The International CBX Owners Association

Following the rebuild of my alternator, I took my CBX out for a short drive.
All was as before, the 'racket' still very much there, and at least we now all know it had nothing to do with the alternator.

After the bike was nice and warm I made a recording of the racket which I attach below.
{Ooops - no wav files allowed. In any case the racket frequency is one sixth the overall bike RPM (although I didn't run a Fourrier analysis, and can clearly be heard in the recording}
What is interesting is that it certainly comes from cylinder no 1 (LHS) and using a very long screwdriver as a stethoscope it was extremely loud on the engine cover cyliner no1 exhaust side, bit less so near cylinder 1 inlet side, SUBSTANTIALLY attenuating as I moved on to cylinder no 2.
It was also definitely a top end issue as the racket was much less at the level of the crankshaft.
MOST INTERESTINGLY, the racket went 100% away every time I run the engine with the no 1 plug cup off
I also remind everybody it is not heard at idle, it manifests itself, loudly around 2.5K and 3.5K RPM, especially during acceleration.
Your thoughts and suggestions most welcome!
Cheers, Aris
P.S. As I suspected this from before, I only recently redid the valves (as some of you know ) and had a good look at the area but could not find anything.

Ouch!

A noise that goes away when you unload a cylinder usually turns out to be a rod bearing or a wrist pin

I hope it turns out to be something simpler

What do you know about the history of this engine . . . . prior to your rebuild?

Don

I can't think of anything that runs at 1/6 the engine speed. If this problem involves one cylinder, it would have to be either the same as the engine speed, or 1/2 engine speed.

Since the noise goes away when you remove the plug cap, maybe you have an ignition problem. Bad Plug? Bad coil? Something else?

Even though you can't attach a wav file, I believe you can include video with sound. I've never done it, so don't ask me how, but I think it can be done. Maybe you'd have to use Youtube.

If the noise is leakage past a tight/bent valve, it would be at 1/6 engine speed. The big hint is that it goes away when he pulls the plug wire.

Rick Pope wrote:If the noise is leakage past a tight/bent valve, it would be at 1/6 engine speed. The big hint is that it goes away when he pulls the plug wire.

How did you figure that, Rick A four-stroke has an ignition every other revolution. That means the valve cycles repeat every other revolution, thus the cam rotation at half engine speed. The piston comes up against a closed intake valve at (basically) every revolution and against a closed exhaust every other turn. Gas blowing by a closed intake could happen at every revolution, either compression or exhaust cycle and gas blowing by an exhaust could happen every other revolution , during the compression cycle.

Chaps, I think I am unknowingly confusing everybody.
Forget the 1/6th, I should say it is at a lower frequency. Apologies, my mistake.

Aris:
I fear, as Don said, you have a bad rod bearing, or a bent rod. Did you carefully check all the rods to be sure that they were not bent before assembly? These are very easy to bend or slightly twist, usually as a result of a hydro lock. However, on Don's bike, I found 2 slightly bent ones as a result of the long cam chain breaking. You could barely see it with the eye, but a laser check on a flat table revealed it.

Or, you have the incorrect size bearing in the big end of number 1. I assume the rod and main bearings were all new? It is very easy to get one wrong and the only way to be sure you have them correct is to plastigauge every one before final assembly. But as thorough as you are, you probably did that.

The engine is for sure going to have to come apart again to investigate - I know that is a crushing feeling - been there a couple of times.

If you can tell us a bit more about the engine build, maybe we can nail it down further. Wow - this is getting to be quite a project!

Dave

Aris:
After reading your description again, it would seem not to be the bottom end bearing. But if allowing the piston to be just a passenger by pulling the plug wire removes the noise - it almost has to be a bearing. The valves still move regardless of fire or not. Quite a mystery.

Dave

I am also inclined to believe this is an engine out / engine to pieces job.
It is not a problem!
I love working with these engines and frankly I have my GL1000, CX 650 Turbo and Commando to ride during the long, hot summer. Actually, I am intrigued ..
My only concern is that I do not take the engine to pieces only to realise it was something simple (although this doesn't seem to be the case).

I have no previous knowledge of the history of my bike other than that at some point it must have belonged to an ape, with a chisel for screwdriver and a hammer.
However:
I took everything appart and had the crankshaft professionally checked.
I used all new big end bearings and platigauged everything several times. I used NOS conrods and NEVER thought about checking them
The block was rebored and NOS oversize pistons & rings used, gudgeon pis were also new.
In fairness, I did not measure any new things as I took for granted. Now I know better...

So I will look now for a nice 'engine removal' thread although I think I am pretty good at it by now

Thanks, and if there any other ideas, let's have them.
I will keep you all posted.
Aris

Here's the sound embedded in a short uTube video
http://www.youtube.com/watch?v=CLr-ud4izQU
Thanks

Aris,

Maybe, just maybe . . . . an exhaust leak on #1??

What sort of gaskets are you using? The copper ones or the white asbestos looking ones?

It doesn't sound like a bearing or a wrist pin or bent rod to me . . . . for what little that is worth - I'd do lots more playing around with it before I decided to take out the engine

Don

Aris:
I'm with Don - I'd check for an exhaust leak on #1. If you are using copper gaskets and have had the pipes off and on more than once, they crush beyond usefulness easily. Now that I hear the noise, that's what it sounds like, but likely you've looked into that already. Either end rod bearing noise is not like that, from what I can hear.

And yes, I'd be doing everything I could think of before dropping the engine. Just might be something that simple. You'll get it, I'm sure.

Dave

I hear you both and although it would be nice, this is not an exhaust gasket

The 'racket', as I have tried to show in the clip, is only there when briskly opening the throttle. Which is not to say the bike is perfect at all other circumstances. But is is most evident when briskly accelerating. And it does go away when plug cap 1 is removed.
If I could describe it in other words, it sounds like a loose baffe inside a silencer which resonates as the revs race. nice thought but no such luck ...

Spent lots of time last night going through my notes of few years back. I discovered that the conrods were NOT renewed as their small ends measured well withing tolerance, sorry if I misled you. They were NOT renewed.
So may be in its past life my bike had suffered the dreaded hydrolock. I bought the bike and immediately dismantled to restore ... did not ride and stupidly never checked the rods for straightness . Visually they all looked right, but no actual measurements were taken for straightness.

Are my symptoms relevant to a (slightly) bent con rod?
That is, "no pro at idle or constant revs, then a 'racket' under load (acceleration)?
Also no 'racket' with cylinder no 1 disconnected?"
Most important: wouldn't a (slightly) bent rod make the entire engine a bit vibey, throw it out of balance?
Just some thoughts before I get my surgical instruments out .
Cheers, Aris

And why wo

daves79x wrote: Don's bike, I found 2 slightly bent ones as a result of the long cam chain breaking. You could barely see it with the eye, but a laser check on a flat table revealed it.

Dave, out of curiosity, how did you check rods on a flat table using a laser?

Thanks, Aris

Aris:
A friend has a machine shop with a fancy machine that, when you lay the rod horizontally, makes two virtual cylinders of the bearing bores and compares them for perfect parallel. This insures they are not twisted. Length measurements are taken then from a known good rod and compared. But the parallel cylinder measurement to me is most important since I've never seen a hydrolocked rod that was not twisted as well as shortened.

Again, usually the reason a knocking disappears when the plug cap is pulled is that that cylinder is now not 'working', it's just along for the ride. Play in a bearing is not as noticable if that piston is not being 'powered' by spark.

One thing you can check is the compression. Even a very slightly shortened rod will lower the compression dramatically in that cylinder. Also, and I don't know what this would have to do with the spark plug cap being pulled, but I've seen a valve train that had the 'A' and 'B' shim buckets randomly mixed between the 'A' and 'B' bores and this resulted in valves sticking and a whole bunch of clatter on the top end. But I'm sure you were careful to get those right.

Any hydrolocked engine I've seen run had a deep knocking in the bottom end from the piston hitting the crank flyweight at BDC. I've seen others that locked up due to the rod being so twisted and bent that the piston could not travel it's entire path without binding.

So I'm betting that if the noise is something to do with a bad rod, its the small end failing for some reason. Still not sure it's that. Sounds more like something in the valve train coming and going. Good news is that the entire top end is servicable with the engine still in the frame, unless you would find a bad small end rod, then it would be splitting the cases again. Carry on and keep us posted!

Dave