help me identify my XJ750 seca rattle

well i have a rattle on my bike when it is idling . It goes away when revved but is quite loud on idle and annoying . First I thought it was the cam chain tensioner but that has been tightened up and its definately not that , If fact I made a manual tensioner for it .


the noise sounds like a cam chain but obviously isnt .
what other chains are there on the bike and are they adjustable or what else could it be , Is it a common thing ?????

help me guys

 

This is the same thing that happened to me. Rattle at idle and it goes
when you have revs on the motor. I found that it was the timing chain.
When I replaced the timing chain every thing came good again. Once
a timing chain stretches and the links move apart there is nothing that
you can do to (fix) it. The chain is worn out and there is no fast fixes.
If you cant do it your self take it to a mechanic and get them to replace the chain. If the chain breaks your engine will destroy its self
in about half a second. If this happens then you will really have to out
lay some serious money.

Buy a manual for this make and model of motorcycle and study it. You
can get one off Ebay.

 

A question then some suggestions: how many miles on this bike?

First off, I'd either re-install the original tensioner or install a YAMAHA (not DIY) manual tensioner before you do more harm than good. Even the "manual" one is spring loaded.

You could have a broken cam chain guide, front or rear, and overtightening the chain would just make it worse.

There is a "primary" chain in the motor; it drives the jackshaft from the center of the crank. Its solid cast-plastic tensioner is known to disintegrate. Usually, but not always, this will manifest itself by jamming the shift mechanism. At the very least you'll start finding hunks of black plastic in the sump. This guide can also break loose without disintegrating and make an awful racket.

There is a small chain behind the clutch that drives the oil pump. It rarely fails.

It might only sound like a chain...

The clutch hub could be loose.

You could have an exhaust leak between one of the headpipes and the head, this will sound for all the world like a mechanical rattle.

Any one of the four exhaust header collars could be loose; you could have a head pipe loose at the collector (assuming stock exhaust) a muffler loose at the collector, or a loose collector vanity heat shield.

Don't guess, diagnose. And don't make home-made solutions to non-problems, or you'll cause some new ones.

Use a long screwdriver with the butt end of the handle jammed in your ear, as a stethoscope to "probe" the motor. You'll find it.

 

Remove the "Home-brew" Tensioner.
Install a Automatic Tensioner.

After you install the Auto-tensioner, ...
MANUALLY present Chain Slack before it.

Flag and Probe.

Probe:
Using 3-1/2 Feet of Wooden Dowel or Fiberglas Driveway Marker.
Fabricate probe.
Sand one end to a Point.
Sand other to a Dome.
On the Dome end, ... Drill and glue a Small 1-Inch Rubber Ball
http://www.gollygear.com/rubberball.htm

Congratulations!
You made a Rattle-finder!

Place the Pointed-end of the Probe on the Engine.
Place your Ear to the Ball.

You should hear "Normal" Engine noises.
Primarily, ... Rotational noises.
You will hear unusual sounds if present.

Flag:

Tape a Small "Flag" of Tissue to the Pointy-end of the Probe.
Hold the Flag to where there might be an Exhaust Leak.
No movement: No Leak.
Flutters: Exhaust Leak.

Remove Cam Cover.
Lift Cam Chain off from Guide Bridge between Cams.
Chain lifts ::: Troubleshoot Tensioner and Guided
Chain don't lift ::: Probe, Measure Valves, Listen for loose Shafts and Worn Bearings.

 

righty ho !!! manual cam chain re installed and rattle finder made . definitely not the headers. Seems to me like the primary chain slacking so I balanced and reset the carbs and it gets betterand goes completely when warm so i guess the uneven running was causing it to snatch , with the colourtune I couldn't get a "rich yellow" flame until the mixture screw was 5 turns out yet the plug was black so the carbs are coming off for a good thorough cleaning . Spraying easy start imbetween carbs 1 & 2 resulted in increased revs so i guess whatever joins them is leaking in air . all valve clearances have just been reset and the bike has done 40,000 km. Its spent most of its life in America so I guess the heat( whatever that is ) may have got to the rubbers.

 

Hello Rastacia..you're on the right track, keep following the logic of that infernal combustion machine, you are in charge. That way you two will get on well.

 

So you have a vacuum leak between carbs......could be throttle-shaft seals, could be fuel-rail seals. Time to tear the rack apart. It's NOT an impossible job. Go SLOW, take pics, draw, write, whatever to keep track of where things go. We're here if you get stuck.

Check your carb boots while you're at it just to make sure they aren't cracked or loose.

Colortune......you don't want yellow....you want a bunsen-burner blue. Finding yellow is ok just to know how far is too far. Too rich is yellow, too lean is white. Nice bunsen-burner blue (xjBikes blue!?!?LOL) is in the middle.

Get the carbs/shafts/boots done before trying to colortune again.

Rattle.............could also be the chrome sides to the collector box, or even the mufflers rattling, too.

dave fox

 

BUNSEN BURNER BLUE is an Ideal Mixture for IDLE.

To insure that there isn't a hesitation going from
Idle -to- Off Idle
As in ... at a light and getting out of the hole.

Get the Mixture BLUE.
Increase the Richness until the Blue shifts to a Purple or Orange.

You need supplementary richness to sustain combustion's.

 

it was bunsen blue with the mixture screw shut all the way to 5 turns out , with the carbs apart I have found the float height to be 10mm on some carbs which wont have helped .

 

I know I'm late to this thread. My recently revived XJ750RJ Seca was whining loudly at any engine speed. I took the head cover off to check the valve clearances and the cam chain and the chain seemed way, way too tight. Upon removing and resetting the auto CCT and torquing the bolt down slowly to the proper torque setting I only heard it click 3 times on the way in. The previous owner may have over-torqued the retaining bolt given how hard it was to remove. Plus, the rubber tip of the plunger that presses in the guide is pretty warped.


I realize this will probably change when I crank the engine a few times. The cam sprockets all looked fine. My question is this: if it tightens up too much again, is it safe to shim the bolt a little or should I just replace the CCT and/or the chain? There is supposed to be a little give in the chain, right? Maybe it's just stretched to the point of being about to snap? Maybe try shimming 1 or 2 washers under the retaining bolt and hear what happens?

This my first foray into the cam arena, aside from doing a successful valve adjustment on my XS400 a couple of years ago before I had a nasty wreck on it. Any advice here would be appreciated.