Hello everyone. I'm currently doing a desmo on my MTs 1200s 2010. I've closed the cylinder and I'm putting the belts back on. When I removed them, I put the horizontal cylinder on tdc and marked the position of every single camshaft relevant to the belts. Basically a dot in the tooth of the belt and one in the corresponding camshaft. Now I've put all back again as it was. Mark for Mark. But when I manually turn the engine (using the rear wheel in 6th gear) after few rotations the marks never align again. I'm puzzled now. I thought after a while they would match again. Before I continue I'll wait for your opinions. Thanks a lot.
Hi mate, you have marked the belt and not the pulleys!! The pulley should be marked not the belt, have they got there own timing marks on there?? As long as the pulleys line up it won't matter
As long as they lined up when you installed them, that’s what is important. Due to the teeth on pulleys and belts, they won’t realign after just a few turns. It would be interesting to know just how many turns of the crank results in the marks realigning - I have never bothered to count/work it out. Also, I suspect that different models will have different pulley/belt ratios so it will vary from model to model.
I think they're all the same pulley-wise? and then, obviously all the pulleys need to be the same tooth count or it would run out of time. Belt length/number of teeth would make a difference though. Also, it's good the belts don't come round the same every revolution, this way you're spreading/evening out any wear much like chains. But yes, use the marks on the pulleys (I can see they are present) as your reference.
Is your concern that the marks don’t line up after a rotation or that the engine doesn’t do a full rotation without locking up?
From memory you need something like 37 rotations of the engine to have the marks you made on the belts line up with the marks on the pulleys again. It may be more than 37 but it’s a lot anyway, they won’t line up after just one or 2 rotations. As long as the camshaft pulleys were in their correct position in relation to the crankshaft pulley when the new belts were put on then all will be fine. Next time you do it, or anyone, once it’s at TDC horizontal mark the camshaft pulleys, and the cylinder head casing (if it doesn’t already have marks) and the belts. I also mark the belts and the pulley at the crankshaft. Remove the old belts, count the teeth between the marks and transfer the marks to the new belts. Refit the new belts with the marks thereon lining up with the marks on the various pulleys whilst making sure the marks on the pulleys are still in line with their corresponding marks on the engine casings. Apply some tension, rotate several times by hand to make sure all is ok and to settle the new belts then apply correct tension and the job’s done. Don’t worry the marks on the belts don’t line up with the marks on the pulleys after just a few rotations.
Just a curiosity. If the alignment was wrong and I was to turn the engine by hand, what would happen? Would I hear a noise when the piston hits the valve, or would just the rotation stop?
Not sure on Ducati but my VF 750 just stopped no noise of note just stopped rotating, which left to much scratching of head?
Depends if the piston just 'kissed' the edge of the valve or a full on hit - that 'kiss' might not feel much by hand but at 10,000rpm it could be catastrophic. If in any doubt, check it again and/or get a second opinion from someone knowledgeable.
In my recent experience, if one of the belts is off by one teeth, you can rotate the engine by hand without sensing any interference at all. When this happened, I did not start it until I had got things back to perfect, so I do not know what would have happened…
It's not that complicated. Start with the marks all lined up. Change belts and make sure marks are still aligned. Turn the engine 2 full rotations by hand and check the marks are aligned again. If they are, all is good. If they're not or you can't turn the engine by hand something's not right. There is no need to mark the belt and not much point. On a 916 for example the pulleys have 18 teeth and the belt has 95. That means 5.27 pulley rotations for one belt rotation. It's many many rotations before the marks on the belt and the marks on the pulley all line up again. 390 rotation of the pulleys so 780 engine rotations to be precise. Marking the belt may help someone with ensuring they have the right number of teeth between the pulleys. I personally don't bother. Either the pulley marks are in the right place or they are not. If the number of teeth between the pulleys is not correct the pulleys won't line up correct when tensioned.
Belt marking is pointless. There are 5 specific points to look at. 4 camshafts which need to be in the correct position and the crankshaft marking If the belts are on and tensioned and all 5 marks are correct then good to go. Keep it as simple as possible and you're less likely to make a mistake.
That was a few years back now, I also remember you were quite surprised how quick and easy a job it is if you stick to the basics.
Agree with all the above, just use the pulley timing dots. To add, I always think marking the belt is pointless, along with counting the teeth between pulleys - I mean, can you even fit the belts with less/more teeth between the pulleys, they're not made of elastic!
Whilst I agree it’s not necessary to mark the belts, for those not familiar with the process it’s helpful to ensure there are the correct number of teeth between pulleys before tensioning. No, the belts aren’t made of elastic but it is possible to fit the belt, on certain models, with no tension applied, such that over the long run the belt is out by 1 tooth. When the tension is applied the person then finds they either can’t get the correct tension or the marks on the cam pulleys are pulled out of alignment, resulting in puzzlement and frustration. There have been numerous threads over the years in here and other forums where first time cam belt changers are puzzled as to why it doesn’t work for them.
