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I have found out that it is preferable to fashion a T for a vacuum gauge if you must use an occupied port. All things should be hooked up that are normally hooked up. A lot of people forget about OAI flappers, exhaust air vacuum motors, etc. Spark advance being the only exception.
So, I think at this point I'm going to do the compression tests more so as a formality, but I'm strongly leaning toward just pulling the engine. I'm not really set up for it, but either I pull it and have it gone through, or I have more pages of scratching heads and frustration. The more I think on the process, the less confident I am. The engine was "zero decked", and balanced at shop A. Shop A couldn't commit to assembly, so it was taken to shop B. where it was discovered that shop A had missed the fact that rods were bent and the skirts on the cast pistons were hitting the counterweight. So at that point, we moved to different rods/forged pistons but I cant swear that the height was the same. Also at shop B, they cleaned/checked the intake and went ahead and assembled..but I'm not sure they took into account the "zero deck". I've thought about putting the smoke machine on it, but that won't help low compression numbers. Even if it showed a leak, I doubt there will be one visible to make up 4+" of vacuum that I've not already seen.
If I for sure go that route, I know I'm not taking it to either place that's already had their hands in it.
nope..you post the same bs garbage about vacuum readings all the time like it’s the be all to end all..when it’s a load of crap.
posting a pic that says ALL engines need to have between 15” and 22” of vac at idle is a lie.
you’re giving misleading and false information..you don’t know what you’re talking about. I’m giving factual correct info…you aren’t
I appreciate your compassion. Nearly every aspirated ICE falls between 15"Hg - 22"Hg. The data is neither false nor a lie. Is it possible this fairly decent sized cam on this engine can't achieve >8"Hg? I truly don't have the data to back it up; yet, I'm suspicious 8"Hg vacuum remains too low.
Correct. I just hadn't ever thought about lifter/oil pressure having effects as referenced earlier.
That really shouldn’t make much of a difference.
You can even pull all the plugs to allow it to spin more freely etc., but it’s not absolutely necessary if you have a good battery.
And let me reiterate, the wideband is as much for a reference value, not an end all be all.
Last edited by cutlassefi; Oct 17, 2024 at 06:10 AM.
That really shouldn’t make much of a difference.
You can even pull all the plugs to allow it to spin more freely etc., but it’s not absolutely necessary if you have a good battery.
So, I think at this point I'm going to do the compression tests more so as a formality, but I'm strongly leaning toward just pulling the engine. I'm not really set up for it, but either I pull it and have it gone through, or I have more pages of scratching heads and frustration. The more I think on the process, the less confident I am. The engine was "zero decked", and balanced at shop A. Shop A couldn't commit to assembly, so it was taken to shop B. where it was discovered that shop A had missed the fact that rods were bent and the skirts on the cast pistons were hitting the counterweight. So at that point, we moved to different rods/forged pistons but I cant swear that the height was the same. Also at shop B, they cleaned/checked the intake and went ahead and assembled..but I'm not sure they took into account the "zero deck". I've thought about putting the smoke machine on it, but that won't help low compression numbers. Even if it showed a leak, I doubt there will be one visible to make up 4+" of vacuum that I've not already seen.
If I for sure go that route, I know I'm not taking it to either place that's already had their hands in it.
This is a bold move. You're adamant that its a carb issue as the motor runs fine with the other carb, but now you wanna pull the motor and inspect everything? Is there more to this story?
This is a bold move. You're adamant that its a carb issue as the motor runs fine with the other carb, but now you wanna pull the motor and inspect everything? Is there more to this story?
Compression lower than it should be, vacuum lower than it should be. Unable to verify things were done correctly at the machine shop, which could be the culprit of both the compression and vacuum issues.
I think the carb has a little to do with the bouncing of the needle (more than usual) and probably the slight detonation, but that's about as much as I'd pin on the carb.
I think the carb has a little to do with the bouncing of the needle (more than usual) and probably the slight detonation, but that's about as much as I'd pin on the carb.
Yes, hard to imagine you'd be having detonation issues with those compression numbers unless timing is thoroughly FUBAR or carb is very, very lean.
IMO; You have a high overlap camshaft. That means the intake valve will open sooner and the exhaust valve will close later. This improves cylinder scavenging but will cause lower cranking compression. On that note your compression numbers look ok to me. I am in agreement with the engine assembler this is a tuning problem, not an internal/mechanical/compression problem. Stop blaming the builder! The engine has sufficient cranking compression, it doesn't smoke, it has compression and it doesn't knock. What more do you want from them?
You already stated that the engine runs better with a different carburetor. Why are you scratching your head. The carb you are trying to tune by adjusting the idle mixture screws is the wrong calibration for that camshaft on crack you are trying to run. That cam is border line non street-able. That cam requires a 4:56 rear gear, no A/C, no PB, and a wide ratio MT or a 3500+ RPM min stall torque convertor. As far as vacuum readings do not expect any higher than 13" and a bouncing needle that will be perfectly rhymic with the lope of the camshaft. That cam will not idle at less than 1000 RPM. You are trying to tune a border line race cam to idle smoothly at stop lights on your way to pick up groceries.
Change the cam to a more streetable grind or change your expectations.
The above suggestions are pulled from the schooling I received from some of the best NYC '70's street racers and my own personal/professional experience. YMMV. Good luck!
The builder unfortunately has plenty of reasons to be suspect about, not just pertaining to this engine. He installed the distributor 180 degrees out (A), He did NOT degree the cam, beyond that swore that degreeing a cam wasn't necessary (B), they charged me for break-in and pulls on the dyno, as well as a carb rebuild..but claimed they "didn't have time" and only broke the cam in using a "shop carb" (C)
I'm not blaming the assembly shop for the machine work, and while it would've made sense for them to check the intake wasn't going to be a problem, I unfortunately can see it being an oversight if they didn't do the machine work.
As for the cam, I have heard both this is "too much cam" and that this cam "provides plenty of vacuum". Usually the "plenty of vacuum" supporters are those who've run this cam. I'm not opposed to it, but I know if I'm going through the work of changing cams, I'm going to verify the block and intake issues at the same time.
IMO; You have a high overlap camshaft ... That cam is border line non street-able. That cam requires a 4:56 rear gear, no A/C, no PB, and a wide ratio MT or a 3500+ RPM min stall torque convertor. As far as vacuum readings do not expect any higher than 13" and a bouncingat will be perfectly rhymic with the lope of the camshaft. That cam will not idle at less than 1000 RPM.
Which is pretty much antithetical to the low end limited RPM nature of the long-stroke, small-bore 400G.
The block is fine, and you proved there are no intake issues when you stated the engine runs fine with the Jet carb.
fine meaning the vacuum is more stable. It's still only every pulled a max number of 9, and the timing is a mess. I called the dyno, explained the status and he didn't think the cam was that radical to create the vacuum issues, instead suggesting I send it to their "vacuum guy" and let him sort it before they dyno it. That way variables are addressed and they can properly tune on it for best drive ability and performance.
The builder unfortunately has plenty of reasons to be suspect about, not just pertaining to this engine. He installed the distributor 180 degrees out (A), He did NOT degree the cam, beyond that swore that degreeing a cam wasn't necessary (B), they charged me for break-in and pulls on the dyno, as well as a carb rebuild..but claimed they "didn't have time" and only broke the cam in using a "shop carb" (C)
I'm not blaming the assembly shop for the machine work, and while it would've made sense for them to check the intake wasn't going to be a problem, I unfortunately can see it being an oversight if they didn't do the machine work.
As for the cam, I have heard both this is "too much cam" and that this cam "provides plenty of vacuum". Usually the "plenty of vacuum" supporters are those who've run this cam. I'm not opposed to it, but I know if I'm going through the work of changing cams, I'm going to verify the block and intake issues at the same time.
dont listen to the uneducated…it’s a mechanical issue. even your highest compression reading is a poor one.
I said this right from the start..it’s got **** poor static compression, probably awful quench distance and a cam that’s not advanced enough.
pull it and we’ll walk you through checking everything out. hopefully you’ll listen.
another thing I would like to know is how fast the needle on the compression gauge goes to on the first and second hit ? that’ll tell you if your ring seal is good. mine get to 85 or 90% on the first hit on basic builds … If yours is taking 4 or 5 kits to reach that poor number..you also have ring seal problems
dont listen to the uneducated…it’s a mechanical issue. even your highest compression reading is a poor one.
I said this right from the start..it’s got **** poor static compression, probably awful quench distance and a cam that’s not advanced enough.
pull it and we’ll walk you through checking everything out. hopefully you’ll listen.
another thing I would like to know is how fast the needle on the compression gauge goes to on the first and second hit ? that’ll tell you if your ring seal is good. mine get to 85 or 90% on the first hit on basic builds … If yours is taking 4 or 5 kits to reach that poor number..you also have ring seal problems
video the gauge when you do the test and post it
IIRC, the needle jumped after 2, maybe 3 rotations. The cam was something like 20° retarded at the time, and like I said I've not tested since. Not sure if that much difference can be made up in that instance, but I am for sure curious.
The guy that works on our trucks & trailers at work also brought up the smoke machine idea and the leak down test. He doesn't have the smoke machine, but does have a leak down tester. I know you can get machines online for pretty cheap, but I struggle to see how you'd see smoke if it's leaking internally.
Do the new compression test and go from there, 20 degrees more advance should bump compression a lot. If it is still low, then leak down test. Do it step by step till it fails the tests.
When I first watched the video in #87 thread I had to look close to make sure you have the gauge hooked to direct intake vacuum...you do.
The secondary AVS door is opening way too quickly. Probably do to the low vac signal. That will cause a bog/stumble.
The engine actually sounds good. The vac signal, be it low, is fairly steady. And it hops up above 15+ upon deceleration. That tells me you have retarded timing due to the distributor or timing chain alignment.
I cant clearly see the dwell meter. Are you on 6 or 8 cylinder at 30°?
Your centrifugal advance mechanism looks a little dry and the weights could be coming in too early if the springs are too light. Do you know what RPM the advance starts?
Rocketmans that backyard suggestion of spraying carb cleaner down the oil fill is brilliant!
When I first watched the video in #87 thread I had to look close to make sure you have the gauge hooked to direct intake vacuum...you do.
The secondary AVS door is opening way too quickly. Probably do to the low vac signal. That will cause a bog/stumble.
The engine actually sounds good. The vac signal, be it low, is fairly steady. And it hops up above 15+ upon deceleration. That tells me you have retarded timing due to the distributor or timing chain alignment.
I cant clearly see the dwell meter. Are you on 6 or 8 cylinder at 30°?
Your centrifugal advance mechanism looks a little dry and the weights could be coming in too early if the springs are too light. Do you know what RPM the advance starts?
Rocketmans that backyard suggestion of spraying carb cleaner down the oil fill is brilliant!
The timing is currently 16 degrees BTDC, and acts like its a bit too far advanced. I had been running it at 18 degrees, but backed it off thinking that was the cause of the detonation (before sending carb back the first time to find out the secondary pickup tube had fallen out of place). The dwell meter at the time of recording was set to tach (it is a dwell/tach combo meter), but I have verified dwell is solid at 30 now. I do not know at what point the advance starts to come in, as up until I got this tach/dwell meter, I have not had a trustworthy tach. (One was from a timing light, and the one in the car seems to have issues).
The carb cleaner down the oil fill unfortunately did not yield any obvious results unfortunately..but I'm not above saying I didn't miss anything or get it confused with the normal stutter then engine has.
You've stated in this post and others have mentioned timing as well...not only in this thread, but your other threads:
timing is a mess
Relative to your "detonation" issue & discussions pertaining to possible resolution(s);
I can't help but suspect either one or two fundamental scenarios where you might focus on this "timing is a mess" issue:
(1) Your timing set is incorrect/misaligned. The cam:crank ratio (alignment) may have slipped, broken/sheared/loose (not torqued) cam bolt?; or,
(2) Misconfiguration of the valve train.
The cam:crank ratio (alignment) establishes the proper cam lobe cadence for the opening/closing of valves. If exhaust air remains in the chamber because the spent air wasn't evacuated during exhaust valve opening, you can't create sufficient vacuum or compression to draw air into the chamber if residual spent air remains in the chamber when the intake valve opens & the exhaust valve closes. Additionally, any timing adjustments you attempt to make will not be accurate if the timing set is misaligned. Therefore, timing to 18° BTDC may actually mean - nothing. Same holds true for the valve train configuration. You need to be on the correct/proper alignment of each cam lobe when the down stroke occurs so each valve operates/opens/closes to provide good vacuum/compression.
You've stated in this post and others have mentioned timing as well...not only in this thread, but your other threads:
Relative to your "detonation" issue & discussions pertaining to possible resolution(s);
I can't help but suspect either one or two fundamental scenarios where you might focus on this "timing is a mess" issue:
(1) Your timing set is incorrect/misaligned. The cam:crank ratio (alignment) may have slipped, broken/sheared/loose (not torqued) cam bolt?; or,
(2) Misconfiguration of the valve train.
The cam:crank ratio (alignment) establishes the proper cam lobe cadence for the opening/closing of valves. If exhaust air remains in the chamber because the spent air wasn't evacuated during exhaust valve opening, you can't create sufficient vacuum or compression to draw air into the chamber if residual spent air remains in the chamber when the intake valve opens & the exhaust valve closes. Additionally, any timing adjustments you attempt to make will not be accurate if the timing set is misaligned. Therefore, timing to 18° BTDC may actually mean - nothing. Same holds true for the valve train configuration. You need to be on the correct/proper alignment of each cam lobe when the down stroke occurs so each valve operates/opens/closes to provide good vacuum/compression.
Uhhh, I’m not sure what you’re driving at here, but cam and ignition timing are totally unrelated.
And the ability, or inability for the cylinder to evacuate enough spent gases to operate correctly, is mainly determined by lift, duration and LSA. If the cam timing has “slipped” as you suggest, he has other problems, not related at all to what you’re suggesting.
Sorry.
Uhhh, I’m not sure what you’re driving at here, but cam and ignition timing are totally unrelated.
And the ability, or inability for the cylinder to evacuate enough spent gases to operate correctly, is mainly determined by lift, duration and LSA. If the cam timing has “slipped” as you suggest, he has other problems, not related at all to what you’re suggesting.
Sorry.
Sorry, not following. The position of a piston & position of a valve aren't related to "ignition timing"?. The cam:crank position is not related? Man, I'm lost but that's OK. I'll enjoy the popcorn.
I didn't mention "ignition timing" I referenced the timing set. The relative position of the cam to the crank. I hope the positions of the cam lobes (established by the timing set) has a direct relationship to "ignition timing". Why have "ignition timing" &/or a distributor, coil or spark plugs if cam position is not related to "ignition timing". Sorry, not following. The piston(s) & valves need to be in the correct positions when the spark plug fires. Guess I'm not following. Sorry.
Totally and completely unrelated? I'm going to just hibernate. I'm lost. I always "thought" ignition timing was the precise moment a spark plug ignites air-fuel mixture in the combustion chamber. I'm clueless and I'll just enjoy the popcorn and learn something new.
Lets go back to the basics...
Pull #1 plug
Stick finger in hole
Bump engine until it spits out your finger.
Bring the damper mark to 0° on the timing indicator tab.
Where is the distributor rotor pointing? If its not pointing directly to #1 ignition wire tower on the cap fix it.
Vintage chief, No. The ignition timing will be what it is no matter what the valve timing is. They’re NOT connected. They can be adjusted/altered independently.
And cam syncs on newer vehicles serve one purpose and one purpose only, to tell the computer where No.1 cylinder is so it’ll fire the correct coil and injector, that’s it.
So to be frank, if you don’t understand something, ask. Please don’t post if you’re unsure about what is being discussed. It only muddies the water.
Thank you.
Last edited by cutlassefi; Oct 19, 2024 at 07:08 AM.
Vintage chief, No. The ignition timing will be what it is no matter what the valve timing is. They’re NOT connected. They can be adjusted/altered independently.
And cam syncs on newer vehicles serve one purpose and one purpose only, to tell the computer where No.1 cylinder is so it’ll fire the correct coil and injector, that’s it.
So to be frank, if you don’t understand something, ask. Please don’t post if you’re unsure about what is being discussed. It only muddies the water.
Thank you.
Mark - I accept responsibility for my statements & thought I had adequately comprised the message demonstrating they were independent yet related but I can understand this did not come across as such. To that end, I'm going eat some popcorn (buttered, of course) & remain on the learning side of the curve. I appreciate your input.
Well, bronchitis hit the house pretty hard last night..so we've been kind of a mess today. I did go out and get the cold compression test done. There was some improvement in most, but cyl 6 & 8 still leave some questions.
I think the best thing to do is just walk away for a bit. Unfortunately, its probably best to yank it and have it gone through, but I've lost enough sleep/energy trying to find an alternative.
IIRC, the needle jumped after 2, maybe 3 rotations. The cam was something like 20° retarded at the time, and like I said I've not tested since. Not sure if that much difference can be made up in that instance, but I am for sure curious.
The guy that works on our trucks & trailers at work also brought up the smoke machine idea and the leak down test. He doesn't have the smoke machine, but does have a leak down tester. I know you can get machines online for pretty cheap, but I struggle to see how you'd see smoke if it's leaking internally.
when you do the compression test again, post a video of the gauge as you’re cranking it
