Checking the cam timing

When I planned the assembly of my engine I thought that it might be a good idea to check and reset the cam timing. Ducatis are not famous for perfect timing and normally it is performance to gain by setting the cams correct. I have been doing cam timing a few times on rubber band Ducatis and was thinking that it should not be to difficult .  The question is what is correct timing? To prepare my self I had been studding Peter Shearmans The Black Mystic Art of Cam Timing so I was prepared to do my bevel. Cam timing can be checked in several diferent ways and the way that I have used earlier are the most used I think. You just rotate the engine and check when the valve opens and  closes and compare it to the specification for the cams. Easy. Normally it is specified at 1mm lift. This means that the values are not opening and closing values. It is actually when the valve is open 1mm and close is when it is still 1mm open and are closing. The problem with bevel Ducatis is that Ducati specifies the timing at running clearance. What is running clearance? I found out that it is 0,20mm lift. This is not a very good way of doing it as it is not very accurate but it had to work. The way that Peter Shearman describes in The Black Mystic Art of Cam Timing is a totally different way. Basicly it tells you to find the point of max lift of inlet and exhaust valves. Measure how many degrees it is between the two max lifts. Take the difference and split it in two and put the exhaust max lift that amount of degrees Before Top Dead Center (BTDC) and the inlet max lift the same amount After Top Dead Center (ATDC). If for example Exhaust max lift is at 252 degrees (crank shaft degrees) and inlet max lift is at 87 degrees it all turns out like this 360-252 (to see how many degrees before BTDC that the valve has max lift) + 87. Then divide this by two.  This gives 108+87=195. Divide this by two to get the middle. 195/2=97,5 So the answer to the question is that exhaust should have max lift at 97,5 degrees BTDC and inlet should have max lift at 97,5 degrees ATDC. Simple isn’t it. Peter Shearman also says that based on experience it is good to advance the cam shafts 3-4 degrees to get a good compromise for street riding so it will turn out  to be 102,5 BTDC for the exhaust and 92,5 ATDC for the inlet. Based on my own limited 2 valve experience I found that if you take the valve timing at and find the middle of opening and closing (lobe center) at 1mm lift and measure it in degrees BTDC and ATDC and advance the cam shafts so the inlet has a number that is between 5 and 12 degrees (depending on bike) lower then the exhaust it will be good. As an example inlet center lobe is 107ATDC and exhaust center lobe is 114BTDC is good. If it is 114 BTDC and 107 ATDC it is not so good. Too much advance gives more midrange and kills top end and to much retard does the opposite.

So what do we need to check the timing? One degree wheel, one dial gauge and some way of attaching it to the engine. One modified sparkplug to find top dead center. Feeler gauge to check valve clearance and finally time.

First thing to do is to find the Top Dead Center. This is done by inserting a modified sparkplug that is extended and will act like a piston stop. Install it, rotate the engine forward, read the angle on the degree wheel, rotate backwards. Read the angle on the degree wheel. Calculate how many degrees it is and divide by two to get the middle. If you get for example 329 degrees forward and 246 degrees backwards this will make the following. (329-236)/2=46,5  Now you turn the crank forward until the piston hits the stop. Adjust the degree wheel to 46,5 degrees. If you rotated then crank the opposite it will make contact 46,5 degrees Before Top Dead Center (BTDC) and indicate 313,5 degrees (360-46,5=313,5)

Piston Stop

Goes in here

Rotating Forward. Stops at 236 degrees

This is against the stop in FWD position

And this is against the stop the other way

Next step is to check the valve clearance at the opener. This needs to be used when you measure the cam shaft opening later. Install the dial indicator and position it so you can measure the valve opening. The best is if you have the adapter that fits on the closer shim. If you dont have one it normally works to put the dial indicator on the rocker. Now we are ready.

The left picture is with the adapter on the shim and the right is on the rocker. Using the rocker version is not perfect but it still works alright

Now it is just to start rotating and take readings. If you use the values in the manual it should be measured at 0.20mm opening. To find this take 0.20 minus your valve clearance. If your clearance is 0,07 mm you will check the degree wheel at 0,13mm (0,13+0,07=0,20). Now it is just to rotate the wheel and do the readings. If you go to far and miss the specific valve opening dont go back. Just continue to rotate and take the reading the next time it cams up. When I am finished with the check I always do the same but backwards. I only do this to make sure that the readings are correct. Normally it is 2-4 degrees different on rubberband Ducatis if you rotated the engine backwards. On Bevels I dont know.

To make the check easier I did an Excel sheet that I inserted all the values in. Click here to show. Values in purple are at 0,20mm lift according to the manual, Values in blue are at 1mm lift and yellow values are at Shearmans max opening of the valve. So now we have to think about what we have and what we want. I wanted to put my cams to the standard specification. As you can see the in the feld "Correction required for front Cam" the front cylinder opens 4,25 degrees to early and as you can see inte feld "Correction required for rear Cam" the rear cylinder opens 6,25 degrees to early. If we look at the 1mm opening in the blue feld for the front cylinder inlet  at Lobe center ATDC we have 94,5 degrees ATDC.  If I retard the front cam shaft 4,25 degrees to get to the specifications we will get 98,75 degrees ATDC. For the exhaust we have 111 degrees BTDC and if I retard it 4,25 degrees we will get 106,75 degrees BTDC. For the rear cylinder I will retared the cam 6,25 degrees and the inlet from 92,75 to 99 degrees ATDC. The exhaust will go from 113,25 to 107 BTDC. The cams will end up 98,75/106,75 for the front and 99/106,75 for the rear Remember that I earlier said that based on my own limited rubberband 2 valve experience  inlet should have a number that is between 5 and 12 degrees  lower then the exhaust. This will end up on 8 degrees that is spot on. So lets check out what we get the the Shearman way. That is the yellow one at the Excel sheet. When I took the readings I did not know at what opening I should do it so I did it at 0,05mm, 0,10mm, 0,15mm and 0,20mm just to see if it is any difference. I found it to be just about a degree difference or so we will look 0,10mm from fully open as it is a good average. Here are the values. Front cylinder Inlet, 87,75 ATDC, Exhaust 107 BTDC. Rear cylinder Inlet 85,25 ATDC and Exhaust 108,5 BTDC. After adjustment of the Camshafts we will end up at 92/102,75 and 91,5/102,25. If we calculate the cams the Shearman way we will get the following. Front 92+102,75/2=97,375. Rear 91,5+102,25/2=96,875. Then we should advance the cams 3-4 degrees acc to Shearman and Voila. We get 93,375/101,375 for the front and 92,875/100,875 for the rear. Lets say 93/101. We are 1,5 degrees out of his recomendations. Not bad. It looks to me like the standard timing ís not bad after all. The problem is that no bikes were delivered with timing set to the specifications. Now we just have to adjust the camshafts to the correct position.

Adjusting the Cam timing

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