degreeing a slant camshaft with no cam card

[1930]

Has anyone here ever figured out how Chrysler originally measured their cams for the slant engines, what was their standard? I have what little specs they give me in the FSM but they are still useless to me ( as far as I know ) unless I have a baseline.

At this point the standard @ .020 measurement would be the closest I have come and would mean the stock cam in my un-touched slant engine is 3 degrees retarded.

Dont know if they retarded the cams upon installation in 83 and even if so by how much.

At this point these are the only specs I have avail to me

 

[krazykuda]

You have all the information that you need right there.


Intake:

6+180+42 = 228°

228/2 = 114°

114-6 = 108°

So your intake centerline is: 108°


Exhaust:

36+180+12 = 228°

228/2 = 114°

114-36 = 102°

Exhaust centerline = 102°


Lobe center = 108+102/2 = 210/2 = 105°


Overlap:

6+12 = 18°

Here you are:

IVO = 6°
IVC = 42°
EVO = 36°
EVC = 12°
Overlap = 18°
Intake Centerline = 108°
Exhaust Centerline = 102°
Lobe center = 105°

 

[1930]

You have all the information that you need right there.


Intake:

6+180+42 = 228°

228/2 = 114°

114-6 = 108°

So your intake centerline is: 108°


Exhaust:

36+180+12 = 228°

228/2 = 114°

114-36 = 102°

Exhaust centerline = 102°


Lobe center = 108+102/2 = 210/2 = 105°


Overlap:

6+12 = 18°

Here you are:

IVO = 6°
IVC = 42°
EVO = 36°
EVC = 12°
Overlap = 18°
Intake Centerline = 108°
Exhaust Centerline = 102°
Lobe center = 105°

I do not understand some of this above but I need to figure it out and am going to work on doing so.

Where did you get the 180 from, is that degrees or half a camshaft or what?

 

[krazykuda]

Where did you get the 180 from, is that degrees or half a camshaft or what?

The intake and exhaust open/close specs are given before tdc or after bdc.

If you map out the cam, you see that the Intake valve opens at 6° before TDC and closes at 42° after BDC. There is 180° of rotation to get from TDC to BDC. So you take the intake open and intake close specs and add 180 to it to get the duration.

6 + 180 + 42 = 228°


This also matches the spec for intake valve duration.

Now to find the centerline of the intake valve, divide the duration in half and subtract the intake valve open point.

228/2 = 114°


Now subtract the intake valve open point:

114-6 = 108°


This is 108° AFTER TDC.

To find the intake open, you have to convert 108° AFTER TDC to define it to BEFORE BDC. To do this, you just subtract the intake centerline from 180°:

180-108 = 72°

So now the intake valve is open for 72° BEFORE BDC, and you have to find out when it closes. Just subtract the before BDC number from half the intake duration:

114-72 = 42° AFTER BDC

The same applies for the exhaust side....


Once you find the intake and exhaust lobe centerlines, you then calculate the lobe centers (how far apart the exhaust valve centerline is from the intake valve centerline). To do this, you just add the two centerlines together and divide by two (the crank spins twice as fast as the cam).


Overlap is simply the intake open point plus the exhaust close point. In this case:

6+12 = 18°


Hopefully you can follow this. Ask if you need more explaination...

 

[1930]

The intake and exhaust open/close specs are given before tdc or after bdc.

If you map out the cam, you see that the Intake valve opens at 6° before TDC and closes at 42° after BDC. There is 180° of rotation to get from TDC to BDC. So you take the intake open and intake close specs and add 180 to it to get the duration.

6 + 180 + 42 = 228°


This also matches the spec for intake valve duration.

Now to find the centerline of the intake valve, divide the duration in half and subtract the intake valve open point.

228/2 = 114°


Now subtract the intake valve open point:

114-6 = 108°


This is 108° AFTER TDC.

To find the intake open, you have to convert 108° AFTER TDC to define it to BEFORE BDC. To do this, you just subtract the intake centerline from 180°:

180-108 = 72°

So now the intake valve is open for 72° BEFORE BDC, and you have to find out when it closes. Just subtract the before BDC number from half the intake duration:

114-72 = 42° AFTER BDC

The same applies for the exhaust side....


Once you find the intake and exhaust lobe centerlines, you then calculate the lobe centers (how far apart the exhaust valve centerline is from the intake valve centerline). To do this, you just add the two centerlines together and divide by two (the crank spins twice as fast as the cam).


Overlap is simply the intake open point plus the exhaust close point. In this case:

6+12 = 18°


Hopefully you can follow this. Ask if you need more explaination...

You are amazing and your time is appreciated.

I am working on a graph right now in another window that will help me to understand all of this better. Will post the image when I am thru.

 

[1930]

The intake and exhaust open/close specs are given before tdc or after bdc.

If you map out the cam, you see that the Intake valve opens at 6° before TDC and closes at 42° after BDC. There is 180° of rotation to get from TDC to BDC. So you take the intake open and intake close specs and add 180 to it to get the duration.

6 + 180 + 42 = 228°


This also matches the spec for intake valve duration.

Now to find the centerline of the intake valve, divide the duration in half and subtract the intake valve open point.

228/2 = 114°


Now subtract the intake valve open point:

114-6 = 108°


This is 108° AFTER TDC.

To find the intake open, you have to convert 108° AFTER TDC to define it to BEFORE BDC. To do this, you just subtract the intake centerline from 180°:

180-108 = 72°

So now the intake valve is open for 72° BEFORE BDC, and you have to find out when it closes. Just subtract the before BDC number from half the intake duration:

114-72 = 42° AFTER BDC

The same applies for the exhaust side....


Once you find the intake and exhaust lobe centerlines, you then calculate the lobe centers (how far apart the exhaust valve centerline is from the intake valve centerline). To do this, you just add the two centerlines together and divide by two (the crank spins twice as fast as the cam).


Overlap is simply the intake open point plus the exhaust close point. In this case:

6+12 = 18°


Hopefully you can follow this. Ask if you need more explaination...

Maybe a stupid question but does this always match the spec for the intake valve duration? Quote: This also matches the spec for intake valve duration.

 

[1930]

Quote: Now to find the centerline of the intake valve, divide the duration in half and subtract the intake valve open point............End quote

I know we do want to know the valve centerline but dont we want to know the centerline between the intake and exhaust lobe or am I mistaken? I have not read that we need to find the intake valve centerline ( again unless I am mistaken ) ( again )

EDIT: Ok I need to spend more time on what info you have given above before I ask you to answer any more questions. Thanks

 

[krazykuda]

Quote: Now to find the centerline of the intake valve, divide the duration in half and subtract the intake valve open point............End quote

I know we do want to know the valve centerline but dont we want to know the centerline between the intake and exhaust lobe or am I mistaken? I have not read that we need to find the intake valve centerline ( again unless I am mistaken ) ( again )

Yes, you want to know the centerline between the intake and exhaust lobe. That is called the "lobe center" and I described finding it above.

Just add the intake valve centerline with the exhaust valve centerline and divide by two (the crank turns 2x faster than the cam).


Study up and figure out what you can from my above post and then ask any questions after you have had time to think about it a little. I will try to explain it as simply as I can.

 

[krazykuda]

Here are a few drawings that may help you figure it out:

Intake:

View attachment Intake valve A01 B2.jpg

Exhaust:

View attachment Exhaust valve A01 B2.jpg

 

[1930]

Here are a few drawings that may help you figure it out:

Intake:

View attachment 1714734161

Exhaust:

View attachment 1714734162

Ok now I am a bit confused, this is as far as I have gotten so far but it looks like by your intake drawing ( didnt look at the exhaust yet ) that you are going in a CCW direction with your valve measurements.

See my drawing.......may not be legible enough

Red indicates intake valve opening of 6 degrees BTDC and intake valve closing at 42 degrees ABDC

Green indicates Exhaust valve opening @ 36 BTDC and closing @ 12 ATDC

EDIT: Yes looks like I am incorrect on my exhaust as well?

EDIT: ........I see, I did not think about this until now but when degreeing the cam we must always turn the crank in a CW rotation which of course would mean that on paper ( and the wheel ) the readings are going to show from left to right or CCW!

Very interesting and exciting stuff !! Thanks

Back to the drawing board on my graph I guess

EDIT: I thought looking at the degree wheel below that we had TDC ( upper top center.......... to the right was after TDC down to the 1st 90 ( 12 -3 ) degree mark and then between 3 oclock and 6 o clock was after BDC and then from 6-9 was after BDC and then from 9-12 was BTDC ( as it is )

Viewing this video [ame="https://www.youtube.com/watch?v=gqerHlVIqS4"]Camshafts (Part 2) - Characteristics of a performance camshaft - YouTube[/ame] ( and your comments ) as I have done a dozen times cleared that up for me now

So again with that in mind wouldnt my 42 Degree intake valve closing happen to the left of the BDC on the degree wheel you drew above since this is After BDC?

 

[1930]

Wouldnt this be more accurate for the intake and exhaust opening/closing points?

Red indicates intake green exhaust

I guess I am still off though cause you are in fact reading your wheel in a CW rotation according to the intake drawing above and it appears CCW according to your drawing above?

EDIT: I hope you can see where some of my confusion is coming from. Obviously with my drawing the exhaust valve ( for instance ) is not open 228 degrees.

 

[1930]

You show this as exhaust valve opens 36 degrees BDC= Before Bottom dead center in the text but drawing indicates 36 degrees after botom dead center.

FSM shows it as 36 degrees BTC= Before top dead center

Why?

 

[krazykuda]

Don't get confused by my drawings. they are not to be taken for direction of rotation, just to show graphically how the cam is mapped. This is how most manufacturers show cam information.

It is to show how far the valve is open.

 

[krazykuda]

You show this as exhaust valve opens 36 degrees BDC= Before Bottom dead center in the text but drawing indicates 36 degrees after botom dead center.

FSM shows it as 36 degrees BTC= Before top dead center

Why?

My drawing shows that the exhaust valve opens before Bottom Dead Center (BBDC). It opens 36° before it gets to BDC then stays open to TDC, then another 12° after TDC.


I think that you are confusing Bottom Dead Center (BDC) with Before Bottom Dead Center (BBDC).

There is Before Bottom Dead Center (BBDC) and After Bottom Dead Center (ABDC).


TDC it shown at the top of the drawing.

BDC is shown at the bottom of the circle.

 

[krazykuda]

Here's a few examples how the cam drawings illustrate the valve events. Don't pay attention to the numbers as they are not for your particular cam, but pay attention to the duration, lobe centerlines, and overlap. I tried to use the circle drawings as shown in the first two pictures, but trying to show only one valve at a time to try to keep the drawing less confusing.

View attachment Cam timing A01.jpg

View attachment Cam timing A03.jpg

Here's the other way that they show it:

View attachment Cam timing A02.jpg

View attachment compcams_overlap.jpg

 

[1930]

My drawing shows that the exhaust valve opens before Bottom Dead Center (BBDC). It opens 36° before it gets to BDC then stays open to TDC, then another 12° after TDC.


I think that you are confusing Bottom Dead Center (BDC) with Before Bottom Dead Center (BBDC).

There is Before Bottom Dead Center (BBDC) and After Bottom Dead Center (ABDC).


TDC it shown at the top of the drawing.

BDC is shown at the bottom of the circle.

I think some clarification/getting back to the basics might help. MY FSM reads

Intake opens ( BTC ) Does BTC stand for Before top dead center?

Intake closes ( ABC ) Does ABC stand for After bottom dead center ?

Exhaust opens ( BTC ) Does BTC stand for Before top dead center ?

Exhaust closes ( ATC ) Does ATC stand for after top dead center ?

Is the 4 relative corners I have printed on the degree wheel correct?

 

[krazykuda]

I think some clarification might help. MY FSM reads

Intake opens ( BTC ) Does BTC stand for Before top dead center?

Intake closes ( ABC ) Does ABC stand for After bottom dead center ?

Exhaust opens ( BTC ) Does BTC stand for Before top dead center ?

Exhaust closes ( ATC ) Does ATC stand for after top dead center ?

Is the 4 relative corners I have printed on the degree wheel correct?

Yes.

The factory manuals shorten the abbreviation and leave out the "D" for Top "Dead" Center and Bottom "Dead" Center. Then the first letter designates either BEFORE or AFTER.

ABC = After Bottom Center
BBC = Before Bottom Center

ATC = After Top Center
BTC = Before Top Center


Most of your statements above are correct accept the one for exhaust opens. Exhaust opens before BOTTOM CENTER, not TOP CENTER. BBC vs BTC. It gets more confusing when you try to shorten the abbreviation to three letters vs four.... :banghead:

 

[1930]

Yes.

The factory manuals shorten the abbreviation and leave out the "D" for Top "Dead" Center and Bottom "Dead" Center. Then the first letter designates either BEFORE or AFTER.

ABC = After Bottom Center
BBC = Before Bottom Center

ATC = After Top Center
BTC = Before Top Center


Most of your statements above are correct accept the one for exhaust opens. Exhaust opens before BOTTOM CENTER, not TOP CENTER. BBC vs BTC. It gets more confusing when you try to shorten the abbreviation to three letters vs four.... :banghead:

Thats bologna, why do they abbreviate it than BTC, that for me is Before Top dead center, but you are saying it should read BBC
​

 

[krazykuda]

Thats bologna, why do they abbreviate it than BTC, that for me is Before Top dead center, but you are saying it should read BBC
​

It could be a typo. It should be BBC.


My 68 manual shows BBC on Page 9-88 for the slant 6 camshaft exhaust open.

 

[1930]

It could be a typo. It should be BBC.


My 68 manual shows BBC on Page 9-88 for the slant 6 camshaft exhaust open.

I have a notion to contact Chrysler Corp and give them a piece of my mind, suggest they issue a recall or refund my money for the manual. That little typo has screwed me up bad for a long time now. :banghead:

 

[1930]

Ok I will start my drawing again and submit as far as I have gotten when I get to the point of getting stuck. Do you accept paypal

 

[1930]

Here is where I am at so far along with a few questions. When you have the time.

Quote: If you map out the cam, you see that the Intake valve opens at 6° before TDC and closes at 42° after BDC. There is 180° of rotation to get from TDC to BDC. So you take the intake open and intake close specs and add 180 to it to get the duration.

6 + 180 + 42 = 228°..........End quote

I am clear on this, and too add to it I am clear that valve duration is obviously how long the valve is open and yes this is the same spec that they give below of intake valve duration, you have shown me how they came to this conclusion.

_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


Quote: Now to find the centerline of the intake valve, divide the duration in half and subtract the intake valve open point.

228/2 = 114°


Now subtract the intake valve open point:

114-6 = 108°


This is 108° AFTER TDC. End quote..............

You say now to find the centerline of the intake valve.....would another way of putting it be now to find the center of the intake lobe?

You say this is 108 after TDC......why would we not start the degree count from the 6 degrees BTDC since that is where the valve starts opening? I understand that you say to withdraw the 6 degrees intake valve point but unclear why the intake valve/or is it lobe centerline would be at the 72 degrees BBDC location as apposed to the 78 BBDC position on the degree wheel?

Thanks

 

[krazykuda]

Quote: Now to find the centerline of the intake valve, divide the duration in half and subtract the intake valve open point.

228/2 = 114°


Now subtract the intake valve open point:

114-6 = 108°


This is 108° AFTER TDC. End quote..............

You say now to find the centerline of the intake valve.....would another way of putting it be now to find the center of the intake lobe?

You say this is 108 after TDC......why would we not start the degree count from the 6 degrees BTDC since that is where the valve starts opening? I understand that you say to withdraw the 6 degrees intake valve point but unclear why the intake valve/or is it lobe centerline would be at the 72 degrees BBDC location as apposed to the 78 BBDC position on the degree wheel?

Thanks

Yes, another way is to find the center of the intake lobe.

However, the lift of the valve is so slow at the peak of travel that it may be at "zero" for a few degrees and that may affect the accuracy of your measurement, that it's more accurate to measure intake open point and intake close point and take "the average" so to speak.

Another way is to use the @.050" method. This is where you find where the valve is open .050" in the up-stroke, and then the down-stroke and find the center. You can do this at any lift as long as both points are measured at the same lift value.


Now for your question, quote:

why would we not start the degree count from the 6 degrees BTDC since that is where the valve starts opening?

Because the engine cycle is defined by the crank position.

And different camshafts open at different points. They all don't open at 6 BTDC, so the common/more reliable reference is to reference from the crankshaft using TDC and BDC.

So by referencing off of TDC, you can compare cams "apples to apples" as the intake valve timing will not affect the reference position. Especially when you advance/retard the cam if you choose to.


Also, if the cam happened to be ground wrong, let's say like 3╖ off, your reference point will be off. Your duration will be the same, but you won't be able to catch that the lobe position is off in reference to the crank. By referencing the crank at TDC, you can catch if the cam was ground correctly or not.

 

[1930]

Yes, another way is to find the center of the intake lobe.

However, the lift of the valve is so slow at the peak of travel that it may be at "zero" for a few degrees and that may affect the accuracy of your measurement, that it's more accurate to measure intake open point and intake close point and take "the average" so to speak.

Another way is to use the @.050" method. This is where you find where the valve is open .050" in the up-stroke, and then the down-stroke and find the center. You can do this at any lift as long as both points are measured at the same lift value.


Now for your question, quote:

why would we not start the degree count from the 6 degrees BTDC since that is where the valve starts opening?

Because the engine cycle is defined by the crank position.

And different camshafts open at different points. They all don't open at 6 BTDC, so the common/more reliable reference is to reference from the crankshaft using TDC and BDC.

So by referencing off of TDC, you can compare cams "apples to apples" as the intake valve timing will not affect the reference position. Especially when you advance/retard the cam if you choose to.


Also, if the cam happened to be ground wrong, let's say like 3╖ off, your reference point will be off. Your duration will be the same, but you won't be able to catch that the lobe position is off in reference to the crank. By referencing the crank at TDC, you can catch if the cam was ground correctly or not.

Alot of this is starting to make sense, some of it I have to work harder at to understand.

I will continue to work at this and will continue to ask questions. Thanks very much

 

[moe7404]

and to think all i ever did was match the dots. JOKE, JOKE