Help with engine diagnosis. Knocking sound.

L

laran

Active Member
I'm trying to figure out what to look for on my ailing motor.

Here's a video I took just before I started rebuilding the bike. You'll hear a loud knocking sound. You'll also see the oil light and the way it's behaving.

CB550SC engine noise

I'm trying to figure out what the problem is.

My first guess was tappet noise caused by low oil pressure. I dropped the oil pan yesterday expecting to find gunk in the strainer. Instead I found a very small piece of metal. After a little research I found a post by someone saying that the cam chain can get loose, and if it get's too loose it can actually knock flecks of metal off of something, which will then show up in the oil. So I'm thinking that may be the case.

Another candidate is rod knock. I've heard that this is really bad news when it happens.

Anyone have a good idea what's causing the noise and an idea of what's needed to fix it?

Dig deep on this one guys. I don't want to see this bike go to the junkyard.
 
i hope someone can chime in here. i have a similar noise and i have checked and re-checked valves and tried to tension cam chain over and over.
 
Drain the oil and look for flecks of metal, in fact peel the oil filter apart and separate the filter and look for metal. If you find rubber and aluminum in the oil probably a cam chain tensioner=tear down.

Terry
J'ville, Fl.
 
Terry said:
Drain the oil and look for flecks of metal, in fact peel the oil filter apart and separate the filter and look for metal. If you find rubber and aluminum in the oil probably a cam chain tensioner=tear down.

Terry
J'ville, Fl.
Click to expand...

By tear down you mean what exactly? Top end rebuild? I've heard that in some cases the cam chain can cause big problems.
 
Sound didn't come over very well on my computer, even with ear-buds instead of built in speakers.
Could almost be exhaust leak but sounds more like piston hitting head which means crank is dead.
Was it like that when you bought it?
Have you changed oil?
Did you change filter?
Oil light could be wiring fault but is more likely NO oil pressure (Honda generally use a 4psi switch)
Only way to know for sure is pull top end.
If it's been run with dirty oil and blocked filter the bypass will open and feed dirty oil to valve adjusters (hydrualic)
At very least you will need a set of them (16)
Personally I don't like that motor, I've had issues with crank failing on 750's when oil wasn't changed regularly
Reading you other post, it could be the fact it's running on 3 cylinders.
Buy the carb set if it has good diaphragms (check with seller) you may only need one now but the others are the same age

PJ
 
crazypj said:
Sound didn't come over very well on my computer, even with ear-buds instead of built in speakers.
Could almost be exhaust leak but sounds more like piston hitting head which means crank is dead.
Was it like that when you bought it?
Have you changed oil?
Did you change filter?
Oil light could be wiring fault but is more likely NO oil pressure (Honda generally use a 4psi switch)
Only way to know for sure is pull top end.
If it's been run with dirty oil and blocked filter the bypass will open and feed dirty oil to valve adjusters (hydrualic)
At very least you will need a set of them (16)
Personally I don't like that motor, I've had issues with crank failing on 750's when oil wasn't changed regularly
Reading you other post, it could be the fact it's running on 3 cylinders.
Buy the carb set if it has good diaphragms (check with seller) you may only need one now but the others are the same age

PJ
Click to expand...

It wasn't like that when I bought it. It was making some noise, but it wasn't as bad and it wasn't as constant as it is in the video. Keep in mind that I bought it with 79K miles on it. It's got about 81K on it now.

I did change the oil. The oil was low when I took it in. I think it was down at least a quart. I'm not a professional mechanic, but that seems like a lot to be low.

I did change the filter. I actually had it changed for me so that I could have the mechanic take a look at things as well. He said that he thought the old oil filter had been put in slightly wrong. Dunno what effect that would have had.

Another guy said he thought it might be a wiring fault as well. Dunno.

What would I look for on the tappets to check if they're bad? There's a bit in the Clymers manual about checking them for compression and free length. Anything else I should look for?

You think the noise could be happening from running on 3 cylinders? Meanwhile I'll check on that carb set.

Thanks so much for the input. Back to wrenching ...
 
81k? man it could be all sorts of things. that motor was due for a rebuild 50k ago in my book


full tear down is in order. i get the feeling cam chain tensioner is completely shot. could be all sorts of things. hope it was maintained well, otherwise that motor is going to have all sorts of issues with that kind of milage.
 
David, it's a 100,000 mile motor, IF it gets correct maintainance at correct intervals.
I had a Kawasaki GPZ 750 that sounded like that but owner wouldn't pay for investigating and took it back as it was (never found out what happened to it)
You have to either get it running properly on all four cylinders or pull top end apart before you can say it's definitely an engine problem.
Should be able to pull oil pump out without stripping engine, it's going to need stripping and checking, broken trochoids are not too uncommon
 
The fact that the light goes out when you rev it leads me to believe there actually is no oil pressure. As PJ said, the fact that its running on 3 cylinders probably isnt helping at all, but the idle doesnt seem all that bad and it seems to be idling high enough to build pressure even running on 3 cylinders.

From the video the cam chain sounds really loose and loud, and it definately sounds like a top end rattle rather than rod knock which is usually a bit deeper and "lumpier" sounding.

Metal in the oil and the tapping and chain noise and the oil light would make me guess cam is destroyed, but youre definately gonna have to tear into the motor to find out exactly what is wrong (could be multiple things, and revving it with no oil pressure and the engine tapping like that definately isnt helping). Unfortunately i doubt theres a quick fix you can do.
 
So ....

I took the valve cover and oil filter off. In the oil filter I didn't find anything that seemed major to my untrained eye. There was a little bit of grit in there. But it was really a little bit, and I really don't think it was metal.

Now the bad news. Here are pics of what I found under the valve cover. The right hand exhaust-side of the motor was clearly cooked. The other three corners of the motor looked fine.

Here's a couple of pics which shows the two camshafts.
http://picasaweb.google.com/Laran.Evans/CB550SCCamshafts?feat=directlink

This one in particular shows the differences between the two shafts:
http://picasaweb.google.com/lh/photo/gh8EcYJemSo2d4hrto9uGQ?feat=directlink

The second piece of bad news is that I saw what looked like a small mound of dirt or gunk near the center of the motor, between the camshafts. I don't know what it is.

You can see the gunk in this photo: http://picasaweb.google.com/lh/photo/zBZuWz8OJ-jVJpO5gqDrfA?feat=directlink

So, what are my options? What's in order to get this motor back in order?
 
You may as well just pull motor out of frame and stip it completely.
The metal pile in head indicates there is so much debris floating around it will be in every oil gallery and passage,
Motor is probably 'toasted', will have to strip and find extent of damage

PJ
 
This is the worst of the scoring:
http://picasaweb.google.com/lh/photo/uY-J0SNhwRe7_QkwjhkceQ?feat=directlink

There's similar scoring in other spots, but not quite as much.

For example:
http://picasaweb.google.com/lh/photo/XKgn4m8mVQg_YE_4xRNJXQ?feat=directlink

As for the pile of gunk sitting in the middle of the motor, I think I might know what it is. Silicone. You can see how whatever jabroni opened the motor last applied so much silicone that it squeezed out of seal and into the motor. In fact, I'm not sure I even saw a gasket in there. Could they have just used silicone? Here's a pic which shows how far over the inner edge the silicone sits:
http://picasaweb.google.com/lh/photo/qw6p9JKXaMMju8N8AkC3Mw?feat=directlink

One last thing I noticed is that the part in the top-middle of this photo (which isn't numbered and therefore not named in the schematic on bikebandit) is bent up a bit. Sorry for the slightly fuzzy photo.
http://picasaweb.google.com/lh/photo/m_Aqob77EcptS-TSnkOGBg?feat=directlink

The other three seem to be fine (straight). So, A) what's the part called? And B) is it really bad that the part is bent? I'm pretty sure it can't be good or even normal.

So, I've been doing all of the work on the bike myself to this point. The motor is clearly going to be a project unto itself. Anyone know any good books on engine rebuilding?

I know of a motor for this bike for sale on ebay for $50. It's in unknown condition with unknown mileage. Would it be a good move to buy it?

The bottom line question here is, can this bike be fixed? It's a rare model. Honda only made the DOHC motor for one year. So parts for the most part have to be scavenged. NOS/OEM parts are nearly impossible to find, at least they have been so far.
 
Its possible that silicone leaked into the oil galleys and deprived the top end of oil. Those lobes on that cam look burnt. Best case scenario, you tear down the entire motor and only need a new cam, after cleaning it thoroughly. Worst case, theres other damage that you havent seen yet because you only have the valve cover off so far.
 
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