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Shockwave78 · 08-09-2023, 04:56 PM

Quote:

Originally Posted by Gach

The very first thing I’d check is the cam, make sure it’s in at 109. Its best to Eliminate that as a possibility of being the issue.

The first thing I'm going to do when I get home is check the cam timing as Cliff said. Spinning the engine until the #1 intake valve opens and checking the timing mark on the damper against the cam card specs. It seems an easy enough way to check that doesn't require any disassembly.

Gach · 08-09-2023, 05:01 PM

Quote:

Originally Posted by Shockwave78

The first thing I'm going to do when I get home is check the cam timing as Cliff said. Spinning the engine until the #1 intake valve opens and checking the timing mark on the damper against the cam card specs. It seems an easy enough way to check that doesn't require any disassembly.

Oh yeah remember reading that.

Stan Weiss · 08-09-2023, 05:05 PM

Quote:

Originally Posted by steve25

Slowbird yes it can be pointing to a issue.

The air flap will only open when there is air demand even though the second secondary throttle blades may be fully open.

Lack of normal air demand as rpms go up may be due to wrong cam timing as we have been discussing at nauseum here, or the firing order being wrong.

These are the only two things that I can see taking place which is assuming that since he has no valvetrain noise his cam and lifters are ok and opening and closing the valves with the lift that it’s designed with.

Steve,
Yes, be isn't that USER adjustable, and maybe it is miss adjusted.

Stan

Shockwave78 · 08-09-2023, 05:08 PM

correction:

The valve lift would be 359.5/383.5 for a cam with a 1/8" smaller base circle. However, in practice, I would think this would not matter unless a non-adjustable valvetrain was used. With an adjustable valvetrain, it seems to me like the extra adjustment would take out any pushrod slack and the full lobe lift would still be imparted on the lifter and pushrod, which would translate to full valve lift.

steve25 · 08-09-2023, 05:15 PM

Shockwave, take the extra time to pull all of your plugs before checking the timing,
It will then be way easier to get 1 where it needs to be.

Stan Weiss · 08-09-2023, 05:17 PM

Quote:

Originally Posted by Shockwave78

correction:

The valve lift would be 359.5/383.5 for a cam with a 1/8" smaller base circle. However, in practice, I would think this would not matter unless a non-adjustable valvetrain was used. With an adjustable valvetrain, it seems to me like the extra adjustment would take out any pushrod slack and the full lobe lift would still be imparted on the lifter and pushrod, which would translate to full valve lift.

It has been a long day. But isn't the difference in lift the difference in the radius of the base circle?

Stan

Shockwave78 · 08-09-2023, 05:28 PM

Quote:

Originally Posted by Stan Weiss

It has been a long day. But isn't the difference in lift the difference in the radius of the base circle?

Stan

I should have clarified, the eighth-inch difference is the diameter. For the lift difference, I used .0625

Gach · 08-09-2023, 05:37 PM

Quote:

Originally Posted by Shockwave78

correction:

The valve lift would be 359.5/383.5 for a cam with a 1/8" smaller base circle. However, in practice, I would think this would not matter unless a non-adjustable valvetrain was used. With an adjustable valvetrain, it seems to me like the extra adjustment would take out any pushrod slack and the full lobe lift would still be imparted on the lifter and pushrod, which would translate to full valve lift.

Gotcha

slowbird · 08-09-2023, 05:44 PM

Based on the cam he has and the fact he states engine has 8:1 compression, just how much cranking compression you guys think he should have? The cylinders he has test showed 140-150 according to him, and he states idle vacuum is 15".

Stan Weiss · 08-09-2023, 05:57 PM

Quote:

Originally Posted by Stan Weiss

4.12" bore, 3.75" stroke, 6.625" rod, 8.0:1 CR, 270 intake duration 109 ICL (26/64), should at sea level should produce about 148 psi cranking compression.

Stan

Quote:

Originally Posted by slowbird

Based on the cam he has and the fact he states engine has 8:1 compression, just how much cranking compression you guys think he should have? The cylinders he has test showed 140-150 according to him, and he states idle vacuum is 15".

Brian,
That is from page 2. I don't believe his problem is cam phasing.

Stan

slowbird · 08-09-2023, 06:06 PM

Quote:

Originally Posted by Stan Weiss

Brian,
That is from page 2. I don't believe his problem is cam phasing.

Stan

I agree, i wouldn't bet the farm on the cam being out of timing, but you never know.

Stan Weiss · 08-09-2023, 06:25 PM

Brian,
The above is based on 8.0:1 CR. I believe the W72 was rated at 7.6:1 CR if nothing was done and it is still 7.6:1.

4.12" bore, 3.75" stroke, 6.625" rod, 7.6:1 CR, 270 intake duration 103 ICL (32/58), should at sea level should produce about 148 psi cranking compression.

Stan

KEN CROCIE · 08-09-2023, 06:32 PM

a quick and dirty way to check if the the cam is close , is to make sure the height of the pushrods are about the same (rockers off) at true tdc overlap.

Gach · 07:27 PM

Quote:

Originally Posted by slowbird

Based on the cam he has and the fact he states engine has 8:1 compression, just how much cranking compression you guys think he should have? The cylinders he has test showed 140-150 according to him, and he states idle vacuum is 15".

And when he did valve adjustment it went up to 175. So sounds like those valves was definitely hanging open for those cylinders he retested.

Gach · 08-09-2023, 07:26 PM

Quote:

Originally Posted by Stan Weiss

Brian,
That is from page 2. I don't believe his problem is cam phasing.

Stan

So what do you think it is C’mon spill the beans.

Shockwave78 · 08-09-2023, 07:42 PM

Just rough checked the valve timing per Cliff's directions and it seems to be spot on. I did a compression test on the rest of the cylinders and they all returned 150, I'm not sure if the 175 was a fluke, or that was a side effect of the rockers being adjusted a certain way. I have studs arriving tomorrow as well as poly locks because I was planning on doing that anyway. I will be doing a compression test after I get the new studs installed to see if that makes a difference. My next step is pulling the carburetor off to see if there's any junk in it from sitting

Shockwave78 · 08-09-2023, 07:47 PM

I also checked the firing order and it was good

Gach · 08-09-2023, 07:55 PM

Quote:

Originally Posted by Shockwave78

Just rough checked the valve timing per Cliff's directions and it seems to be spot on. I did a compression test on the rest of the cylinders and they all returned 150, I'm not sure if the 175 was a fluke, or that was a side effect of the rockers being adjusted a certain way. I have studs arriving tomorrow as well as poly locks because I was planning on doing that anyway. I will be doing a compression test after I get the new studs installed to see if that makes a difference. My next step is pulling the carburetor off to see if there's any junk in it from sitting

Well thats good news.