decompression mechanism ticking ? (video)
 

My motor makes a ticking noise when warm.

I adjusted the valves already three times, I also replaced the timing chain, but tickings continue when engine is warm ..

At this point, I am convinced that it is not valves noise and not timing chain,
After a bit of web research I realized the ticking can be from the decompression mechanism ?

Do decompression system can make noise only when the engine is warm?
How can I check the integrity of the system?
I'd really appreciate your opinion

If you go back to your OP on this I mentioned this as one of the possible causes of your rattling.

http://www.xt660.com/showthread.php?t=23700

As I said then, it's the decompressor pin that is usually at fault - either loose, worn, broken etc. It is a known fault but not all that common. You will need to investigate the mechanism and replace the pin.

You can inspect and check the operation of centrifugal weights and spring easily enough on the cam sprocket, but you will need to access the camshaft itself to inspect the decompression pin (3) and the shaft (4) which links the centrifugal weights to the pin (and the correct operation of the whole decompression system).

Here's a picture that may help...

http://i864.photobucket.com/albums/a...psja2eyo9a.png

Pleiades thank you so much!, u did mention that, i should have read that post more times..

It took me some time and yesterday i checked the operation of this decompression mechanism, actually i couldn't find any thing or probably i cant spot it,
i took a video, maybe u can see something i can't ..
dont really know what to look for, or where too look next..

*actually when i compere the pin position in the picture to the pin in my motor, looks like it is upside down?
the grooved side of the pin is on the upper side in the picture, and in my motor is down side ?

When you say...

...do you mean the first video shows the position of the decompression shaft when you pulled of the cam sprocket?

If it is, then I think you have found the problem. It looks like the decompression shaft was inserted 180 degrees out which would mean the lobe on the end of it wouldn't have been acting on the decompression pin (and it would just be rattling about doing nothing) or even causing it to act in the opposite direction?

The lobe on the end of the decompressor shaft should be acting on the upper end of the slot in the pin, pushing it out of the crank lobe (and opening the exhaust valves slightly) when the camshaft is stationary. As soon as the camshaft starts spinning the centrifugal weight overrides the spring and turns the decompression shaft anti-clockwise, causing the lobe on the end to act on the lower part of the slot in the pin pulling the pin inwards away from the face of the exhaust cam lobe.

By the look of the second video (assuming you took this after the first?), you have the decompressor shaft located correctly. The slot that operates it should be pretty much level with, or slightly anti-clockwise of the notch in the camshaft end.

The only thing is, I'm not quite sure how the weight could have even been engaged with the decompressor shaft at all if the shaft was 180 degrees out?

Anyway, from where I'm sitting, everything looks in the right position in the second video, so give it a go and see if the motor is quieter. Just make sure that the decompression shaft is engaged correctly with the pin, and make sure the weight is engaged correctly in the slot on the outward end of the shaft.

This may help.

With the motor at TDC (all valves closed) and the cam sprocket removed everything should align something like this...

http://i864.photobucket.com/albums/a...psxfztijcm.jpg

Note the notch on the decompressor shaft is at about 11-12 o'clock, the camshaft notch is at 12 o'clock and the lobe on the inner end of the decompressor shaft should be facing the front of the bike. (Make sure the lobe is engaged in the slotted part of the decompressor pin).

thank you so much for all this helpful information.

when my motor is at TDC the decompression shaft is on the right position (like the second picture you uploaded) same as the camshaft notch.

but the decompression pin (#3 on the first picture) looks like it is with the little slot on the edge of the pin is facing up, while in my motor the slot is facing down when at TDC,

assuming this picture (first one) is illustrating the cam and pin at TDC then my motor decompression pin is upside down.

on the second picture you uploaded i can't really see the where the slot on the pin is facing.

http://i864.photobucket.com/albums/a...psja2eyo9a.png


this is my motor decompression pin at TDC, if you can see, the little slot on the left edge of the pin is facing down, and in the sketch is facing up.


https://c1.staticflickr.com/1/430/19...705bb6f5_z.jpg

is it possible to pull out this pin without pulling the cam out ?

As far as I can tell the decompression pin on yours is the right way round. The biggest cylindrical part (which has a domed top) will be the bit the raises out of the cam lobe.

TBH you can't really check anymore than you have without removing the camshaft, which isn't particularly difficult to do. In fact the only way you can really tell that the pin is working correctly (moving in and out) is to have the cam out.

With the cam removed and sprocket and decompression shaft and pin fitted you can check that (a) the pin is raised above the exhaust cam lobe under the spring tension of the weight mechanism, and (b) that is retracts when the weight is flung/moved outwards.

If the pin stays sticking out, you will get a tapping from the top end, loss of a little compression and a little more back firing.

I'm still thinking that the shaft might have been 180 degrees out though?

This video, although on an air-cooled XT600 motor, explains pretty well (in a redneck tone) what the pin does and what happens if the shaft is out of place.

OK then tomorrow i will remove the camshaft and inspect it.
do i need a special tool to remove it ?

You will need to remove the rockers to get the camshaft out. Pulling out the rocker shafts is the hard bit (depending on how tight they are). You will need to screw a 6mm bolt into the end of each shaft so you can get some grips on the bolt head and pull the shaft out. Once you've got the rockers out the camshaft should pull out.

Or you can make a puller like Kev did here...

http://i201.photobucket.com/albums/a...rockerrods.jpg

Just a note: If you've removed the rockers, you can actually see the decompression pin and check that it's working without actually pulling the camshaft.

Ok, i couldn't take the camshaft out, but i could see the pin near the exhaust valve rockers, i checked to see if is working as u said,
"the pin is raised above the exhaust cam lobe under the spring tension of the weight mechanism, and (b) that is retracts when the weight is flung/moved outwards"

every thing is working fine, so i closed everything and started the engine.
I was sure that the knocking will continue because in fact I have not changed anything (that I know about).

To my surprise, the ticking stopped! don't know how but I guess what happened is what you said, "it looks like the decompression shaft was inserted 180 degrees out which would mean the lobe on the end of it wouldn't have been acting on the decompression pin"

thanks to you and your explanations ticking are over now.

thank you so much for your help !