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Old 03-21-2006, 11:10 PM
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Degreed the Cam -- 40 Degrees Advanced!!!

I degreed the cam in my 1971 Olds 350 -- not a perfect job under best conditions, but close enough to tell me it is way off.

I was able to verify that TDC was within one degree of the mark on the harmonic balancer by checking with a piston stop.

Because the engine is in the car, I used a xeroxed copy of a degree wheel glued to a cardboard backing and taped to the front of the crank pulley with a center hole cutout that allowed me to get a socket on the crank bolt and turn the engine. Put a dial indicator on the #1 intake pushrod with the hydraulic lifter still in place, couldn't get a solid lifter today.

Anyway, the centerline for my 204/214 cam turned out to be 66 degrees ATDC instead of the 106 degrees it is supposed to be. Intake opening of 0.50 occurred at 36 degrees BTDC instead of 4 degrees ATDC. I got a duration of 223 degrees instead of 204 degrees but I believe I had some slop in the mounting of the dial indicator plus inaccuracy from the hydraulic lifter.

So, those who told me a year ago to go back and check the cam timing were offerring good advice. I had complained that this stock engine with Performer cam, QJet, and 3.42 gears just didn't have the get up and go that I expected.
I didn't put the cam in myself, but thought mechanic that did would have done it correct. New Edelbrock timing set was installed along with the Performer cam

Would you even expect a car with the cam timing off this far to even run?

John
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Old 03-21-2006, 11:47 PM
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Yeah, if the plugs and cap and rotor are off. Make sure that the rotor is pointing to the #1 spark plug on the dizzy cap. If someone rearranged the plug wires on the dizzy cap, you might be timing from the wrong wire.
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Old 03-22-2006, 12:06 AM
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There are cheap degree wheels for like 10 bucks. Might wanna try one of those. I like going off the valve retainer, to see what the valve is doing. But not necessary. Locate the dail off the rim of the lifter if possible

Measure 3 times cut once.

The timing sprockets are all lined up?


Olds man, of course it'll run
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Old 03-22-2006, 12:10 AM
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Quote:
Originally Posted by JohnTN

Would you even expect a car with the cam timing off this far to even run?

John
Here is a couple of cam timing stories
Chain jumped 4-5 teeth ??
I liked your trick with the xeroxed degree wheel. It is a PITA to degree them in the car ,huh? Later,mikey
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Old 03-22-2006, 06:34 AM
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cam

IMO, you did something wrong....

Are you sure you degreed the intake lifter and not the exhaust????

Explane your steps for finding the intake centerline...


Keith
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Old 03-22-2006, 07:22 AM
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K-star,

I lost sleep last night trying to think of a mistake I made, but I followed the instructions off the cam sites as well as understood what was going on.

Here's what we did:
1. Removed all plugs, rotated engine clockwise off crank pulley
2. As TDC approached, put finger over #1 plug hole and could feel pressure, also noted neither pushrod was moving. and pushrods could be turned
3. #1 plug is forward location on drivers side on Olds
4. At TDC on balancer, observed top of piston was visible through plug hole
5. Rotated engine backwards to 20* (20*BTDC) on degree wheel, inserted piston stop till contact with piston
6. Rotated engine backwards till contacted piston stop at 18* ATDC, verifying TDC on harmonic balancer was within 1*, also noted that intake pushrod was moving
7. Removed piston stop, rotated engine backwards until intake pushrod stopped moving downward plus a little more, about 90* BTDC on degree wheel
8. Installed dial indicator on #1 intake pushrod with rocker arm removed
9. Began rotating engine forward, clockwise; noted intake pushrod started to move up at about 80* BTDC as dial indicator started to move off zero
10. Slowly continued to rotate forward till dial indicator reached .05, noted degree wheel at 34* BTDC
11. Continued rotation until dial indicator peaked at .267, at 66* ATDC
12. Continued rotation till dial indicator returned to .050 at 188* ATDC
13. Rotated engine back to 66* ATDC and noted same peak reading as before
14. Continued rotation back to TDC on degree wheel, noted mark on harmonic balancer was at TDC also.

In order to read the degree wheel mounted on the crank pulley, I positioned the pointer (bent coat hanger) to point to the bottom of the degree wheel. So, TDC on the degree wheel was at the bottom at the pointer when the TDC mark on the harmonic balancer was on zero degrees.

The peak lift of .267 is close to the spec of .28. The difference could easily be in a little slop in the dial indicator setup.

The degree wheel glued to a cardboard backing was attached to the crank pulley with double backed tape the full circumference of the pulley, so it didn't move or slip around on the pulley.

I really think I got a reliable determination, but do wonder how close the piston comes to contacting the intake valve with this early timing. The pistons are stock dished pistons of about 64 cc I believe for compression ratio of 8.5:1. Heads are the stock heads -- they were also used on high compression engines in 1970. Lower compression in 1971 was achieved with the dished pistons.

Let me know if you see anywhere I could have messed up.

Thanks,

John
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Old 03-22-2006, 08:15 AM
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Quote:
Originally Posted by JohnTN
K-star,



10. Slowly continued to rotate forward till dial indicator reached .05, noted degree wheel at 34* BTDC
11. Continued rotation until dial indicator peaked at .267, at 66* ATDC
12. Continued rotation till dial indicator returned to .050 at 188* ATDC
13. Rotated engine back to 66* ATDC and noted same peak reading as before




Thanks,

John

Ok 34 deg plus 188 =222.. divide by 2 and your centerline is 111,,, so your cam is retarded by 5 deg if the card calls for 106 installed...


Maybe a easyer way for you would be to find the top of the valve lift. set you indicator to zero. Rotate the engine counter clockwise untill you past the .050 mark on your indicator. Then rotate in the clock wise direction untill you are at exactly .050 below max lift...record that number... rotate in the clock wise direction past zero untill you get to the .050 reading again. record that number..... Add the 2 and divide by 2 and that is your installed centerline....

By any chance does your cam card have valve events listed????? if so you can real easy verify you opening and closing @.050 readings... if not tell me the duration @.050 and the centerline and i'll give you the numbers....


keith
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Old 03-22-2006, 08:28 AM
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Cam

sorry. i need to read the post closer... i do see you have the event numbers listed... I need to go back and re-read the first post.....


Keith
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Old 03-22-2006, 08:29 AM
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Quote:
Originally Posted by k-star
Ok 34 deg plus 188 =222.. divide by 2 and your centerline is 111,,, so your cam is retarded by 5 deg if the card calls for 106 installed...


I get a centerline of 77* atdc with those numbers
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Old 03-22-2006, 08:36 AM
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Quote:
"The peak lift of .267 is close to the spec of .28. The difference could easily be in a little slop in the dial indicator setup."
]
I would think that the amount of slop you have in your indicator setup could easily throw off your timing events. I would also suspect that to be the case since you say in your first post that your duration @ .050" is 223 instead of the 204* it specifies on the cam card. I would check your dial indicator mount and get that right before you proceed. Just a thought, mikey
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Last edited by powerrodsmike; 03-22-2006 at 08:42 AM. Reason: make a box around a quote
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Old 03-22-2006, 08:47 AM
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cam

Ok now that i looked at the first post closer...

The numbers for your valve events on that cam should be intake opens @-8 deg btdc ,and closes at 32 degrees abdc... this is all @.050

I think you are backwards in your events, But not sure why... go back and check the numbers at -.050 from max lift like i described above...

You have the right numbers but in the wrong place,,, remember that you need to subtract the 8 degrees from you math when figuring the duration @.050


I edited this because for some reason i am brain dead today.....



keith

Last edited by k-star; 03-22-2006 at 09:03 AM.
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Old 03-22-2006, 09:06 AM
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A quick way to see if you're really way out is to look at where you are during the overlap period.

If the cam was straight up both valves should be open the same amount when the motor is at TDC during the overlap phase.
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Old 03-22-2006, 09:13 AM
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What kind of copier did you use to get a duplicate. I work on copiers for a living and I can tell you that most distort the image. Even though it say's 100% image it won't be because of a 97% image margin for error. Most copiers don't do a good job on thick things the optic can't pass through.
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Old 03-22-2006, 09:23 AM
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Keith,

As I understand it the centerline is the absolute number on the degree wheel where maximum lift occurs which in my case was at 66* ATDC by observation of the dial indicator.

The number you calculated of 111* would seem to be the duration divided by 2. That number just represents half of the duration based on my readings, but this point occurred at 66* ATDC when it should occur at 106* ATDC. I still think I am 40* advanced, not 4-5* retarded.

powerrodsmike,

The "slop" in the dial indicator mounting (I really think it was pretty firmly set) could give me false readings at .050 opening and closing, but shouldn't throw off the point of max lift. We could observe the dial indicator come to a slow stop at 66* ATDC and then start back down. Repeated it twice.

The duration based on the .050 readings was 223* which is the number I suspect might be a little off due to "slop" and the fact the hydraulic lifter was not replaced with a solid lifter. If you calculate the centerline using this duration it comes out 77* as previously observed by another poster, but I think the visual observation of the max lift at 66* is more accurate determination of the centerline.

Thanks for the thoughts. I would appreciate more, especially how the car could run in this condition.

I have previously removed the distributor and changed out the worn advance weight mechanisms in the used HEI distributor. When reinstalled a miss at idle and low speeds seem to be eliminated, but power still wasn't there.

Cylinder pressures are in the 158-170 psi range with cam in this condition. Plugs are clean but idle speed adjustment screws don't seem to have much effect on idle quality and exhaust smells rich. Idles with a little attitude, but only 14 in. Hg vacuum. This cam should idle smooth with 18-20 in. vacuum I am told.

I am elated that the problem might have been found, just concerned how it could be out this much and still run. And did I really degree it correctly.

John
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Old 03-22-2006, 09:26 AM
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cam

your engine would never run with the cam off 40 degrees......
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