Cam Duration

Gear Case (cams, idlers, cam cover)
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Hauula Pan
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Cam Duration

#1

Post by Hauula Pan »

Does anyone know of a way to measure the duration on the lobes of an uninstalled cam? I'm trying to identify an old cam I pulled out of a motor a while back & it doesn't have any of the usual identifying marks on it. I know how to find duration on an installed cam using a piston stop, dial indicator & degree wheel, but can not figure out a way to figure it out on an uninstalled cam. Measuring the lift was easy enough, I simply measured from the heel to lobe peak, subtracted the base circle measurement & multiplied the result by the 1.5 rocker ratio. Got .405 lift. Now I need to find a way to figure out the duration, any ideas???
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Re: Cam Duration

#2

Post by Red55FL »

Hauula Pan
Use a set of V-blocks, a dial indicator and a degree wheel, or chuck it in a lathe and use a dial indicator.

Take it easy
Red
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Re: Cam Duration

#3

Post by ingram »

To measure the camshaft outside the block, you can send the camshaft to someone that has a device designed to do that or you will need to make your own device.

You will need to mount the camshaft between centers or you can use V-blocks. If the support journals on the camshaft are not the same size, you will need to shim one or both of the V-blocks to make the camshaft level. A degree-wheel will need to be connected to one end of the camshaft so that it rotates with the camshaft. A pointer for the degree-wheel will need to be made.

For a roller tappet camshaft, this is the difficult part…some type of bushing and support will need to be made that allows the stock tappet to move up and down as the cam lobe rotates against it. A dial indicator will need to be connected to the tappet in order to measure tappet lift.

You cannot just let the tip of the dial indicator ride on the surface of the cam lobe. Either the stock tappet or something of the same diameter/radius as the stock follow wheel must be used. This determines the contact point between the cam lobe and the follow wheel. If the follow wheel used is not the stock diameter, the contact point changes and your duration measurements will not be accurate. Another option is to make something that attaches to the end of the dial indicator that is the same radius as the stock follow wheel.
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Re: Cam Duration

#4

Post by Hauula Pan »

Thanks for the replies, Red & Ingram, I thought of chucking it in a lathe but didn't think about having to account for the area of surface contact of the tappet wheel, thanks for that tip, I would have let the dial ind. ride the lobe & would have gotten inaccurate results. I can see where finding duration is way more difficult than finding lift. It would be much easier if it were installed. Guess I'll just wait until I can throw it into a motor & measure it up then.
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Re: Cam Duration

#5

Post by Cotten »

Ingram!

Wouldn't an ordinary indicator "toe" still be close enough to identify a cam?
(Assumeing we had specs to compare to, of course...)

Thanks in advance,

...Cotten
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Re: Cam Duration

#6

Post by ingram »

Cotten wrote:Ingram!

Wouldn't an ordinary indicator "toe" still be close enough to identify a cam?
(Assumeing we had specs to compare to, of course...)

Thanks in advance,

...Cotten
You would be too far off for the data to be of any use.

Look at where the stock follow wheel makes contact with the lobe during rotation. The contact point is not inline with the centerline of the tappet during most of the rotation. The contact point will be at an angle to the tappet centerline. The small contact point on the dial indicator would be way off from the stock follow wheel contact point.

It’s one of those things that makes more sense when it is observed. Drawing a picture will help a lot.
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Re: Cam Duration

#7

Post by kitabel »

A simple dial indicator + degree wheel will allow you to compare it to another cam, but of course won't give actual data. Has to begin with the same timing mark; the easiest comparo is to advance 1 tooth at a time. If the results are fuzzy do several passes and average them. Just do as many points as you can on both, particularly the rear intakes.
If the base circle appears untouched, there is no "H", etc. stamp, and the lift is .270" it's not an FL cam or a re-grind. Very few actual replacement cams were made "back in the day" (pre-1965?).
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Re: Cam Duration

#8

Post by Cotten »

Ingram!

I found that it at least gives you a guestimate of lift, and by process of elimination from the catalog, usually identification is obvious.

Its not like we are indexing a gear, yet.

Why can't I cut an arc from a tappet roller, and silver-solder it to an indicator stem for a toe?

....Cotten
Last edited by Cotten on Wed May 08, 2013 9:08 pm, edited 2 times in total.
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Re: Cam Duration

#9

Post by ingram »

Cotten wrote:Ingram!


So how much of an arc from a tappet roller should I silver-solder to an indicator stem for a toe?

....Cotten
90-degrees is more than enough. 45-degrees on each side of center.
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Re: Cam Duration

#10

Post by Cotten »

Hope this is in focus (can't tell on PC stuck in safe mode), Folks),...
CAMTOE.jpg
Like that, Ingram?
Is it going to give me different readings than a simple point?

A degree wheel that will stick to the journal is next....

....Cotten
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Re: Cam Duration

#11

Post by ingram »

You are on the right track Cotten…looks good.

The critical part is obviously the “toe” on the end of the dial indicator. Your measurements will only be as accurate as this radius. It will certainly be closer than the pointed tip.

Remember…the duration measurements you get will be in camshaft degrees. Published camshaft durations are in crankshaft degrees. You will need to double the camshaft degrees to get crankshaft degrees. The camshaft rotates half the speed of the crankshaft/flywheel.
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Re: Cam Duration

#12

Post by Cotten »

Ingram!

Its a piece of a roller, so its gotta be ideal, right?

And its going to give me 'far off' different readings from a normal toe, right?

Uh oh.

I must have done something wrong.... .. .. . .

.....Cotten
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Re: Cam Duration

#13

Post by ingram »

Cotten wrote:Ingram!

Its a piece of a roller, so its gotta be ideal, right?

And its going to give me 'far off' different readings from a normal toe, right?

Uh oh.

I must have done something wrong.... .. .. . .

.....Cotten
If it's a section of the stock roller wheel, that's great. The alignment would be my only concern. Basically that section of the roller wheel needs to duplicate the position of the stock follower. From the picture, it appears to be out of alignment with the centerline of the indicator travel. It may just be the angle of the picture.
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Re: Cam Duration

#14

Post by Cotten »

Ingram!

Its pretty square.
I would really be surprised if it was skewed to exactly the degree where it reads the same as a simple rounded indicator attachment.

But it does.

....Cotten
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Re: Cam Duration

#15

Post by ingram »

Here is a picture that may help explain.
Cam.bmp
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