warmed through, about 4 miles in my case. Just keep the revs lower whilst it's warming up.

They shouldn't leak oil. Breather blockage is possible and then increased pressure forces oil to find the path of least resistance. In my case, I had a perished / damaged rubber in one of the rocker caps (easy fix), a sheared front head bolt and a badly damaged gasket face in the top of the head and valve cover (I think a chisel or screwdriver had been hammered in to separate the cover from the head!). They were not easy fixes, but rewarding to sort out. Take your time to pinpoint the source of the leak.

50 years of life and some impatient previous owners take there toll.

[dave500]

dont let it idle when its cold,hold a fast idle while you gear up then ride it,these aint fuel injected and dont idle well when cold at all,if yours has the throttle friction screw lock use it to hold that slightly fast idle.

[newday777]

dont let it idle when its cold,hold a fast idle while you gear up then ride it,these aint fuel injected and dont idle well when cold at all,if yours has the throttle friction screw lock use it to hold that slightly fast idle.

He might not know what a "throttle friction screw lock" is, depending how old he is ............

[Oddjob]

Plus the 550F never got it fitted and according to CMS only the 550K0 got it, the K1 and K2 for some reason show it but there is no parts number shown, odd. Most don't work anymore as well as the sleeper ramp invariably falls out when you remove the switchgear from the bars and if you don't notice it fall out then it doesn't work again afterwards.

Breather blockage, no, design of cover doesn't lend itself to blockages, breather pipe blockage though is another story. Just remove the pipe from the cover and if it helps it's the pipe blocked.

I'd suspect a carb inbalance before anything else. Either a partially blocked pilot jet or carbs way out of sync. Do the basics first though, timing , tappets, camchain. Also check for exhaust leaks.

[dave500]

without seeing the bike it may be just an idle speed set too low?adjusting the tappet has nothing to do with the piston striking the valves(man if thats happening your in a world of #$%*),as oddjob suggests start with all the basic tune up settings first,rule number one,get the ignition set up and squared away first before you #$%* around with the carbs!!

[Stev-o]

When was the last time it had a "3000 mile tune up"?  If you dont know, it may be time.   And after that, you should do a "carb sync", very simple procedure but you will need a special tool, this has been known to quiet down an engine.

As far as the oil leak, doubt the blockage theory, some guys use white baby powder on the motor to determine exactly where it is leaking.

My sync tool...

[Amann31]

Thanks for all of the input guys. I am working my way through the 3000-mile tune-up and I will see if the chatter gets better. Next step is carbs, but I might have a shop do it because I live in a dorm and it is hard to keep equipment. As for the oil leak I was thinking about using Brakleen and Simple Green to clean it off and then start it and look for the leak. Any thoughts on Brakleen damaging the exposed part of the gaskets?

Oddjob,

 

Plus the 550F never got it fitted and according to CMS only the 550K0 got it, the K1 and K2 for some reason show it but there is no parts number shown, odd. Most don't work anymore as well as the sleeper ramp invariably falls out when you remove the switchgear from the bars and if you don't notice it fall out then it doesn't work again afterwards.

What are you referencing here?

Also I have been working my way through the service manual for each part of the tune up. If you guys have seen any other resources that you like I would love to hear about them. Thanks again.

[scottly]

Just how fast and how much oil leaked out? Have you checked the oil level? BTW, you unscrew the dipstick, wipe it off, and then re-insert it without screwing it in to check the level.

[Amann31]

I have been checking the oil hot and unscrewed. It was a slow, constant leak but after riding yesterday a larger amount leaked out while the engine was hot and stopped as the engine cooled off. I may have overfilled the oil by a bit as it seems to be at full when checked hot post-large leak. Full oil and filter change is planned for tonight.

[Oddjob]

The throttle friction screw lock was a thumb wheel screw fitted in the right hand switchgear between the 2 throttle cables, you wind it in and it stops the throttle grip from turning gradually, you can keep the engine running faster whilst you check things, primarily fitted to allow for testing of the advance/retard unit.

[Amann31]

Thanks Oddjob, it looks like I don't have one on my bike. Here are some videos of the chatter/knock. First video is semi-warm, second is cold idle, third is hot after yesterday's ride, the first time the chatter was present while the engine is hot. Any ideas as to what it could be would be awesome. I also did the cam chain adjustment and an oil change but I am waiting to start it until I can figure out how worried I need to be about the chatter.
https://youtube.com/shorts/klYLN_9lJy0?feature=share
https://youtube.com/shorts/QNk2kWLBDEY?feature=share
https://youtube.com/shorts/V-Knn0X8kU0?feature=share

[dave500]

ok apart from the sound thats hard to pinpoint on phone audio you have an electronic ignition which means no points and condensors,so long as it was timed correctly in the first place your ignition should all be well,as far as the noise maybe its just the normal noise these older bikes made even when new?these are no way as silent as new bikes as far as internal engine noise.

i also see you have pod foam airfilters,try and source the factory airbox and plenum intake system,i think its just idling a little low,wind up the idle screw maybe till it sounds better?because you have electronic ignition(which in my opinion is good)go straight to a carb sync if you can,you also have the good early carbs which we all like.

[Oddjob]

That doesn't sound nice at all. The way it revs makes me suspect it's not running right, maybe a carb problem. I'd agree the tickover sounds a little low as well, what is it set at?

Are the rocker shafts pinned? On a 550 they should be BUT it's getting on now and the camcover could have been swapped over at some point. If you take off the breather cover and see 8 nut heads they are pinned, if just 4 then they aren't.

[bryanj]

Only the 77/78 were pinned before that same as 500

[Oddjob]

Fairly sure the last 500s were pinned Bryan, not 100% sure when the 550 started to be pinned as we didn’t get them until the F1 and K3. Think they were pinned.

[Deltarider]

Fairly sure the last 500s were pinned Bryan, not 100% sure when the 550 started to be pinned as we didn’t get them until the F1 and K3. Think they were pinned.

It depends on the enginenumber and only the parts lists will inform you in detail from what enginenumber on they were pinned. I once saw a CB550K2 aka CB550K76 in Holland and according to its enginenumber it was not pinned...

[Oddjob]

The 500K3 was pinned, the 550K engine didn't get pinned until 1083640. The 550F engine got pinned after 1133172. According to CMS anyway.

[denward17]

My '76 K2 was not pinned in the US, not by the time I got it anyway.

Engine #1083036

[Oddjob]

You missed it by 604 😀😀

[Amann31]

Well guys I put rotella T4 oil in it, did the valve lash, cam chain, new spark plugs, and turned up the idle and the chatter seems to have gone away. Not sure if it ended up being the diesel truck oil or the idle adjustment but the knock is way better. I can still reproduce it when I turn down the idle super slow but the engine sounds way healthier and produces more lowend power for whatever reason. I will tune the carbs next and see if that helps when its idling slow. I have no idea what speed my idle is set to, but a tach is in the mail. Thanks for everyones’s help and ideas.


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[HondaMan]

IT sorta sounds like the normal chatter heard when the primary chain is getting a little worn and the idle isn't smooth and even - which is most 550s these days? When you get the tach, try the idle at around 1100 RPM to see how it sounds.
For sure, if the oil was/is too thin (like 10w40) it will make the engine much noisier: use of at least 15w40 or 20w50 is recommended.

[dave500]

good one,im leaning to the idle speed was too low,new oil helps off course.