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Discussion Starter · #1 · (Edited)
I am 99% sure that center line refers to the mid point of a cams duration. However it also gets tied to peak lift. This always gets my brain going as I would like to think that there are camshafts out there that the peak lift DOES NOT match up with mid point of duration. Either a steeper ramp to peak lift or a steeper ramp off peak lift could throw peak lift off of center line. However it would seem as though all camshaft specs, their center line is also peak lift. I plan to degree my cams by finding the mid point through valve open and close events, not by lift. But you could do lift as well if peak lift is indeed always center line. So is this the case? Is center line always peak lift and cam profiles are symmetrical? color copies online near me
 

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BATSLOMAN GIVES NO FUCKS.
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Centerline position is typically expressed in degrees relative to TDC, derived from an average of degree wheel positions 0.050" before and after peak lift.

Here is a really good video that explains this:



The centerline check is near the end of the video.

Keep in mind, this guy hits advertised centerline for his cam right off the bat. This is because he is doing this on an in-bore camshaft V8, where the distance between the cam and crank never change, therefore the timing marks on the crankshaft/camshaft sprockets will always line up in relation to TDC being 0 degrees.

This can change on our engines, where decking the head/block can change centerline relative distance to TDC. This is why it is critical after so much material removed from either block/head, that an adjustable cam gear set be used to bring TDC back to normal, and centerline back relative to TDC.

I guarantee if I took 0.010" off my head and block and tried to use a stock cam gear to find centerline, I would be at least a couple degrees off of advertised.
 

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A quick google search found a good post on the centerline method:


Intake Centerline Method
The intake centerline method finds the location of the intake lobe centerline relative to TDC. The recommended intake centerline is indicated on the cam card, and when correct it should yield the specified intake opening and closing points when you degree the cam. Finding the centerline is easy.

Rotate the engine clockwise until you find the maximum lobe lift, then zero the indicator. Now rotate backward about 0.100 to 0.150-inch to compensate for timing chain slack. Then rotate clockwise until you reach 0.050 inch. This is 0.050 inch before max lift.

Note the reading on the degree wheel. Then continue over the nose of the cam until you reach 0.050 inch again. This is the 0.050 inch after max lift. Note the degree wheel reading again. Now add the two readings together and divide by 2 to find the center line. It should match the cam card.

For example, if your numbers are 80 and 132:
(80 + 132) ÷ 2 = 106-degree centerline

The cam card indicates the correct installed intake centerline. If it calls for 106 degrees and you come up with 108 degrees, the cam is early and you have to retard it 2 degrees to bring it into spec. If you get 104 degrees the cam is retarded and you have to advance it 2 degrees to correct it. If you have degreed the cam with the intake centerline method, go back and check to see if the intake opening and closing points match those indicated on the cam card. If incorrect, determine the direction of error and reposition the cam accordingly.



Substitute "rotate counterclockwise" whereever it says "rotate clockwise", and "timing belt" for "timing chain lol.
 

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Brokedick Millionaire
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Centerline position is typically expressed in degrees relative to TDC, derived from an average of degree wheel positions 0.050" before and after peak lift.

Here is a really good video that explains this:



The centerline check is near the end of the video.

Keep in mind, this guy hits advertised centerline for his cam right off the bat. This is because he is doing this on an in-bore camshaft V8, where the distance between the cam and crank never change, therefore the timing marks on the crankshaft/camshaft sprockets will always line up in relation to TDC being 0 degrees.

This can change on our engines, where decking the head/block can change centerline relative distance to TDC. This is why it is critical after so much material removed from either block/head, that an adjustable cam gear set be used to bring TDC back to normal, and centerline back relative to TDC.

I guarantee if I took 0.010" off my head and block and tried to use a stock cam gear to find centerline, I would be at least a couple degrees off of advertised.
1/2 degree cam timing difference....
 

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1/2 degree cam timing difference....
Interesting, I didn't realize 0.020 will be that insignificant!

I have 0.020" off of mine from stock right now. Still pending time to do a proper degree session, so I'm honestly not sure how far it will be off, was thinking at least 1-2 degrees.

But only 1/2 a degree in your experience?
 

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Brokedick Millionaire
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the original .010" = a degree was off by a factor of Pi.
cam gear 38 teeth = 380 mm, divide that by 360 degrees.
 

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Brokedick Millionaire
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IIRC, one tooth = 9.75 degrees, one tooth is 10mm.

1/2 tooth timing issue between D15 (207mm) and D16 (212mm) deck heights difference of 5 mm = 4.75 degrees.

So if approx. 1mm = 1 degree, .020" = .5mm, aka 1/2 degree cam timing.

I used to be able to do all that mathing in my head, but since Dec 2017 major concussion, I can't most of the time.
 

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Brokedick Millionaire
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Oh shit! What happened man?
Major tumble down the stairs, ripped the hand railing out of the wall. Ended up in pile on the landing. Once I got up to my feet I took Advil and IB and went to lay on the couch for 2-3 days. Worse than any car crash I'd been in, and there have been a few I wasn't at fault. I was bruised in places I didn't think you could be.

Since that event, my grey matter hasn't been quite right and my fuse is shorter.
 
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