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Old 10-02-2020, 12:36 AM   #41
Russ/40
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Default Re: Question on Cam Gear Marks - UPDATE

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Russ, Please clarify "almost closed".

Mart.
Mart, after further scrutiny of number 6 with 1 at TDC, i think both valves are closed. if any valve is off the seat, I cant really see it. Rocking the crank back and forth opens and closes both valves in opposition.

Brian, I've had the heads off this thing three times. In the past I have never had to do that even once. It would be my very last ditch effort to do it again. Can the cam be degreed without removing the heads?

Last edited by Russ/40; 10-02-2020 at 01:50 PM.
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Old 10-02-2020, 01:56 AM   #42
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Default Re: Question on Cam Gear Marks - UPDATE

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Mart, I don't know how else to state it. The exhaust valve on number 6 is barely perceptible to be off the seat, and the intake is closed when number one is at TDC. One thing puzzles me Mart. How is it we are talking about number 6 in this timeing discussion.

Brian, I've had the heads off this thing three times. In the past I have never had to do that even once. It would be my very last ditch effort to do it again. Can the cam be degreed without removing the heads?
When number 1 is at TDC firing, number 6 is at TDC overlap. The easy way to find TDC firing on number one is to put number 6 on TDC overlap.
Overlap is when the intake and exhaust valves are both off their seats at the same time for a few degrees at or near TDC number 6.
number 1 & 6 come to TDC at the same time, one is firing the other is
overlapping.
Intake valve opens 0 degrees BTDC on a stock 59a , so if the intake on number 6 just starts to open at TDC the valve timing is correct.
Bill
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Old 10-02-2020, 08:06 AM   #43
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Default Re: Question on Cam Gear Marks - UPDATE

Just a shot in the dark here so don't laugh. Is the cam gear a press on? If so, could it have slipped to cause this problem? If it is a bolt on cam gear and possibly slotted, could it have moved?
Ken
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Old 10-02-2020, 08:36 AM   #44
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Default Re: Question on Cam Gear Marks - UPDATE

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Intake valve opens 0 degrees BTDC on a stock 59a , so if the intake on number 6 just starts to open at TDC the valve timing is correct.
Bill
Keep in mind this is not a stock cam, so there is overlap. The intake on number 6 will not be just starting to open in this case. Needs to be in a positions such that the exhaust and intake are the same height above the valve seat.

If the cam spec posted is correct, it would be intake 19 deg BTDC and exhaust 19 deg ATDC. A problem is there is very little valve movement at these positions, that is why cam numbers are given at 20 or 50 degrees, so you can actually detect valve movement.

I have never tried to degree a cam with the head on. I would think you could at least check the exhaust valve if you can get a dial indicator through the sparkplug hole and on the edge of the valve such that it can move without rubbings on anything. If alum head, need to figure out a way to mount the base. Looking for very slight movements during part of the cycle, so everything needs to be very secure.
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Old 10-02-2020, 08:54 AM   #45
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Default Re: Question on Cam Gear Marks - UPDATE

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Keep in mind this is not a stock cam, so there is overlap. The intake on number 6 will not be just starting to open in this case. Needs to be in a positions such that the exhaust and intake are the same height above the valve seat.

If the cam spec posted is correct, it would be intake 19 deg BTDC and exhaust 19 deg ATDC. A problem is there is very little valve movement at these positions, that is why cam numbers are given at 20 or 50 degrees, so you can actually detect valve movement.

I have never tried to degree a cam with the head on. I would think you could at least check the exhaust valve if you can get a dial indicator through the sparkplug hole and on the edge of the valve such that it can move without rubbings on anything. If alum head, need to figure out a way to mount the base. Looking for very slight movements during part of the cycle, so everything needs to be very secure.
There is overlap on a stock cam as well, the point is if the overlap occurs at TDC the valve timing is right .
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Old 10-02-2020, 09:42 AM   #46
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Default Re: Question on Cam Gear Marks - UPDATE

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Put a buzz box on the dizzy to confirm its operation. Rotor Wrench will chime in as it is used often on aircraft engines.I made mine 50 + years ago when I was involved in a C dragster. They work no problems in determining point action. I am sure Tub Man has used one as well. I guess a digital multi meter with continuity test could do it also.


R
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Old 10-02-2020, 01:56 PM   #47
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Default Re: Question on Cam Gear Marks - UPDATE

In post 41 I revise my observations of cylinder 6, for which Mart asked me to clarify "almost closed." Both valves are closed as best as I can tell. This must be the overlap that I really cant see. When turning the crank by hand, it is really hard to make observations.
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Old 10-02-2020, 02:02 PM   #48
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Default Re: Question on Cam Gear Marks - UPDATE

To be honest, I can't remember using a stock cam. I did use an EAB cam in the 289, but never checked it. I did however use the original alum timing gear. Runs great so far.
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Old 10-02-2020, 04:45 PM   #49
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Default Re: Question on Cam Gear Marks - UPDATE

A 77B at TDC overlap will have both valves open about .030.
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Old 10-03-2020, 08:56 PM   #50
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Default Re: Question on Cam Gear Marks - UPDATE

I don't think you could visibly tell through the plug hole whether both valves are open .030" or closed. Especially if they sit low in their seats. JMO
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Old 10-07-2020, 03:41 PM   #51
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Default Re: Question on Cam Gear Marks - UPDATE

You guys are probably giving up on me, wouldn't blame you, but I still need some help.
I have set up a few different distributors, and I am sure my problem is not ignition. Engine runs and starts best at 20+* advance. And distributors are set correctly. Retard the timing and it runs like s##t. I even modified a distributor to increase the range of adjustment, and no improvement.

I wish I had, as you have suggested, degreed the cam. I have never done so, and wouldn't know where to start. I'm thinking the cam needs to be retarded, but the question would be "do I and how much". What would rotating the distributor do for the situation? I would have to create a mount to do so. If one of you true tech savvy guys could give me a recommended simple test where I could measure exhaust valve timing with a dial indicator to determine the number of degree correction of the cam, I can work out a cam timing adjustment.

I wanna screem! If I can't fine a solution soon, i will sell the dam thing for parts.

Last edited by Russ/40; 10-07-2020 at 03:47 PM.
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Old 10-07-2020, 04:54 PM   #52
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Default Re: Question on Cam Gear Marks - UPDATE

Just to go over the timing once again: Are you still saying that it has 20 degrees of advance at startup . . . and about 35 when running at a decent RPM (say 2500)? If this is still the case, then my guess is either the CAM is off, or your TDC and timing marks are off. It should start just fine with low advance and the total should be in the 22 - 25 total degrees of advance range.
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Old 10-07-2020, 05:17 PM   #53
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Default Re: Question on Cam Gear Marks - UPDATE

Try this; remove timing cover, line up your existing timing marks, undo the 4 bolts holding the camgear on. Remove cam gear. Replace gear after moving cam [edit]clockwise sufficient to be able to bolt gear back on with its timing mark one tooth to the [edit] LEFT of that on the crank gear. bolt everything back. You have just retarded the cam [and timing] by 16 odd degrees. See how it runs now. Good luck
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Old 10-07-2020, 05:22 PM   #54
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Default Re: Question on Cam Gear Marks - UPDATE

You cannot get 35* advance out of a distributor, unless the slot it engages in is out.
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Old 10-07-2020, 06:46 PM   #55
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Default Re: Question on Cam Gear Marks - UPDATE

With #1 spark plug out, you can get a dial indicator on the exhaust valve. Get a degree wheel, set up a pointer and degree the exhaust event.
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Old 10-07-2020, 11:46 PM   #56
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Default Re: Question on Cam Gear Marks - UPDATE

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Just to go over the timing once again: Are you still saying that it has 20 degrees of advance at startup . . . and about 35 when running at a decent RPM (say 2500)? If this is still the case, then my guess is either the CAM is off, or your TDC and timing marks are off. It should start just fine with low advance and the total should be in the 22 - 25 total degrees of advance range.
Bored&Stroked, Yes, it has 25* static advance and with RPM will hit 35* with the vacuum brake full on, bolt fully in. Keep in mind, the distributor thinks it is zero* at TDC, so I'm only getting 10* advance from the distributor.

TDC was determined two ways, with a dial indicator when the heads were off. After heads on, I did the double stop method with a big zip tie. Both TDC's agree by a degree or so. What should the base (static) timing be for an Isky 77-B cam? I can't find that anywhere.

Flatjack9, I'll see what I can do with the exhaust event plot. That may take me awhile.

Thanks guys
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Old 10-08-2020, 12:36 AM   #57
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Default Re: Question on Cam Gear Marks - UPDATE

Russ, you 'know' this cam is right because it's previously run very satisfactorily in an earlier engine. You 'know' where TDC is. BUT, you don't 'know' how the camshaft is timed to the crankshaft. Please, follow flatjacks or my advice. Your original question pertained to timing marks. Whatever 'marks' you have ultimately used, obviously are wrong. Until you have established actual cam timing events, anything else is pure conjecture. I'm not going to post anymore on this thread. I can only offer advice, if you choose not to follow it, so be it. Again, good luck!
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Old 10-08-2020, 05:14 AM   #58
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Default Re: Question on Cam Gear Marks - UPDATE

You might try to put air pressure into #1 to find out the actual cam timing. Fit a degree disc to the crank. As soon as a valve opens you will hear a hissing sound in the carb or exhaust. That indicates that the valve is lifted off the seat. By turning crank slowly both directions and hearing the changing hiss you can get the timing almost as precise as with a dial gauge on the valve.
cheers, Harty
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Old 10-08-2020, 10:02 AM   #59
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Default Re: Question on Cam Gear Marks - UPDATE

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Bored&Stroked, Yes, it has 25* static advance and with RPM will hit 35* with the vacuum brake full on, bolt fully in. Keep in mind, the distributor thinks it is zero* at TDC, so I'm only getting 10* advance from the distributor.

TDC was determined two ways, with a dial indicator when the heads were off. After heads on, I did the double stop method with a big zip tie. Both TDC's agree by a degree or so. What should the base (static) timing be for an Isky 77-B cam? I can't find that anywhere.

Flatjack9, I'll see what I can do with the exhaust event plot. That may take me awhile.

Thanks guys
Faulty timing light?
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Old 10-08-2020, 03:33 PM   #60
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Default Re: Question on Cam Gear Marks - UPDATE

Flatjack9, My light has no advance detection ability, so it can only work correctly or not work at all.

Brian, thanks for your patience. I will take your advice and try to degree the number one exhaust valve to find where the cam is relative to the crank. When I have some data, maybe you can help me interpret it. Your idea of advancing the cam is interesting, and hopefully degreeing the exhaust valve will result in info confirming or nixing the wisdom of changing valve timing. It looks more all the time like the cam gear could be the culprit. I used a used gear with no known history that I have not used prior.

Vincent, thanks for the idea of pressurizing the cylinder to define opening and closing valve points great idea.

Again, thank you all for thinking it through.
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