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

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 :)

X66 will you just align the dots and move on...............:lolhit:........my ADD cant comprehend posts of multiple paragraphs ....:D

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.

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. :picard1:

It's always a good idea to degree. Each piece could be off, crank, cam and each socket.

Plus degreeing verifies you assembled correctly.

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.

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).

His cam came out of my stock 1998 502 MPI. It’s definitely a factory Merc/GM cam.

Because it comes from Tom's motor, I trust him and my methods aren't perfect is why I'm going through all this. I need to correct my notes for next time.
The negatives are where I threw you I know. Intake was atdc and needs to be a negative. Minus a minus becomes a positive. That's why you see me write it one way in one formula and different in another. Confusing. You're right. I'm consolidating different people's methods until I've got it fine tuned. I'm pretty confident in my measurements and calculations now.
Thanks to everyone that stuck around and saw me through till I got it right. Not trying to close this down if anyone has anything to add.
Billk, still would live to see what you come up with.

I still say you are installed almost "straight up" rather than the +6 or +9 that Merc specs them. Again, I believe ICL of 109 is where it's "supposed to be".

https://cimg2.ibsrv.net/gimg/www.off...6f708c4abe.jpg

Let's say I was, and I probably am, how would you install the cam? I mean physically from step one. On mine everything except the timing set is stock. Dot to dot leaves me 2° retarded, it seems like I'd have to advance it back to where it caused all my problems to get the 109. Is that pic something you made using my measurements?

Those are your measurements.
If your measurements are accurate, then your cam is 1 degree advanced.

I keep reading that Merc specs that cam on a 109 ICL which is 5.5 degrees more advanced than you've got it.
Offset bushings (for the cam sprocket) can be used. A bushing that offsets the cam 2 degrees equates to 4 crank degrees..
Lower sprockets with multiple keyway can be used.

It doesn't hurt my feelings where you decide to put your cam,, but I do want you to be sure that you know where it is.

On a single engine cruiser, you don't really want to soften the midrange torque in exchange for a little more up top. Or at least I wouldn't think so.

Now, the way I understand it, you never knew where the cam was originally installed. This time you're gonna know exactly where it is.

I don't know if your heads are bolted down and torqued yet, but I do hope that once you get the cam where you want it, that you run clay snakes across a piston and bolt on a head (using an old gasket) install some lightweight testing valvesprings, oil up and bleed the lifters and drop em in, pushrods, zero lash the rockers and slowly turn the motor over at least 2 full rotations. Watch the lifters and make certain that they don't collapse any (which is the reason you use test springs and bleed the air out of the lifters..).
Then (and only then) will you know your true piston to valve clearance when you measure the thin sections of the smashed clay snakes.

Great info ^^^^^

My goal is to install it correctly. If it's supposed to be an ICL of 109°, that's where I want it. My problem right now is wrapping my head around the fact that as it stands now I need to install it so far advanced from dot to dot. I get stacking tolerances and poorly made parts will cause you to have to move things around a little, but 8°? Is it me or does that sound like a ton?
I just got my head back last night with a new valve seat. They won't go back on permanently until I get this right and I've checked the PTV correctly.
So for me to move the ICL from where it is at 114.5° to 109°, am I correct in saying I need to move my adjustable crank sprocket another 5.5° advanced? That would have me putting it at 8° how it's marked.


https://cimg3.ibsrv.net/gimg/www.off...c6db4bccd2.jpg

I would think as long as you have the opening and closing events at .050 right you would be good to go. Then check the center line.

To add to my last post, this is what's confusing me with this cam. My Lunati cam was ground with 4° advance. I had to install it dot to dot. Not 4° advanced with the adjustable timing set.
here are my calculations when I did that. Cam card and my hand written notes. Where you see two numbers written for IVO etc, one is from the card and the other is my measurements.

https://cimg3.ibsrv.net/gimg/www.off...b348417d86.jpg
https://cimg8.ibsrv.net/gimg/www.off...2005cc0d1c.jpg

I put a Lunati hrdo roller in the 427 for the Vette, it was ground 4* advanced and I installed it straight up as per the instructions

Looking at your numbers you are very, very, very close. Your set up of the dial indicator could be off a little.

Exactly. No messing around with advancing the cam 4° further with an adjustable timing set. Is it just that Mercruiser grinds their cams differently?

I’m not being the voice of opposition here… more on the side of reason…

You’re making this too hard on yourself. That is a stock cam. Grab the stock timing set and put it in and go. Or install it dot to dot and zero and be done.

I completely understand the want to get the math right, but for your build having it advanced or retarded by a degree or two isn’t going to make any noticeable difference in how your engine performs. The season is going to be done soon… get your boat back together. You said you got two other cores to play with. I’d mess around with cam math on those instead of delaying with your boating time.

Just some helpful advice. :ernaehrung004:

TZ

[QUOTE=TomZ;4802522]I’m not being the voice of opposition here… more on the side of reason…

You’re making this too hard on yourself. That is a stock cam. Grab the stock timing set and put it in and go. Or install it dot to dot and zero and be done.

I completely understand the want to get the math right, but for your build having it advanced or retarded by a degree or two isn’t going to make any noticeable difference in how your engine performs. The season is going to be done soon… get your boat back together. You said you got two other cores to play with. I’d mess around with cam math on those instead of delaying with your boating time.

Just some helpful advice. :ernaehrung004:

TZ[/QUOTE

yep see post 3............:D

I hear you guys and can appreciate what you're saying, but if I did that I'd have been 8° retarded right? Not a degree or two. She's not going back together until I figure out the right answer.
It's more important to me in the long run to get this figured out right than to get it back together.

Id go get a stock timing set put it in and recheck your events,

Tom paid you to say that didn't he? LoL I have a couple that I can throw in it.

Someone give me a quick summary. Too much reading.

Why can’t this cam be installed 109 icl (6* advance) to 111icl (4* advance)

mcollister explained how snd why to do it real well

i lose attention to long posts. Be easy on me :)

I missed the Evelyn Wood speed reading course........:readinghelp:

I don't think anybody said it couldn't. It's the why it's not at approximately the correct or at exactly the correct advance when it's dot to dot like other cams.

I’ve run into many that aren’t where they should be.

Even pre internet was common knowledge to degree in cams. I would say most that are off, are retarded. OE’s loved cams in retarded * positions. Smoother idle and emissions I guess.

Most off the shelf performance cams are ground 4* advanced for a reason.

Cool. So I guess that's really the answer I've been looking for. I'm going to throw a stock timing set in from one of my other blocks for SnGs and to double check it against my a/m one. If it's retarded like I think it'll be, I'll put my a/m set back in at 8° advance which is really 6° or 7° and check it.
Thanks again for everyone's input.

OP. taking about advance and retarding cams, you may believe the below quote of myself is interesting. Take a look at the flat tappets:


​​​​​​​

edit: I was wrong. Close, but different. They did use the same cam as the one before and just advanced it though. Is that what you were pointing out?

If I recall, you are putting together an L29, correct?
If they are factory GM L29 valvesprings, please do:
1) measure the installed height of the spring (telescoping gauge between the retainer and the spring seat.
2) take a few springs to somebody with a spring checker and find out the spring pressure AT THAT COMPRESSED HEIGHT.
3) smash it another .490" and take note of the pressure AT THAT HEIGHT as well.

L29's came in trucks with straight springs and later conical or beehive springs, neither of which are considered performance springs.

I would want to see 90 lbs on the seat (usually at 1.88" ht) and over 300 lbs at max lift.

Right. It's an L29 including the heads which are 297s. When I had the engine machined, I also had the machinist check the springs. They're the ones that came with the cam. They spec'd out well.

Here are the numbers:
145# @ 1.88"
360# @ 1.297"
Coil bind 1.130"

When I built the heads, I measured the valves and used shims to get everything in spec. I set them at 1.88". I also removed the rotators and cut them for posilocks at the same time.
If I were building this for a car, I never would have gone with a used cam and springs. After this whole debacle I'll never use a used cam again though...

https://cimg1.ibsrv.net/gimg/www.off...fc31e3286f.jpg
https://cimg9.ibsrv.net/gimg/www.off...8c4ccb589b.jpg
https://cimg5.ibsrv.net/gimg/www.off...5d39aa414d.jpg
https://cimg3.ibsrv.net/gimg/www.off...a77f485ec7.jpg

What’s wrong with the used cam ?

Nothing physically. It's just been all the problems I had with not having a cam card. Now that I know all the specs for a 1622, it wouldn't bother me to use a good one of those again.

If you bought that cam new, it would not have come with a cam card; t's OEM. The cam is within the OEM tolerances. You're so deep in trying to figure out a detail that doesn't really matter for what you're doing, that you're missing the forest for the trees at this point.

You've made this much more complicated than it needs to be. And there is nothing wrong with that cam.

I wouldn't have bought a factory cam new. I don't understand how you think these details aren't important. If I had thrown it in dot to dot and been done with it I'd be 6-7 degrees retarded. How is that ok? Seriously. If I'm in error tell me. I told you from the minute I started screwing with it that I didn't think there was anything wrong with your cam. Don't think for a minute I think there is.
What's made this difficult is me doing something wrong and trying to learn from it. From this **** up I've learned a ton more that I thought I already knew.

Here’s my 2 reasons for telling you to put it in 109-111 icl.

#1: you have been using a degree wheel kit and are using a multi keyway timing set. So why wouldn’t you install it for better midrange power even if not a set world on fire difference? But there will be a difference.

#2: see #1

What movie was this ? “The resistance runs strong.”

I agree. This whole thing has been painful.

Lololololol Oh well.