400 Bandit Engine Rattle / Electrical Problem

[DunkTheBandit]

Hello all, first post from me.  I've recently bought a 1991 UK B4 after taking a break from biking after loosing my bikes in a fire.  Although unfortunately with a few issues, when I got the bike it barely ran so I rebuilt the carbs, changed exhaust, tweaked fueling and got it running spot on, idle at around 1400rpm, pulls like a train to the redline with no flat spots. Since then it has developed a few issues, yesterday morning when I fired it up I noticed an engine rattle, first thought was the automatic cam chain tensioner playing up, its hard to describe the sound, almost like a knocking kind of rattle, most noticeable around 5-6k rpm (more noticeable under load rather than stationery), engine feels more course, louder and less smooth than usual. When riding the rattle goes away when you back off the throttle, as soon as you apply any throttle above 4k it starts again. But tonight the instrument lights (mostly) and head / tail light started flickering, when at a stand still the engine revs fluctuate very slightly with the flicker. I stopped off at a shop and it failed to start (battery flat) which brings me on to my next question, the rattle is more noticeable on the left side of the engine so my theory is it could be related to the alternator?

Going to give it a good service this week, oil & filter, valve clearances etc

Can anyone help shed light on the problem?

Dunk

[Squishy]

Yeah, doesn't sound like the usual cam chain because those are usually audible at idle or when you let go off the throttle..
I would check the valve clearance first. Doesn't hurt to do it anyway...

Also check whether it disappears/changes when you use the clutch or switch to different gears. Also does it happen in neutral?

You could try using a screwdriver and putting it on the engine/bike at different places while putting your ear next to the end of the screwdriver.. you might be able to pinpoint the location more accurately.

[DunkTheBandit]

Just fired it up, let it warm up till the fan cut in and its not noticeable at idle, when you hold the revs above 5k or so you can hear it but its not as noticeable at a stand still. It's there in gear or out, clutch in or out.

Much more noticeable when riding and coming under load above 4-5k, under 4k its not noticeable at all. It's coming from the left side of the engine. When riding above 8k the engine makes a more harsh wiring sound, not smooth like before, as if somethings spinning off balance.

Need to collect my tools and start pulling it apart, will check with a screwdriver to try narrow it down.

[Squishy]

My 2nd 400 sounded harsh and valve clearances were off.
When was the last time it was checked? I'd do that first

[DunkTheBandit]

Cheers Squishy. Not sure when they were last done, get my tools back tomorrow so will check them although I'm unsure how one day the bike was fine and the next this problem started. Just been for a ride, rattle  / knock if anything is worse, it's there all the time your on the throttle but goes completely when off the throttle, engine feels very harsh and less happy to rev freely (as if somethings off balance / oscillating) , if anything down on power slightly. What constantly moving parts are in the gearbox that would cause said symptoms if suffering from for instance, bearing failier? Gearbox seems very clunky and whiny compared to normal. Seems its coming from down the bottom rather than the top end.

Dunk

[greg737]

  Much more noticeable when riding and coming under load above 4-5k, under 4k its not noticeable at all. It's coming from the left side of the engine. When riding above 8k the engine makes a more harsh wiring sound, not smooth like before, as if somethings spinning off balance.

This sounds familiar, or at least somewhat similar, to the problem that another forum member (bdouvill) has been working on lately: http://forums.banditalley.net/index.php?topic=13872.0

The bearing he is replacing is on the left-hand end of the gearbox output shaft, right where your noise is coming from.

Seeing you come along with a similar sounding problem makes me wonder if that output shaft bearing is the "weakest link" in the 400 engine.  Maybe that bearing is the first component that gets oil-starved if the owner lets the oil level get low or if the oil is allowed to get too old.

The oil system that Suzuki engineered into the GSXR400/Bandit400 engine is absolutely superb.  It boasts many of the same oil system features that were eventually incorporated into the "SACS" (Suzuki Advanced Cooling System) GSXR750. 

The history documents and reviews of the "SACS"  air-oil cooled GSXR750 engine always point out that the GSXR400 engine was used by Suzuki engineering as a developmental step toward the GSXR750.  The GSXR400 engine came off the drawing board in 1983 and was in production by March of 1984, slotting it right in between the development of Yoshimura's TT-F3 racer GS1000R and the arrival of the GSXR750 in March of 1985.

[DunkTheBandit]

Good shout Greg,

But would this cause there to be a rattle / knock when the engines being revved at a standstill in neutral?

Want to be sure what the issue is before I move forwards and waste valuable time / money trying to find the problem as I'm currently using the bike as my daily transport.  I'm a lorry mechanic by trade but tackling gearbox problems, especially on bikes has never been my strong point, considering my old dears other half used to build race gearboxes for Williams F3 cars my solution is buy a complete motor, swap them over and give the stripped down engine to my old dears other half to rebuild the gearbox, then fully rebuild the original engine and swap back.

[greg737]

But would this cause there to be a rattle / knock when the engines being revved at a standstill in neutral?

I'm not a gearbox expert, but my understanding of how they work tells me this:

If it is a bad bearing there will be noise any time it is made to spin.

And, when a "constant mesh" type gearbox is in Neutral and the clutch lever is released the engine will still be spinning the gearbox shafts (both input shaft and output shaft).

Neutral doesn't mean the gearbox internals are "stopped" it just means there's currently no connected pathway through the gearbox (any one of the 6 selectable ratios) transmitting the engine's power to the rear wheel.

Even with the bike in Neutral and the clutch held in there may be a residual "drag" situation that might still "idle" the gearbox.

A way of testing (isolating) this gearbox output shaft bearing for noise would be to put the bike on a stand (rear wheel suspended) with the engine off.  Select neutral on the gearbox.  Take off the countersprocket cover so you have access to the area around/near the output shaft bearing.  Now have somebody spin the rear wheel while you use a "mechanic's stethoscope" to listen to the area right around the output shaft bearing.

[DunkTheBandit]

Update: Just bought a 89' GSXR GK73 400 engine complete with carbs, 27k km on it for £175. Gonna swap them over and strip the original engine to find out what the issue is, will keep it documented to help others who experience similar issues.