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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 7 Oct 2013
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1989 XT600 (kick start) timing question

I am getting a clicking sound from top end. Motor is new to me, its had a recent top end rebuild (piston, chain and clean up) before I bought it.
I checked the chain and it is on the 1st wear mark (new).
loosened and tighten decompress cable and no change to clicking.

Timing mark question.
When my rocker arms have a little movement they are at the mark with the little circle and line through it. Which is not TDC
When I turn the flywheel till the "T" the rockers have no movement but the piston is TDC (checked also with screw driver).
I am wondering if the clicking comes from the valves being maladjusted?
The book says the the rockers should have a little play at TDC

The bike runs strong now and idles smoothly, just worried about the top end noise.

Am I thinking this through correctly?
Thanks
Greg
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  #2  
Old 7 Oct 2013
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I know nothing of your particular bike, but on any four stroke there are in effect TWO TDC positions 360 degrees apart. On either compression stroke when both valves should be closed so tappet clearance can usually be detected. The other is at the end of the exhaust stroke, and by then the inlet valve may well be open as well. you will not have any play there. just make sure you are on the compression stroke when you are looking for tappet clearances.

Hope that helps.
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  #3  
Old 8 Oct 2013
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These bikes do have some top end noise. It is important to verify your valve clearances are correct. Also, verify you have .5mm free play in your decompression cable. If there is NO play, you may be hearing noise from that. There is an in-line adjuster to set that free play.

For valve clearances you need the manual for your bike. Correct position for setting valves is TDC when both intake and exhaust valves are not depressed. You set the flywheel at the TDC mark, engine cold and adjust for the proper clearance. My 86 setting are: intake .0028-.0047 in. 3 thousandths nominal and exhaust .0047-.0067 in or 5 thousandths nominal.

After setting, recheck after tightening the lock nut. When tightening the lock nut, hold the adjuster still so it will not move. Feeler gauge should have a slight drag feel and not sloppy loose for a correct setting. You set both sets of valves at the same time, same timing mark TDC setting.

Hope this helps. Too loose or too tight is bad so check it.
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  #4  
Old 8 Oct 2013
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Noise is top end, sounds like valves
flywheel has 3 marks: circle with line, H and T
TDC is at the "T", i can see this is the max height of piston
Both inlet and outlet were tight at T position. Adjusted them to spec with engine cold.
Same ticking

Decompress decmp cable only loosens the one exhaust valve correct? Would it be louder then perhaps on that side? Sounded the same to my ear on both sides.
Also decomp setting: if using my hand and pulling toward back of bike i should set for 5mm before the pressure begins? So this would be very immediate?
Thanks
Greg
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  #5  
Old 8 Oct 2013
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Decompression cable is 1/2 mm not 5 mm free play. This is just to make sure the decompression lever in the rocker box is NOT engaged in the running condition. If it were too tight, the rocker arm of one exhaust valve, the right side, would be tapping against it making noise.

So you have set the valves? Did you have a slight drag on the feeler gauge? If it is too loose, will rattle.

If your decompression cable is too loose, you will not get the full effect of the decompression and starting will be harder to accomplish. Set correctly, the correct procedure is to depress kicker until it clicks, allow kicker to come to the top the kick fully and hard. Learning the starting procedure for your bike is the key. They are all a bit different.
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  #6  
Old 8 Oct 2013
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Intake adjusted to .08 slight drag feeler gauge
exhaust adjusted to .14 slight drag feeler gauge
Both these measurements are in spec
sounded a little worse i think

Can I easily disconnect the decom cable to see if that helps?
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  #7  
Old 8 Oct 2013
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Maybe take a bright flashlight a have a look inside the rocker cover just to see if any damage can be seen. You'd be looking for a worn cam or rockers that don't move as much as the others.Pay closer attention to the one by the decompression lever.
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  #8  
Old 8 Oct 2013
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this is a video of problem -https://vimeo.com/76435964

When i open the caps (valve checks) i can see there is oil circulating.

otherwise runs good starts fairly easy as well.
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  #9  
Old 8 Oct 2013
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Which type of feeler gauge are you using, a US Inches or a Metric? Sounds like too much gap... .003" or .005" intake or exhaust. .003 and .005 is inches or put another way 3 or 5 thousandths of an inch. By the clack sound, it sounds like 8 and 14 thousandths of an inch.
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Old 8 Oct 2013
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i'll give another check
When I started it made same sound. So before I made any adjustment. At that point the valves were tight with no room to get the smallest feeler in. After loosening valves to what I believe to be spec I have the same clicking.
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  #11  
Old 8 Oct 2013
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That doesn't have the exact sound of loose valves, from what I could tell. To me it sounded like that decompressor hitting . Start the bike up again and feel the decomp lever to see if it is moving . Another thing to try is with one adjuster cap off, with it running take a oil squirt gun and quickly squirt a whole bunch of oil over the rockers and parts to see if things really change. It will make a bit of a mess but may tell you if it is an oil supply problem or if one particular rocker is doing it.
Just make sure you don't put the tip of the squirt gun inside and have it get pinched by the rocker.

After listening to it several more times, it kind of sounds like the left side is louder(as your sitting on the bike). By the tempo it definitely has the valve train speed and sound.

When you recheck clearances, grab each rocker a try to wiggle it, see if any have a bunch of side to side movement or feel different than the others.
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  #12  
Old 8 Oct 2013
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This is interesting, please keep us in the loop. if you just cannot come up with anything, it is time to remove the rockerbox and have a good look at the cam and individual rocker arms. The rockerbox does NOT have a gasket, you just need some Yamabond #4 or similar to seal it back up. Valves need to be rechecked after reassembly. Take pics and post here.

This procedure can be done with the engine still in the frame but you will need to remove one bolt underneath the back side, top hangers as well as front bolts then the engine will tilt downwards allowing the rockerbox to be removed. There is at least one bolt inside the rear valve opening and one on the very top in the recess. You will need a 5mm hex socket. Seems like there may be a extra bolt somewhere starting with the '88 model. Not sure as I have an 86 and 84 model.
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  #13  
Old 9 Oct 2013
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The valves were loose, I didn't adjust properly. I readjusted to spec but have same noise/clicking. It is perhaps less so but still there.

Question- when adjusting valves: I am turning flywheel ccw till reach "T" to TDC. Would i need to go another 360 deg if I'm not at correct spot of stroke? Another words every time the T shows on the flywheel is that the correct spot to adjust valves?

I'll take off the rocker head and post findings.

Do i need to drain oil?
recommended sealant other then yamabond:?
thanks
Greg
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  #14  
Old 9 Oct 2013
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NO, you must be on the compression stroke. This is indicated by both intake and exhaust valves being closed. You align the T mark to make sure you are at the very top and the valves are at the very loosest spot for adjustment.

No you do not have to drain oil. Just make sure you have some sealer, like Yamabond #4 to reseal the rocker box. You put the sealer on both surfaces after a good cleaning to remove old sealer and any oil. Apply sealer and let air dry for 3 or 4 minutes to get tacky then assemble. Once assembled it is good to let sit for a few hours or a day to allow the sealant to dry and not leak.

The sound on your video does sound like loose settings. Just make sure you are at TDC on compression. TDC on exhaust stroke you will see exhaust valves close then intake open, just rotate to the next TDC. Looking at the stator, CCW is the correct direction to turn.
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  #15  
Old 9 Oct 2013
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Thanks Steve
This video was after I readjusted, hard to tell if there was an improvement.
https://vimeo.com/76520601
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cam chain, tdc, timing, top end noise, valves


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