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Camshaft question
https://slantsix.org/forum/viewtopic.php?t=55813		 Page 1 of 3
Author:  1930 [ Sat Jul 19, 2014 1:29 pm ]
Post subject:  Camshaft question
I have two slant engines that @.006 the degree wheel reads 6 degrees BTDC. Image

I also have one ( my newly re-built engine ) that reads @.006 11.5 degrees BTDC.

I have no choice but to assume at this point that would mean that the newly re-built engine is showing 11.5 BTDC cause the cam is retarded 5 1/2 degrees.

I dont have the timing covers off of any of these engines at this point but is there a way to say how many teeth that this might be off on the sprocket?

Too correct this would it mean leaving the crankshaft where it is and moving the cam and how is this typically done with a standard timing set that has no multiple keyways? I have read about drilling and inserting a cam bushing but have not seen any pictures of what all this looks like and am not positive that this is the only method.

Maybe that 5.5 degrees is a very minute amount when looking at the overall picture and isnt something that should be concerned with but if Im correct this would mean that the engine would be firing 5.5 degrees before it is supposed too which would mean if I were ( for instance ) reading 10 degrees ATDC on the timing gun I was actually only reading 4.5? Does this sound correct?

Sounds like sort of a big deal too me. The more I think about it the more it seems to me that this would make for a sluggish, hard to start engine.

Would that amount have affected engine vacuum to any large degree?

Thanks
Author:  Reed [ Sat Jul 19, 2014 1:31 pm ]
Post subject: 
What lobe are you measuring and what event are you measuring occurring at .006 lift at 6 degrees BTDC?
Author:  1930 [ Sat Jul 19, 2014 1:41 pm ]
Post subject: 
Quote:
What lobe are you measuring and what event are you measuring occurring at .006 lift at 6 degrees BTDC?
Intake lobe/intake opening

Measuring the intake opening lobe at .006 rise
Author:  Reed [ Sat Jul 19, 2014 1:59 pm ]
Post subject:  Re: Camshaft question
Quote:
I have two slant engines that @.006 the degree wheel reads 6 degrees BTDC.

I also have one ( my newly re-built engine ) that reads @.006 11.5 degrees BTDC.

I have no choice but to assume at this point that would mean that the newly re-built engine is showing 11.5 BTDC cause the cam is retarded 5 1/2 degrees.
No, advanced 5.5 degrees. The further before TDC the valve event occurs, the more "advanced" the cam is. Making the event happen later in relation to TDC "retards" the cam event.
Quote:
I dont have the timing covers off of any of these engines at this point but is there a way to say how many teeth that this might be off on the sprocket?
Not without pulling the timing covers. The degree wheel reads degrees of crank position. The crank turns 1/2 half as fast as the cam.

To find the degrees of crank rotation per crank gear tooth, count the number of teeth on the crank gear and then divide 360 by that number. The result is the number of crank degrees each tooth represents.

To find the degrees of crank rotation per cam gear tooth, count the number of cam gear teeth and divide 180 by that number. The result is the nuber of crank degrees of rotation each cam gear tooth represents.
Quote:
Too correct this would it mean leaving the crankshaft where it is and moving the cam and how is this typically done with a standard timing set that has no multiple keyways? I have read about drilling and inserting a cam bushing but have not seen any pictures of what all this looks like and am not positive that this is the only method.
It is pretty much the only way to do it, other than doing some carful measuring and drilling a second cam dowel locating pin. The operation is simple. Order a set of cam advance bushings and drill out the cam locating dowel hole in the cam gear to the size required for the advance/retard bushing. Install the bushing you want (they come in 1/2 degree increments up to around 10 degrees) in the correct orientation and bolt it all back together.
Quote:
Maybe that 5.5 degrees is a very minute amount when looking at the overall picture and isnt something that should be concerned with
No, it is worth worrying about.
Quote:
but if Im correct this would mean that the engine would be firing 5.5 degrees before it is supposed too which would mean if I were ( for instance ) reading 10 degrees ATDC on the timing gun I was actually only reading 4.5? Does this sound correct?
No. What you are measuring is when the intake valve starts to open in relation to the piston reaching TDC. Advancing and retarding the cam changes the valve events in relation to the piston travelling up and down in the cylinder bore. Advancing the cam makes the intake and exhaust valves open sooner, retarding the cam makes the intake and exhaust valve events happen later.

Camshaft advance has absolutly nothing to do with timing advance or base timing setting since the engine is timed in relation to the timing marks on the crank mounted vibration dampener.
Quote:
Would that amount have affected engine vacuum to any large degree?
Yes.

Generally, advancing a cam increases low RPM torque at the expense of high RPM horsepower. In your truck you want as much low RPM torque as you can get, so I say leave the newly rebult engine alone with the intake valve beginning to open at 11.5 BTDC.

Are these all stock cams? What are the advertised durations, lobe separations, and lift specifications of the cams?
Author:  1930 [ Sat Jul 19, 2014 2:03 pm ]
Post subject: 
Just to clarify this is how I am taking my readings Image
Author:  Reed [ Sat Jul 19, 2014 2:12 pm ]
Post subject: 
I can't tell- is there a lifter in the block and you are reading off the lifter or does the plunger on the bottom of the dial gauge ride directly on the cam? Normally a lifter is in place and the dial gauge rides in the cup for the pushrod in the top of the lifter.
Author:  1930 [ Sat Jul 19, 2014 2:24 pm ]
Post subject: 
Quote:
I can't tell- is there a lifter in the block and you are reading off the lifter or does the plunger on the bottom of the dial gauge ride directly on the cam? Normally a lifter is in place and the dial gauge rides in the cup for the pushrod in the top of the lifter.
I am reading off this tool that I made. Hard too see in the pic maybe cause I painted one end ( the big end ) black so that it would be easier to identify. Image
Author:  1930 [ Sat Jul 19, 2014 2:29 pm ]
Post subject: 
I was going to question you on this cause it did not make any sense but now that I worked it out with the crayons it makes perfect sense that as the engine is turning clockwise 11.5 would mean that it was firing earlier which means in this case advanced.

Thanks




Image
Author:  Reed [ Sat Jul 19, 2014 2:29 pm ]
Post subject: 
OK, that should work just fine. Looks like you have the correct method of meauring.
Author:  1930 [ Sat Jul 19, 2014 2:40 pm ]
Post subject: 
Everything else you said makes perfect sense to me now, yes they are stock cams, I am still working on getting all of the specs in order.

At this point I am still working on trying to determine a way to say for sure where the cam is located in relation to the crankshaft and how that corresponds with the cam numbers I have from my factory service manual.

At this point it has been determined by those with more experience than I that without knowing what the original standard of measurement was for the cams that it is impossible to degree in the cams properly.

For now I am left with comparing two other slant engines that as far as I know are stock/untouched to determine whether or not the cam that is in my newly re-built engine is where it is supposed to be. ( or not )

You are telling me that the 5.5 degrees advance is a good thing so what can I say at this point.

I do understand from what I have read that these cams like a 4 degree advance for good low end torque.

Thank-you for your experience once again
Author:  Rick Covalt [ Sat Jul 19, 2014 2:43 pm ]
Post subject: 
Quote:
What are the advertised durations, lobe separations, and lift specifications of the cams?
I was going to ask if you have a cam card and what does it tell you about where it is supposed to be. I have never measured mine to .006 lift, always to max lift.

Rick
Author:  1930 [ Sat Jul 19, 2014 2:45 pm ]
Post subject: 
Quote:
Quote:
What are the advertised durations, lobe separations, and lift specifications of the cams?
I was going to ask if you have a cam card and what does it tell you about where it is supposed to be. I have never measured mine to .006 lift, always to max lift.

Rick
I do not have a cam card, all I have are these measurements given to me from my FSM Image

And I have mapped out the two un-touched engines at several different points to compare with my re-built engines camshaft.

Image

I do not still at this point know how to use any of these numbers to tell me how I can see if the cam in my re-built engine is in correct time with the crank so as mentioned all I can do at this point is compare some of these measurements between the 3 engines.
Author:  Reed [ Sat Jul 19, 2014 2:47 pm ]
Post subject: 
Happy to help. For what it is worth, the slant six in my brother's 1983 van is running a stock 1983 hydraulic cam that it 8 degrees advanced and the motor runs great and has 21 inches of vacuum at idle.

From the 1983 Factory Service Manual for a Dodge van, the hydraulic cam events are as follows:

Intake valve opens 6 degrees BTDC
Intake valve closes 42 degrees ATDC
Exhaust valve opens 36 degrees BTDC
Exhaust valve closes 12 degree ATDC

Valve overlap = 18 degrees
Intake duration = 228 degrees
Exhaust duration = 228 degrees

Looking at that, I say your non-rebuilt slants look fine and the rebuilt slant lookes like it has been set up for a little more low-rpm power. Leave them all alone and you will be good.

EDIT- looks like you already knew all this. I still say those cams are installed fine. I surmise that the factory used the .006 lifter movement as the measuring point for cam timing events. I read somewhere that .006 is the ASE standard measuring reference.
Author:  1930 [ Sat Jul 19, 2014 2:50 pm ]
Post subject: 
Quote:
Happy to help. For what it is worth, the slant six in my brother's 1983 van is running a stock 1983 hydraulic cam that it 8 degrees advanced and the motor runs great and has 21 inches of vacuum at idle.

From the 1983 Factory Service Manual for a Dodge van, the hydraulic cam events are as follows:

Intake valve opens 6 degrees BTDC
Intake valve closes 42 degrees ATDC
Exhaust valve opens 36 degrees BTDC
Exhaust valve closes 12 degree ATDC

Valve overlap = 18 degrees
Intake duration = 228 degrees
Exhaust duration = 228 degrees

Looking at that, I say your non-rebuilt slants look fine and the rebuilt slant lookes like it has been set up for a little more low-rpm power. Leave them all alone and you will be good.
I know this should be good news but I was hoping to find something way off explaining the poor vacuum issue I was having I.E 13 at idle off the manifold.
Author:  Reed [ Sat Jul 19, 2014 2:55 pm ]
Post subject: 
Quote:
I know this should be good news but I was hoping to find something way off explaining the poor vacuum issue I was having I.E 13 at idle off the manifold.
(1) vacuum leak
(2) timing way off
(3) some other vacuum related issue

Have you verified that the timing mark on the vibration damper you are using is accurate? It doesn't matter if it is new. I have purchased brand new dampers only to measure them and find that the timing mark was 4 degrees off.

Have you verified that all vacuum hoses are routed correctly? PCV valve in good shape? Choke pulloff vacuum diaphragm still holding a vacuum? All ports on the carb that should be capped ARE capped?

Does the truck have power brakes? Have you done a vacuum reading with the brake booster disconnected and the line to the booster plugged? Boosters can fail in ternally and booster check valves can also fail.

Just a quick check- you are setting yout timing in degrees BTDC, not ATDC, right? That is the kind of mistake I would make (and have made), which is why I ask.
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