Only if it's a 2 stroke Remember Jeremy that a 4 stroke engine needs 2 complete revolutions to return to the same point in the firing cycle.
Never was good at sums... last time I did my belts, I got into a right pickle after turning the crank backwards 90 degrees for the v cylinder. The cam really didn’t want to stay in position and then spun round. Aargh... I fitted the belt, having set the cam with the ‘T’ perpendicular to the crank and turned the engine over very, very gingerly. All seemed well, so I fired her up and all was well. Phew... Would turning the engine forward the 270 degrees have prevented this?? Maybe a cam locking tool is worthwhile after all...
Oldrider. Did you not mark your old belts before disassembly and then use them to transfer the old marks onto the new belts? I know what you mean about trying to fit the belt onto the vertical cylinder, as if you turned the engine over backwards 90' the helper spring would be 'active' and I found it difficult, although not impossible to revolve the camwheel against the tension of the spring whilst trying to slip the belt into the appropriate place.
Well, yes but you shouldn't be turning the engine at all to fit belts. The belts should be fitted with the engine at the 'timing position' - Horiz cylinder at tdc on start of firing stroke and both valves closed. The vert cylinder is half way down the intake stroke with the inlet valve more or less fully open. This is why the inlet cam wants to turn. When fitting the belts to a testastretta engine cam lock tools should be used but it can be done without them. If you have any doubt make your own marks on the camshaft pulleys, referencing them to a fixed point on the engine like the joint between the cylinder head and cam cover.
I've never had a need to put marks on belts - but then I seem to have a better understanding of how it works
Oh dear... More confessions being squeezed out of me. I read a thread where people were saying why bother with marking and I thought I’d give it a go. Only afterwards did I realise they were talking about the desmoquattro engine and not all of what was said applies to the Testastretta. I found myself really wishing I’d done the marking and counting thing. It would have saved a lot of stress and time too...
Before taking the belts off make your own marks. Centre punch a dot on each cam pulley in an appropriate place. Make marks against them on the cylinder heads too if it helps. Then put a dab of tippex or white paint on each of them and you will have points of reference for every future belt change. All you'll have to do is line the dots up
According to Chris’s Video, on the Testastretta, all the timing marks go all over the place once the engine starts to spin. I did have previous marks on my pulleys but they didn’t seem to line up exactly
oldrider. I think I know what is confusing you. You don't need to turn the engine over to fit the belts. You do need to turn the engine over to enable you to set the belt tension correctly.
The factory marks on the Teststretta don't mean anything, I think they are a hangover from the Desmoquattro. But I can assure you that all the cams are in their same relative positions at TDC at the start of the firing stroke of the horizontal cylinder and this occurs every second revolution. If they weren't the engine couldn't run but would just self-destruct.
Don't be too hard on yourself oldrider, I had to give it a considerable amount of thought before I did it successfully the first time. The second time I was helping someone with the belt change on his 1098R , which I seem to remember went reasonably smoothly because I was familiar with the procedure, and with 2 people working in unison it was easier than on my own. This time I have gone to do it and realized I had forgotten the most important part of the whole process; how to set the H.Cyl on TDC firing stroke, which thanks to the helpful input from the contributors I now eventually fully understand.
I break the rules. After I fit the horizontal, I make sure both cams of the vertical cylinder are rotated 135 degrees CCW from the marks, then I rotate the engine 270, taking the vertical to TDC (valves being shut), which brings the drive pulley round 135 degs also, then I fit the vertical belt loosely (and without drawing blood fighting the springs). l then gingerly rotate the engine back and double check that all the marks line up, then take it round another 270 and tension the belt properly. It would've been helpful if Ducati had put a H and a V on each pulley, 135 degrees apart, instead of 1 mark
It took ages for the various pennies to drop for me....it was like playing on one of those slidey things in a feckin' arcade.
I’d only done it once before on a 4 valve engine and this was my first attempt without marking the belts, so had a right panic when the cam spun. As I realised at the time though and as Derek has reinforced here, there can only be one position for the cam and that should be pretty obvious. The rest I put down to early onset...
