Xt 600 e 4PT -- weird noise
 

Here's the story so far, after a coil failure and replacement ,I heard a metalic clang/ping ,seemed to be coming from the right side of the cylinder barrel ( could be resonance from the fins ). The noise appears at around 2000rpm if the revs are brought up slowly ,or the choke has the engine running at that speed .
The pings seem to correspond with a slight hesitation in running which can just be detected in the exhaust note . No noise if the throttle is opened quickly ,at higher revs or on the overrun.
I had thought that maybe the coil failure had damaged the TCI unit and upset the advance around the 2/3000rpm range and was causing pre ignition ,so I swapped it with a known working unit ,no change .
Before the coil failure I heard no noise but this could be coincidence.
The bike rides fine ,it's jetted to suit the open airbox and after market silencer and will manage about 95 mph on a 16 tooth gearbox sprocket .
The bike starts fine if the air temp is 5deg C and above ,a bit difficult at lower temps but only after the coil failure ,before that it started fine at -10 deg C. 50,000kms on the odo ,uses a wee bit of oil .
Any suggestions before I dismantle it to check the piston and bore ?

http://www.horizonsunlimited.com/hub...eck-your-73934

Mezo.

I couldn't get Mezo's link to work, but here is another link
http://www.horizonsunlimited.com/hub...eck-your-73934

Make sure you check both the crankshaft keyway and the adjacent balance shaft keyway.

Bob

is this really that bad ?
 

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[IMG]http://i241.photobucket.com/albums/f...o/IMG_1411.jpg[/IMG]

This is the key out of the crankshaft ,the nut wasn't very tight ,awaiting a clutch holding tool before dismantling the balancing shaft ( left hand thread ? )
Could this really have caused the noise ?
Assumption ,Bobmech, damn right , I was assuming the fault was related to the coil failure .

Key play and rattly noise /
 

Having taken off the clutch and drive pinions ,I can point out ,that the big key that gets the hammer is the crankshaft pinion key . The balance shaft key is tiny by comparison ,also the crank nut if torqued to 85 ft/lb ,the balancer to 43 and the clutch to 65 .Just puts into proportion load .
I filed down 7mmx8mm key steel ( a common size in engineering )to 7x7.1mm. I arrived at the 7.1 width after starting at 7.25 and filing down to a snug fit ,tells me the crank keyway is a little worn . No idea if this cures the noise ,still waiting for new tab washers before putting it all back together and trying it .
THE BALANCE SHAFT NUT IS NOT LEFT HAND THREAD ,in spite of the marks on the nut flats that either indicate unf or left hand thread as in fuel gas unions .

that would be an ok key in my book.
for whatever it's worth,in the only motor i opened that had a sheared key, it was the balancer shaft one.
if there's on ething i would check is that the rotor (and therefore ign. timing) has not sheared the key.... easy to verify

The fact that indentations can be seen on the key ,indicate that movement has occurred,and the crank nut wasn't tight . the balance shaft nut was tight but the key looked to be about half the length it should be . I won't know how it should look until the new one arrives .
the tab washers were butchered so I guess the nuts have been loose before and re tightened ,but probably not done well .

New tab washers and balance shaft keys finally arrived ,stuck it all back together and ,no damn difference .
thinking its down to my original diagnosis now ,i'ts a misfire causing piston slap when on a very light throttle ,as I mentioned originally the clatter corresponds with a change in the exhaust note .
Facts .although on a very light throttle it also happens on choke ,so I think ,not a lean mix ,if it was a lean mix it would be in the area covered by slide cutaway .
Not TCI unit ,I have changed that .
Question . Is the ignition advance controlled by the TCI ?

With 50,000km on the odo it could be piston slap or piston tilting and just so tapping the bottom of the head , often that heard when rpms are coming down not at a steady rpm and such a low rpm . It should get worse at higher rpms. I'd do a compression check and leakdown test if compression is low to see just what the condition is inside.

Do a lookover of all bolts, guards, washers, ect.. just to make sure something on the outside isn't vibrating just right at that rpm and causing the noise , they tend to sound like they're coming from different spots with echoing and sound bouncing around . More than once I've had a bad sounding motor noise that really seemed to be inside only to find a loose frame bolt and the washer or plate it's holding causing the noise. Those are usually very rpm specific .

When the bike broke down with a duff coil there was no irregular pinging .
Now this pinging isn't regular ,and definitely has an effect on the exhaust note like a misfire .
When I started it with a new coil there was .
The coil is aftermarket ,cost £20
original yamaha coil is £80 +vat and postage .
Makes no sense to me but ,could the coil cause a very early spark 2000rpm to 2500 rpm . In my job , a dilemma like this would simply go like:- whats changed , change it back , see if it changes , but in my job ( distillery engineer) I don't pay for the parts .

The coils are rated at a certain output and have X amount of resistance ect... may be possible the new coil is firing hotter or something but I really don't see how it could change spark timing at all. I've replaced a few coils and never really paid close attention to getting the exact size but do try to keep close to what the book states. Any way to find a used oem one on ebay ?

If you have a Yamaha service manual post up what the specs are for the oem version and also the one you have.

Thanks for your reply , Got to thinking ,that the coil will be right even though an after market one ,the co. that supplied it "WEMOTO" have been supplying parts for Yamaha for decades and won't have got it wrong .
Next step ,when I can manage without it for a few days, is cambox off to check cam chain and head off if the chain is ok .