Aligning the ignition timing, crank, and valve gear dots?

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desmorider450
Posts: 8
Joined: Wed May 13, 2015 2:49 am

Aligning the ignition timing, crank, and valve gear dots?

Postby desmorider450 » Wed May 13, 2015 3:04 am

Hi there. I have a new to me 450 desmo. It was running okayish (besides a fuel problem). I removed the right side cover that houses the points and timing gears. Upon doing this, the timing gear came out and I didn't realize that it was all lined up etc until too late. Now I go back to put it back in and line it up but can't seem to figure out exactly what should align with what because the images in the manual are too small to see what dots they are referring to.

On my ignition timing gear I have a yellow painted dot and an indent dot. On the crank gear I have 2 indent dots that are about 30 degrees apart. On the valve timing gear I have one dot. I seemed to make out in one diagram that one dot on the crank should align with the valve dot and the other dot on the crank should align with the dot on the ignition timing. If so, what is the yellow dot?

Also, in my search I saw someone mention that the bike can be timed with messing with the gears and if that is done then that means that the timing marks mean nothing and it is done with a strobe. After some looks it seems that the dots don't line up. The dots on the bevel valve gears in the head where the tach drive goes in don't seem to ever line up. The dots on the valve gear and crank gear don't seem to line up ever (although I read that it takes six turns for them to do so and I'm not sure if I turned it six times, but I'm not sure why it would take six times). If this is the case, and this special case has been done, then would that mean that the yellow dot is my new line up mark?

And then when aligning these dots: must they align on the compression stroke? So I find where it starts to compress on that stroke and make sure that they line up on that rotation?

I am a little confused on this but it seems like it should be very simple. I appreciate the help!

desmorider450
Posts: 8
Joined: Wed May 13, 2015 2:49 am

Re: Aligning the ignition timing, crank, and valve gear dots

Postby desmorider450 » Wed May 13, 2015 3:09 am

Here is an image of what I am referring to. It seems from this that the valve gear dot points up and the crank dot aligns with the ignition dot. If so, which dot on the crank does it align with? And what is the yellow dot on mine?
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StewartD
Posts: 104
Joined: Wed Mar 20, 2013 2:21 am
Location: Melbourne, Australia

Re: Aligning the ignition timing, crank, and valve gear dots

Postby StewartD » Wed May 13, 2015 8:17 am

Ducati manual fig 82.jpeg



Desmorider,

All the indentations in the timing case gears should line up as shown in the Clymer manual figure 82, which I have attached. The top bevel gears at the overhead cam should line up at the same time, as shown in the Clymer manual figure 90, also attached.

If they are not all timed at the same time, and the motor is turned before lining up the other indentations, then the pair that were timed first, will probably never line up, no matter how many times you turn the motor over.

If a ratio of 2:1 was used for the lower bevel gears and 1:1 for the upper pair then it would be ok to turn the motor over after timing the timing case gears. In this scenario, if the motor is turned two full turns, then the indents will line up again. Putting the head on now, with the head bevel gears lined up will result in correct timing.

Ducati do not use this system though, and the reason is to have a cam drive that lasts longer. The drawback of this cam drive design is in the ratio of the bevel gear pairs that must be used for reduced wear.

Overall the ratio for the cam drive, in any petrol four stroke motor, is 2:1; the cam only rotating at 1/2 the crankshaft speed. If a ratio of 2:1 was used for the lower bevel gears and 1:1 for the upper pair then the same teeth would always be engaged at the time in the cam’s rotation when the heaviest lifting is occurring. These teeth would wear much faster than the other teeth. To mitigate wear the ‘Hunting tooth” principle is used. This principle requires that the ratios are chosen so that while the overall ratio of the two gear sets is as required, in our case 2:1, the ratios of the pairs are such that each tooth of the second and third gears of the train are in turn engaged at the time of heaviest loading. It is unavoidable that the heaviest load is always taken on a small number of adjacent teeth on the first and fourth gears of the train.

Ducati use 21 and 30 tooth bevel gears on the lower pair and 20 and 28 tooth bevel gears on the upper pair. The larger gear in each pair is the driven gear. The lower pair ratios are 30/21 = 1.42857 and the upper pair ratio is 28/20 = 1.400 but the overall ratio is 28 x 30 / 21 x 20 = 2.

It can be seen from this that if the crank is turned inadvertently, even though the sleeved coupling appears in the right orientation for engagement it may have turned a full turn, but the crank shaft would have turned (30/21 =) 1.42857 turns.

Cheers,

Stewart D
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desmorider450
Posts: 8
Joined: Wed May 13, 2015 2:49 am

Re: Aligning the ignition timing, crank, and valve gear dots

Postby desmorider450 » Wed May 13, 2015 1:05 pm

Thanks a bunch for all of the information.

So from what I can gather: since I only removed the ignition timing gear and put it back (not correctly) then I will just have to rotate the engine until the crank gear dot lines up with the valve timing gear and then the ignition one should line up with the right crank dot like in the diagram? I have rotated the gears till the crank gear dot lines with the oil pump gear dot and then inserted the ignition gear so at that point so the dot lines up with the other dot on the oil pump gear. This then only lines up again perfectly in about 6 or 7 revolutions of the engine. Is that right? Also, when these dots line up the dots on the gears in the head for the valves don't line up. What am I doing wrong?

StewartD
Posts: 104
Joined: Wed Mar 20, 2013 2:21 am
Location: Melbourne, Australia

Re: Aligning the ignition timing, crank, and valve gear dots

Postby StewartD » Thu May 14, 2015 7:30 am

If you did not remove the head and turn crank or cam, before replacing the head, then if you rotate the crank 10 times, eventually all bevel gear indentations will line up. If they don't, then your cam timing was wrong to start with.

When they all line up, then it is an easy job to line up the oil pump and points drive gear indentations.

If this is still a bit unclear, then consider the rotation of the shafts in order:

The bottom bevel gears are 21 and 30 tooth respectively for crank and vertical drive shaft. Every 10 turns of the crank the indentations of the bottom gears will line up. When the crank turns 10 times the vertical drive shaft will rotate (21/30 x 10) = 7 times. (In 10 turns of the crank (21 x 10 =) 210 teeth of the crank gear will have engaged the vertical shaft gear. 210 is the lowest multiple of 21 that is divisible by 30)

When this vertical shaft turns 7 times then the cam will turn (7 x 20/28) = 5 times.

Once you are sure that cam timing is right, then If you wish to remove the head and do not want to take off the upper inspection cover, then you must be careful not to allow any idle spectators to lean on the kickstart or play with the head. You can then replace the head without checking the timing. The 'D' coupling of the vertical cam drive shaft can only be assembled correctly.

This is a very nice design for quick removal of head, but you must be wary of the hunting tooth drawback. On one occasion when my 450 Desmo of 1974 was fitted with a non desmo head and an Amal concentric carburettor, part of the slide broke away and became stuck under the inlet valve. This caused instant zero compression.

This was on the first day of my club’s 1982 tour of Tasmania so I experienced that sinking feeling at this mysterious sudden loss of power. We were fairly near a town so someone towed me in and parked near a convenient pub.

After a few minutes the slide problem was spotted and the head taken off, with exhaust pipe and cam drive tube still attached. The inlet valve inspection cover was taken off. The inlet valve was pushed down from above and the valve seat and valve were scraped from below. The head was put back on and lacking a torque wrench, care was taken that the head bolts were evenly torqued. Since neither pair of bevel gears were disengaged, and the motor or cam weren't turned then reassembly could only be correct, whether the indentations had been lined up or not.

The bike was fired up and the boys only had time for one pot of beer in the pub!

desmorider450
Posts: 8
Joined: Wed May 13, 2015 2:49 am

Re: Aligning the ignition timing, crank, and valve gear dots

Postby desmorider450 » Thu May 14, 2015 4:45 pm

StewartD wrote:If you did not remove the head and turn crank or cam, before replacing the head, then if you rotate the crank 10 times, eventually all bevel gear indentations will line up. If they don't, then your cam timing was wrong to start with.

When they all line up, then it is an easy job to line up the oil pump and points drive gear indentations.

If this is still a bit unclear, then consider the rotation of the shafts in order:

The bottom bevel gears are 21 and 30 tooth respectively for crank and vertical drive shaft. Every 10 turns of the crank the indentations of the bottom gears will line up. When the crank turns 10 times the vertical drive shaft will rotate (21/30 x 10) = 7 times. (In 10 turns of the crank (21 x 10 =) 210 teeth of the crank gear will have engaged the vertical shaft gear. 210 is the lowest multiple of 21 that is divisible by 30)

When this vertical shaft turns 7 times then the cam will turn (7 x 20/28) = 5 times.

Once you are sure that cam timing is right, then If you wish to remove the head and do not want to take off the upper inspection cover, then you must be careful not to allow any idle spectators to lean on the kickstart or play with the head. You can then replace the head without checking the timing. The 'D' coupling of the vertical cam drive shaft can only be assembled correctly.

This is a very nice design for quick removal of head, but you must be wary of the hunting tooth drawback. On one occasion when my 450 Desmo of 1974 was fitted with a non desmo head and an Amal concentric carburettor, part of the slide broke away and became stuck under the inlet valve. This caused instant zero compression.

This was on the first day of my club’s 1982 tour of Tasmania so I experienced that sinking feeling at this mysterious sudden loss of power. We were fairly near a town so someone towed me in and parked near a convenient pub.

After a few minutes the slide problem was spotted and the head taken off, with exhaust pipe and cam drive tube still attached. The inlet valve inspection cover was taken off. The inlet valve was pushed down from above and the valve seat and valve were scraped from below. The head was put back on and lacking a torque wrench, care was taken that the head bolts were evenly torqued. Since neither pair of bevel gears were disengaged, and the motor or cam weren't turned then reassembly could only be correct, whether the indentations had been lined up or not.

The bike was fired up and the boys only had time for one pot of beer in the pub!




Thank you for the reply. I think that I fully understand how the gears should line up, but am having trouble because the top bevel gears in the overhead cam don't line up at the same time. I am not sure whether the pump, ignition, and crank and aligned and then they won't be alined when the dots on the bevel gears in the head are aligned? When the top bevel gears dots line up then the dot on the crank gear lines up with the dot on the vertical gear that drives the gears. This is seen in picture 1 and 2. I have not done anything more than remove the timing gear and the bike was running and driving before, so the timing of the other gears should be correct (from what I understand).

1) Image

2) Image

Now, I rotate the crank by turning the rear wheel in gear until the dots line up as shown in picture 3 and 4. The problem is that when these dots are lined up the top bevel gears in the head don't line up. Is that wrong? Also, what is the yellow dot on my ignition timing gear? Does that mean anything?

3) Image

4) Image

You can just see the yellow dot in this picture: Image

Jon Pegler
Posts: 459
Joined: Sun May 16, 2010 6:19 pm

Re: Aligning the ignition timing, crank, and valve gear dots

Postby Jon Pegler » Thu May 14, 2015 5:03 pm

It's not easy to see in your photos but have you got the large idler gear that drives the oil pump in the right place?
It looks to be about three teeth out.
With both sets of bevel dots lined up, the idler gear should have it's upper left hand dot aligned with the dot on the crankshaft gear.
That dot is quite hard to see, being behind the bottom bevel gears and stamped on the end face of a gear tooth.
With the oil pump idler gear correctly positioned, the points drive gear can then be fitted.
You will still need to check the ignition timing after re-fitting the timing cover.

Jon

desmorider450
Posts: 8
Joined: Wed May 13, 2015 2:49 am

Re: Aligning the ignition timing, crank, and valve gear dots

Postby desmorider450 » Thu May 14, 2015 5:21 pm

Jon Pegler wrote:It's not easy to see in your photos but have you got the large idler gear that drives the oil pump in the right place?
It looks to be about three teeth out.
With both sets of bevel dots lined up, the idler gear should have it's upper left hand dot aligned with the dot on the crankshaft gear.
That dot is quite hard to see, being behind the bottom bevel gears and stamped on the end face of a gear tooth.
With the oil pump idler gear correctly positioned, the points drive gear can then be fitted.
You will still need to check the ignition timing after re-fitting the timing cover.

Jon

I don't think I ever removed the large gear that drives the oil pump, however, it may be possible. How is that able to be checked? When you say 3 teeth out, how do you know? Since I know that the bevel gears are lined up, should I get those to line up and then get the oil pump gear to align with the crank gear? When the bevel gears in the head line up then the crank gear lines up with the vertical drive gear as shown in those two first pictures. Hmm

Jon Pegler
Posts: 459
Joined: Sun May 16, 2010 6:19 pm

Re: Aligning the ignition timing, crank, and valve gear dots

Postby Jon Pegler » Thu May 14, 2015 5:42 pm

To remove the oil pump gear you have to remove the bottom bevel gear from the crank.
Even if you haven't taken that off, it doesn't mean that the oil pump gear is correctly meshed as it can slide out of mesh and the timing dots can become misplaced.
To re-set;
Align top and bottom bevel dots correctly.
Pull the oil pump gear out of mesh and turn until the LH upper dot lines up with the dot on the crankshaft.
This dot is behind the bottom bevel gear and marked onto the end of a tooth on the crankshaft.
It is not easy to see.
Once the oil pump gear is in the correct position, fit the points drive gear dot in line with the RH dot on the oil pump gear.

Jon

graeme
Posts: 938
Joined: Sun Mar 25, 2012 12:00 am
Location: Tasmania Australia

Re: Aligning the ignition timing, crank, and valve gear dots

Postby graeme » Thu May 14, 2015 10:10 pm

Don't forget that 450's use the slash "I" and not the dot for setting the points gear.


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