Engine Vibration

[b.walker5]

After almost a year of rebuilding (1 week short) I finally got out for a decent ride today. A few simple problems were encountered, like left front and right rear, and right front and left rear indicators working together, and the neutral light coming on in gear, etc and were dealt with accordingly but the one that has me a little worried is an engine vibration between 4 and 5k that I never had before, or at least it wasnt as noticable, and the thing that makes it most noticable is that the rev counter goes nuts through that range, flicking wildly from 2 to 6k. It flattens out again at 5k which is 120km/h (20km/h and $120 over our speed limit) I first though generator plug but it's fine so now i'm thinking oob rotor which may be producing fluctuating voltage at that rev range. Has anyone encountered this before?? and what are the likely options??

[bikerphil]

Sometimes engine vibration is caused by loose exhaust system mounting points. For the tach, make sure the connector comming from the alt. behind the fuse panel is clean. I had a problem like that once, and it ended up being the connections at the board inside the tach itself. I cleaned them up and reheated the solder joints, it was fine then.

[XJOK2PLAY]

Hey, B.Walker 5...

I'd been having a vibration for a while that had me, Tod, & Cody kinda concerned for a while... (we were afraid I might have fubarred the crank bearings when I had my oil pump fiasco in Colorado last summer... and it was just now showing up!)

Turns out... engine's perfect! I had added some aftermarket mufflers, and the pipes had gotten up against the frame underneath at one point... so at about that same rpm range you spoke of, it would really vibrate... right through the footpegs!

I scored a good set of stock XJ pipes... whallah! No more vibration!

Boy... was I relieved! I was actually considering dropping some serious coin for another engine at one point!

Who knows, it may not be your problem... but it might pay to check your exhaust out & see if it's up against the frame somewhere... especially around the collector areas... JAT
Bob

[b.walker5]

Okay, hadnt thought of exhaust issues. I had the exhaust off and just refitted it last week. It's a locally made 4 into 1 with a rubber mount at the muffler end. I may have overtightened which would explain the vibe, but the rev counter issues may be harder to track down. The wiring plugs behind the fuse block are fine, almost new in fact, but I had the headlight off so there may be an issue in there somewhere. Just seems a little too convenient that it coincides exactly with the vibration.

[b.walker5]

Lesson learned..... The Hard Way

Unless you need to know how fast the contents of the sump can be pumped out all over your leg DONT START YOUR ENGINE WITH THE ALTERNATOR COVER REMOVED..

I went for another ride this evening and then decided i'd check out the oob rotor theory. Removed the stator, disconnected all the wiring plugs from the alternator and regulator etc (didnt want to fry anything with a "no load" voltage) and started the engine. Let it idle for a few seconds and started to rev it up slowly, watching for any wobble in the stator. Sounds reasonable, doesnt it??? did to me anyway. At about 3k i heard a strange noise on the other side of the garage and my foot started to get real hot. WTF! I look down and find about 2 litres of hot oil all over my leg. quickly shut it down, done a one legged jig around the garage, tripped over a jack, tore a hole in my jeans on the way down, and then spent the next two hours searching for the spat out oil gallery plug, and cleaning up the oil.

If that wasnt bad enough, as soon as I seen what happened I realised that I knew the damn plug was there. Talk about Dumb and Dumber. Shoulda stayed indoors and watched TV.

[jmnjrpa]

You're killing me! LOL

I could have happened to me.Thanks for the heads up!

[wingnut]

There is a inherent harmonic in these engines at right around 5K rpm. My xj650 also developed it really bad after a low speed lay down in the grass. It does seem to be related to the exhaust system. I've been chasing it for 2 years. I tried adding rubber spacers to the muffler mount and no joy. You might try repositioning the exhaust system by loosing every thing up and moving it a little. That seemed to help mine. And thanks for the heads up on the oil plug. That's a dance I don't want to do

[XSokieSPECIAL]

Rotflmao

Ha ha....Wish I had been there to see that Brian!

Although my experience with these bikes is quite limited, I have a great deal of automotive experience and what you seem to be describing is a vibration due to a mounting problem.

Either exhaust or engine.

Check all of your mount points and make sure the engine isn't touching the frame or mounting bolts anywhere and none of the rubber mounts have failed in any way.

IMHO

[trbig]

Yup.. went out one morning to the garage, in my shorts barefooted, coffee in hand and thought I'd fire up the bike for a sec just to hear it run. That wasn't something it had done much at that time. The alt cover was off still but knew it would run on the battery alone for quite a while. I stood on the right side and started it.. let it run a few seconds, then blipped the throttle just a bit. The galley plug shot out and it shot most of the contents of the oil pan all over my legs.

Problem is.. I also knew all about that galley plug. I'd always had problems with it seeping oil. I put in new O-rings, wrapped it in teflon tape, even Yamabonded it in.. to no avail. I eventually finally tapped it and screwed in a plug with teflon tape to stop it.

Anyway.. sorry to get off course here.

Tod

[bikerphil]

a rubber mount at the muffler end. .

Had a problem with my old Mac 4-1 can mounted to the rubber grommet by the rear foot peg, it would vibrate like hell. Once I mounted it metal to metal, vibration gone.

[Larrym]

Is you is or is you ain't..

b.walker5,

The fluctuating tach reading may be due to the mechanical vibration or due to an electrical problem in the input signal.

Mechanically remove the tach/speedo assembly from the headset and start/run the engine with the tach electrical connections intact. If it still misbehaves then the engine vibration is not the cause.

If it still misbehaves then the problem is either in the tach itself or the input signal.

To check the input signal, disconnect the tach leads and place an analog voltmeter set to read 20-50 AC volts across the tach inputs from the stator windings. Start/run the engine and if the problem is an intermittent stator signal then the analog meter might "flake out" and behave erratically: needle jumping/swinging.

If the input signal is solid then the problem is in your tach. Substituting another tach would confirm (or not..) the problem.

Just something to consider while your sweeping up the contaminated sawdust/sand......