engine knock

So, I finally got some time today after work to mess with the bike. I had pulled apart the clutch, because the knock seemed to be coming from inside that case. Noticed the part labeled as an "oil scraper" in the diagrams wasn't located properly, so I repositioned it. After checking everything else in there, I couldn't see anything else that looked even remotely wrong, so I figured I'd button it back up and see what happened. Before doing so, I pulled the plugs and spun the motor with the starter, to see if I could hear anything. Not a sound. No knocks, pings, clicks, nothing other than the starter spinning the motor.

All seems well. I button her back up, replace the spark plugs, fill the oil, replace the tank, and hit the button. Fires right up! (Yay clean carbs, i suppose!) No abnormal noises! Great! Climb on and am about to push it off the center stand to take it for a test ride when it starts knocking again. I quickly hopped off and did the 'probe around with a big stick' method of diagnosis.

Knock is coming from behind the right-side crank-case cover. Specifically, about an inch behind, right at one of the corners in the molding of the case.

Sounds to me like a main bearing. Any ideas?

I'm about to cancel my insurance, looks like she's down for the season

Edit: I just went out and fired her back up. Pulled plug #4, no change, still knocked. Pulled plug #3, and it was still knocking, but the bike died. Not sure if it was cuz I pulled that wire or because I cut the choke too far back, probably the latter.

Definitely sounds like a main bearing to me

 

Sorry to hear that switch - hope you get it sorted quickly.

 

uneven combustion could cause a knock in these engines. if you have one cylinder fighting the rest, it would sound like it's about to come apart. what do the plugs look like?...

also, if you pull one plug and RPM doesn't drop or only drops a little, and then pull a different plug, and the engine dies, that usually means that something's out of balance. have the carbs been synced/colortuned?

 

stereo, yeah the carbs are relatively in sync (don't have a YICS block tool), and all 4 plugs are a healthy tan.

I pulled each plug 1 at a time and restarted the bike just a bit ago, and i get the exact same knock at the same spot, every time, regardless of which plug is unhooked.

So yeah. Definitely smells of main bearing to me. There was gas in the oil I pulled out too, no idea how it got there, as the float levels are set low enough there shouldn't be any way it's pouring into the cylinders.

I think she's done, at least for the season. I'm calling my insurance company to cancel and get at least some money back here in a few minutes.

 

This may sound a bit off base, but--what oil are you using? You MAY be hearing big-time primary chain slap does the "knock" go away when you rev it up a bit, or just get louder and more frequent?

 

This isn't really a very good test as without the plugs, you are just spinning freely with no resistance. Does the sound lessen or go away with more rpms?

 

Seems to lessen quite a bit, but I honestly may be mistaken because the engine is so much louder.

Edit, for the record i DID pull one plug at a time and run the engine that way. Still was knocking, coming from seemingly right under the right-hand side (as you sit on the bike) crank case cover.

 

So I tried it again, revved it up to about 4k or so, the knocking went away completely... cam chain? it seems to be alot louder on the right than the left of the bike, and i thought the cam chain was in the middle?

 

Pull the Valve Cover.
Try lifting-up the Cam Chain off the Giude Bridge between the two Cams.
If the Chain lifts off the Bridge ... the Cam Chain needs to be tightened.

Altlernatively:
You can just do a Manual reset of the Tensioner without checking.
Nothing to lose.
That Bike has an Automatic Cam Chain Tensioner.

Pull the Plugs
Pull the Left Side Crankshaft Cover.
Use a wrench on the Flats of the Ignition Rotor.

Turn over the Engine in its Normal rotational direction for two full revolutions.
Come to a slow and gradual stop.
Then, quickly reverse direction and listen closely for the Cam Chain Tensioner to take-up the slack.

It helps to have an assistant tapping lightly on the Hex Bolt end of the Tensioner with the Butt-end of a Hammer handle to encourage the Tensioner to move while you present the slack in front of the Tensioner when you make the move to turn-over the Engine in the reverse direction.

 

I still think you're hearing the primary chain, the clutch is on the right and "maginfies" it--does it seem to "change" (at all) when you pull in/release the clutch?

 

Honestly I don't have a clue, clutch is unhooked from being pulled, haven't hooked it back up yet. Before I tore into the bike, though, I do remember that it seemed to be a bit quieter if revved up slightly, and I seem to recall pulling the clutch quietened it down some, but I can't remember for sure. I'm gonna pull the valve cover tonight, made a new friend down the road who has a better garage than i do, so I guess i'll see what I see when I get in there.

 

I've ran the bike several more times since starting this thread ... the 'knock' pretty much goes completely away once i get the bike revved past about 4k. Zero rattle, just the sound of the powerplant going to town, doing what it does best.

I can't imagine that if this was a rod bearing or a main bearing, that the noise would lessen when I revved it up. Am I mistaken there?

Oh, and rick, I pulled the valve covers, cam chain has barely any play in it at all, let alone enough to need re-tensioned.

Any ideas gang?

 

bump ... someone's gotta have an idea!

 

Switch I had similar noises and wound up with 2 causes - 1 was normal valve tap - I had reshimmed to loosen so it was a bit louder. But it combined with an exhaust leak. That turned out to be the clamp where the headers join the pipes was stripped so would not tighten. I added a nut and the noise resolved to just the valve tap.

May not be your issue but take a look

 

Bill, thanks for the quick reply... I'm pretty sure it isn't JUST a valve tap, everything is pretty wicked clean under that cover. I'm sure they could stand an adjustment, but all seemed fairly well when I was in there.

I didn't even think to check the exhaust collars. Definately going to look into that as soon as I get home ... I'll kick myself if thats all it is!

Edit: Am I right that if it was a main bearing or rod bearing, the knock would get worse at higher rpms, not apparently go away? Seems logical to me, but i've been known to be .... well stupid about these things before. =)

 

That Knock ... a real Knock ... wouldn't "Go Away" when the Engine is run at higher revolutions.
But, the Knock ... and we are presuming it IS a Knock ... would diminish; concealed by Engine noise and Oil Pressure.

If you want to check and see of you really have something KNOCKING ... you have to set yourself up to LISTEN for it.
You need a long PROBE to listen too.
I use a section of Fiberglass Driveway marker with a Rubber Carb Manifold Sync Nipple Stopper pushed-on to the end.
While listening to the Engine I touch my ear to the rubber stopper.

If something IS Knocking, you can Listen to see if it reacts to LOAD.
Probe the area of #-1 while the engine is running.
While the engine is running listen for the knock.
PULL theh Plug Cap OFF Number-1 and LISTEN for the Knock.
Don't get distracted by the engine stumbling without No.-1 firing.

Listen to the Probe.
If the Knock goes-away when the Cylinder IS NOT firing ... that is an indication that there is a bearing problem.
If the Knock is a LOW "Note" ... its likely to be a MAIN Bearing.
If the Knock is a High "Note" ... ist likely to be a Connecting Rod Bearing.

The Knock goes away when the Cylinder connected to the Knock is not firing and returns when the Cylinder is firing.

 

Rick, I did the probe thing, but I didn't think to try it while pulling that plug wire off. I'll give that a shot tonight as well.

 

I have seen engines with bad crank bearings that knock at idle and the sound goes away when the rpms increase. I believe the sound may stop at higher rpms because the oil pump is pumping more oil at higher pressure and the oil fills in the play in the bearing.

I do know one thing for certain though...it's not the primary chain as the 750 does not have a chain between the crank and the transmission.

 

The 750 has a chain that Yamaha CALLS the "primary chain" it runs between the crankshaft and the starter. It is also infamous for its tensioner disintegrating and falling into the gearbox. You are correct in that it doesn't drive the transmission like the one in the 550 does though. Just thought it might be a candidate for the source of the noise.

 

Don't forget about carbon deposits and/or abnormal combustion or low octane fuel which can cause engine knock.

Web The Causes of Internal Engine Knock

 

I'm definately going to be checking this ... I was looking at the parts diagrams and that definately seems a likely candidate .... thats RIGHT in the area my noise is coming from. I'm very definately going to have to figure out how to get to that little bugger and check it!!!

 

also, if you pull one plug and RPM doesn't drop or only drops a little, and then pull a different plug, and the engine dies, that usually means that something's out of balance.


ACCORDING TO EXACTLY WHAT YOU WROTE ABOVE, YOU HAVE JUST SHOT YOURSELF IN THE FOOT, IF YOU PULL ONE PLUG, THEN ANOTHER PLUG, .......WOULDNT YOU SAY YOU HAVE CREATED AN OUT OF BALANCE IGNITION SEQUENCE IN FIRING....

LETS TRY..PULL A PLUG, REPLACE IT BACK ON, THEN PULL ANOTHER PLUG...

 

Rick-O,

Great technical advise there, question, what if you dont have a knock in that main bearing area behind the cover, but
sort of a ...dam this is the hardest noise to describe ive ever seen... its like....rolling a metal garbage can down the street... it gets better once the bike is warmed up well, maby half or less of what it was.. ill try to make an audio recording of it...

 

im thinking this weekend im going to flush this entire engine out with
shaler rislone and marvel mystery oil combo.. clean every trap, filter, crankcase, ect.. then add new filter and new oil.... it will either get rid
of the problem or fall apart...LOL

 

Switch; unfortunately, that chain and its tensioner are only accessible by splitting the (crank) cases. One diagnostic aid would be to drop the oil pan (yes its a pain but not as big a pain as yanking the motor) and check for chunks of black plastic debris from the tensioner, if you begin to suspect that. Yankee, if you are getting the noise you describe, are you sure it's not coming from the CLUTCH cover? More stuff in there capable of causing that type of noise. Do the screwdriver stethoscope trick and see if you can pinpoint it.

 

We are at the point where guessing about a noise isn't going to cut it.
It could be a lot of things.
Dealing with it in Forum messages we type and read isn't going to substitute for a trained individuals assessment of it after actually hearing the noise.

Give some kid with his new iPhone a few bucks to capture the noise on his Gadget Phone and put the Audio-Video on PhotoBucket or YouTube and let's play:

XJ-Sho-'n-tell.

The right kid ought to be able to have it online and an attachment to a Post before the end of the Baseball Game ... and that's cutting him a lot of slack!

 

Excellent idea.

 

Something loose inside the center section of exhaust?

 

I'm with Rick and Carl; lets hear it! Doesn't even have to be video, an audio file isn't that big.

 

I'll see what I can do about getting a video up tonight. I'll have to find my better camera, as I'm pretty sure my cell phone's vid camera isn't going to record good enough audio quality to have any idea what's going on.

 

A rod knock will get louder under acceleration. When the engine is "cruising", not under a load the knock will quieten a bit. A main bearing will typically be loudest at low RPMs, sort of a thundering effect, or sound.
By removing the spark plugs you en effect let the engine kind of "coast" with no load on the rods. A rod knock will be at it's loudest during rapid acceleration and deceleration and should quieten a bit between.
I don't know if the Xjs have roller bearings or babbit bearings in the rods. Rollers typically last quite a bit longer because of less friction. The chain should not have any slack. Very little won't cut it for proper adjustment.
Kind of hard to diagnose a problem over the net without being able to hear it. Ask if anyone on the board lives close to you that would be willing to "Lend and ear".

Ed

 

heh, i was just gonna dig up this thread and post an update. I've started a pretty major teardown on the bike. I have the frame nearly completely naked, and we're pulling the motor tomorrow =) So I'll know soon what I need to fix!

After the engine is gone through, we're most likely converting the bike to a monoshock, bobbing the tail, and coming up with some kind of custom rearsets.

I'm having serious issues figuring out how to make a new seat. :-/

 

Do work!!

started the full teardown since we're pulling the engine to track down this knock.




The pile of spare parts keeps growing! :rock:

 

Check your primary drive gear if its even missin 2 teeth it will not. Thats what my knock was right on the left hand side behing case doesnt hurt to look. either way you need to split the case bearing or primary drive ear going to shaft

 

Well, ... if you are successful in making it a Mono-Shock Bike ...

"Dibs on the Stock Twin Shocks" ...

 

does anyone know the tension or length specs on the primary chain in the cases? Like ... the one that goes from the crank to the generator inside the cases?

Mine seems to have an awful lot of play in it. When we split the cases, there doesnt seem to be any damage at all to anything in there. The only thing that looks out of whack is that that chain seems awfully loose.

 

I looked all through a Factory Book and didn't see a word nor a spec for the Primary Chain.

 

Hang on one sec rick ... lemme pull it up on the exploded parts view and show you. It doesnt look like a chain, per se, on the diagrams, just one link of it shows.

edit: number 22 in this:

 

I think the Factory Book calls it the "Hi-Vo" Chain.

 

yeah, that chain rick. the "HyVo" one. That is the ONLY thing in the cases that even REMOTELY shows any signs of wear, and only because there's a bit of slack in it.

 

#23 is the chain guide/tensioner; is it worn or starting to crumble?

 

nope, no wear or breaks in that guide fitz. I've been talking with several buddies of mine locally with more experience with bikes than I have. I have lots of scuffs and a couple gouges in the clutch housing, and after talking with MiCarl and RPGoerlich in the chat yesterday, I'm pretty certain that all my issues were clutch related, and maybe a bit of the hyvo-chain slap. I'm ordering a new clutch soon, picked up some yamabond today so I can button the case back together when the clutch and new main bolts get here.

Thanks for everyones help, once I start in on my actual build on Nov 1st or shortly thereafter, I'll be posting a new thread in the XJ Mods section documenting all my work. Keep an eye out!

If anyone has any more suggestions for me please let me know, it's gonna be a week or two before we button the case back up so I have plenty of time to check more stuff!

 

While you have the Cases Split ...

DO SOME PREVENT!

Replace that Chain Guide with a NEW one.
Overhaul the Starter Clutch components.

 

Definitely in the plans Rick, but thanks for the reminder! I'm building a parts list so I can start getting my orders together and nearly forgot those ones!