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Cam degree calculation questions

Old 08-19-2021, 08:33 AM
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Default Cam degree calculation questions

Two questions for anyone that can help school me a little more on cams...

1. Why did I need to advance my stock mag roller cam 2* using an adjustable keyway timing set? A stock timing chain doesn't add 2* so does that mean they're all running retarded when they're installed dot to dot?

2.I'll post up my cam degreeing steps that I use. Would someone take a look at them and tell me if anything looks off?


1. Write down what is on the Cam Card so you can compare your numbers as you measure them and not destroy your original cam card.

2. Find True TDC by dial gauge or using piston stop.

3. Zero the degree wheel. Use the shortest pointer possible.

4. Install Lobe Lift tool with dial indicator and zero. #1 exhaust is the first cam lobe on the driver's side.

5. Turn crank clockwise until on the base circle of lobe. Zero dial indicator.

6. 1st Reading. Valve Opening @ .050 (lifter should be on base circle.)

a. Rotate engine clockwise.

b. Stop when the dial indicator reaches .050".

c. Look at the degree wheel. Write down the number. Opens. (black #s)



7. 2nd Reading. Max Lift:

Note: The dial indicator should be at .050" from the previous reading. It moved .050" from the base which means if you add another .050" it will equal one complete revolution or .100" on the dial indicator.

a. Rotate the crank clockwise.

b. Watch the dial indicator. The needle will stop and begin to go counterclockwise. In between that spot, take your reading and write it down. This is your lift. ie. .3675"

c. Multiply the lift from step 7b by your Rocker Arm Ratio. ie. .3675"x1.7=.62475" . This is Max Lift.

8. 3rd Reading. Exhaust Closing @ .050"

a. Rotate the crank clockwise.

b. The dial indicator needle will start to turn counterclockwise as the exhaust is closing. Keep track of the number of revolutions.

c. Stop when you get to .050" before the base. If you pass it, go back further than .050" and come back to .050".

d. Look at the degree wheel and write down the number. Valve Closes. (black #s)

9. 4th Reading. Duration @ .050".

a. Add your 1st and 3rd readings plus 180. (Open + Close + 180= Duration @ .050")

10. 5th Reading. Lobe Center Line.

a. Two readings are being taken. One reading on each side of the lobe at Max Lift measuring down .050".

b. Rotate the engine so the lifter is at max lift. Zero out the dial indicator.

c. Rotate the engine Counterclockwise one full dial indicator revolution or .100" to remove

timing chain slack.

d. Rotate the engine Clockwise to .050". Look at the degree wheel and write down the number. (white #s).

e. Rotate the engine Clockwise to max lift.

f. Rotate the engine Clockwise until the dial indicator reads .050". Look at the degree wheel and write down the number. (white #s)

g. Add the two numbers together from step 10 d and step 10 f. Divide answer by 2=Center Line of Lobe.



Remove the Lobe Lift Tool and dial indicator and move them to the other Lobe. Repeat steps 5-10 for Intake/exhaust.



Lobe Separation Angle: Once you have both the Exhaust and Intake readings, compute the Lobe Separation Angle.

a. (Center Line Exhaust + Center Line Intake)/2=Lobe Separation Angle.



Note: If your cam is off by a few degrees, you can adjust the position of the Crank Timing Gear Sprocket if you have an adjustable timing set.

IMPORTANT: The cam is connected by a 2:1 ratio sprocket. The cam only turns once to the cranks two turns. Two Crank degrees equals One Cam degree.


3.Can someone explain how to come up with the listed 109* ICL/122*ECL on the factory mag roller? I was calculating lobe c/l I thought.
I'm sure the cam is ok now, but I wanted to know for next time or where I'm speaking the wrong language/using a wrong formula.

My measurements/calculations:
Duration @ .050" (2* crank advance)
Intake -2+47+180=225*

Exhaust 49-5+180=224*

IVO -2*
EVO 49*

IVC 47*
EVC -5*

Valve lift .284"/.284"

Centerline
ECL (167+63)/2=115
ICL (63+167)/2=115
LSA 115*

If I calculate the ICL/ECL & LSA using the formula with measured duration 225/224 & Valve Opening I get the following:

ICL=(intake duration/2)-IVO
(225/2)+2=114.5

ECL=(exhaust duration/2)-EVO
(224/2)+5=117

LSA=(ICL+ECL)/2
(114.5+117)/2=115.75

Last edited by HawkX66; 08-19-2021 at 08:51 AM.
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Old 08-19-2021, 08:45 AM
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Originally Posted by HawkX66 View Post
Two questions for anyone that can help school me a little more on cams...

1. Why did I need to advance my stock mag roller cam 2* using an adjustable keyway timing set? A stock timing chain doesn't add 2* so does that mean they're all running retarded when they're installed dot to dot?
Possibly because the adjustable keyway set is not made properly ? Thats why we check them.

Originally Posted by HawkX66 View Post
2. Find True TDC by dial gauge or using piston stop.
Which method did you use ? The only correct method is using a piston stop.

Originally Posted by HawkX66 View Post
4. Install Lobe Lift tool with dial indicator and
zero.
Does you tool have two ends ? One rounded and the other flat ? You have to use the rounded end on roller cams. Even then if the diameter is not the same as your lifter wheel it can affect the readings some. You could try it with an actual lifter and see what you get.

Are you absolutely certain that the cam you have is what you think it is ? I actually have a 454 mag mpi on the stand right now but I dont have the pistons in it yet. I wasnt going to degree the cam because I am not changing anything in the valve train but because of this post I think I will Probably wont be till next week sometime though.

Dont have time to look at your other readings right now. Maybe later on this afternoon.

Just thinking out loud

Last edited by BillK; 08-19-2021 at 08:49 AM.
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Old 08-19-2021, 08:52 AM
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X66 will you just align the dots and move on.......................my ADD cant comprehend posts of multiple paragraphs ....
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Old 08-19-2021, 08:57 AM
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Originally Posted by BillK View Post
Possibly because the adjustable keyway set is not made properly ? Thats why we check them.



Which method did you use ? The only correct method is using a piston stop.



Does you tool have two ends ? One rounded and the other flat ? You have to use the rounded end on roller cams. Even then if the diameter is not the same as your lifter wheel it can affect the readings some. You could try it with an actual lifter and see what you get.

Are you absolutely certain that the cam you have is what you think it is ? I actually have a 454 mag mpi on the stand right now but I dont have the pistons in it yet. I wasnt going to degree the cam because I am not changing anything in the valve train but because of this post I think I will Probably wont be till next week sometime though.

Dont have time to look at your other readings right now. Maybe later on this afternoon.

Just thinking out loud
Thanks a lot Bill. Summit timing set is possibly off, but I'm not going to say that until someone who really knows what their looking at says it. I'm still going to say it was me if anything is wrong for now...
I used the piston stop.
I used the rounded end of the tool, not the squared attachment.
The cam was used, but came from a stock mag motor that someone is building. No reason to think it's anything other than what was claimed. It's stamped 1622 also.
I'll be real curious to see what you come up with when you degree yours. I think so many guys just take it for what it is and don't go through the full degreeing process.
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Old 08-19-2021, 08:59 AM
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Originally Posted by F-2 Speedy View Post
X66 will you just align the dots and move on.......................my ADD cant comprehend posts of multiple paragraphs ....
My ADD can't handle not knowing 100% of what the problem is!!! It's like this little itch in the back of my brain that won't go away. I'm not taking the short block apart again, so this is just for my own knowledge at this point... Bah! lol
BTW, you know what happened when I just aligned the dots! I was 2 degrees retarded. I know... 100% retarded at this point.

Last edited by HawkX66; 08-19-2021 at 09:01 AM.
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Old 08-19-2021, 09:59 AM
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It's always a good idea to degree. Each piece could be off, crank, cam and each socket.

Plus degreeing verifies you assembled correctly.
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Old 08-21-2021, 01:07 AM
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1- never put your indicator directly on the cam lobe. It will NOT move the same amounts as your lifter will due to the dramatically different contact face, and you will have parallax error with the degree wheel. Your dial indicator must measure the movement of a lifter, rocker, or spring retainer depending on exactly what you want to see. The lifter (with no pushrod installed) is the preferred measurement point, but if your motor has an intake on it, you can measure the spring retainer movement. Some motors (Chrysler LA) have terrible valvetrain geometry and different pushrod lengths and cam combos can shift the ICL around weirdly.
2 - On your measurements, I see an intake centerline of 112.5 (-2 + 180 + 47) = 225 2 = 112.5.
I see an exhaust centerline of 112 (49 + 180 -5) = 224 2 = 112.
Your lobe separation is 112.25 (112.5 + 112) 2.
Your cam is retarded 1/2 a degree..
With 1.73 rockers, your measured valve lift would be .491 (.284 x 1.73).

These numbers are in the ballpark for a 454 Mag, but it should show a 115 degree lobe separation.

So, double check your numbers. A 112 lobe separation is not a Merc mag grind..

As far as WHERE it should be installed,, the Merc Mag cams were 115 lobe separation installed 6 degrees advanced to yield a 109 degree intake centerline.

The only reasons you might want to run your cam straight up would be if you have too much dynamic compression and need to bleed pressure or if you want to lose some midrange punch and planing torque.




Last edited by mcollinstn; 08-21-2021 at 01:15 AM.
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Old 08-21-2021, 06:52 AM
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Originally Posted by mcollinstn View Post
1- never put your indicator directly on the cam lobe. It will NOT move the same amounts as your lifter will due to the dramatically different contact face, and you will have parallax error with the degree wheel. Your dial indicator must measure the movement of a lifter, rocker, or spring retainer depending on exactly what you want to see. The lifter (with no pushrod installed) is the preferred measurement point, but if your motor has an intake on it, you can measure the spring retainer movement. Some motors (Chrysler LA) have terrible valvetrain geometry and different pushrod lengths and cam combos can shift the ICL around weirdly.
2 - On your measurements, I see an intake centerline of 112.5 (-2 + 180 + 47) = 225 2 = 112.5.
I see an exhaust centerline of 112 (49 + 180 -5) = 224 2 = 112.
Your lobe separation is 112.25 (112.5 + 112) 2.
Your cam is retarded 1/2 a degree..
With 1.73 rockers, your measured valve lift would be .491 (.284 x 1.73).

These numbers are in the ballpark for a 454 Mag, but it should show a 115 degree lobe separation.

So, double check your numbers. A 112 lobe separation is not a Merc mag grind..

As far as WHERE it should be installed,, the Merc Mag cams were 115 lobe separation installed 6 degrees advanced to yield a 109 degree intake centerline.

The only reasons you might want to run your cam straight up would be if you have too much dynamic compression and need to bleed pressure or if you want to lose some midrange punch and planing torque.
Thanks alot for the info. I'm going to have to go through piece by piece and see why my numbers don't jive with yours.
As far as your comments in #1 about the indicator, I'm using a lobe lift tool. The indicator is never riding on the cam lobe by itself.

Isn't Intake Lobe Centerline calculated by dividing the duration by two and subtracting the IVO? The ECL should be duration divided by 2 minus EVC right?

ICL (225/2)+2=114.5
​​​​​​ECL (224/2)+5=117.
LSA (117+114.5)/2=115.25

ICL 6 deg adv 114.5-6=108.5
ECL 6 deg adv 117+6=223

Max lift .284 x 1.7 = .4828"

The ICL is off 1/2 and ECL 1. For my purposes I'm just going to chalk that up to either my measurements or more likely now, cam grind variations. Either way I'm not going to sweat it for my purposes.

The weird thing in all this is when I have a new cam with a cam card to compare my numbers to, I don't have all these problems degreeing.
Last thing. Are the cams installed 6 deg or ground 6 deg advanced? I know guys aren't using adjustable timing sets and installing them 6 deg adv right? I'm sure most are going dot to dot and calling it a day.

Last edited by HawkX66; 08-21-2021 at 09:21 AM.
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Old 08-21-2021, 10:26 AM
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Depends.
using + and - on valve events can cause confusion. It is always more "accurataccand prevents confusion and math errors to list them as

X degrees BTDC
X degrees ATDC
X degrees BBDC
X degrees ABDC

Here's my math from your numbers. Correct me where I'm misinterpreting your readings.

your intake opens at 2 ATDC (START COUNTING)
turn 178 to BDC
It closes at 47 ABDC

That is 178 + 47 = 225 duration.
centerline would be 112.5 + 2 = 114.5 ICL

your intake opens at 2 BTDC
Turn 180 to BDC
it closes at 47 ABDC

That is 2 + 180 + 47 = 229 duration
Centerline would be 114.5 - 2 = 112 5 ICL

As far as how cams are ground, and how timing sets are marked, I've seen them every way imaginable.

If you use a mercruiser part number cam and a mercruiser part number timing set, you MAY be safe to install straight up,, but I've even caught that kind of stuff being off (due to supplier changes).

My rule of thumb..
If it is a Japanese/Korean/German car, and you are using oem parts,, then trust the marks..
If it is ON or FOR an American auto engine,, then pull out the piston stops (for the TDC mark on the balancer), the degree wheel,, and the indicator (for the valve timing).
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Old 08-21-2021, 10:49 AM
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His cam came out of my stock 1998 502 MPI. Its definitely a factory Merc/GM cam.
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