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I was checking the cam timing this evening on my 3.0L build, and this is the first time I've done it, so bare with me.
I have found TDC no problem, have the cam wheel on, etc.
From TDC, with the cam gear aligned to it's reference mark, the first intake to open is cylinder 4. This is the one at the back of the engine (closest to the flywheel).
Did I f*ck something up? Is this normal? The crank key can't be 180 degrees off so I don't get it.
I expected that at TDC, with the cam set to it's reference mark, the first intake valve to open would be the 1st cylinder, closest to the front of the engine. Is that just a stupid assumption?
With the marks lined up for TDC, #1 cylinder is "about to fire" between compression and power strokes, and #4 is starting its intake stroke.
Sometimes they call it "#1 ignition top dead center"
Ah, thank god for that. I thought I was going nuts. I even mounted the rotor to figure out which plug was firing, and yeah, that lines up with what you said.
I'm having a hell of a time measuring cam timing without solid lifters. These lifters keep going soft even after I pump them up with a vacuum line. And I have a hard time getting a straight line on to the lifter itself from the cam housing.
That said, the timing seems way off. With the webcam, I'm supposed to see intake open at 5 degrees before TDC. It's happening several degrees after.
You need to check how much the #1 intake valve is opened when #1 is at non-firing TDC. Non-firing TDC will be when the cam gear mark is 180 degrees from the housing mark.
Pretty good write up here but his description of how the Variocam works is incorrect:
At TDC with the cam on the reference mark, the 4th cyl intake valve doesn't even begin to open until after I rotate the engine clockwise a degree or two.
Am I right in calling this *after* top dead center? If the intake is supposed to open before top dead center, I expect the intake valve to be open when the engine is AT TDC, correct?
15 after bdc should be 195, no?
lifters don't collapse that far.
your cam is obviously advanced 1 tooth/9 degrees by the picture above.
correct that and re-measure.
also, are the published webcam numbers advertised duration or at 0.040/1mm or 0.050"?
can be huge variations in measured duration depending on your gauges.
like my reground stock 944S cams, webcam's card says around 266 degrees seat to seat (advertised duration) but per the WSM specs at 1mm lift they are like 216.
you sure that's not intake open 11 before TDC?
maybe there is some variance of the lifters here.
lifter not pumped could mean cam has to turn more to make the lifter move enough to lift valve.
Yeah, positive the intake is opening well after TDC with this set up. That's why I thought I might have to advance the gear by a tooth, it's so far off. I can watch the valve opening well after the piston has started to move down. So, it may not be 11 degrees exactly, but it's very much after TDC.
But it's not as simple as advancing the timing as the duration is way off, which is why advancing the timing *really* pooches intake closing.
I really wish I had the ability to construct a solid lifter at the right height for this measurement.
But yeah, with a collapsed lifter, the valve is going to take longer to open. 16 degrees seems excessive however.
It would also mean the valve doesn't stay open for as long. In my case, it's closing 13 degrees earlier than it should.
I'm not sure why those numbers don't match. I have to assume it has something to do with lobe angles being different. But no idea.
02-13-2017, 08:13 PM
Cam Timing Question
