Determining Cam specs without removing cam from engine

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gzig5

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I would like to know what the specs of the cam in my 340 are. Curiosity is killing me. I saw a video of a guy doing it a while ago but can't find it at the moment. I have the timing cover off to check the timing chain, which is in good shape. I have a degree wheel I printed out and fabbed a mount to put it on the front of the balancer. I have an indicator stand and a good dial indicator. It then occurred to me that I may not get accurate measurements because of the hydraulic lifters? In the video he definitely put in light springs and I think maybe solid lifters but not sure on that. So, can I get a reasonably accurate measurement of lift and duration going off the top of the rocker arm on the pushrod side, or the spring keeper on the valve side?
 
The problem is what you mention... what are the lifter pistons doing relative to the lifter body? The difference can be waaay off.

See if you can rig up a solid rod parallel to the pushrod to get right to the lifter body. Or pull off the intake and go right to the lifter body... the coolant is already out. Duration will be unchanged, spec's are .050" are usually for lift at the lifter, and you can just estimate the valve lift from there.

And you have to make sure the dial indicator rod motion is perfectly parallel to the motion of the lifter or that will also be a source of error for both lift and duration.
 
It's pretty hard. You can do it three times and get three different readings, and even if you do it 100% right, you still have the monkey motion of the rocker gear and the pushrod angle to deal with .
But here's a trick; the lobe lift doesn't lie. Compare yours to a short list of cams in the ballpark, and the duration will usually come out from the confusion.

Of course on a running street engine, you can usually guess within a size or two...... because lobe separation not withstanding,there are only about 4 or 5 sizes to choose from,and each one has a particular, maybe even peculiar, personality.
 
And you have to make sure the dial indicator rod motion is perfectly parallel to the motion of the lifter or that will also be a source of error for both lift and duration.
And the LA pushrod is not parallel to the lifter which gives inherent underlift to the rocker- and the rockers wear further reducing lift
The valve motion ends up nothing like the cam- which is true to some extent for all engines
That's why modern cam designs start off with the desired valve motion and work backwards
computers
 
many dial indicators have removable tips that allow you to replace the std rounded contact end with a different shape tip which can better contact the rigid, thin edge of lifter body, instead of the movable hydraulic plunger.
I think Goodson used to sell a temporary replacement lifter tool which is just an appropriately sized metal slug to act like cam follower for just this purpose of cam degree in or lift measurement.
Or why not just buy one solid lifter to use, then you could use your existing indicator with its current tip?
Or just pull the cam out and measure it with a dial caliper with one jaw on the base circle and the other jaw on the nose of the cam. Just remember the cam lobe is tapered, so you want to take your measurement of the higher side edge of the lobe.
 
Starting to sound like more effort than I want to put forth this weekend. I need to button it up and get it back on the ground running so I can address other areas. I think I'll leave it alone and maybe after the snow flies, I'll just pull the cam and set it up in the lathe to measure the lobes directly.
 
I used to pull my engine out every winter for teardown and inspection. I was broke and it seemed like gaskets were cheap compared to what I had in that engine. Three times I averted disaster. Once I had to replace a lobe-casting cam, and twice I found nothing; so then I stopped inspecting.
Since spring of 2005 I have just beat the snot out of her.
I had installed mostly reuseable gaskets and so it only cost me a few bucks for the inspection. I was so broke, and so cheap, I reused the FellPro 1008? headgaskets from 2000 on. They're still on there, lo, these many years later.
Only the first year did I replace some non-FellPros. I had to. The .028s couldn't take 11.3 Scr, and I caught them trying to escape into the valley. Then I recut the deck and popped the pistons up out of the holes and regrouped with the .039 FellPros. The net result was the sameish .034Quench vs .028.
So what's that got to do with anything? IDK, but I can see where you're going,lol.
 
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