degree a cam?

bikesandcars

bikesandcars

True Classic
with all the changes I've made to my race motor (decked head, shaved block, re-grind cam), mix and matched parts, unknown pedigree on cam pulley.... etc .... I think I'm in need of re-orienting my valve timing.

we fooled with the cam timing last test day and advancing it made an improvement, but we chickened out after one adjustment because we didn't want to bend anything.

Has anyone here degree'd a cam in the engine?

I'm good with confirming engine TDC, but I'm a little confused about locating intake and exhaust degree's with the space allowed under the cam box. Maybe I need to degree the cam off the car?

Any help appreciated. I know we have more power in this engine and I think the valve timing is getting in the way (slightly)
 
Just did it this weekend. I always do it with the cam box off the head. Setup a dail indicator on the bottom side of the #1 intake tappet. Put a degree wheel on the cam wheel. Fashion a pointer from a piece of wire attached to the cam box. Find maximum lift, dial in the cam's offset (55 degrees typically). To find maximum lift, it's best to find 2 points either side of maximum and then split the difference.
 
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Here you go:

1GB752.jpg




CALMOTION said:
Screenshot pleas :)
Click to expand...
 
nice! that picture is worth 1000 words to me!

question: where did you get that small aluminum degree wheel?

based on this photo I'm going to do a few things here then:
1) pull cam box
2) create a better valve-timing indicator, either from wire or bent steel, that will allow me to more accurately dial-in the cam
3) degree the cam and find out the lobe-centers, lift and duration.
4) find exact TDC and degree the timing with the cam back on the car with a crank mount degree wheel.
 
It is all in the details

To degree a cam, you are setting it match the crank (and hence piston) position. There are many how to descriptions on the web that you can google. I did a quick look and here is one example:

http://www.thedirtforum.com/degree.htm

It is necessary to find true top dead center on the crank and set the degree wheel to that point (check to see that your engine tdc indicators are correct at that time), and then degree it by its chart or by lobe centers (see the descriptions).

Advancing the cam gives more top end, retarding it more bottom.

Paul Davock
 
Thanks Paul, I had done similar research but then realized a key step.

Most of those guides reference a cam "chart" or other information provided by a cam grinder or supplier (often crane cams or other production line stuff).

Since I'm using a custom grind cam with no chart, I'm in the deep waters.

I'm going to have to blueprint the cam first as I have no chart (custom grind). I guess I'll put that in excel, I might even compare it to a stock 1500 and a 40/80 cam I have, I'll see where I stand.

As I'm far off into experimental mode right now (beyond build-by-numbers) I need to get the cam(s) figured out and then move forward.... i.e... need to figure out lobe centers first :). I could just set the cam "straight-up" (i.e. middle of lobe centers), but I want to see what those lobe centers are first just to understand my different cams
 
PaulD said:
Advancing the cam gives more top end, retarding it more bottom.

Paul Davock
Click to expand...

I thought the same, but I did more research and got confused. this is actually really bugging me because I thought I had this all figured out.

some forums / pages say that advancing the cam gives more bottom end, while retarding the cam gives more top. which is it? that was mainly from v8 / musclecar type forums.

I thought getting the intake valve open sooner (and exhaust closed sooner) helped scavenging at higher rpm.

People have said that advancing the stock cam a couple degree's gives more power, but was that because it was too retarded from the factory (no pun intended)?

I've heard Spark advance helps with the flame front, advancing timing helps top end power, but are optimal spark and cam advance divergent?
 
I do it in the Car.

You need to find TDC on the bell housing end of the fly wheel. At the that end on the transmission you will see the marks 0 5 and 10. With a marker mark Zero on the fly wheel and turn the engine 10 degrees backwards make another mark. Now look at the intake valve on #4 and use a .002" feeler gauage under the intake valve cam lobe. Turn the engine back 10 more degrees and mark again. Keep turning backward and marking until the feeler touches the cam lobe. Add up all of the marks. If the cam is timed correctly 40-80-80-40. The intake valve lobe will touch the lifter at 40 degrees before top dead centre. If it does not then you will have to adjust the cam belt a tooth remembering it is 8 degrees a tooth. If it is less than 8 degrees then you will need an adjustable camshaft pulley to place the camshaft in the correct location to time your engine correctly.


I have a 40-80 camshaft in my car. I ran it one summer retarted 1 tooth. Although sprited the top end suffered but the bottom end had a better idle and lower torque. The following year I advanced the camshaft 1 tooth and found that the idle to be a bit rough and had to increase the rpm to about 1100. The top end took off and pulled strongly to 8000 RPM, I had to richen the mixture as it became too lean at the top end. Either way the car ran great. Just a note though by advancing it I had to rescale my MegaSquirt VE table because mixture became too lean. The engine was flowing better and at about 6000 rpm with the headers as every thing seemed to come together at that RPM and above. Fixed cam timing does that there is a sweet spot in the RPM range that the engine really comes alive, however there is little driving done at 6000 rpm except on a race track. The rest of the time it is a trade off.


TonyK.

Grimsby Ontario Canada.
 
Thanks Tony. I would be happy to increase the top-end a little,

What started this quest is that the motor's got ok torque from 4,000 but is flat from 6,000. A/F ratio is around 11:1 through 7,500 rpm... It pulls at 7500 but is flat from 6 to get there (no real advantage).

I degreed the two cams I have (PBS B3 and stock) B3 was 110 lobe centers, Stock was 112. You can see the difference!

Now I just need to pull the custom grind out of the car and compare that. Last year with the BVH the custom grind worked really great,

I'm holding further comment until I blueprint the custom cam and see how my valve timing lines up, I haven't put it all together yet.




here is my "rig"

 
additional note: I did not degree the wheels from the cam pulley, rather oriented them by center line.

A very important consideration, the 40/80 cam appeared to be about 1.5 degrees retarded from the stock cam (cam degree), which would mean it was about 3 degree's retarded in relation to crank angle. Note this this could be due to my measurement method (lining up marker positions on timing gear), or the nature of the cam, or a combination. I wasn't too concerned about this as I was studying lift/duration. I'll worry about orientation when I get it on the car.
 
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