Topic: Camchain procket broke off. Fixed it up it still clunks

[jacquesleclochard]

UPDATE: I found out what happened. Scroll down for damage assesment pictures. Had to replace the camshaft because the mickey ears broke off. Now how is this possible?




Hey gang. After taking the top apart to fish out a lock nut, I drove a few miles with the wrong valve clearance on the 4th. After parking the bike for two hours, the engine had a new perk: Clunkety-clunk. Not cool and rather... scary.

I can hear the noise when I turn my engine over without starting, so it probably has nothing to do with the carbs. I readjusted the valve clearance, that is good too. This noise is heavier than your average misadjusted valve ticking.

The top end seems to be getting oil. It is a constant noise. I am thinking something is wrong with my rocker arms, but I tend to see the end of the world looming around every corner. So maybe the cam chain is hitting something it shouldn't?

Please anyone, halp and put a troubled mind at ease! Idea's or suggestions where to look or what it could be would be very welcome.

[jacquesleclochard]

Update: Tightened the chain. Noise is still there. White smoke emits from the exhaust as it revs.

[jacquesleclochard]

There is a slight skip at every valve when it clunks. It seems to skip near the 1/4 and 2/3 markers, as the shaft turns.

[scunny]

does it do this with the spark plugs removed ?

[camelman]

Poorly adjusted clearances can create spalling on the camshaft and rocker arm.  You might have messed up the camshaft lobe for that lifter. Try turning the engine by hand with the tappet cover off for that valve and your finger on the rocker.  If you feel a click, then I think you need to consider camshaft or rocker arm damage.

Camelman

[jacquesleclochard]

Poorly adjusted clearances can create spalling on the camshaft and rocker arm.  You might have messed up the camshaft lobe for that lifter. Try turning the engine by hand with the tappet cover off for that valve and your finger on the rocker.  If you feel a click, then I think you need to consider camshaft or rocker arm damage.

Camelman

Oh man... It is definately a click, a skip that is noticable.

Also, how much oil pressure should I notice: squirts or oil drips with the tappet covers off?

[mystic_1]

Check your cam chain tension?  Sounds like it could be very loose.

mystic_1

[jacquesleclochard]

Now this is sexy... I tore it apart and found that the sprocket broke loose of the camshaft! There were two tears in the camshaft where the sprocket connects to it, and one half was missing. There was a nasty cut in the aluminum where the chain had connected...

I'll post pictures in a few hours, got to reinstall my new camshaft before it gets dark.

What could have caused this? Could it have been my kickstart from a 2 hour cooldown??

[Duke McDukiedook]

Things fall apart. 

[jacquesleclochard]

Things fall apart. 

I suppose! Here are two pictures. It shows where the cam broke off and the chunk that the chain took out of the engine.

My chain guide and tensioner rollers also show excessive wear. They were fine when I finished rebuilding less than a month ago.

[turboguzzi]

was the missing "ear" still attached with its bolt to the sprocket or did you remove it before taking the picture?

if it was missing I believe that you simply forgot to put thread locking compound in the cam bolts.

nasty mistake indeed. my condolences...

TG

[jacquesleclochard]

if it was missing I believe that you simply forgot to put thread locking compound in the cam bolts.

I never heard of that tip. Is it necessary?

The missing ear fell down into the carter and was easily retrieved. The aluminium shards were cleaned out. I already have a new old camshaft, so all is well. Not too sure what to do with the excessive wear that my camchain guide and rollers show, though.

[jacquesleclochard]

So I replaced the camshaft, built the thing back up, and installed the rockers and valves. It still clicks/skips! I can't seem to pinpoint it timing wise, but the 3d intake valve and the 2nd exhaust valve block shaft access to my rocker when the cam is aligned properly. I have to move the cam around in order to fit the shafts in. It looks as if those are the two skips. The noise comes from the camchain and sprocket skipping. I guess that is the reason it broke.

BUT WHAT THE HELL!? Where should I look? ANYONE?

[jacquesleclochard]

BUT WHAT THE HELL!? Where should I look? ANYONE?

I am sorry to chime in like this, Jacquesleclochard, but it sounds to me like you have one or more bent valves.

[jacquesleclochard]

I am sorry to chime in like this, Jacquesleclochard, but it sounds to me like you have one or more bent valves.

OH NO! 

How do I find out which ones are bent? And this is going to cost me a fortune! Is it?

[jacquesleclochard]

Well they don't appear to be bent, so that probably isn't it. Could it be that the camshaft I got was of the wrong type? But that still won't explain the skip/click... Maybe a stretched cam chain?

PEOPLE I am going nuts here. Am I seeing something that isn't there? Could someone just take a look at my train of thought (read the above) because I appear to be stuck.

[paulages]

Well they don't appear to be bent, so that probably isn't it. Could it be that the camshaft I got was of the wrong type? But that still won't explain the skip/click... Maybe a stretched cam chain?

PEOPLE I am going nuts here. Am I seeing something that isn't there? Could someone just take a look at my train of thought (read the above) because I appear to be stuck.

are you sure about no valves being bent? likely a piston or two caught a valve while you ran it with the cam ears broken... doesn't take much of a timing error to cause contact. a stuck valve will show itself as you spin the engine through. usually it will stick, then pop back when the piston rises and touches it.

[jacquesleclochard]

How do I check? Ofcourse there are special tools, but I am in between houses (moving) and most of my gear is boxed up. So I'll have to do with a measurer.

I just took out all the valves, and they came out with ease. None of them were stuck or anything.

[ekpent]

Your bike Def has some other issues but I also had a weird click,a double click when manually turning over the engine.Turned out to be the cam chain.  Read-  http://forums.sohc4.net/index.php?topic=59144.0

[turboguzzi]

hei jacques,

we understand that you are a clochard, moving houses and all, we all been there, fixing bikes with no money.... but after such a major disaster, closing the engine back "with a new cam" without splitting the cases, thorough clenaing and inspecting other damage + excessive wear on the tensioner is really a bit too much and asking for more expensive damage.... not surprised at all that you still hear "some clunks"

And putting loctite on the bolts is not a tip, its a must do! now you know why

now for an interesting question, how are you taking the valves out so quick? A CB750 requires engine removal to lift the head? or do you have removable frame tubes? just curious

TG





 

[jacquesleclochard]

Guzzi,

I had already removed everything from top down to the pistons, so a quick peek in the valves wasn't a problem. A makeshift valve removal tool did the trick. I never split the cases before and I am not really in a position to do so (with only a duffel bag and the hospitality of others ). Prego, what makes you think that my problem lies down in the deep end?

[turboguzzi]

Jacques. if you had no strange noises after your fix, nobody would say anything, other than lucky you!

but seemingly, something is wrong, hard to tell you what and where just from so few details.

understand your reluctance to split the cases but if the motor is out of frame, would at least open the sump and have a good look there for "strange looking" stuff

TG

[jacquesleclochard]

Yea, I am sorry for not being clear, I did that. Found the engine aluminum and pieces of black plastic, most likely the tensioner and guide.

Let me update the current status of the engine:

After I figured out what made the clunk-sound (read above), I took out the engine. The top end is dismantled. The pistons are out and checked out to be okay. So no damage there. On the cylinder head there is some apparant aluminum wear, caused by the broken sprocket and the loose chain (see pictures). I filed that off and it is smooth now. The head cover is good.

I replaced the cam chain rollers and the guide. I am not sure wether I should replace the chain itself, as it did take chunks out of the walls but it looks okay to the eye. The new camshaft fits in nicely and checks out okay for wear. The valve stems are straight as they go in and out of the guides with ease. They don't stick or jam up.

When I try to install the rocker arms, the rocker arm shaft jams up on the second exhaust and the third inlet valve. The lobe of the camshaft lifts the rocker up too high and causes the rocker arm shaft only to fit if I turn the camshaft a few degrees, lowering that particular lobe. I have to turn it forward for the third, and backward (from the marked position) for the second rocker to fit. This causes the mark to move.

This workaround results in a constant tension on those two valves when their rockers are in contact with the lobes. Tension on the valves, tension on the rockers, tension on the camshaft, and the camchain tends to skip (with a clunk) a few teeth on the sprocket as the camshaft turns to open or close the valves. This is not normal, is it?

If it is, I will gladly buy the forum a beer and salut my stupidity. At least I will have solved my problem, because there would not be one. But right now I am really confused. It has been a long day.

[turboguzzi]

are you using the workshop manual to set up your motor? if not, use it.

you should have the two bolts that hold the sprocket torqued (and loctited) and the chain tension set before you install the rockers, that way, the timing of the cam is set. This way, it doesnt matter if you turn the motor to allow for rocker mounting.

The day is not over, still quite few hours till sun rise I still remember the 36 hours straight I put to finish my bike for its first race...

TG
 

[scottly]

This doesn't look like a bolt simply backed out of the cam sprocket to me: both ears are broken off the cam. Plus the reported wear of the tensioners and guide? Was the cam chain way too tight? Maybe the cam chain was not properly located on the crankshaft sprocket? In any case, I would replace the cam chain.