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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 31 May 2009
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help my crankshaft
hi there im after some help on my 1985 xt600 43f when i take the big plastic plug out of the left hand side genarator casing and grab the nut with pliers there is pull push movement the best i can measrer this is about 0.4 millimeter with verners, there is no up down movement. the bike runs fine and has no bad vibes , there is a noise sometimes when you turn the engine off and the crank is just cumming to rest plus some times when i am kicking it over slowly to find compression to start it but not all the time . the bike has about 23000 miles on it. about 2000 miles ago i removed the clutch casing to check the primary drive nut , this was tight but by pulling and pushing on the crank there was movement although i did not measrer it. in the last 2000 miles its hard to say if it has got worse i bought the bike with 17000 miles on it ,and it had been stood for a few years in a garden , but with fresh petrol in it it started 2nd kick and the oil bled streght away and has run strong since. so how much movement is ok i can find no info in my clamer manual on crank end flote . i know the mains are odd bearings class 3 or c or something could someone give me info on these, sorry this is a long question zigzag
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  #2  
Old 1 Jun 2009
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What you are describing is 'endfloat'. I don't know the figures for your engine, but the old engineering rule of thumb was that there should be 'barely perceptible' movement. I think less than half a mm comes into that category, and if it was my bike I wouldn't be worried. Sorry I can't be more specific.
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Old 2 Jun 2009
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C3 bearings have more endfloat & more clearance than normal bearings.
I'm not sure of the exact endfloat, but I would consider 0.4 mm endfloat to
be normal.
Bob
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Old 2 Jun 2009
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hi there thanks for your input guys , ive been to see a couple of pro mechanics today and both seemed to think the pull push movement is ok ,one even seid 1 mm is ok . if any one has any more info on this please tell , the odd noise, when i turn it off and the engine is just about to stop which sounds like its coming from the crankshaft ,but dos not do it all the time ,again the mechanics seem to say is ok . if i can i will take the bike to one off these guys to let him hear it , so i may be concerned over normal noises. zigzag
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Old 3 Jun 2009
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I think the noise you hear just before the engine comes to a full stop is just the starter/sprag clutch letting the engine "kick back" slightly.
This is 'cos the piston is on it's way up on it's compression cycle,and as the motor is not actually running the compression is enough to stop it going over TDC,and so pushes it back down the bore slightly.
Nothing to worry about
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Old 3 Jun 2009
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hi ten 660 i know the noise you mean a couple of mates have jap inport srx 600s with electric starters. my xt has only a kickstarter ,i think the guys in the gararges may have been thinking along your lines i did not say it had only a kicker , and i forgot electric starter xts do make a noise when turned off , so thanks for the reminder. i am going to look in to this some more , so you xt kicker guys any odd noise from yours , just as the engine is coming to rest. zigzag. 1985 xt600 43f (kickstart only)
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Old 3 Jun 2009
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Quote:
Originally Posted by Ten660 View Post
I think the noise you hear just before the engine comes to a full stop is just the starter/sprag clutch letting the engine "kick back" slightly.
This is 'cos the piston is on it's way up on it's compression cycle,and as the motor is not actually running the compression is enough to stop it going over TDC,and so pushes it back down the bore slightly.
Nothing to worry about
Cool. That saves me making another post entitled 'WTF is that noise when the engine comes to rest?' A clunk and a slight hiss. Makes sense.
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Old 4 Jun 2009
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zig ten660 is still on the right track its kick back from the compression stroke it reverses the transmition and the noise you hear is probably the back lash from the gearbox.

BlackDogZulu lol i'd have thought you'd known that by now i guess that st of yours must have a pre-engage starter motor
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Old 4 Jun 2009
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Hehe. Not sure about the ST - it just works, smoothly, all the time (which is why I like my XT so much - it's a hooligan). I've had singles before, and I'm used to a bit of a sigh as they come to rest, but the XT sometimes does a loud 'clack' along with it, which none of my singles before has ever done. Ten660's explanation about the sprag clutch just sounded 'right', if you know what I mean.
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  #10  
Old 5 Jun 2009
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hi there and thanks for the input guys , the kick back theary sounds good although it dos not sound to be doing that. i will listen with a more neutral head on instead of my it must be the crank head on . the fact that it only dos it every now and then and the bike seems fine vibe wise may point to the fact that im hearing things that are normal . my other bike is a smooth old z650 kawasaki which dos not help , dont you just love old bikes, never a dull moment. zigzag
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Old 5 Jun 2009
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i love all my bikes my gsxr750 is 19yrs old!!! and is still a hooligan!

the xt started off as a cheep bit of fun and has been such fun i turned it into a hooligan lol

i'll sort some pics out and start a thread on it when i get a chance (making the most of the good weather at the mo) the progress has slowed at the min due to broken milling machine
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