Setting cams properly.
Posted: Sat Feb 16, 2008 10:11 am
I finally had my 3liter 12v cams made and I couldn't wait to put them in. Well, found some time, took the Motronic cams out and in went the 11.8mm jobs. I had specified 110* lobe centers and I installed them lining up the marks with the corresponding marks on the bearing caps like any Alfa mechanic or DIY would do. Good thing I wanted to be thorough...I decided to do it properly and mounted a dial indicator with a special long tip resting on the follower, a protractor attached to the cam hub and a pointer (see pic below). After adjusting and zeroing the pointer on the protractor (lobe full lift) I checked the lobe centers...98* instead of 110! Both cams were off by 12*!!! Since I have slotted the hubs to make them adjustable, I easily set the cams where they should be. Most definitely, setting at the actual marks and starting the car would result in many bent valves with these high performance profiles having pronounced lift at around TDC.
Its not the first time I find cams with wrong timing marks. The moral of the story is: whatever performance cams you buy, doublecheck the actual timing; do not rely on what you see and trust no-one! In any case, do the make or break test (literally!): when you're finished with everything, bring the engine to TDC overlap and check valve/piston clearance by jamming a screwdriver under the cam, pushing down on the follower until you feel it stop (piston/valve contact). Do this for cylinders 1 and 5 as you can see the TDC mark on the crank pulley. You must have at least 1.5mm intake and 2mm exhaust travel. Its your money you're playing with so take care, these can be very expensive oversights!
Jim K.
Its not the first time I find cams with wrong timing marks. The moral of the story is: whatever performance cams you buy, doublecheck the actual timing; do not rely on what you see and trust no-one! In any case, do the make or break test (literally!): when you're finished with everything, bring the engine to TDC overlap and check valve/piston clearance by jamming a screwdriver under the cam, pushing down on the follower until you feel it stop (piston/valve contact). Do this for cylinders 1 and 5 as you can see the TDC mark on the crank pulley. You must have at least 1.5mm intake and 2mm exhaust travel. Its your money you're playing with so take care, these can be very expensive oversights!
Jim K.