I would appreciate some clarity with determining TDC on the firing stroke on the horizontal cylinder on my 848EVO. This is something I've done a couple of times before previously, but when I went to do it again I have got confused. In the Chris Kelly video-Part 1: he explains and shows that on the horizontal cylinder, with the driven cam pulley dot lined up with the slot in the crankcase , and with the orientation of the slots in the camshafts in a straight line, that is TDC on the firing stroke. My confusion is how does he know that that TDC is the firing stroke, and not the inlet stroke? As if the crankshaft is rotated 180' the piston is again at TDC -but is it on the firing stroke, or the inlet stroke. I appreciate I could work this out by removing the air box, and then the cam cover on the horizontal cylinder, but am reluctant to do this as I don't want to break the seal unnecessarily. I think I'm missing something but can't work out what it is. Help appreciated please. Btw in the Ducati workshop manual it states. "Position the crankshaft so that the piston of the horizontal cylinder is at TDC of its power stroke. This is achieved by aligning the timing mark on the driveshaft pulley with the reference mark on the crankcase.
The lower pulley mark and the slot on the cover only line up when the horizontal cylinder is at TDC at the start of the firing stroke. Remember that the pulley rotates at half engine speed.
Thanks for your reply Derrick it's appreciated. I did an experiment ( one of many) and with the marks lined up as you mention above, I lowered a rod into the sparkplug hole and found the piston was indeed at TDC. I then turned the camshaft driven pulley 360' ( so equating to 180' crankshaft turning if I'm correct), so the above mentioned marks are now lined up again, and found that by lowering my rod into the spark plug hole the piston was at BDC.
That doesn't make sense. If the drive and cam pullies have rotated 360 from the marks then the marks will be lined up again and the horizontal cyl will have returned to TDC on the comp/firing stroke. Also, the crank will have rotated 720degs not 180.
I think the pennies slowly dropping ! And about time too ffs. As you say PeteW if I rotate the camshaft pulley 360' as it's turning at 1/2 the speed of the crankshaft it means the cranshaft has turned 2 complete revolutions- 720'. Thanks for the clarification, I believe I finally have it. When the marks are lined up the piston is at TDC on it's firing stroke. Thanks for your help.
Correct, but obviously only the horizontal piston. The vertical will be half way down on its intake stroke. When the vertical piston is at TDC on its firing stroke the pullies will have moved 135 degs counter-cw from the marks (270 on the crank).
Or, as Chris Kelley suggests, you can turn the crank 90 degrees backwards to put the vertical cylinder on tdc
Yes, but at the top of the exhaust stroke and both valves will be partially open. I never turn the engine backwards because it transfers the timing gear backlash to the other side of the teeth and puts the tension on the wrong side of the cam belts. This is no good if you are trying to accurately check timings for example.
@oldrider This seems to be a controversial point. I've heard some say turning 90' backwards is incorrect, and others ( including the Ducati workshop manual ) say the correct way is turning the engine forward 270'. I was aware of this the last time I changed the belts on my 749S, and because I was a virgin on the Testastretta engine I fixed a degree wheel to the crankshaft so as I could learn what exactly was going on with both methods. Of course turning the engine backwards seems counter intuitive as this introduces backlash into the equation, so turning the engine forward seems the natural way to go to me. Just for 'fine tuning', I lowered a stick into the plug hole on the vertical cylinder and inched the engine forward and backwards until I was happy the piston was indeed at perfect TDC. I would like to add I'm a bit slow on the uptake when working all this out, I'm aware it aint rocket science, but I believe that with discussion and helpful input from other more knowledgeable peeps I get there eventually, and we all benefit.
Turn it backwards a little over 90 degrees and then forwards to take up any backlash. I don't see any reason why you can't turn it backwards, it won't break it.
I agree with you Dukedesmo, turning the engine backwards isn't going to break it. When you are unfamiliar though, and doing it for the first time, especially when you are not using the crankshaft turning tool, but turning the engine over with the rear wheel in gear, it can easily get confusing how many degrees you have turned the engine over. That's why I fixed a degree wheel to the end of the crankshaft so as I didn't make a mistake.
But as Derek said, turning it back 90 degrees puts the vertical cylinder at TDC on its exhaust stroke, with the valves slightly open and the cam [still] wanting to rotate.
I put a chopstick gently down the vertical and turned the rear wheel forward, it went down then when it came back up to the highest point I was at TDC.
So, turning back 90 degrees (360-90=270) does not give the same result as turning forward 270 degrees.
Side note: the amount of times a chopstick has come in really handy/useful is long and varied but not once while trying to eat rice.
