another valve problem

[stef]

After the waste of time that was loosing the halfmoon down the engine, here is a new, weird one:
the opening clearance on the front inlet was originally 0.04mm... too tight.
Hence the reason for all this work.
tonight, i started reffiting the shims back on, for the adjustment. the closer on the inlet required some work. I took a slighlty wider shim, and proceeded to gradually sand paper it down, until i got a decent fit (until i go the cam to turn without binding).

then the opener:
i took the original one, which gave me a 0.04mm clearance, took a hundreth of mm off, and reffited to check. amazingly, clearance seemed good at 0.11mm ! (it should have been 0.05mm.)
so, since it was good, i refitted the small clip that keeps the rocker in place.
I then remeasured the clearance: 0.05mm.
took the clip off again: 0.11mm
check i wasnt turning the cam, fitted the clip: 0.05mm
removed the clip: 0.11mm.
refitted: 0.05mm
then i got bored.

with the clip in place, It looks like if i pull hard on the rocker, i can measure the clearance at 0.11mm. but it goes crap again as soon as i let go of the rocker arm.
i checked the clip for obvious damage, but it's fine.

what's going on ?

[Dookbob]

The sideways movement that the clip is causing could be finding a low spot between the rocker and top of the shim. Something might need to be flattened off.

[stef]

The sideways movement that the clip is causing could be finding a low spot between the rocker and top of the shim. Something might need to be flattened off.

I thought of that, so i spinned the shim around on the valve stem, but that doesnt make a difference. i tried various angles of measurements, it's all good as long as the clip is off.

[utopia]

It could be just a question of "feel".
I did mine recently and found that, due to oil on the various components, it was neccessary to pull upward on the rocker to insert the feeler (which otherwise appeared far too tight to go in, but was fine once it was in there).
Maybe the drag between the shim washers, clip and rocker are causing a difference in feel.

To be honest, I can't see how its possible to accurately measure down to a hundreth of a mm anyway (half a thou in old money) in a set-up with multiple components which are covered in a film of oil.

I'm not a fan of "sanding" down shims either......its far too easy to remove material unevenly, putting the working faces out of parallel/flatness. I'm particularly wary of using replacement shims that have been sanded by others. In fact the mere use of the term "sanded" fills me with horror as it suggests a fairly coarse process ....careful lapping with fine wet/dry paper is more like it. It should be possible to adjust within tolerance using std shims.

Final point...the half-moon retainers bed in slightly and new ones can restore clearances temporarily, until they eventually bed in too. This appears to be directional, ie if you put old retainers back in the other way up they need to bed in again. The situation is further complicated if only one of them is inverted. With care and a magnifying glass its possible (just) to see this wear and therefore replace them the correct way up, but next time I do mine I intend to mark them before removal.
I would suggest that old, bedded retainers give better results than new ones.

That lot may or may not help....hope it does.
Note that I speak as one with an engineering background and lots of biking, but I don't have vast experience of ducatis or desmo valve systems as such.....comments to be judged accordingly.

[stef]

It could be just a question of "feel".
I did mine recently and found that, due to oil on the various components, it was neccessary to pull upward on the rocker to insert the feeler (which otherwise appeared far too tight to go in, but was fine once it was in there).
Maybe the drag between the shim washers, clip and rocker are causing a difference in feel.

To be honest, I can't see how its possible to accurately measure down to a hundreth of a mm anyway (half a thou in old money) in a set-up with multiple components which are covered in a film of oil.

I'm not a fan of "sanding" down shims either......its far too easy to remove material unevenly, putting the working faces out of parallel/flatness. I'm particularly wary of using replacement shims that have been sanded by others. In fact the mere use of the term "sanded" fills me with horror as it suggests a fairly coarse process ....careful lapping with fine wet/dry paper is more like it. It should be possible to adjust within tolerance using std shims.

Final point...the half-moon retainers bed in slightly and new ones can restore clearances temporarily, until they eventually bed in too. This appears to be directional, ie if you put old retainers back in the other way up they need to bed in again. The situation is further complicated if only one of them is inverted. With care and a magnifying glass its possible (just) to see this wear and therefore replace them the correct way up, but next time I do mine I intend to mark them before removal.
I would suggest that old, bedded retainers give better results than new ones.

That lot may or may not help....hope it does.
Note that I speak as one with an engineering background and lots of biking, but I don't have vast experience of ducatis or desmo valve systems as such.....comments to be judged accordingly.


thanks for the reply.
I am not sure on the difference of feel thing. The 0.1mm blade simply does not fit between arm and shim. if i force it in, i'll bend it.
the 0.05 does fit in nicely.
on the other hand, pulling on the rocker, i can easily fit the 0.1mm, the 0.127mm fits nicely and the 0.15 is too tight.

i guess we are not talking 0.01mm just yet, it's more like 5 hundreth (half a tenth)

good point on the half moons. i suppose this will have an effect. but this is not mentioned anywhere. reading the step by step instructions or videos, it all seems so simple..

[utopia]

My technique for inserting the feeler is to place its side next to the gap then use a pinching of thumb and forefinger between feeler and rocker, while pulling upwards on the rocker.
This way the feeler is too rigid to bend.
The guy in the ducati-tech videos doesn't do it this way, but its clear from the sound of his components that they are completely free from oil, and I think that difference is crucial.

[manwithredbike]

i had exactly the same experience earlier in the year while doing my shims. clip on -vs- clip off, different clearance on at least one of the openers. I can remember reading something about it among the dozens of articles that i trawled during the protracted process. i can't find it now. i ended up with ok measurements with the heads fitted and the clips on but i can't for the life of me remember how i resolved the clip-gap issue. old age and all that.
i'll do a wee search later to see if i can dig up the article, can't even remember if it was any use.
i do remember being baffled as there was no obvious explanation and thinking it was just one of those things that nature gives us to scratch our head at - like jelly fishes

[stef]

i had exactly the same experience earlier in the year while doing my shims. clip on -vs- clip off, different clearance on at least one of the openers. I can remember reading something about it among the dozens of articles that i trawled during the protracted process. i can't find it now. i ended up with ok measurements with the heads fitted and the clips on but i can't for the life of me remember how i resolved the clip-gap issue. old age and all that.
i'll do a wee search later to see if i can dig up the article, can't even remember if it was any use.
i do remember being baffled as there was no obvious explanation and thinking it was just one of those things that nature gives us to scratch our head at - like jelly fishes

oh, please, dont mention the jelly fish..

[Chris & Nean]

Do you have the heads off stef ? I have done 'the valves' 3 times now, twice on my bike and also on my buddy's bike, and I have to say that even with benefit of having the heads off and held in my hands and being able to easily adjust the cam wheels (to best obtain the best sliding feel of the gauge) I still struggled to get them accurately adjusted.

To to get the clearances right while the cams are still under control of the crankshaft 'via the belts' obviously shows huge skill and experience by the operative is all I can say.

[Dukedesmo]

I've not done 2v shims yet but have some experience with 4v heads so thought I'd chime in with my findings FWIW.

I usually go for tight (0.05mm) closers on the 916 but the measurement is slightly 'variable' depending on exactly where the cam is when it is measured.

You can feel clearances of over 0.05mm with a 'click' but not if under 0.05mm but as an extra check I always rotate the cam with a feeler in the gap to see if it drags at some point.

I use fine emery lubed with WD40 to reduce shim sizes slightly because sometimes the next size is too much and no matter how many shims I have I always need one that I haven't got plus I like to set at the 'correct' setting, not some wide tolerance made for ease of servicing and reduced costs.

Also I highly recommend the MBP retainers instead of OEM half-rings as they don't wear (or break) like the rings, at least that is my experience on the 4v, and I have bought MBP retainers for the Monster.

[manwithredbike]

http://www.ducatimonster.org/forums/tech/106654-unloaded-gap-measures-tighter-rocker-arm-clips-removed.html

found this but sure it was another article or write-up i read

[stef]

thanks for this.
it's exactely the problem i am facing.
however, i am not reaching the same conclusions as on the link.
to me, the gap is the distance from the maximum position of the rocker, to the point it hits the valve stem.
this is the distance that should be covered when the camshaft will turn and push the rocker.
fair enough, if the rocker is slightly forward, because of the clip, the camshaft will have nothing to push on for some part of its rotation. but the rocker being slightly forward does not make this its normal resting, maximum position.

another way to think of this is to consider the force applied by the clip (which ever way it comes from) to be just comming on top of normal gravity.

forget the clip: if there was so little friction (and oil) in the engine so that the rocker would just "rest" on top of the stem (0mm gap), you would have to lift the rocker to its maximum postion to measure the gap. that would seem normal, since gravity alone maybe enough to lower the rocker to touch the stem, but not strong enough to push the valve down. that would still be the cam's job.

besides, they mention that noone is pulling on the rocker when the engine is running.. i beg to differ.
inertia, vibrations and all sorts of force applied 2000 times a minute will probably make the rocker go right up against the cam.

so i guess i will be lifting the rockers to their maximum position now, just to make sure.


unless someone with solid arguments has a better answer ?

(as an aside, i have the belts off, so i can turn the cam as easily as if the head was on the bench)

[Dookbob]

After giving all the comments on this thing a good thinking about, I would prefer to go for the clip off setting. The clip is merely a spacer and as such is not relavant to the up and down movement of the rocker. Also, a gap is a gap wether you pull up on the rocker to check it or not , pulling the rocker up to check the gap only helps to get the feeler in easily. Like Desmo, I prefer the MBP colletts too.

[Dookbob]

I,m having second thoughts on this already. If there is a slight amount of bedding in or wear on the rocker shaft where the rocker sits with the clip in place, then a slight sideways movement on the rocker while checking the gap could explain the difference in the reading. So I am changing my stance on this to checking gap with clip on which would allow for the wear if present.

[stef]

I,m having second thoughts on this already. If there is a slight amount of bedding in or wear on the rocker shaft where the rocker sits with the clip in place, then a slight sideways movement on the rocker while checking the gap could explain the difference in the reading. So I am changing my stance on this to checking gap with clip on which would allow for the wear if present.

i would think that if there was any wear on the shaft, the gap would increase, rather then decrease..
and also, i would think that clip on or off is not really the issue, all that matters is that the rocker is pulled to it's max position (against the cam) to measure the gap.

[utopia]

Interesting link....its seems that others have adopted the rocker pulling technique too.
I agree with your conclusions, Stef.

[Pomp1]

Measuring of the gap needs to be done with the clip off, but then is a case of measuring and "feel" the gap when refit and if necessary take it off and sand the shim. Ideally you should change the clips too. If the clips are not taken into account, you'll end up bending a valve.

[manwithredbike]

^^ not sure about this one ^^

would be good to hear from a mechanic who does heads often like rich from louigi or the likes for an opinion/explanation. (apologies in advance if any of the posters happen to be ducati mechanics!)