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Old 10-21-2020, 06:30 PM   #1
Russ/40
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Default Finally some Cam Degree Numbers - Now what?

I'm back, and have no idea what I am supposed to make out of the numbers. Here they are. If you recall I have been reluctant to pull the heads, and it was suggested I degree the exhaust valve on number one.

Reconfirmed TDC and very repeatable.
The info I found on the 77B: Int and Exh durations 260* or 220* at .050"
Lobe separation 111*, lift .325* Lash .014".

I got: .050" open at 148*
Exhaust starts to open @ 120.5*
Exhaust starts to close @ 348.5*
Exhaust is closed at 9* ATDC
Exhaust Lash is .014"

Is this enough to get a feel for the cam location? What else need I do. Exhaust centerline?
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Old 10-21-2020, 06:44 PM   #2
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Default Re: Finally some Cam Degree Numbers - Now what?

I know I have degreed a 77B. When I get down to the shop I'll see what kind of numbers I have
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Old 10-21-2020, 06:56 PM   #3
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Default Re: Finally some Cam Degree Numbers - Now what?

I assume you have the cam timing specs? It is not totally clear from what you posted what lift you are checking at. The spec is for .020 valve lift with zero valve/lifter clearance. There is a second set of specs for .050. Values are in BBDC and ATDC. Sorry, looks like they are measuring at .014 valve/lifter clearance (I would call and check on that one).
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Old 10-21-2020, 09:59 PM   #4
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Default Re: Finally some Cam Degree Numbers - Now what?

I think they measure from the base circle.
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Old 10-22-2020, 05:57 PM   #5
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Default Re: Finally some Cam Degree Numbers - Now what?

I think Jack is right, ie, they measure from base circle...
however, going by your numbers you have;
ex opens 59.58 BBDC
ex closes 9* ATDC
This gives a duration of 248.5* as opposed to their stated 260*
Looks like your opening is close, however the closing is too early.
The closing events are more important than the opening....so, if you retard the cam by the one tooth as I suggested earlier, the new figures will be;
open 51.5* BBDC
closes 17* ATDC
duration obviously remains the same @ 248.5*
Furthermore, by doing this the distributor timing will be knocked back 16* and will be near where it should be.
My opinion....
I would have checked both inlet and exhaust timing events during the initial assembly
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Old 10-22-2020, 07:11 PM   #6
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Default Re: Finally some Cam Degree Numbers - Now what?

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Problem is if the valve lash is in there it will change the opening and closing events. I have always used zero valve lash, but the cam specs are a bit confusing on that.
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Old 10-23-2020, 02:24 PM   #7
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Default Re: Finally some Cam Degree Numbers - Now what?

You should do it with zero lash - and use the .050 numbers (they tend to be more accurate). We have no idea as to how the opening ramps influence the timing - only way to figure it out is with the heads off and checking the timing of both valves - and I'd do both at .020 as well as .050 (to compare). Given your lash of .014, you can look at the .020 timing to get a rough idea as to how close you are.

Just from what you've posted, seems the cam does not truly have the duration that it was advertised with. Comparing .020 to .014 lift, the valve should open SOONER than the timing tag and close LATER - it closes quite early.
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Old 10-23-2020, 03:44 PM   #8
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Default Re: Finally some Cam Degree Numbers - Now what?

Think I would stick a shim in between the lifter and the valve stem to get the valve lash out of the process.
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Old 10-23-2020, 06:05 PM   #9
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Default Re: Finally some Cam Degree Numbers - Now what?

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Think I would stick a shim in between the lifter and the valve stem to get the valve lash out of the process.
Or, if you have "adjustables", just back out the adjuster until you feel it tight against the valve (when the lifter is on the heel of the cam). Even if you go a bit too far, you've taken up the slack.
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Old 10-23-2020, 07:16 PM   #10
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Default Re: Finally some Cam Degree Numbers - Now what?

Quote:
Originally Posted by JSeery View Post
Problem is if the valve lash is in there it will change the opening and closing events. I have always used zero valve lash, but the cam specs are a bit confusing on that.
The cam card clearly denotes what it SHOULD be - and that the checking clearance is 0. What he is probably going to find is that the cam does not match the card - which I've seen MANY times. If the grind itself is off, there is nothing he can do to "fix" it . . . he can advance/retard it, but that is it.
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Old 10-23-2020, 10:39 PM   #11
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Default Re: Finally some Cam Degree Numbers - Now what?

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The cam card clearly denotes what it SHOULD be - and that the checking clearance is 0.
That's the way I would read it as well (and the way I have always checked a cam). But I can see how it is somewhat confusing to then put a valve clearance in with the event specs.
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Old 10-24-2020, 01:15 AM   #12
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Default Re: Finally some Cam Degree Numbers - Now what?

Quote:
Originally Posted by Russ/40 View Post
I'm back, and have no idea what I am supposed to make out of the numbers. Here they are. If you recall I have been reluctant to pull the heads, and it was suggested I degree the exhaust valve on number one.

Reconfirmed TDC and very repeatable.
The info I found on the 77B: Int and Exh durations 260* or 220* at .050"
Lobe separation 111*, lift .325* Lash .014".

I got: .050" open at 148*
Exhaust starts to open @ 120.5*
Exhaust starts to close @ 348.5*
Exhaust is closed at 9* ATDC
Exhaust Lash is .014"

Is this enough to get a feel for the cam location? What else need I do. Exhaust centerline?
Russ, A 77B intake opens 19* btdc exhaust closes 19* atdc for a total of 38* overlap. So as Ron says if you split the overlap you're at tdc. Probably the best way to check valve opening and closing is to pull the intake manifold and put an indicator on the cam followers. Then you don't have to worry about valve lash. If when you split the overlap the piston is at tdc the cam is timed correctly.
Bill
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Old 10-24-2020, 07:27 AM   #13
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Default Re: Finally some Cam Degree Numbers - Now what?

Bill has it correct - as this particular cam has the same exhaust lobe profile as the intake. There are other cams where the profiles are different and the split overlap method doesn't work - you actually have to know where a particular lobe is in relation to TDC . . . and hopefully the profile matches the CAM card.
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Old 10-24-2020, 11:30 AM   #14
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Default Re: Finally some Cam Degree Numbers - Now what?

Is the opinion the duration is 248 vs 260 due to the .014" lash? It seems logical to me. In any case, is the deviation from 260 durationan issue responsible for the extreme static advance I see at idle (.025*)?

I'm trying hard to follow all the observations and to make sense of it all.

Bill, I find your comment of using an indicator to track the followers from inside the valley interesting, but not practical, as I can't imagine accomplishing that with the heads on. That would be the parallel of how it would be done on an overhead valve engine. The lash compensation with a shim or lifter adjustment sounds reasonable to me.

I hope we are focusing on the way to use this cam and at the same time correct the overriding concern which is making the engine run reasonably well. Remember the cam ran well before in a different engine with different crank and cam gears.

You guys are great, sharing your knowledge with me, and I am learning a lot about cam timing. I think I'm close to the next thing that I must do to solve the problem, and that I think is to retard the cam. Should I recheck everything with zero lash at this point or would It be reasonable to back the cam. Off one tooth now?
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Old 10-24-2020, 11:50 AM   #15
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Default Re: Finally some Cam Degree Numbers - Now what?

I dug out an old profile I did of a 77B. Looking at 014 lift figures, I have the valve opening at 86 BBDC and closing at 25 ATDC. These numbers don't correlate will with advertised numbers and I measured .360 lift, so not real confident in this cam. Someone may have put a regrind on it.

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Old 10-24-2020, 12:59 PM   #16
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Default Re: Finally some Cam Degree Numbers - Now what?

The only number you really need to properly degree the cam is the "ICL", this number tells the whole story! You don't check this with any lash included, it's normally done with the lifter riding on the #1 intake lobe and the dial indicator on the lifter!

Don't confuse this with the "LSA", two totally different animals!

I would not pay too much attention to the "events", it's difficult at best to dial in any cam with the "4" event numbers!

Thanks, Gary

P.S. Been using the "ICL" method for more than 55 years now in all our builds!
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Old 10-24-2020, 01:54 PM   #17
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Default Re: Finally some Cam Degree Numbers - Now what?

Quote:
Originally Posted by Russ/40 View Post
Is the opinion the duration is 248 vs 260 due to the .014" lash? It seems logical to me. In any case, is the deviation from 260 durationan issue responsible for the extreme static advance I see at idle (.025*)?

I'm trying hard to follow all the observations and to make sense of it all.

Bill, I find your comment of using an indicator to track the followers from inside the valley interesting, but not practical, as I can't imagine accomplishing that with the heads on. That would be the parallel of how it would be done on an overhead valve engine. The lash compensation with a shim or lifter adjustment sounds reasonable to me.

I hope we are focusing on the way to use this cam and at the same time correct the overriding concern which is making the engine run reasonably well. Remember the cam ran well before in a different engine with different crank and cam gears.

You guys are great, sharing your knowledge with me, and I am learning a lot about cam timing. I think I'm close to the next thing that I must do to solve the problem, and that I think is to retard the cam. Should I recheck everything with zero lash at this point or would It be reasonable to back the cam. Off one tooth now?
You should find out where you're at before you start retarding the cam.
Better verify the cam is timed wrong before you change it.
Bill
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Old 10-24-2020, 02:04 PM   #18
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Default Re: Finally some Cam Degree Numbers - Now what?

Quote:
Originally Posted by Russ/40 View Post
Is the opinion the duration is 248 vs 260 due to the .014" lash? It seems logical to me. In any case, is the deviation from 260 durationan issue responsible for the extreme static advance I see at idle (.025*)?

I'm trying hard to follow all the observations and to make sense of it all.

Bill, I find your comment of using an indicator to track the followers from inside the valley interesting, but not practical, as I can't imagine accomplishing that with the heads on. That would be the parallel of how it would be done on an overhead valve engine. The lash compensation with a shim or lifter adjustment sounds reasonable to me. , It's a lot more correct the overriding concern which is making the engine run reasonably well. Remember the cam ran well before in a different engine with different crank and cam gears.

You guys are great, sharing your knowledge with me, and I am learning a lot about cam timing. I think I'm close to the next thing that I must do to solve the problem, and that I think is to retard the cam. Should I recheck everything with zero lash at this point or would It be reasonable to back the cam. Off one tooth now?
Russ ' It's a lot more practical than retarding a cam when you don't know where it's at! You don't know for sure that it is a cam timing problem.
You should find out where you're at before you start retarding the cam.
Better verify the cam is timed wrong before you change it.
Bill
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Old 10-24-2020, 02:14 PM   #19
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Default Re: Finally some Cam Degree Numbers - Now what?

Quote:
Originally Posted by GOSFAST View Post
The only number you really need to properly degree the cam is the "ICL", this number tells the whole story! You don't check this with any lash included, it's normally done with the lifter riding on the #1 intake lobe and the dial indicator on the lifter!

Don't confuse this with the "LSA", two totally different animals!

I would not pay too much attention to the "events", it's difficult at best to dial in any cam with the "4" event numbers!

Thanks, Gary

P.S. Been using the "ICL" method for more than 55 years now in all our builds!
With the 77B, the exhaust c/l will be the same as the intake c/l. Isky says 111* for both. Also Isky specs their cam events at .020 lift. By using Russ/40 numbers, I come up with 120* c/l which would indicate the cam timing is off by one tooth,

Last edited by flatjack9; 10-24-2020 at 02:30 PM.
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Old 10-25-2020, 09:52 AM   #20
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Default Re: Finally some Cam Degree Numbers - Now what?

How is the compression? Retarding it will be losing compression, advancing it will add compression. It won't be much, maybe 20 pounds but its noticeable. Advancing it more than 4 degrees will start to lose compression again. Installing at the highest compression will be the best running, but that's a lot of dicking around to find it. I would go with a intake center line spec if you have it.
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