Bevel gears timing marks

[ecurbruce]

Jordan says"
" The main thing to know is that the coupling can go together, but that doesn't necessarily mean the crank-cam timing is correct. "

Bob says"
____ I sure as-heck learned that-FACT back when I was a teenager (before I bought my first Ducati workshop-manual), which is how I had learned that installing the cyl.head without having the lower tower-shaft's male-tip PERFECTLY-set (in properly-timed orientation), will most certainly lead to some way-off cam-timing that will-NOT allow the engine to start & run ! "


So, with head assembly removed, prior to re-assembly, the timing marks at the cam-bevel shaft, and timing marks at the crankshaft gears need to be positioned correctly, and then oldham joint will position correctly, and cam-crank timing will be correct.

That I did not do, which would account for the cam-crank timing being off. If all the bevel gears were the same size with the same amount of teeth, that would not be a problem. However, the oldham joint is not turning at the same RPM's as the crankshaft, due to the different size gears. It puts itself out of phase for that specified number of turns, and makes the timing off.
So for each revolution of the oldham joint the cam-crank relationship is "off", progressively further wrong...until it comes back around to "right".

Bruce

[Jordan]

All that roundabout way of designing the timing gear is to get the "hunting tooth" principle, which is good for gear tooth longetivity.
I think you also need to consider the ignition point, when working "half blind" on the bevel gear timing.

[DewCatTea-Bob]

So, with head assembly removed, prior to re-assembly, the timing marks at the cam-bevel shaft, and timing marks at the crankshaft gears need to be positioned correctly, and then oldham joint will position correctly, and cam-crank timing will be correct.

That I did not do, which would account for the cam-crank timing being off. If all the bevel gears were the same size with the same amount of teeth, that would not be a problem. However, the oldham joint is not turning at the same RPM's as the crankshaft, due to the different size gears. It puts itself out of phase for that specified number of turns, and makes the timing off.
So for each revolution of the oldham joint the cam-crank relationship is "off", progressively further wrong...until it comes back around to "right".

Bruce

____ It seems that you have a fairly good understanding of what's-what on the subject now Bruce.


" So, with head assembly removed, prior to re-assembly, the timing marks at the cam-bevel shaft, and timing marks at the crankshaft gears need to be positioned correctly, and then oldham joint will position correctly, and cam-crank timing will be correct. "

____ YES, your wording seems correct. ...
____ In other words,, with the cyl.head's pair of bevel-gear timing-dots set lined-up, the upper tower-shaft's male half-moon tip-end will then be properly aligned & faced so that it's flat mating-surface is correctly positioned DIRECTLY fore&aft, for a straight-forward slip-in fit into & against the corresponding flat mating-surface of the male half-moon tip-end of the lower bevel-shaft (that's also been already properly set). ...
__ The hassle-saving trick involved with this mating-operation however, is to save one from having to pull-off the timing-gear cover in order to actually see that the lower bevel-gear timing-dots are actually lined-up ! ...
Of-course the cyl.head won't be able to drop-down all the way into place atop the cyl.jug if the upper & lower bevel-shaft tip-ends aren't correspondingly aligned. _ So ya of-course realize that there's no-use in trying to put things together wheneve it's OBVIOUS that those two tip-ends are-not both set to be matched together.
However there are a couple of points (when the crankshaft is at TDC) where the lower half-moon tip-end looks to be pretty-CLOSE to the specified fore-&aft alignment position to become matched-up with the upper one, and with just a little twisting (& slight misalignment of the timing-dots on the camshaft bevel-gears), the cyl.head can then possibly be dropped-down and (improperly) fitted into place (at one of those two [wrong] locations). _ However, fitted in either of those two fittable possibilities, the engine will-NOT run !



" That I did not do, which would account for the cam-crank timing being off. "

____ Yes, seemingly so. _ That you managed to refit the head without bothering to check that the camshaft-to-crankshaft timing was properly set, could indeed most-likely lead to mal.timing between the two.
__ However since you somehow found a way to fit the complete cyl.head back on AND-also get the engine runnable as well,, means that you must've reinstalled the head someway without even checking for proper alignment of either the lower or upper bevel-gear timing-marks, (and just happened to [rather somewhat luckily] discover a cam & crank setting-arrangement which somehow still allowed the camshaft to be timed close enough to run the valves in time for the piston-movement) !? _ Which even-still seems like would be a quite unlikely circumstance to simply chance upon.



" If all the bevel gears were the same size with the same amount of teeth, that would not be a problem. "

____ Right, but the camshaft has to somehow be geared-down to half-speed of the crankshaft,, and while Ducati still could've used an EVEN-number of bevel-teeth gear-ratios to obtain that same required 2-to-1 rotational-reduction, (as Jordan has already pointed-out), Ducati didn't want all the very-same bevel-teeth to always fall into contact with just the very-same corresponding teeth repeatedly all the time. _ And-so their chosen odd b.gear-ratios were meant to address that bevel-teeth matching-up concern.



" However, the oldham joint is not turning at the same RPM's as the crankshaft, due to the different size gears. "

____ Right,, as the tower-shaft must turn slower than the crankshaft, yet faster than the camshaft.



" It puts itself out of phase for that specified number of turns, and makes the timing off.
So for each revolution of the oldham joint the cam-crank relationship is "off", progressively further wrong...until it comes back around to "right". "

____ Indeed the timing-phase between the camshaft & crankshaft (when separated) partially falls-apart further until the fifth crankshaft-rotation, (when they are then 180-degrees opposed), and then begin to come-back closer together until the tenth crankshaft-rotation, at which point they are then once-again both back 'in-time' as normal !


____ To complicate things still/even further,, some of the crankshaft bevel-gears have their timing-dot misplaced in relationship to the crankshaft's key-slot, (as Eldert has pointed-out at-least once before) ! _ And that situation somewhat spoils the perfect fore&aft half-slot center-line (between the coupling-faces) from being exactly parallel-aligned with the crankcase seam-lines (as otherwise is expected) !
__ So it can certainly pay to ether be an experienced/expert Duke-mechanic, or bother to consult one,, before assuming how such parts all go back-together !


Dukaddy-DUKEs,
-Bob

[ecurbruce]

Bob says"
____ It seems that you have a fairly good understanding of what's-what on the subject now Bruce."

Yes, thanks Bob and Jordan, for the guidance.

Bruce

[ecurbruce]

Hey, Jordan, or Bob,
Just to review before I remove the head assembly tomorrow,,,

To be sure I can reassemble the oldham coupling in the proper position and my cam timing be correct,-
Prior to disassembly, I should be sure the upper bevel gear timing dots are aligned. That will put everything from there down to the crankshaft in alignment for reassembly.
Providing the bottom end stays undisturbed, and the upper bevel gear timing dots align, it should all be correct for reassembly, right?

Bruce

[DewCatTea-Bob]

[quote= ecurbruce ...
" To be sure I can reassemble the oldham coupling in the proper position and my cam timing be correct,-
Prior to disassembly, I should be sure the upper bevel gear timing dots are aligned. That will put everything from there down to the crankshaft in alignment for reassembly.
Providing the bottom end stays undisturbed, and the upper bevel gear timing dots align, it should all be correct for reassembly, right? "

____ Yes but,, actually, if the "bottom end"/crankshaft's exact position remains undisturbed after the entire cyl.head (with tower-shaft) has been disconnected from the motor, then it doesn't mater whatever timing-position the cyl.head-parts & bottom-end parts happen to be randomly set-together at when they're separated-apart,, so long as BOTH top & bottom ends are re-mated back-together exactly the same as they were before, of-course ! _ (In other-words,, of-course a complete-engine's random-happenstance timing-position could be left wherever it had happened to become randomly settled at, when the cyl.head then becomes removed from the bottom-end,, PROVIDING that neither of those two separated sections get that random-timing of their's disturbed or altered, before finally being recombined back together.)
Trouble is however,, once the top & bottom ends have been separated, then at-least one or the other duly comes to get it's timing-position disturbed in relation to the other. _ So that's why it's recommended to preferably remove the top-end's cyl.head only with both it's bevel-gear timing-dots perfectly lined-up with each-other,, so that not-only will the valve-springs not be possibly left inclined to cause rotation of the camshaft's timing-position, but also, so that the bottom-end's internal timing will then likewise be left set in a properly 'timed' position as well.
That way, (even though all the bottom-end's various timing-dots possibly may or possibly may-not happen to then be all completely aligned-up), either the top-end's or bottom-end's timing-position could then be allowed to be disturbed, and-yet still be rather simple & easy to reset for reassembly back together, without loosing their original timing-relationship with each-other ! _ As the normal/regular cyl.head-timing can relatively easily be brought-back, by simply resetting it's bevel-gear timing-dots back into alignment once-again,, or, once-again have all the bottom-end's involved timing brought-back (to any of it's many possible working-combinations), by simply rotating the crankshaft to reset the bottom-end's OHC.drive-shaft back into it's factory-intended/(normal-timed) matching-position* (before finally recombining the top & bottom ends back together).
(* Note that the timed 'matching-position' [of slot-faces between bevel-shafts] has the lower-shaft's tip-end obviously, [as seen from the seated rider-position], positioned at 12-to-6 o'clock* [for 'timed' mate/matching-position with the upper-shaft's tip-end]. _ [* Which only happens every 10-rotations of the crankshaft, (although a similar-appearing but irrelevant reverse/6-to-12 alignment-position occurs every 5-revs after).] )
So it now ought-to be realized that if the cyl.head won't drop-down all the way into place atop the cylinder (while keeping it's bevel-gear timing-dot pair totally lined-up), then the bottom-end's particularly positioned timing must not be properly in-time (with that of the cyl.head) !
____ As always, if anyone finds ANY of my worded-points meanings to be less than perfectly clear, then please quote the wording in question and ask for further elaboration of it's intended point, (to be done in other-words).

____ Bruce, so what's the reason for why you're intending to remove the cyl.head from it's engine ?
__ For the help-sake of this thread,, if it's not too much trouble for you, then once the cyl.head is taken-off & out of the way,, how about then taking overhead-viewed pic.shots of the lower-shaft's tip-end (as seen down within the motor-casework), while place-fixed in all ten of it's various TDC.positions ?
Then you could email your 10-pix to me, and I'd then edit & label them for posting here, so that everyone could then SEE exactly how the lower-shaft's tip-end must be arranged in order to be set in-time along-with a cyl.head that's been (more obviously) set 'in-time' (with t.dots aligned).
That way, our readers could then possibly be spared from the trouble of always having to remove the right-front engine-cover to reset all the bottom-end's timing-dots (every time the bottom-end's timing happens to get moved out-of-sync with the cyl.head-timing).



Hopeful-Cheers,
DCT-Bob

[ecurbruce]

As I read back through this thread, in preparation to add something to it,, I see that I never saw the entire posting ( sorry Bob,).
A couple of things,

Bob says"____ ... actually, if the "bottom end"/crankshaft's exact position remains undisturbed after the entire cyl.head (with tower-shaft) has been disconnected from the motor, then it doesn't mater whatever timing-position the cyl.head-parts & bottom-end parts happen to be set-together at when they're separated-apart,, so long as BOTH top & bottom ends are re-mated back-together just as they were before, of-course ! _ (In other-words,, of-course the engine's timing-position may be left randomly set when the cyl.head is removed from the bottom-end, PROVIDING that neither of those two separated sections gets it's timing disturbed/altered before finally being recombined back together.) "

Yes, that's the procedure I followed, and this time, all went back together well.

Bob says;"__ For the help-sake of this thread,, if it's not too much trouble for you, then once the cyl.head is taken-off & out of the way,, how about then taking overhead-viewed pic.shots of the lower-shaft's tip-end (as seen down within the motor-casework), while place-fixed in all ten of it's various TDC.positions ? "

That would have been nice, but since I didn't see the post in time, no photos were taken this time. The job has long been completed and I've moved on to other stuf. Sorry maybe next time...

Bob says;"____ Bruce, so what's the reason for why you're intending to remove the cyl.head from it's engine ? "

Yes, that first time the head was off was to cure a excessive smoking problem where I found the top compression ring on upside-down...(problem solved)
During reassembly on that process is when I got the bevel gears timing so out of wack. Also during that reassembly, I pinched the big O-ring at the base of the bevel shaft housing, which created quite the oil leak... So the head back off to replace an 0-ring.(that problem solved now, too).

Here's what brings me back to this thread...
As I was researching and trying to figure out the timing issues of these bevel gear sets, and learning about the manipulation of them also posted in some other threads in this forum, (viewtopic.php?f=3&t=1302&hilit=Bevel+gears&start=30#p8833) and others like this one, I started figuring out what I could actually do with these gears. Thought I would post it here, since I don't find this information posted here anywhere else. I did some math and here's what I got...
Each tooth of the 21 tooth crank gear is 17.142 degrees.
That translates to 8.571 degrees at the camshaft.
Each tooth of the 28 tooth cam gear is 12.857 degrees at the cam.
Advance the crank gear 1 tooth = 8.571 deg. at the cam.
With that crank gear advance, retard the cam gear 1 tooth
(12.857 deg.) = -4.286 deg. Retard at the cam.
Advance crank gear 2 teeth, and retard cam gear 1 tooth, gives 4.285 deg cam advance.
Advance crank gear 3 teeth, and retard cam gear 2 teeth, gives 00.00 cam advance.
Advance crank gear 4 teeth, and retard cam gear 2 teeth, gives 8.57 deg cam advance.
That cycle repeats throughout all 21 teeth of the crank gear.
Here's the kicker... If you do that process in reverse, you get different numbers!
Retard crank gear 1 tooth, advance cam gear 1 tooth, gives 4.286 deg. cam advance.
Retard crank gear 2 teeth, and advance cam gear 2 teeth, gives 8.57 deg cam advance.
Retard crank gear 3 teeth, and advance cam gear 3 teeth, gives 12.858 deg cam advance.
(The next one is odd in that 4 retard and 4 advance gets you too far advanced, and takes you out of a cycle pattern)so next it goes...
Retard crank gear 4 teeth, and advance cam gear 3 teeth, gives 4.28 deg cam advance.
Retard crank gear 5 teeth, and advance cam gear 4 teeth, gives 8.57 deg cam advance.
This pattern continues all the way around the 21 teeth of the crank gear.

In my mild tuned monza 250 NC, the sweet spot to me is to retard the crank gear one tooth, and advance the cam gear one tooth for 4.286 degree advance of the cam.
It gives me better mid range and quicker acceleration to top-end. It also leaned out a little, so I have to re-tune the carburetor again. I had plenty of bottom end torque, so a little less bottom end is not noticeable.

I bet some of you guys already knew all of this....

Bruce

[Jordan]

Well that is interesting, I guess!
You'd have to remember or make notes on the non-standard cam timing. It's already fairly confusing as standard.

Leaking at the bottom of the singles' bevel tubes is common. The tube is fastened at the top, and restrained at the bottom by the O ring.
The seal isn't able to cope with the vibrations, and most tubes have visible fretting where they've walloped the O ring. It can get so that even a new ring won't seal.
Some engine sealant smeared around it is all that's needed to fix it.

Jordan