Camshaft 101

saturn
vue

#1

Installing timing belt on my dohc motor.
Cyl 1 is at TDC.
But I see that cam 1 which is exh cam, FYI, is under tension trying to open/close valves on cyls 3 or 5.
Is that fairly common on most multi cam ohc motors?
Cam 2 is also under tension but cams 3 and 4 are slack. They will stay in place
With no locking fixture required.
Are there ANY 4 cam motors that do not require locking cams in position during a belt change?


#2

I changed the timing belt on my 2005 DOHC V6 Camry without “locking cams in position” . . . that was a few years ago

3 liter 1MZ-FE


#3

hmm, 1mz-fe cam gears mesh together so maybe the twist from 1 cam is countered by adjacent cam?


#4

It IS dohc. You can tell from the shape and width of the valve cover. And if you’re still not sure, just pop off the valve cover. Please trust me, it is dohc

Just because there’s only one belt-driven cam sprocket per head doesn’t automatically make an engine sohc

Toyota is one of those manufacturers that has dohc heads, but only one cam is driven by the belt. The second cam is geared together with the first

Mazda also used a similar setup on some engines. dohc head, one cam driven by the belt, the other was connected to the first with a chain

Just goes to show there are almost countless ways to achieve something


#5

my car has 4 cams, 4 timing sprockets. the 2 cams on the rear head are trying to open valves when motor is at TDC. so, they do tend to try to rotate when you install the timing belt. you have to position each cam and lock them prior to belt installation.