How do I check cam lift? Motor currently in car. - Chevelle Tech
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  #1  
Old Sep 19th, 06, 9:38 PM
james a larson james a larson is offline
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Unhappy How do I check cam lift? Motor currently in car.

Just did a search on checking cam lift; but the cam was not in the engine. I am new in working on engines and plan to replace valve springs, since I broke 2 in the last year (think they are originals from 1966). Don't know much about the engine other then it's a CE 402 block from 1970, 66 heads, & intake. Think the cam is stock with a rebuild in early 80's. If it's a stock cam from 1970 It could be one of 3 cams depending upon what HP it was built for: 265,350, or 375. I would like to measure the lift to determine which cam I have. Could someone expain in a little more detail how to measure the lift? Thanks.
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  #2  
Old Sep 19th, 06, 10:42 PM
rednecks70 rednecks70 is offline
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Default Re: How do I check cam lift? Motor currently in car.

If the cam is not in the engine you may want to contact a machine shop. The shop I use said he can put a cam in a lathe (sp?) and measure the lift with a dial indicator. It's seems like a simple 10 minute thing so a local guy may do it cheap or for free to get your business.

If the cam is in the engine with the intake manifold and valve covers off I would rotate the engine manually until I see an intake lobe with the lifter on the base of the cam. Then setup a dial indicator (on a magnetic stand) with the tip of the dial indicator touching the tip of the push rod (rocker has to be removed). Zero the indicator and rotate the engine and record the highest reading. Repeat the process for the exhaust lobe and it would be a good idea to measure several lobes as they could be worn.

There's a couple of engine builders on this site Wolfeplace, BillK, etc. that may have a better way or a better explanation. Good Luck!
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Last edited by rednecks70; Sep 19th, 06 at 10:56 PM.
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Old Sep 20th, 06, 11:05 AM
james a larson james a larson is offline
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Default Re: How do I check cam lift? Motor currently in car.

Intake is still installed. Valve covers off. If I use a dial indicator what do I do, just measure the change in the height of the push rod? Or do I measure the change in valve spring height?
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Old Sep 20th, 06, 11:34 AM
tpshea tpshea is offline
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Default Re: How do I check cam lift? Motor currently in car.

Quote:
Originally Posted by james a larson View Post
Intake is still installed. Valve covers off. If I use a dial indicator what do I do, just measure the change in the height of the push rod? Or do I measure the change in valve spring height?
Jim,

If you check at the valve spring, you are going to get a lift number that will include the increase factored in by the rocker arm ratio. To get JUST cam lift, you want to do it at the pushrod. Your '66 is gorgeous by the way!
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Old Sep 20th, 06, 2:03 PM
rednecks70 rednecks70 is offline
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Default Re: How do I check cam lift? Motor currently in car.

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Originally Posted by tpshea View Post
Jim,

If you check at the valve spring, you are going to get a lift number that will include the increase factored in by the rocker arm ratio. To get JUST cam lift, you want to do it at the pushrod. Your '66 is gorgeous by the way!
Very good point. I found it's easier to keep the tip of the indicator on the valve spring retainer rather than the push rod tip. Then take your reading and divide it by your rocker ratio and that should give you cam lift. Sorry, I should have thought of this last night when I responed but it's been a while since I measured cam lift.
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Old Sep 20th, 06, 7:09 PM
6cylcecil 6cylcecil is offline
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Default Re: How do I check cam lift? Motor currently in car.

I'm not sure this is the most accurate way, but I put a dial depth gauge on the rocker over the push rod and measured to the head while someone rotated the engine slowly. The measurement seemed to be close to the lobe specs. I wasn't checking specs exactly, but rather looking for a difference between the other lobes. Even rotating slowly the lifters seem to pump up a little so be careful to allow a few seconds before recording a reading then multiply by rocker ratio. seems easy enough, but I'm certainly not an expert
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Old Sep 20th, 06, 7:24 PM
furball8994 furball8994 is offline
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Default Re: How do I check cam lift? Motor currently in car.

Correct me if I'm wrong, but isn't advertised lift, gross lift. Which means that its measured with the respective rocker ratio calculated in. (1.5sbc/1.7bbc). So with that, the way to check your cam would be to measure it on the valve side of the rocker.
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Old Sep 20th, 06, 7:43 PM
6cylcecil 6cylcecil is offline
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Default Re: How do I check cam lift? Motor currently in car.

It would probably give a final answer quicker, skip the math.
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Old Sep 21st, 06, 12:38 AM
james a larson james a larson is offline
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Default Re: How do I check cam lift? Motor currently in car.

Now I am confussed again, advertized lift? Kind of a novice in this area. What I want to find out is which one of the 3 possible cams that might have been installed originaly in a 1970 CE (replacement) short block was actually installed. Pretty sure cam has never been replaced. I thought I could do this by checking the lift. The spec say intake lift is either .398, .461, or .520 depending on which cam is installed. So what are the numbers I look for if measuring at the push rod. The above numbers divided by 1.7. Would I just use the above numbers when measuring at the top of the valve spring? Think the rocker ratio is 1.7:1; that's what I measured it at and it's a BB.

Just got through measuring at the valve spring and this is what I got:
.458 on the intake valve . And 4.67 on the exhaust valve. I only measured one intake and one exhaust valve. The respective lift for the exhaust are .398,.480, and 5.20 respectively. If I am interperting this correctly allowing for some error is measurement and some wear then I would have the cam that originaly had a .461 intake lift and a .480 exhaust lift. Do you think my reasoning is correct? Thanks,













Thanks.

Last edited by james a larson; Sep 21st, 06 at 7:14 PM.
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  #10  
Old Sep 21st, 06, 5:18 PM
6cylcecil 6cylcecil is offline
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Default Re: How do I check cam lift? Motor currently in car.

Jim, if I wanted to know the valve lift, regardless of ratio, I would measure the valve movement. Sorry for any confusion I may have caused talking about push rods.

With a depth gauge I would find a stationary point of reference and allow another person to slowly rotate the engine while holding the depth gauge on the valve side of the rocker and observe the reading as the valve reaches full travel.

This may be a little crude as the lifter pump up and bleed will play with the readings. There must be a dead accurate way, but this seemed to be close to the specs when I did it.

Good luck
Cecil
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Old Sep 21st, 06, 10:18 PM
6cylcecil 6cylcecil is offline
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Default Re: How do I check cam lift? Motor currently in car.

Yes.

I took pains when I did mine to be as accurate as possible, be repeating the measurement about 7 or 8 times.

In the case of wanting valve lift I would take the reading as the engine rotates slowly to observe the peak travel reading.

If you are getting a consistant reading or close groupings I would feel like you are accurate with those measurements. Rotating the engine will pump the lifter a little.

Just for kicks stop the rotation on the peak reading and take a 2nd measurement again a few seconds later without rotating the engine. It should be less lift, and not the reading I would use.

I'm not an expert Jim, just recently involved with the same desire to know whats up with my cam. Hope this helps, again I would go with your conclusion about the cam that is in your engine, if you had steady hand and consistant readings.

Good luck
Cecil
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Old Sep 21st, 06, 10:50 PM
BillK BillK is offline
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Default Re: How do I check cam lift? Motor currently in car.

James,
Measuring the lift at the valve would be the most accurate but ......

1. It does not take into effect the fact that rocker ratios vary a BUNCH, especially stock type rockers.

2. If it is a hydraulic cam, the valve spring will probably cause the lifter to collapse some and you will not get the correct reading.

Check it at the pushrod and multiply it by the rocker ratio.
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  #13  
Old Sep 22nd, 06, 12:13 AM
james a larson james a larson is offline
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Default Re: How do I check cam lift? Motor currently in car.

I took the reading about 6 times for both the exhaust and the intake valve. And got the same reading within .001-.002. Thought that with the age and wear that reading would be a little less then new and it was. Measured the rocker ratio and it was 1.7:1; Pretty sure there stock 66 rockers. I would have to be off by .050 to indicate a different cam. See by the service manual that there should be a little attachment for the dial indicator to go over the push rod and I don't have one. Is there something that you can put over the end of the push rod, so that there is a flat surface to work with?

Bill whats the best way to measure the rocker ratio? Think I will try to do the push rods method tomorrow.
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