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Old 11-08-2014, 07:32 PM   #1
timeOday OP
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KTM 640 Adv (LC4) Manual Decompressor Problem

I am re-assembling my 2003 Adventure 640 after rebuilding the water pump and adjusting the valve lash (relying largely on the great howtos on this site - thanks!)

I have run into unexpected trouble with the manual decompressor. (I shouldn't have removed it at all). The problem is it appears that if I re-assemble it, it won't do anything.

Here is how I have the lever installed (sans spring):



That's right, isn't it? (Not flopped?)

Here is the corresponding position of the decompressor:



It looks like it is positioned almost against the rocker, ready to press it down and open the exhaust valve.

The problem it is actually makes no contact until this point (notice the lever is now raised):



Plus when it does finally hit the rocker arm, it has that terrible metal-on-metal feeling. There isn't a nylon cam lobe that slips over the decompressor shaft or something is there?

If I rotate the shaft 180 degrees it can still mate with the lever, but doesn't look right at all:




So, I guess my theory is the decompressor isn't engaging soon enough because I made a thicker gasket for the valve cover? I used Permatex No. 3 and the correct torques.

Or am I missing something?
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Old 11-08-2014, 07:41 PM   #2
gunnerbuck
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The first and second picture is the correct way... Is it possible that the position in the engines rotation has the camshaft to rocker arm already putting downward pressure on the valve? Try rotating the engine a bit and see if the rocker comes up...
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Old 11-08-2014, 08:13 PM   #3
timeOday OP
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Originally Posted by gunnerbuck View Post
The first and second picture is the correct way... Is it possible that the position in the engines rotation has the camshaft to rocker arm already putting downward pressure on the valve? Try rotating the engine a bit and see if the rocker comes up...
Thanks but that's not it, because I can measure the valve clearance (after all I just adjusted it) and it is not 0. I have also turned the wheel with the bike in gear to watch the valves move and make sure they're still closed.
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Old 11-08-2014, 08:40 PM   #4
timeOday OP
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Originally Posted by timeOday View Post
So, I guess my theory is the decompressor isn't engaging soon enough because I made a thicker gasket for the valve cover?
I just realized that makes no sense because the rocker arms and decompressor shaft both mount to the valve cover; the gasket is not between them.

I could swear I have used the decompressor on this bike before, and it worked.
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Old 11-08-2014, 08:47 PM   #5
gunnerbuck
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Originally Posted by timeOday View Post
Thanks but that's not it, because I can measure the valve clearance (after all I just adjusted it) and it is not 0. I have also turned the wheel with the bike in gear to watch the valves move and make sure they're still closed.
Did you set your clearance on the right stroke as to where the cam lobes were pointing downward?
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Old 11-11-2014, 10:49 AM   #6
timeOday OP
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I put the covers back on last night and fired up the bike. It sounds good, although the starter could barely turn it over and the manual decompressor no longer works.

Here's what I think it is - the sealant I used makes a thinner gasket than the OEM 3-bond. This does not move the rocker pivot towards or away from the decompressor, but it does make the rocker arm tilt a little more when the valves are closed. I had noticed when checking the valve clearances they were all way too tight and now I think that's why - with this design the thickness of the gasket would alter the valve clearances. But whereas the valve clearances are adjustable, the manual decompressor clearance is not, so mine won't work for now.

If/when I take off the valve cover again, I'm going out of my way to get the 3-bond. Until then, I'm just going to put in synth oil and hopefully the bike will start without the decompressor over the winter.
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Old 11-11-2014, 11:54 AM   #7
gunnerbuck
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Quote:
Originally Posted by timeOday View Post
I put the covers back on last night and fired up the bike. It sounds good, although the starter could barely turn it over and the manual decompressor no longer works.

Here's what I think it is - the sealant I used makes a thinner gasket than the OEM 3-bond. This does not move the rocker pivot towards or away from the decompressor, but it does make the rocker arm tilt a little more when the valves are closed. I had noticed when checking the valve clearances they were all way too tight and now I think that's why - with this design the thickness of the gasket would alter the valve clearances. But whereas the valve clearances are adjustable, the manual decompressor clearance is not, so mine won't work for now.

If/when I take off the valve cover again, I'm going out of my way to get the 3-bond. Until then, I'm just going to put in synth oil and hopefully the bike will start without the decompressor over the winter.
The thickness of the sealant really should not make much difference, you could lay the cover flat on the head without sealant and the decomp lever should still tip the rocker and slightly open the valves.. Is the cable slack adjusted properly?

If the starter is having difficulty turning the engine over then you may have another issue or issues: Your auto decomp may no longer be working, as a test,listen for the loud click it emits as you slowly roll the engine over... If you hear nothing then the deomp cam is no longer engaging...

If you do hear the click as the auto decomp cam sets itself then possibly your starter brushes are worn and need replacement, or your battery is not up to snuff...
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Old 11-12-2014, 02:48 PM   #8
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Thanks, I will keep that in mind. For the moment my hope is that the battery is a bit low from not running for a few weeks while I waited for parts and time to fix it. (Granted I could whip out a voltmeter and settle that one...)

Also the new water pump assembly is certainly stiffer than the old one when turned by hand (of course, the old seal didn't hold water and the bearings had noticeable play...). I don't know if that would be significant overall, but presumably it will break in soon.
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Old 12-06-2014, 08:37 PM   #9
timeOday OP
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It looks like your first guess was right. I was adjusting with the piston at the top, but of the wrong stroke, so the rocker arm was already depressed a bit. So then I had adjusted the valve clearance WAY too lose. The funny thing is it still ran quite well. But it was hard to start or even turn over, I suppose because the valves were hardly opening and only briefly. The tipoff was that the exhaust adjusters were nearly all the way up, with lots of threads showing. After removing the whole cover, it was easy to see the cams were up. I sure feel dumb.

timeOday screwed with this post 12-06-2014 at 08:59 PM
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Old 12-07-2014, 12:19 AM   #10
gunnerbuck
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Quote:
Originally Posted by timeOday View Post
It looks like your first guess was right. I was adjusting with the piston at the top, but of the wrong stroke, so the rocker arm was already depressed a bit. So then I had adjusted the valve clearance WAY too lose. The funny thing is it still ran quite well. But it was hard to start or even turn over, I suppose because the valves were hardly opening and only briefly. The tipoff was that the exhaust adjusters were nearly all the way up, with lots of threads showing. After removing the whole cover, it was easy to see the cams were up. I sure feel dumb.
It is very easy to get the valves set on the wrong stroke as the engine always wants to spin past the compression TDC when you roll it over... Because it does it so fast 2 revolutions often feel like 1...

Glad you got it solved..
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Old 12-07-2014, 12:26 AM   #11
bmwktmbill
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Quote:
Originally Posted by timeOday View Post
It looks like your first guess was right. I was adjusting with the piston at the top, but of the wrong stroke, so the rocker arm was already depressed a bit. So then I had adjusted the valve clearance WAY too lose. The funny thing is it still ran quite well. But it was hard to start or even turn over, I suppose because the valves were hardly opening and only briefly. The tipoff was that the exhaust adjusters were nearly all the way up, with lots of threads showing. After removing the whole cover, it was easy to see the cams were up. I sure feel dumb.

You are not dumb at all.
Intake compression power and exhaust, 1234 stroke engine. Down up down up piston motion.

Put the machine in 5th gear, remove the spark plug, turn the engine over with the wheel in the direction of forward motion, put your thumb over the plug hole, when you feel compression starting(air is being pushed out) insert a steel rod and carefully follow the piston up to top dead center. The valves are both closed now and you are at the top or end of the compression stroke(this is the only position in which they are both closed.)

Set the valves.


bill
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