I've checked my rocker gaps on a takeover ducati 600ss. All good except that I am puzzled by one observation on my present setup. Given that the exhaust closer gap at TDC should be, as given by Setting desmo valve clearance , nominally close to zero as possible, but not banging the valve into its seat, and so practically: .025mm to .06mm (.001 inch to .0025 inch): I measure the gap as less than 0.05mm, which is the smallest gauge I have until I get to the shop. However, unlike the three other of the closers, I cannot push the closing spring down - there is no movement there. The shim of the closer in question does rotate but not quite as freely as the other three. Q. Does this indicate a gap of less than zero or, something else perhaps?
If the shim rotates then it's not really tight but how tight is it? After I've set mine (0.05mm closer), to double-check I stick a feeler equal to the measured opener and closer clearance in the gap and then turn the cam to gauge exactly how tight it is. If it drags then it's too tight...
Oh yes, that's a good point , something which I practise. I'll need to go down to a smaller gauge first, to see if I can attempt that. I do wonder what no spring compression at TDC might mean though... and if anyone is familiar with this observation. I tried hard, several times.
In his Ducati Maintenance and Modification Guides, L T Snyder says that when pressing down against the closer spring you won't feel movement if the gap is less than 4 thou (0.10mm).
Excellent. Thanks Derek. I'll make sure I have some gap - off to get a new set of feelers now. I had been wary, that perhaps the valve is sitting slightly off the seat or some such thing John
Depending on how the engine has been running, there may be particles of carbon on the exhaust valve & seat, which may make the closing clearance seem a bit tight. If you adjust the clearance shimming to make it looser, the carbon may go away and you will then be left with clearances which are too loose. And you might be wishing you had left well alone.
THat's a very good point to consider Pete.. You know, I've decided to run bike on road for a couple of hundred or so before I may do anything later on... fortunately its the exhaust valve, horizontal, so easy access. The bike had been running poorly when I received it - rust in tank, clogged carbs, probably at wrong setting. The plugs appeared rich. I think you may be onto something... Thanks very much for that pointer. BTW I couldn't get a feeler less than 0.05 mm today - or in imperial on my outing. I'll get one eventually and try that too. Excellent. John
Take the belt off that cylinder and rotate the cam by hand. You should be able to feel if the valve is binding, but as has been said, so long as you can rotate the closer shim by hand it's fine.
I must do that, yes, thanks Samurai ! I'd forgotten to mention it.. or even think of it in my summary at this point... its in my notes... next on list.. but pouring down today. I may have even forgotten in my muddle of web pages in search for a decent feeler set down to .001" I found them in Amazon. Also, A USA-made Starrett 6671 Feeler Strip - 0.001" at about £3.90 on toolnet.co.uk
The easiest way to measure the closer gap accurately is to use the 'loaded' opener clearance method. Set the cylinder at TDC on the compression stroke and measure the opener clearance as normal. Next use a screwdriver or similar to push firmly downwards on the closing rocker arm and at the same time re-measure the OPENER gap which should now be greater than before. The difference between the 'loaded' and 'unloaded' gap is the CLOSER clearance. What you've actually done by pressing down with the screwdriver is to overcome the 'helper' spring that assists the valve in remaining fight against it's seat to help with starting primarily. I alwys check that you can rotate the closer shim by hand as well as a double-check. If the clearance is close to or slightly less than the minimum tolerance I'd take the belt off and feel for binding as I previously mentioned. Worth bearing in mind that if you've fitted New half rings in the process of changing the closer (recommended), then you can get away with going down to hear zero as the rings will squash in use and give you back some gap. Just ensur the cam doesn't bind though.
Thanks, yes came across that method, and worthwhile it is. Observation here I have described is that pressing down on horizontal exhaust closer gap spring, i get no movement on spring. A 0.5mm feeler will not pass between shim and closer. Additionally, the opener on this exhaust port is > 0.5mm < 0.2mm. I ask, what could this mean, other than possibly zero or less than zero closer gap? I shall be checking for bind on removal of side covers shortly... just been engaged with timely garden jobs as weather is suitable past couple of days.
I wouldn't even consider leaving the belt on, how can you get any feel for tightness from turning the engine via the crankshaft?...
Hmm.. at TDC that would be, tight before, during and after.. a lack of relief with no gap.... well optimistically speaking, perhaps if I took a long apprenticeship in safe cracking?
I'm not suggesting that you'd be able to feel binding with the belt still attached, but if your closer gap is within the assembly value tolerances then why would you need to check for binding? I usually only do that if the clearance is on the border of 0.05mm or less.
But of a waste of time trying to measure such a small gap using that method IMHO. Why bother when the loaded gap method is easier and more accurate. If you've got no gap using that method then you are correct that, well basically . . . you've got no gap and the shim probably needs changing!
Yep that's true. Mainly, what I was checking was the meaning of the observation that the closer rocker spring would not depress, in order to carry out measurement. It's been usefully confirmed that this is expected with a closer close to zero. SO, I cannot determine the gap on a newly taken over bike (my first ducati) by such a method. The gap might be less than zero. I can only rely on the smallest feeler coupled with feeling for binding. Other thoughts that occurred to me are, although valve face deposits have been mentioned, which would close the gap and stop spring action, a slightly bent valve hasn't. To rule that out, I can use cylinder compression readings. The corresponding opener gap of 0.2mm - which is at the limit of stated service tolerances - suggests that this port has been reshimmed to give a larger gap, likely due to recession.. however a bent/unseated valve would also increase the gap . I have a compression tester, but await a suitable adapter, ordered by post yesterday. Thanks folk, for kind advice. I'll report on findings very shortly.
Why not slip the belt off, as suggested and try turning the camshaft to check for binding - is that not the definitive test? Interesting thread btw...
Because I'm on other work... !! Bear with me. I'll report back. However, before asking here I did not know it was the definitive test in the context of loss of closing rocker spring compression because I am new to ducatis, and had not got that far. So, all's good so far..
If you're checking valves then the belts need, at the very least checking for tension. It only takes a few minutes to take them off/refit and in doing so you get to check them over or even replace them, especially if last replacement is unknown as on a bike new to you. If a closer is binding you may not feel it unless turning by hand, as mentioned above gaps of less than 0.05mm won't be easily felt by depressing the rocker (no 'click') which is why I use a feeler in the gap and turn by hand to determine if it's binding or not. And it saves you getting silly thin feelers as, for example if you have a 0.10mm opener and 0.05mm closer clearance then a 0.15mm in the gap will make the cam tight to turn on the closer but a 0.14mm should turn as freely as with no feeler inserted - makes for an accurate go/no go situation as a double-check IMO.
No criticism, honestly. I'm full of admiration for the way you're tackling a tricky job on a totally unfamiliar machine Btw, @Exige on here will do you some belts at a great price and I'd also recommend a starting circuit cable kit from him as well. My SS was always an incredibly reluctant starter, even with a new battery. When I got my 999, I expected it to be different but it wasn't well, not in that respect anyway I got a cable kit and a new Yuasa and the bike was absolutely transformed - starting issues totally banished
