Degreeing in 40/80 cam shafts

[jon8christine]

Ok, finally got the valves all shimmed for the new 40/80 cam shafts from Vicks. They call for .014 intake and .016 exhaust. For degreeing the cams you just leave it shimmed for running right?

Checked valve clearance using clay method and am all good there with Vicks 8mm dome pistons (plus 100 thou).

Time to degree in the cams. I set my pointer and printed out degree wheel to 0 at TDC using a piston stop. So far so good. Pulled the stop and set up my dial indicator after reading some good posts by Nut, Ford the interweb etc. thx. I started on the exhaust and before I got started noticed that at #1 piston TDC both the #1 intake and exhaust valves are cracked open. I just wanted to make sure that was right and they are supposed to be in their overlap zone at TDC? Or is that just this cam?

I mapped out the exhaust cam and calculating the lobe center from closed just as it's lifting I'm at 117.3. Calculating it from fully open I get 118.7, off a little from each other, but pretty close... I'll run the whole lobes numbers and use the average. My question is...what should it be? Do you aim for 110 as a starting point on all cams, or is the target number cam and application specific?

After mapping out the opening and closing of the intake I get 126 both when lifting off and around fully open. I wondered if the intake would be fairly retarded as when installing the timing belt the teeth lined up with teeth on the intake cam gear and I retarded it (CCW) instead of advancing it (CW). I'll rotate the intake cam 1 tooth and try again before messing with the adjustable gears.

[jon8christine]

Ok, advanced the intake cam 1 tooth (turned clockwise if facing the belt) and remeasured... Now have a 108.3 at opening and a 109.5 when measuring it around fully open. I can work with that. Interesting to note that 1 belt tooth was worth about 18 degrees of advance.

[Nut124]

The 40/80-80/40 cams have overlap like you observed. The IN starts opening 40 BTDC. The EX closes 40 ATDC.

You are correct about one tooth being about 18 crank degrees. Actually it is just about 17.0 if you do the math. 2x360/42.

How are you determining cam CL?

I'm in the process of installing a very big intake cam now. Trying to do it w/o removing the head. Need to check valve spring bind height and P2V clearance.

[Nut124]

Regarding cam timing:

The numbers can be very confusing. I find that I need to often review and refer to the diagram:



Below are a few things about cams that I have learned - refer to the diagram:
- The key events are IVC and EVO
- For the engine to function, IVC must not be much above 80 ABDC or all CR is lost.
- The same; EVO must not be before 80 BBDC or the power from the power stroke is lost.
- To get max air into the cylinder, a cam with more duration, lift is needed.
- Valve-train constraints dictate more lift requires more cam duration.
- Cams with more duration need to use C/L numbers smaller, in order to keep IVC at below 80 ABDC.
- Reducing cam C/L makes cam "milder".
- Increasing cam C/L makes cam "hotter".
- in Single cam terms, reducing LSA makes cam milder'
- Hot cams have milder (106 vs 110) C/L to accommodate for the longer duration of the cam, to keep the IVC at below 80
- Hotter cams result in a lot of overlap. This hurts idle and is not in itself desired, but is necessary to keep IVC and EVO below 80.
- Overlap is the result of the desire to to keep IVC at below 80 while running a long uration cam.

[jon8christine]

Thanks for these great summaries. I've been doing a lot of reading as I learn more about this topic. As to how I was calculating lobe centerlines, I liked how you used the average of multiple points around opening and closing to get an average. It seems most websites just use the 0.050" angle. I also learned from this site that calculating lobe centerlines around full lift is erroneous and not really relevant as what really matters is the opening and closing events.

https://www.kelfordcams.com/global/tech ... -your-cam/

Thanks for the targeted Centerline angles of 108 for these cams...couldn't get any help or even a standard cam card from Vicks.

[jon8christine]

Rotated the exhaust gear a hair more and advanced the intake gear a half a mark and got both cams just about 108.

IVC is 46.5 deg @ the typically called out 1mm (0.039")
IVC is 72 @ 0.002"

Does that mean I could go a little "hotter" on the intake cam or would keeping it at 108 be better for low end torque anyway, which is where I want the power and not so much at 7,000 rpm?

EVO is at 50 deg @ the typically called out 1mm (0.039")
EVO is at 77 @ 0.002"

Time to loctite the gear screws and move on. Here's my calculation sheet in case anyone is ever curious.

https://docs.google.com/spreadsheets/d/ ... ue&sd=true

[Nut124]

The nominal C/L for the 40/80 cams is 110. I think my IVC @0.002 is 75 but these very low lift measurements are not as accurate as higher lift. I set my C/L at 108. Made 141HP at the wheels @ 7200-7300.

I doubt that you would notice the difference between 108 and 110. What is your valve clearance? This can have quite an impact on the valve open/close events.

My previous build had the intake retarded about 5 deg. CL 115 or so. It had little power below 4000 and made a lot of induction noise from intake flow reversal. EX cam was off a bit too, opening too early costing power.

My 40/80 IN cam data shows 2 deg more duration than yours. 268.5 @0.010 vs 266.5 yours.

[Nut124]

What adjustable cam pulleys are you running. Some have major problems with concentricity.

I'm in the same situation. I plan on checking the pulley concentricity before starting cam timing.

[jon8christine]

They are from Vick Auto

[Nut124]

I had to put alu shim tape on the cam OD and packaging tape between the two wheel parts to get it to run true. Tolerances too loose. Setting belt tension in one position would make it way tight or loose in others. I could hear the belt whine as the engine was running.

You might get lucky and get it perfect by accident but do check it.

[jon8christine]

They were a little sloppier than I thought they should be when installed but I couldn't get a full wrap of tape around them and still fit
them on. Once the bolts were torqued down they are solid, but I'll keep an eye on that when I get it running.

I want to get the distributor mounted while I have the degree wheel on still. I wanted to keep the timing cover off, mostly for looks but I'm also missing the two top studs with Vicks pointer. I reinstalled it best I could with the two other bolts and checked my crank wheel timing. It's hard to read accurately but looks like maybe 1 degree advanced. I then copied the marks and made my own timing bracket, which checks out when tested with the degree wheel for TDC (long mark), 5 and 10 degrees before.

https://drive.google.com/file/d/19A8nlx ... p=drivesdk

I gotta get a better picture hosting location so I can actually paste the photos sorry

At TDC and timing lined up with the cam pointers, #4 is firing so I'll line the distributor up there. My question is should I start with 10 degrees of advance with this build? To do that I was going to stop the crank 10 degrees short of TDC and install the distributor... right?

https://drive.google.com/file/d/19HkmFd ... p=drivesdk

[Nut124]

It is a very good idea to install your own, accurate timing marks. I kind of like yours. Will those marks work with the front cover on?

I may need to consider something similar. Right now, my custom timing mark bracket is on the other side.

I have always installed the dizzy with crank at TDC, #4 firing and pointed the rotor to #4 electrode. 10deg is a good starting point. However, you will want to check total timing at 4000+. Must not exceed 38 BTDC. I target 36. This max timing should be fully in around 3800-4000 and then the same all the way to top rpm.

If your total timing is more than 38 or less than 34, then may need to adjust idle timing or modify the mech advance system.

If you are running IDFs, the vac advance can be hard to implement. If no vac advance, ideally, I would run 16 at idle and 36 at 4000 and above, but this would required modifying the counter dizzy weights to reduce mech advance.

[jon8christine]

No, the new timing marks I made get in the way of the cover.

Ok, so install the dizzy with #4 at straight up tdc, then turn it during timing to get it dialed. My Haynes manual is where the 10deg static advance came from. Thx

[Nut124]

No, the new timing marks I made get in the way of the cover.

Ok, so install the dizzy with #4 at straight up tdc, then turn it during timing to get it dialed. My Haynes manual is where the 10deg static advance came from. Thx

Yes. You install the dizzy and hope it's close enough to fire and start. Then set the timing with a light while idling. You cannot set ignition timing w/o running the engine. Need reliable timing marks. I'd remove the dizzy before installing the engine in the car just so it does not get damaged somehow.

[jon8christine]

Hmmm, didn't realize the flywheel bolts are stretch bolts that you aren't supposed to reuse... Those are out of stock so I'll have to find the ARP ones.

Also noticed that I'm missing one of the two bell housing to block dowels, which are unobtanium. I think it'll be ok with just one, as that was the way it was before. Have I mentioned lately how I hate COVID. My garage door spring just broke and the price has trippled and they are 5 weeks out!

Nevermind, found a dowel on AR, just wasn't searching right