Cam Chain Jumped a Tooth!?

[Airmotive]

I was out riding and had an unexplained jump in overall 'buzziness' of the engine. I checked all the usual suspects, carb sync, loose engine mounts, frame welds etc.

After getting the valve cover off the engine...

It looks like I may have jumped a tooth on the cam chain!
I'm afraid to make a big, stupid mistake here. BUT, when the pulse generator rotor is aligned with the pick-up coil, the timing marks on the cam shafts are NOT horizontal/180 degrees out of phase.

Naturally, when the timing marks on the cam shafts are horizontal and 180 degrees out of phase, the timing mark on the rotor is about 15 degrees past (clockwise) the pick-up coil. (This makes more sense if you folow along in the Haynes manual.)

I'm absolutely bummed right now.

ANY advice is very much appreciated right now. Could I be wrong about the cam chain? Could that little timing rotor have somehow slipped and be the culprit?

I'm posting this on a couple of other boards, looking for some words of wisdom. Grasping at straws here....

Thanks,
JJ

[solman]

I would think that if you jumped a tooth, you would've ate up some valves and the bike probably wouldn't run too well.

[Bazza]

I can not see how you would possibly skip a tooth. If your cam chain was that loose, you would have not just skipped one tooth, but probably done much damage pounding valves into pistons.

I think you are more likely to have won power ball for this to have happened. I have had 3 similar inline 4 Suzuki engines (some with many miles) and have never seen or heard of this happening. If your cam chain tensioner was gone, you would have noticed the engine getting much louder long before, and a loose cam chain is not a very pretty sound, so you probably would not be riding the bike now. You can have a very loose cam chain, and not skip teeth. This engine is bullet proof, you don't hear of many tearing one apart (short off too much nitrus or turbo boost)

Are you absolutely sure this buzziness is engine? I would bet it's fairing issues.

[Airmotive]

I appreciate your input here bazza.  

I really am grasping at straws now. I've been doing a basic root-cause analysis of this increase in vibes. (I'm going to call it vibration instead of buzziness because it seems that as soon as I say 'buzziness', people think loose fairing.)

There was no change in sound. There was no buzzing sound. There was, however, a step increase in vibrations felt throughout the entire bike...pegs to bars and everything in between. I did not notice any performance change when the vibes started.

So far, I have:
-Thoroughly inspected all major bolts and structural welds
-Checked the sync of the carbs
-Inspect valve clearances.

When getting ready to do the valves is when I noticed the timing marks on the cams did not align with the signal generator. I pulled the can chain tensioner; it looked and functioned as it should. I verified that the #1 piston was at TDC when the signal generator was aligned with its timing mark. At TDC, both cams were ~15 degrees (2 gear teeth) past their timing marks.

I've never had the cams out of this bike (until now!). I don't know if the previous owner did. (A mechanical engineering student....so it's likely he did) Regardless, the cams were the only things I've found wrong.

I've put her back together and test runs reveal I have caused other problems...I think fuel related this time....but I'll worry about those later.

Could I have been riding 15,000 miles on this bike with the cams out of position? (The TPS has always been at been at the extreme end of its adjustment range).

Can open...worms everywhere...

[rider123]

Does the vibration only occur when you're driving? Does it have the same "buzziness" when you stand still and rev up to the rpm which causes the problem. Maybe your chain or drive sprokets are causing vibration? Is it a certain RPM or speed? At 4000 rpm the advance is at its highest degree before TDC thats why I think it gets a little buzzy at that rpm till about 4300. Very weird.

[Airmotive]

Does the vibration only occur when you're driving? Does it have the same "buzziness" when you stand still and rev up to the rpm which causes the problem. Maybe your chain or drive sprokets are causing vibration? Is it a certain RPM or speed? At 4000 rpm the advance is at its highest degree before TDC thats why I think it gets a little buzzy at that rpm till about 4300. Very weird.

Same vibes in neutral, sitting still.
Vibes increase in frequency and amplitute with engine RPM.

I just checked the TPS. 4.7 Ohms on the reference lead, .7-3.8 on the throttle lead.

I'm going to hook everything back up and run it till she breaks. (The advantage of buying a bike for $2K). Either I'll get used to the vibes, the vibes will go away as mysteriously as they appeared, or the vibe-maker will die.

I'm looking at a V-Strom for this fall anyway.

[Kickstart]

Hi

I have had a bike (old FZ750) jump a tooth and not bend any valves. My father had a car where a main dealer put new cam belts on it, one being one tooth out (flat 4 engine), and that did not bend valves but just ran rough.

Can happen.

On the other hand, owner stupidity meant my 1200 Bandit jumped quite a few teeth and bent all 16 valves.

All the best

Keith

[Airmotive]

Ran it....hard.
Runs like a champ.

Did I mention how much I hate getting that valve cover off?

[Red Bandit]

As a side note, if a cam chain is loose enough to skip, it is either stretched really badly or the tensioner has failed. The chan, cam wheels and the sprocket on the crank all work together to provide the proper timing for the engine. If it has skipped, you will notice a moderate to severe change in the engine performance, due to the valve timeing change. It probably would also result in valve or piston damage due to the close clearences in the combustion chamber. Vibration can be from a miss firing cylinder or a carb not working properly causing an imbalance in the power across the line. I once had a bad vibration due to a failed diaphram on a carb.

[Bazza]

Hey Air:

Nice to hear it all came out on the good side!